Developing α-lipoic acid-derived solvent-free bioadhesives via deep eutectic melting

Developing α-lipoic acid-derived solvent-free bioadhesives via deep eutectic melting | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Developing α-lipoic acid-derived solvent-free bioadhesives via deep eutectic melting Kunxi Zhang, Guifei Li, Jiujiang Zeng, Yaowen Zhang, Haowei Fang, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7750130/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Solvent-free molten adhesives normally have high adhesion strength, which are widely used in industry but rare in medicine. Developing molten adhesives with medical potential is attractive. Herein, based on the positive therapy effect of α -lipoic acid (LA) and its significant feature of producing adhesives, a family of LA-derivatives containing terminal hydroxyl groups are synthesized and used to establish a serious of room-temperature molten LA-derived adhesives via deep eutectic strategy. The number of hydroxyl groups and molecular structure significantly affect the deep eutectic behavior and further affect the solidification and subsequent mechanical properties of the molten adhesives. The molten deep eutectic LA-derived adhesives can be applied to wounds and quickly cured under ultraviolet irradiation, forming tight and stable adhesion on moist or greasy tissue surfaces without the need for additional surface pretreatment. In vivo evaluation shows the deep eutectic adhesive successfully sealed gastric perforation that bridged by the regenerated mucosa. Besides the room temperature molten adhesives, LA-derivative with more quantity of terminal hydroxyl groups afforded a structural adhesive with strength equivalent to that of conventional adhesives. The deep eutectic behavior of LA and its derivatives provides a new perspective for the development of various types of LA-based adhesives. Physical sciences/Materials science/Biomaterials/Biomedical materials Physical sciences/Chemistry/Materials chemistry/Biomaterials/Biomedical materials α-lipoic acid bioadhesives solvent-free molten adhesives deep eutectic melting topological adhesion Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Contemporary wound closure strategies in clinical practice primarily utilize sutures and staples 1 , 2 . These conventional approaches present notable limitations such as iatrogenic tissue trauma caused by surgical trauma, along with heightened susceptibility to microbial contamination and compromised wound integrity and require professional skills and equipment 3 , 4 . Bioadhesives has received widespread attention in recent years, because there is an urgent need for bioadhesives in both outpatient trauma treatment and intraoperative procedures 5 , 6 . Skin trauma, visceral trauma (especially those that cannot be sutured), tissue transplantation (corneal transplantation), and other treatments all require the use of bioadhesives 7 , 8 . However, there are currently few products in clinical application. Due to the need to ensure biological safety, the adhesive strength of bioadhesives is much lower than that of industrial adhesives, and is greatly affected by the water/oil interface on the tissue surface, which often leads to the inability of bioadhesives to meet adhesive requirements in practical applications 2 , 7 . Therefore, the development of bioadhesives that do not rely on tissue surface pretreatment and can form strong adhesion properties on water/oil tissue surfaces is of great significance. Normally, adhesives achieve firm adhesion by undergoing interface wetting, diffusion permeation, and solidification 9 , 10 . In industrial applications, considering the environmentally unfriendly drawbacks of adhesives containing organic solvents, solvent-free hot-melt adhesives are receiving more and more attention 11 , 12 . Most of the traditional hot-melt adhesives are solid thermoplastic materials that can be heated to a liquid molten state, which is easy to apply onto surfaces. Upon cooling, they are solidified, forming strong bonding with the target surface. Furthermore, the solidification of solvent-free adhesives can also rely on polymerization or cross-linking. Solvent-free molten adhesives usually exhibit strong adhesion strength 13 – 15 . Adhesives based on the heat-triggered melting and polymerization of α-lipoic acid (LA) are an example of solvent-free adhesive that has received widespread attention in recent years 16 . LA is a crystalline small molecule with a melting point of approximately 63 o C. The dithiolane structure in LA can undergo ring-opening polymerization (ROP) under heating or UV irradiation to from poly( α -lipoic acid) (PLA), which has been widely reported to possess adhesion performance 17 – 39 . It is worth noting that the adhesive strength of the LA solvent-free adhesive prepared by melting thermal polymerization of LA is far higher than that of the PLA hydrogel adhesives prepared by thermal polymerization of LA dissolved in water 40 – 45 . As a small molecule coenzyme necessary for the aerobic metabolism of mitochondria, LA can eliminate superoxide and peroxide free radicals and has been applied in clinics 46 . LA-derived bioadhesives have received more and more attention recently 16 , 47 . Although the solvent-free PLA has significantly higher adhesive strength, like traditional hot-melt adhesives, the adhesion of solvent-free PLA depends on the melting-solidification process. Once PLA is formed, it is a non-adhesive elastomer. Therefore, its application in the biomedical field is limited because the melting point ( T m ) of LA and the temperature required for its ROP (over 70 o C) are much higher than body temperature. In addition, the heat-triggered ROP usually costs long duration. Besides heating, UV can also trigger the ROP of dithiolane and is gentler than heating. In addition, UV-triggered LA-polymerization was reported to yield circular PLA, which possessed better stability. 18 However, UV is rarely reported in PLA-based adhesives preparation. Because UV still needs to act on transparent molten LA, while it is powerless for non-molten LA powder. Therefore, to explore the application of solvent-free PLA adhesives in biomedical application, obtaining molten LA at or below body temperature is crucial. A deep eutectic melting is a mixture composed of hydrogen bond donors and acceptors, characterized by a melting point significantly lower than that of any individual component, typically remaining liquid at room temperature 48 . LA also has the potential in forming deep eutectic melting mixture. Cui et al. have reported the deep eutectic phenomenon between LA and sodium lipoate (LA-Na). However, the T m of LA/LA-Na mixture (the ratio is 3) is 42.3 o C, and still higher than body temperature 23 . Given that it cannot form a molten state at body temperature, it cannot use milder and more efficient UV to achieve solidification. Based on deep eutectic melting principle, by exploring hydrogen bond donors to match with LA to establish deep eutectic melting system, a kind of molten LA-based deep eutectic adhesives that can be UV-cured will be greatly attractive in biomedical application. In the present study, we propose to use LA as the hydrogen bond acceptor and synthesize LA derivatives as hydrogen bond donors to develop LA-based deep eutectic adhesives. By reducing T m through deep eutectic melting, LA can be transformed into a flowing and transparent molten state at body temperature or even room temperature. The deep eutectic adhesives are molten at body temperature and can be injected or spread directly onto living tissue surfaces and subsequently cured via photo-initiated ROP of dithiolane. The amphiphilicity of LA and its derivative molecules allows the adhesive to fully penetrate the water or oil interface before curing, and form a strong interlocking structure after UV curing. This kind of adhesives is anticipated to achieve strong and durable adhesion to oily, wet, dynamic, and complex biological tissues. Result and discussion 2.1 Study of the deep eutectic behavior between LA and its derivatives LA undergoes amidation reactions with ethanolamine (EA), aminopropanediol (AP), diethanolamine (DEA) and tris(hydroxymethyl)amino-methane (Tris) respectively to yield its derivatives, including 5-(1,2-dithiolan-3-yl)-N-(2-hydroxyethyl)pentanamide (ELA), N-(2,3-dihydroxypropyl)-5-(1,2-dithiolan-3-yl)pentanamide (APLA), 5-(1,2-dithiolan-3-yl)-N,N-bis(2-hydroxyethyl)pentanamide (DELA), N-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl)-5-(1,2-dithiolan-3-yl)-pentanamide (TLA) ( Fig. S1 -S4 ). 1 H-NMR spectra, FT-IR spectra and Mass spectra confirm the synthesis of the derivatives and their structures. ELA, APLA and TLA are solids with crystallization, while the DELA is liquid at room temperature (Fig. 1 A). The structure and binding energies between LA and its derivatives are studied based on density functional theory (DFT). The bonding energy of the hydrogen bond between LA dimer is -0.61 eV, while the bonding energies of the hydrogen bonds between LA and ELA, APLA, DELA, TLA are − 0.65 eV, -0.51 eV, -0.62 eV, -0.63 eV, respectively. The results show that the hydrogen bond between LA and ELA, DELA, TLA is stronger than the hydrogen bond between LA dimer, the hydrogen bond between LA and APLA is weaker than the hydrogen bond between LA dimer (Fig. 1 B), but its energies are negative, which are conducive to form the hydrogen bonds. Subsequently, the deep eutectic systems are prepared and characterized by simply mixing LA with its derivatives in different molar ratios ( Table S1 -S4 ). The thermal performances of LA, its derivatives, and their mixtures are measured by differential scanning calorimetry (DSC) (Fig. 1 C). For ELA/LA, the molar ratios of ELA to LA are 6:1, 4:1, 2:1, 1:1 and 1:2, which are named as ELA/LA 6:1 , ELA/LA 4:1 , ELA/LA 2:1 , ELA/LA 1:1 and ELA/LA 1:2 . The melting point ( T m ) of ELA and LA are 39.51°C and 63.54°C, respectively. The T m of ELA/LA 6:1 , ELA/LA 4:1 , ELA/LA 1:1 and ELA/LA 1:2 is 29.38°C, 14.17°C, 47.22°C and 54.20°C, mirroring a typical eutectic phenomenon. Interestingly, when the molar ratio of ELA to LA is 2:1, the T m of ELA/LA 2:1 is undetectable within the detection range of -75°C to 90°C. Similarly, APLA/LA mixtures show a typical deep eutectic phenomenon. The T m of APLA is 59.15°C. When the molar ratios of APLA to LA are 4:1, 2:1, 1:1 and 1:2, the T m of the APLA/LA 4:1 , APLA/LA 2:1 , APLA/LA 1:1 and APLA/LA 1:2 mixture are 45.22°C, 43.00°C, 45.11°C and 50.19°C. When the molar ratio of APLA to LA is 1.5:1, the T m of the mixture is undetectable within the detection range of -75°C to 90°C. For TLA/LA, the T m of TLA powder is 109.46°C, while the T m of the TLA/LA mixture decreases with the increasing addition of LA into TLA. When the ratios of TLA to LA are from 5:1 to 1:2, the mixtures have two T m . With further increasing TLA/LA ratio to 1:3 and 1:4, the mixture has one melting point and is reduced to 60.59°C and 61.82°C, which are lower than that of pristine TLA and LA, mirroring a typical eutectic phenomenon. Differently, DELA is a liquid at room temperature, the T m of which is undetectable within the detection range of -75°C to 90°C. When the molar ratios of DELA to LA is 2:1, the T m of the DELA/LA 2:1 is also undetectable within the detection range of -75°C to 90°C. When the molar ratios of DELA to LA are 1:1 and 1:2, the T m of the DELA/LA 1:1 and DELA/LA 1:2 are 38.13°C and 43.86°C. 2.2 Preparation and characterizes of the ELA/LA deep eutectic adhesive In the ELA/LA deep eutectic mixture, ELA/LA 2:1 is unique. When the molar ratio of ELA to LA is 2:1, the mixture of the two solid powders quickly transforms into a yellow transparent liquid, which possesses thin fluidity and could be easily injected (Fig. 2 A). Therefore, unlike most reported deep eutectic solvents, this ELA/LA 2:1 deep eutectic mixture does not require heating. Rheological testing shows the liquid feature of ELA/LA 2:1 ( Fig. S5 ). Through polarizing microscope observation, it is found that the eutectic mixture of ELA/LA at different molar ratios has liquefying phenomenon at room temperature ( Fig. S6 ). When the molar ratio of ELA to LA is 6:1 and 4:1, there is more ELA in the ELA/LA 6:1 with small ELA crystals. The deep eutectic ELA/LA 2:1 is a flowing yellow liquid at room temperature without crystal structure observed. X-ray diffraction (XRD) is employed to illustrate structural changes of the ELA, LA and ELA/LA 2:1 . Figure 2 B shows that there are highly ordered nanoscale crystal structures in ELA and LA, while the diffraction peaks in ELA/LA 2:1 totally disappeared, indicating the formation of amorphous phase. With the LA ratio continues to increase, LA gradually becomes more abundant in ELA/LA 1:1 and ELA/LA 1:2 . LA crystals are clearly observed ( Fig. S6 ). The existence of the crystal structure also affects the penetrability of visible light. The transmittance of the ELA/LA deep eutectic system is tested by UV-Vis absorption spectroscopy. The results show that the transmittances of the ELA/LA 2:1 , ELA/LA 4:1 and ELA/LA 6:1 are 98.8%, 98.2% and 92.3%, while the transmittances of the ELA/LA 1:1 and ELA/LA 1:2 are 18.6% and 10.3% ( Fig. S7 ). The formation mechanism of the deep eutectic mixture between ELA and LA is investigated by FT-IR (Fig. 2 C). Compared with the stretching vibration peak of O-H and N-H groups at 3301 cm − 1 in ELA, as well as the stretching vibration peak of O-H groups at 3436 cm − 1 in LA, the stretching vibration peak of O-H and N-H groups at 3325 cm − 1 in ELA/LA 2:1 is significantly strengthened and broadened, indicating that there are clear intermolecular hydrogen bonding between ELA and LA. In ELA/LA 2:1 , the stretching vibration peak of C═O group in LA shifts from 1700 cm − 1 to 1720 cm − 1 , and the bending vibration of O-H group in LA shifts from 946 cm − 1 to 888 cm − 1 , the bending vibration of O-H group in ELA shifts from 1056 cm − 1 to 1068 cm − 1 , the in-plane bending vibration of the N-H bond at 611 cm − 1 in ELA/LA 2:1 is significantly enhanced, suggesting that the formation of intermolecular hydrogen bonds affect their vibration absorption. In other molar ratios of ELA/LA deep eutectic mixtures, the intermolecular hydrogen bonds are also formed and detected ( Fig. S8 ). To further investigate the formation mechanism of the ELA/LA deep eutectic system, molecular simulation calculations are conducted on the ELA/LA 2:1 to explore the interaction between ELA and LA small molecules in the molar ratio of 2:1. The results show that there are a large number of hydrogen bonds in the ELA/LA deep eutectic mixture. The O-H group of ELA forms a strong hydrogen bond with the -COOH group of LA. There are also electrostatic interaction forces in other parts. In the process of mixing ELA and LA, the number of hydrogen bonds increases and the total energy value of the system decreases ( Fig. S9 ). Normally, the fluidity of hydrogels and their initial adhesion to the tissues surface require special attention. Because the flowing hydrogels without initial adhesion before curing often suffer from unintended leakage to surrounding tissues 49 . The deep eutectic mixtures of ELA/LA have adhesive ability based on its abundant adhesive groups. They can adhere on gelatin-coated glass slides, exhibiting well-performed initial adhesion that may prevent the loss of the adhesive. The adhesion strengths of ELA/LA 6:1 , ELA/LA 4:1 , ELA/LA 2:1 , ELA/LA 1:1 and ELA/LA 1:2 are ~ 2.29 kPa, ~ 0.76 kPa, ~ 0.93 kPa, ~ 1.47 kPa and ~ 3.17 kPa (Fig. 2 D, S10). For adhesive derived from LA, it is usually achieved by heating to trigger LA polymerization to obtain sufficiently high adhesive strength. But this requires high temperature and longer heating duration. Dithiolane can easily achieve the ring-opening polymerization (ROP) under 365 nm UV light without any initiator. However, this is rarely used for the preparation of LA adhesives, mainly because UV cannot effectively act on LA solid powders. In the present study, the melting of ELA and LA solid powders into transparent melt is achieved through deep eutectic melting, which exhibits sensitive and rapid UV responsiveness (Fig. 2 E). As shown in UV spectra, initially, the ELA/LA 2:1 deep eutectic mixture mainly consists of small molecule monomers, and the absorption peak of dithiolane at 338 nm can be clearly observed. As the UV-irradiation duration increases, the dithiolane of ELA/LA 2:1 undergoes ring-opening polymerization. The absorption peak at 338 nm gradually decreases, while the absorption of linear disulfide in the 250 nm − 300 nm range increases (Fig. 2 F) 18 . As shown in Raman spectra, a distinctive Raman peak of the linear disulfide bonds appears at 525 cm − 1 as the radiation time increases 23 . This characteristic change solidly proved the successful conversion of monomers into polymers by ROP (Fig. 2 G). According to Mass spectra results in Fig. S11 , there are small molecules and oligomers in ELA/LA 2:1 deep eutectic mixture, while polymers in ELA/LA 2:1 @UV with obvious MS signal in a larger m/z range. As well, the cyclic topology of the ELA/LA 2:1 @UV after photopolymerization is proved ( Fig. S11 ). Density functional theory (DFT) is used to study the polymerization process of ELA/LA 2:1 eutectic system, including the possibility of chain segment combination of ELA and LA, and the changes of Gibbs free energy. The results show that in the ELA/LA 2:1 eutectic system, five types of polymerization segments, namely ELA/ELA, LA/LA, ELA/LA, ELA/ELA/LA and ELA/LA/ELA, may occur during the polymerization process, with corresponding Gibbs free energies of -1.811 eV, -1.762 eV, -1.680 eV, -3.807 eV and − 4.047 eV respectively. All five Gibbs free energies are negative, indicating that the polymerization reaction can proceed in the forward direction, and the polymer chain is mostly composed of ELA/LA/ELA polymer segments ( Fig. S12 ). Moreover, according to rheological testing results in Fig. 2 H, the photo-curing duration of ELA/LA 2:1 deep eutectic mixture is about at 43 s. Meanwhile, UV light triggered the ring-opening polymerization of ELA/LA 2:1 deep eutectic mixture in a short time can produce stronger cohesion, leading to the significantly enhanced adhesive strength. The adhesive strength of ELA/LA 2:1 @UV are ~ 1120.2 kPa and ~ 1698.5 kPa after being exposed to irradiation for 5 min and 10 min ( Fig. S13 ). Figure 2 I and Fig. S14 show the UV exposure process of ELA/LA 2:1 eutectic mixture and its ability to withstand a weight of 5 kg in the vertical direction and 400 g in the horizontal direction, manifesting a reliable adhesion ability. In addition, ELA/LA 2:1 can adhere to different substances such as PE, rubber, ceramic, wood and steel, etc. Interesting, after UV exposure, the color of ELA/LA 2:1 eutectic system changes from yellow to colorless, which is different with heat-triggered polymerization (Fig. 2 I, S15). The influence of UV irradiation on the adhesion performance of ELA/LA with different molar ratios is evaluated in the Fig. 2 J. After 5 min of UV irradiation, the maximum adhesive force of ELA/LA 6:1 @UV, ELA/LA 4:1 @UV, ELA/LA 2:1 @UV, ELA/LA 1:1 @UV and ELA/LA 1:2 @UV is ~ 213.60 N, ~ 261.67 N, ~ 335.67 N, ~ 140.57 N and ~ 72.67 N, respectively. Their adhesion strength is 766.50 kPa, ~ 976.57 kPa, ~ 1120.20 kPa, ~ 437.60 kPa and ~ 236.27 kPa, respectively. ELA/LA 2:1 @UV has the highest adhesion strength, possibly because ELA/LA 2:1 has the best liquefaction degree, possessing more small molecules participate in the polymerization under UV irradiation. Meanwhile, the ELA/LA 2:1 @UV will continue to polymerize under natural light, with the cohesion further enhanced, leading to the gradually increased adhesion strength ( Fig. S16 ). Trauma can cause bleeding and exudation of tissue fluid, etc. Underwater adhesion is an important criterion for evaluating biological adhesives 20 , 22 , 50 – 58 . As shown in Fig. 2 K and Fig. S17 , the wet adhesion test of ELA/LA 2:1 deep eutectic adhesive is carried out. ELA/LA 2:1 could be injected and adhered onto the surfaces of substrates such as glass, plastic and metal respectively in water. After being exposed to UV for 5 min, ELA/LA 2:1 @UV could adhere firmly for lifting substrates. As shown in Fig. 2 L, the glass sheets adhered with ELA/LA 2:1 deep eutectic adhesive that exposed to UV light for 5 min are immersed in water. The maximum adhesive force of ELA/LA 2:1 @UV immersed in water for 0 day, 1 day, 3 days, 5 days and 7 days, is ~ 336.05 N, ~ 273.82 N, ~ 316.60 N, ~ 276.39 N and ~ 246.33 N, respectively. Their adhesion strength is ~ 1120.20 kPa, ~ 1057.99 kPa, ~ 1087.15 kPa, ~ 1060.64 kPa and ~ 951.52 kPa, respectively. During the immersion duration of 5 days, the adhesion strength of ELA/LA 2:1 @UV does not decrease significantly, suggesting that it has a relatively stable underwater adhesion ability. 2.3 Preparation and characterizes of the APLA/LA deep eutectic adhesive The similar deep eutectic phenomenon also occurs in the APLA/LA. When the molar ratio of APLA to LA is 1.5:1, the two solid powders mixed at room temperature within 10 min will transform into a viscous liquid that is injectable (Fig. 3 A, Fig. S18 ). Other molar ratios of APLA to LA is set as 4:1, 2:1, 1:1 and 1:2. The appearance and polarized microscope observation are showed in Fig. S19 . The APLA/LA 4:1 and APLA/LA 1:2 are semisolid. When APLA or LA is in excess, APLA or LA crystals exist in the APLA/LA. XRD is also employed to illustrate structural changes in APLA/LA 1.5:1 . Figure 3 B shows that there are highly ordered nanoscale crystal structures in APLA and LA, while the diffraction peaks in APLA/LA 1.5:1 disappeared, indicating the formation of amorphous phase. The formation mechanism of the deep eutectic system between APLA and LA is investigated by FT-IR ( Fig. S20 ). Compared with the stretching vibration peak of O-H and N-H groups at 3343 cm − 1 in APLA, and the stretching vibration peak of O-H groups at 3436 cm − 1 in LA, the stretching vibration peaks of O-H and N-H groups at 3346 cm − 1 in APLA/LA 1.5:1 are significantly broadened and strengthened, indicating the intermolecular hydrogen bond interactions between APLA and LA. For APLA/LA 1.5:1 , the stretching vibration peak of C═O group in LA shifts from 1700 cm − 1 to 1719 cm − 1 , and the bending vibration of O-H group in LA shifts from 946 cm − 1 to 880 cm − 1 . The bending vibration of O-H group in APLA at 1113 cm − 1 and 1049 cm − 1 is significantly weakened, suggesting that the formation of intermolecular hydrogen bonds that affect their vibration absorption. In other molar ratios of APLA/LA deep eutectic systems, the intermolecular hydrogen bonds are also detected ( Fig. S20 ). Meanwhile, the APLA/LA deep eutectic mixture also exhibits UV responsiveness, the photo-curing time of APLA/LA 1.5:1 deep eutectic system is about at 124 s, which is slower than ELA/LA 2:1 deep eutectic adhesive (Fig. 3 C). Moreover, compared with ELA/LA 2:1 , the viscosity of APLA/LA 1.5:1 is higher (Fig. 3 D). The adhesive properties of APLA/LA deep eutectic mixture before and after UV irradiation are evaluated in Fig. 3 E and Fig. S21 . The adhesion strengths of APLA/LA 4:1 , APLA/LA 2:1 , APLA/LA 1.5:1 , APLA/LA 1:1 and APLA/LA 1:2 are ~ 9.80 kPa, ~ 6.77 kPa, ~ 5.24 kPa, ~ 7.40 kPa and ~ 7.95 kPa. After UV irradiation, the adhesion strengths of APLA/LA 4:1 @UV, APLA/LA 2:1 @UV, APLA/LA 1.5:1 @UV, APLA/LA 1:1 @UV and APLA/LA 1:2 @UV are ~ 41.20 kPa, ~ 78.15 kPa, ~ 133.40 kPa, ~ 127.84 kPa and ~ 102.34 kPa. Of note, the adhesive strength of ELA/LA 2:1 @UV is 1120.20 kPa, which is significantly higher than that of APLA/LA 1.5:1 @UV. Therefore, ELA/LA 2:1 is selected as a representative adhesive for in vitro and in vivo tissue adhesion and repair. 2.4 Wet/oil tissue adhesion and application of ELA/LA deep eutectic adhesive Based on the unique feature of ELA/LA 2:1 deep eutectic adhesive, it is used as a new type of photo-curing molten adhesive. Through mixing ELA and LA powder at room temperature, a molten adhesive is quickly formed. After applying or injecting the molten adhesive onto the surfaces of the tissues, significant interfacial adhesion can be immediately formed. Further UV irradiation to trigger polymerization for curing to achieve reliable adhesion (Fig. 4 A). The ability to effectively adhere to various biological tissues and its effect for tissue healing are further evaluated. As shown in Fig. 4 B and Fig. S22 , ELA/LA 2:1 applied onto the surfaces of fresh chicken kidneys, lungs, livers and hearts can effectively adhere to the tissues without loss due to random flow. After being exposed to UV light, it can firmly bond biological tissues. After UV irradiation, the adhesion is strong enough to bear stretching, bending and distorting, as well as PBS and water flushing ( Fig. S23 ). The lap-shear tests confirm that the maximum adhesive force of ELA/LA 2:1 @UV on porcine skin is ~ 3.56 N and the adhesion strength is ~ 52.24 kPa. The maximum adhesive force of ELA/LA 2:1 @UV on porcine lean meat is ~ 2.29 N, and the adhesion strength is ~ 37.17 kPa. The 90-degree peel tests confirm that the maximum peel force of ELA/LA 2:1 on pigskin is ~ 3.45 N and the peel strength is ~ 443.33 N/m, which is significantly higher than that of fibrin glue (~ 45.41 N/m) ( Fig. S24 ). It should be emphasized that these fresh tissues have not undergone any processing before adhesion, indicating the convenience of the application. In practical in vivo applications, in addition to the challenge of adhesion brought by moist environments, the oil on the tissue surface is more challenging 59 . To verify the adhesive's response to this challenge, ELA/LA 2:1 deep eutectic adhesive is applied into the inner section of fresh porcine fat. It is observed that the ELA/LA 2:1 deep eutectic adhesive effectively forms adhesion to the surfaces of the fat ( Fig. S25 ). After UV irradiation, the fat is firmly adhered (Fig. 4 C). The adhesion mechanism belongs to typical topological adhesion, which requires the adhesive to penetrate into the tissue and form an interlocking structure. As shown in Fig. 4 D, because ELA and LA are small molecule in the deep eutectic mixture, they are more likely to penetrate tissues compared to macromolecules. Therefore, after UV-triggered polymerization, the polymer chains form a strong interlocking structure with the tissue. Similarly, adhesives can also penetrate wet tissues rich in water to form strong topological adhesion. To illustrate this point, corneal tissue is used for adhesion test. ELA/LA 2:1 deep eutectic adhesive is applied to two separated corneas and exposed to UV light, the two corneas are firmly adhered together ( Fig. S26-27 ). Therefore, whether it is a wet tissue surface rich in water or a tissue surface rich in oil, ELA/LA 2:1 deep eutectic adhesive can form effective adhesion. There is no need to pre-treat the tissue surface during application, which is very convenient for surgical application. In vivo evaluation was further carried out. As one of the important organs of the human body, liver is easy to cause massive bleeding after injury. In severe cases, it will lead to shock. Unlike other organs, liver is soft and brittle. When traditional suture is performed on the wound, it is not only difficult to operate, but also prone to secondary tears and pinhole bleeding, which is difficult to achieve effective hemostasis. Therefore, a new type of biological adhesive that combines highly efficient hemostatic function with excellent wet adhesion is needed in improving the clinical treatment of liver injury. ELA/LA 2:1 deep eutectic adhesive is used to verify their liver hemostatic ability. As shown in Fig. 4 E, a wound is created on the liver with an 18G needle. ELA/LA 2:1 deep eutectic adhesive is injected at the site of liver injury, followed by UV irradiation. The liver bleeding is observed. The amount of bleeding in the blank group and the ELA/LA 2:1 deep eutectic adhesive group is tracked using filter paper. The results show that compared with the blank group, the ELA/LA 2:1 deep eutectic adhesive group has a significant hemostatic effect. Within 3 minutes, the bleeding volume in the blank group is 30.6 mg, while that in the ELA/LA 2:1 deep eutectic adhesive group is 1.8 mg. At the same time, ELA/LA 2:1 deep eutectic adhesive used as sealants to treat gastrointestinal perforation is evaluated in a rat gastric perforation model (Fig. 4 F). A 3.5-mm vertical perforation is made at the gastric antrum using a scalpel, allowing the gastric lumen to open into the abdominal cavity. The gastric perforations are closed by using a non-absorbable suture, or ELA/LA 2:1 deep eutectic adhesive (0.1 mL). The untreated wound is the blank group. On day 7 after the treatment, general examination on the stomach tissues reveals a significantly smaller wound area in the adhesive treated group (11.65 ± 1.68 mm 2 ) than that in the suture group (16.95 ± 1.66 mm 2 ) and the blank group (68.86 ± 5.50 mm 2 ), indicating better wound healing in the adhesive treated group (Fig. 4 F, Fig. S28 ). Histological staining further shows that the serum muscle layer around the wounds in the three groups had a certain degree of regeneration on day 7. Among the three groups, only the gastric perforations sealed with adhesives are completely bridged with the regenerated mucosa. In contrast, the perforations in the blank group and the suture group showed larger and clearer gaps on the mucosa (Fig. 4 G). Above all, both the ELA/LA and APLA/LA eutectic systems possess the ability to form a molten adhesive simply by mixing two solid components at room temperature. This molten adhesive can be applied or injected onto tissue surfaces. Following UV irradiation, significant interfacial adhesion is immediately formed. These molten adhesives hold promise for applications in tissue dressings for wound healing, injectable adhesives or sealants for tissue repair, UV light-shielding adhesives, drug delivery adhesives, as well as flexible wearables and electronics. 2.5 Preparation and characterizes of the DELA/LA deep eutectic adhesive Different from ELA and APLA, DELA is a yellow transparent thin liquid that possesses fluidity (Fig. 5 A). It also has UV responsiveness. Under UV irradiation, the dithiolane gradually undergoes ring-opening polymerization reaction, the absorption peak at 338 nm gradually decreases, while the absorption of linear disulfide in the 250–300 nm range increases (Fig. 5 B). Meanwhile, UV triggers the ring-opening polymerization of DELA in a short time can produce strong cohesion, which greatly enhances the adhesive strength of DELA@UV. The adhesive strength of DELA@UV after being exposed for 5 min is ~ 477.50 kPa, which is significantly higher than that of DELA without UV irradiation (~ 1.13 kPa) (Fig. 5 C, Fig. S29 ). Of note, DELA can undergo ring-opening self-polymerization under natural light. When DELA is exposed to natural light for 3 days, its viscosity increases significantly, showing no flowing down after inversion (Fig. 5 D). Its adhesion performance also increases significantly (Fig. 5 E). MS signals after 3 day’s self-polymerization of DELA is concentrated between 600 and 3000 m/z, which is higher than the monomer of 293.97 m/z (Fig. 5 F, Fig. S30 ). G’’ and G’ of DELA after 3 days are ~ 24644.5 Pa and ~ 17616.9 Pa (angular frequency at 10 rad/s), which are significantly higher than those of DELA at day 0 (Fig. 5 G). The viscosity of DELA after 3 days is ~ 9821.81 Pa.s (shear rate at 10 1/s), which is significantly higher than that of DELA (~ 16.69 Pa.s) at 0 day (Fig. 5 H). The degree of self-polymerization of DELA under different natural light exposure duration for 0 day, 1 day, 3 days, 5 days and 7 days is monitored by UV-Vis spectra. With the increase of irradiation duration, the absorption peak at 338 nm gradually decreases, while the absorption of linear disulfide in the 250–300 nm range increases (Fig. 5 I). Meanwhile, nature light triggers the ring-opening polymerization of DELA in different days also produce enhanced cohesion, leading to the promoted adhesive strength. The maximum adhesive force of DELA@nature light at 0 day, 1 day, 3 day, 5 day and 7 day is ~ 0.37 N, ~ 23.20 N, ~ 158.90 N, ~ 141.58 N and ~ 114.65 N respectively. Their adhesion strength is ~ 1.13 kPa, ~ 65.27 kPa, ~ 611.87 kPa, ~ 594.30 kPa and ~ 446.73 kPa, respectively (Fig. 5 J, Fig. S31 ). DELA and LA also exhibit deep eutectic phenomena. When the molar ratio of DELA to LA is 2:1, the LA powder can be dissolved in DELA at room temperature within ~ 1 min, producing a thin and transparent liquid (Fig. 5 K, Fig. S32 ). It is found from the polarizing microscope that the complete liquefaction occurs at DELA/LA 2:1 mixture. LA crystals exist in the DELA/LA 1:1 and DELA/LA 1:2 mixture ( Fig. S33 ). XRD curves show that DELA and DELA/LA 2:1 mixture are amorphous phases, while the diffraction peaks of LA appeared in DELA/LA 1:1 and DELA/LA 1:2 mixture. The presence of LA crystals also affects the transparency ( Fig. S34 ). The formation mechanism of the deep eutectic mixture between DELA and LA is investigated by FT-IR (Fig. 5 L). Compared with the stretching vibration peak of O-H and N-H groups at 3393 cm − 1 in DELA, as well as the stretching vibration peak of O-H groups at 3436 cm − 1 in LA, the stretching vibration peak of O-H and N-H groups at 3395 cm − 1 in DELA/LA 2:1 is significantly broadened and strengthen, indicating that there are intermolecular hydrogen bond interactions between DELA and LA. In DELA/LA 2:1 , the stretching vibration peak of C═O group in LA shifted from 1700 to 1723 cm − 1 , and the bending vibration of O-H group in LA shifted from 946 to 860 cm − 1 , suggesting that the formation of intermolecular hydrogen bonds affected their vibration absorption. In other molar ratios of DELA/LA mixture, the intermolecular hydrogen bonds are also formed ( Fig. S35 ). DELA/LA deep eutectic mixture possesses UV responsiveness. The ROP reaction of the dithiolane occurs under UV irradiation ( Fig. S36 ). As shown in Raman spectra, a distinctive Raman peak of the linear disulfide bonds appears at 526 cm − 1 . As the radiation time increases, the absorption peak of the dithiolane at 338 nm gradually decreases, while the absorption of linear disulfide in the 250–300 nm range increases. These characteristic changes proved the successful conversion of monomers into polymers by ROP. The polymerization reaction increases the cohesion of DELA/LA deep eutectic adhesive. As shown in Fig. 5 M and Fig. S37 , the adhesion strength of DELA/LA 2:1 , DELA/LA 1:1 and DELA/LA 1:2 is ~ 1.18 kPa, ~ 2.23 kPa, ~ 3.25 kPa. After UV irradiation for 5 min, the adhesion strengths of DELA/LA 2:1 @UV, DELA/LA 1:1 @UV and DELA/LA 1:2 @UV is ~ 1546.89 kPa, ~ 1362.30 kPa, ~ 618.62 kPa. Meanwhile, the DELA/LA 2:1 @UV will continue to polymerize under natural light, with the cohesion further enhanced, leading to the gradually increased adhesion force and adhesion strength ( Fig. S38 ). In addition, the DELA/LA 2:1 can adhere to different substrates and tissues after UV irradiation to withstand a high separation force ( Fig. S39 ). 2.6 Preparation and characterizes of the TLA/LA deep eutectic adhesives Similar to ELA and APLA, TLA is a solid powder, which, however, possessing higher T m (109.46 ℃). Although there is no liquefaction phenomenon after mixing TLA with LA powder with different molar ratios at room temperature, the T m of the TLA/LA 1:3 is reduced to 60.59 ℃, which is also a typical deep eutectic mixture. Heating the TLA/LA deep eutectic mixtures above their T m , will yield a series of light-yellow viscous liquids of TLA/LA mixtures. At the same time, the ring-opening polymerization of dithiolane is also triggered during heating, resulting in a light-yellow and transparent P(TLA/LA) patch after cooling to room temperature (Fig. 6 A, Fig. S40 ). The formation mechanism of TLA/LA deep eutectic systems is monitored by FT-IR spectra. As shown in Fig. 6 B and Fig. S41 , TLA/LA 1:3 solid powder is obtained by simply mixing TLA and LA powders. The FT-IR spectra of TLA/LA 1:3 powder without heating is a simple superposition of the FT-IR spectra of TLA and LA, with no obvious shift of each characteristic peak. PTLA and PLA are obtained by the polymerization of small molecule monomers TLA and LA, respectively. In their FT-IR spectra, the peak shapes have changed, but the peak displacements have not changed ( Fig. S42 ). While in P(TLA/LA 1:3 ), the stretching vibration peak of C═O group in LA shifts from 1700 cm − 1 to 1706 cm − 1 , and the bending vibration of O-H group in LA shifts from 946 cm − 1 to 893 cm − 1 , the bending vibration of O-H group in TLA shifts from 1020 cm − 1 to 1058 cm − 1 , indicating that the intermolecular hydrogen bond interactions. In other molar ratios of TLA/LA deep eutectic mixtures, the intermolecular hydrogen bonds are also detected ( Fig. S43 ). The tunable melting temperature, abundant adhesive groups, and in situ curing ability after cooling make TLA/LA deep eutectic mixtures excellent hot melt adhesives. The adhesion ability of TLA/LA deep eutectic adhesives to various substrates is investigated by lap-shear testes. As shown in Fig. 6 C, the adhesion strength of P(TLA/LA 1:3 ) to glass and stainless steel is higher than that of to PC, PMMA and PTFE. It is worth noting that the adhesion strength of P(TLA/LA 1:3 ) to glass is about 4.33 MPa, which is higher than that of ELA/LA, APLA/LA and TLA/LA eutectic adhesives. The long-lasting adhesion of adhesives is one of the important indicators of adhesives. Lap-shear tests are conducted at different time. The results show that with the increase of duration, the adhesion strength becomes significantly stronger. After 2 days, the adhesion strength of P(TLA/LA 1:3 ) to stainless steel and glass increases to more than 9 MPa (Fig. 6 D, S44). TLA with more quantity of terminal hydroxyl groups afforded a structural P(TLA/LA 1:3 ) adhesive with strength equivalent to that of conventional industrial adhesives 18 , 22 , 60 . Remarkably, the P(TLA/LA 1:3 ) adhered stainless steels with an adhesion area of 2 ×1 cm could easily lift a weight of person with 65 kg in the vertical direction (Fig. 6 E). Such a powerful adhesive force is not only due to the introduction of the more hydroxyl group, but also the increased cohesion from thermal polymerization. As shown in Raman spectra, the Raman peak shapes of LA and TLA are relatively sharp. After heating, the peak shape of PTA, PTLA and P(TLA/LA 1:3 ) becomes rounded. A distinctive Raman peak of the linear disulfide bonds appears at 523 cm − 1 , confirming the successful conversion of monomers into polymers by heating-triggered ROP (Fig. 6 F). Next, the water-resistance adhesion capabilities of P(TLA/LA 1:3 ) adhesives are examined by soaking the P(TLA/LA 1:3 ) -adhered stainless steels into water for 4 days (Fig. 6 G). The results show that the adhesion strength of P(TLA/LA 1:3 ) do not decrease significantly compared with dry state. The adhesive strength is always maintained at a relatively high level (~ 3 MPa). Remarkably, the soaked P(TLA/LA 1:3 ) -adhered stainless steels with an adhesion area of 2 ×1 cm could easily lift a weight of 30 kg in the vertical direction and 400 g in the horizontal direction ( Fig. S45 ). The adhesion strength of P(TLA/LA 1:3 ) deep eutectic adhesives compared with the LA-based adhesives reported in the representative literatures is shown in Fig. 6 H. It is worth noting that the adhesive strength of the deep eutectic adhesives used in this study is the highest in the UV-triggered preparation of LA-derivatives. In the hot-melt adhesives, the adhesion strength of the deep eutectic adhesives in this study also exceeded that of most reports. Although its adhesive strength is not the highest, the components used in this study are the simplest compared to other adhesives. It is rare to report achieving such high adhesion strength and stability solely through two components with no chemical crosslinking units. More importantly, heat-induced LA-based adhesives inevitably have the problem of de-polymerization. It has been reported in the literature that the researches on anti-depolymerization of LA-based adhesives is conducted by end-capping, introducing halogens or steric hindrance, and intermolecular hydrogen bonding 17 , 23 , 25 , 61 . Similarly, the interactions between TLA and LA endow the TLA/LA deep eutectic adhesives with well performed anti-depolymerization property, cause by intermolecular hydrogen bonding and steric hindrance. As shown in Fig. 6 I and Fig. S40 , LA, TLA/LA 1:2 , TLA/LA 1:1 , TLA/TLA 1:2 , TLA/LA 1:3 and TLA/LA 1:4 after heating and polymerization are monitored for 3 days. Obvious de-polymerization of PLA is observed after 3 days later. However, no de-polymerization is observed in the TLA/LA deep eutectic mixtures ( Fig. S46 ). XRD spectra confirm that no small molecule crystallization peaks of P(TLA/LA) are observed after 3 days ( Fig. S47 ). Raman spectra confirm that the linear disulfide bonds in PLA are significantly weakened due to the de-polymerization of PLA. However, the intensity of the Raman peaks of linear disulfide bonds in P(TLA/LA) show no significant weakening, indicating that P(TLA/LA) does not undergo obvious de-polymerization ( Fig. S48 ). In conclusion, the introduction of TLA with only a relatively small amount has a significant inhibitory effect on the depolymerization of TLA/LA deep eutectic mixture. Of note, similar to most adhesives formed by LA thermal polymerization, the application of TLA/LA adhesives requires placing them on the surface of the substrate and then heating them to achieve a firm adhesion. But if the P(TLA/LA) patch is obtained by heating first, it does not have adhesion ability to the substrate. Because the T m of the TLA/LA mixtures is much higher than body temperature, they are not suitable for tissue adhesion applications through is-situ heating. They also cannot be in-situ cured by UV like ELA/LA, APLA/LA and DELA/LA. However, according to its robust mechanical feature (Fig. 6 J), P(TLA/LA) patch can be used to combine with other deep eutectic adhesives in this study such as DELA to prepare a band-aid. DELA can form tight binding to P(TLA/LA) patch because of the disulfide exchange on their interface during dithiolane ROP. Such Janus structure combines the high cohesion of P(TLA/LA) and the high interfacial adhesion strength of DELA. This band-aid can effectively achieve the sealing of the leaked porcine intestines and stomachs (Fig. 6 K, 6 L). The bursting pressure is ~ 0.094 MPa (Fig. 6 M, S49). This combination implies that LA derivatives and their deep eutectics can be cross-combined to suit different applications. Conclusion In this work, a kind of UV-triggered, solvent-free, LA-based room-temperature molten adhesive has been reported for the first time. The critical discovery is that functionally modified LA (ELA, APLA and DELA) can mix with LA powders to produces a molten adhesive at room temperature via deep eutectic melting. The UV-triggered polymerization of dithiolane in the molten adhesives enables rapid, robust and stable tissue bonding upon contact with wet/oil tissue. These LA-based molten adhesives demonstrate superior mechanical and biological properties compared to conventional medical-grade fibrin glue. 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Supplementary Files TheliquidityoftheELALA.mp4 The liquidity of the ELA-LA ThePreparationoftheELALAdeepeutecticbioadhensives.mp4 The Preparation of the ELA-LA deep eutectic bioadhensives supportinginformation.docx supporting information Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7750130","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":554425224,"identity":"346dedcf-51b2-40bb-8b2c-9b92e33c10a1","order_by":0,"name":"Kunxi 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15:45:10","extension":"html","order_by":17,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":137308,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7750130/v1/d8f2fc45b3fe2e1761c4b64d.html"},{"id":97897519,"identity":"c4dadda8-6a5a-4167-8e0f-f5087248128b","added_by":"auto","created_at":"2025-12-10 15:37:55","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":211519,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe deep eutectic behavior between LA and its derivatives.\u003c/strong\u003e \u003cstrong\u003eA\u003c/strong\u003e, The appearance and polarizing microscope images of the LA and its derivatives. \u003cstrong\u003eB\u003c/strong\u003e, The structure and binding energies between LA and its derivatives. \u003cstrong\u003eC\u003c/strong\u003e, DSC curves of the LA, its derivatives and their mixtures.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7750130/v1/39f81e52d86031d241796646.png"},{"id":97856553,"identity":"b8a27727-cf8b-4592-aa3c-3fd4e26f949d","added_by":"auto","created_at":"2025-12-10 07:56:23","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":270103,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eELA/LA deep eutectic adhesives and UV responsiveness.\u003c/strong\u003e \u003cstrong\u003eA\u003c/strong\u003e, Instructions for the preparation of the ELA/LA deep eutectic adhesive by simply mixing ELA and LA at room temperature, and its injectability. \u003cstrong\u003eB\u003c/strong\u003e, XRD spectra of the ELA, LA and ELA/LA\u003csub\u003e2:1\u003c/sub\u003e. \u003cstrong\u003eC\u003c/strong\u003e, FT-IR spectra to illustrate the interactions in ELA/LA deep eutectic adhesive. \u003cstrong\u003eD\u003c/strong\u003e, Images and adhesion strength to show the adhesion of the ELA/LA deep eutectic systems. \u003cstrong\u003eE\u003c/strong\u003e, The UV responsiveness of the ELA/LA deep eutectic systems. UV-Vis spectra (\u003cstrong\u003eF\u003c/strong\u003e) and Raman spectra (\u003cstrong\u003eG\u003c/strong\u003e) to track the UV responsiveness. \u003cstrong\u003eH\u003c/strong\u003e, G’ and G’’ of the ELA/LA\u003csub\u003e2:1\u003c/sub\u003e under UV in time sweep mode. \u003cstrong\u003eI\u003c/strong\u003e, Images to show the UV responsiveness and adhesion strength of the ELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV. \u003cstrong\u003eJ\u003c/strong\u003e, Lap-shear curves and adhesion strength of the ELA/LA@UV with different molar ratios adhered on glasses. \u003cstrong\u003eK\u003c/strong\u003e, Images to show the application of the ELA/LA deep eutectic adhesive under water. \u003cstrong\u003eL\u003c/strong\u003e, Lap-shear curves and adhesion strength of the ELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV adhered on glasses under water.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7750130/v1/84ad5efed29a249fa79a4628.png"},{"id":97856554,"identity":"e830eeff-b8f5-4fe2-9b10-f6e1054b1df9","added_by":"auto","created_at":"2025-12-10 07:56:23","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":117025,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAPLA/LA deep eutectic adhesive and its UV responsiveness. A\u003c/strong\u003e, Instructions for the preparation of APLA/LA deep eutectic adhesive by mixing APLA and LA at room temperature, and its injectability. \u003cstrong\u003eB\u003c/strong\u003e, XRD spectra of the APLA, LA and APLA/LA\u003csub\u003e1.5:1\u003c/sub\u003e. \u003cstrong\u003eC\u003c/strong\u003e, G’ and G’’ of the APLA/LA\u003csub\u003e1.5:1\u003c/sub\u003e under UV in time sweep mode.\u003cstrong\u003e D,\u003c/strong\u003e Comparison of the viscosities between ELA/LA\u003csub\u003e2:1\u003c/sub\u003e and APLA/LA\u003csub\u003e1.5:1 \u003c/sub\u003eas a function of shear rate. \u003cstrong\u003eE\u003c/strong\u003e, Adhesion strength of the APLA/LA deep eutectic system before and after UV irradiation adhered on glasses.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7750130/v1/5712ab286f766b0696c9bfac.png"},{"id":97898009,"identity":"e45f467e-af57-42d7-9637-57b6c64bcf24","added_by":"auto","created_at":"2025-12-10 15:38:35","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":435413,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eIn-vivo application of ELA/LA deep eutectic adhesive.\u003c/strong\u003e \u003cstrong\u003eA\u003c/strong\u003e, The usage process of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive. The adhesion of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e on chicken kidney (\u003cstrong\u003eB\u003c/strong\u003e) and pork fat (\u003cstrong\u003eC\u003c/strong\u003e). \u003cstrong\u003eD\u003c/strong\u003e, Small molecules penetrate into pork fat. \u003cstrong\u003eE\u003c/strong\u003e, ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive is used in rat liver hemostasis models. \u003cstrong\u003eF\u003c/strong\u003e, ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive for gastric perforation models. \u003cstrong\u003eG\u003c/strong\u003e, H\u0026amp;E, Masson, IL-6, IL-10, CD31, α-SMA staining of gastric perforation repair on day 7 post-surgery (Bar scale: 1mm, 500 μm).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7750130/v1/385bdf7de04b30865c35c28b.png"},{"id":97856558,"identity":"11ee1527-6b6c-444e-ac2d-0fdf976d601c","added_by":"auto","created_at":"2025-12-10 07:56:23","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":218156,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAdhesives derived from DELA and their photo-responsiveness. A,B,C\u003c/strong\u003e, DELA adhesive and its UV responsiveness. \u003cstrong\u003eD\u003c/strong\u003e, Self-polymerization of DELA under nature light for 3 days. \u003cstrong\u003eE\u003c/strong\u003e, The adhesion changes of DELA under nature light for 3 days. \u003cstrong\u003eF\u003c/strong\u003e, MALDI-TOF-MS spectrum of DELA under nature light for 3 days. \u003cstrong\u003eG\u003c/strong\u003e, G’ and G’’ of DELA under nature light for 0 day and 3 days in angular frequency sweep mode. \u003cstrong\u003eH\u003c/strong\u003e, The viscosity changes of DELA under nature light for 0 day and 3 days in shear rate mode. \u003cstrong\u003eI\u003c/strong\u003e, UV-Vis spectra to track the nature light-responsiveness. \u003cstrong\u003eJ\u003c/strong\u003e, Adhesion strength of DELA with different days adhered on glasses. \u003cstrong\u003eK\u003c/strong\u003e, Construction of the DELA/LA deep eutectic adhesive. \u003cstrong\u003eL\u003c/strong\u003e, FT-IR spectra to illustrate the interactions in DELA/LA deep eutectic adhesive. \u003cstrong\u003eM\u003c/strong\u003e, Adhesion strength of DELA/LA deep eutectic system before and after UV irradiationadhered on glasses.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7750130/v1/3e0b1fbf2a0204ee8c415167.png"},{"id":97897527,"identity":"47ebbaf0-7073-40fd-b988-f8925742e4ab","added_by":"auto","created_at":"2025-12-10 15:37:56","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":512713,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTLA/LA deep eutectic adhesive and its adhesion performance. A\u003c/strong\u003e, Construction of the TLA/LA deep eutectic adhesive by simply mixing TLA and LA at room temperature, and its heat responsiveness. \u003cstrong\u003eB\u003c/strong\u003e, FT-IR spectra to illustrate the interactions in TLA/LA deep eutectic adhesive. \u003cstrong\u003eC\u003c/strong\u003e, Adhesion strength of the P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e) adhered on glasses, stainless steel, PC, PMMA and PTFE. \u003cstrong\u003eD\u003c/strong\u003e, Adhesion strength of the P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e) adhered on stainless steel with different days. \u003cstrong\u003eE\u003c/strong\u003e, Images to show the adhesion of the P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e) deep eutectic systems. \u003cstrong\u003eF\u003c/strong\u003e, Raman spectra to track the heat-responsiveness. \u003cstrong\u003eG\u003c/strong\u003e, Adhesion strength of the P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e) adhered on stainless steel under water with different days.\u003cstrong\u003e H\u003c/strong\u003e, Summary of the adhesion strength of various types of dithiolane-derived adhesives on\u003cstrong\u003e \u003c/strong\u003eglass\u003cstrong\u003e \u003c/strong\u003esubstrates developed in representative literature. \u003cstrong\u003eI\u003c/strong\u003e, Images to show the anti-depolymerization of P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e). \u003cstrong\u003eJ\u003c/strong\u003e, Images to show the patch of P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e). \u003cstrong\u003eK\u003c/strong\u003e, Scheme to show the preparation of a band-aid from P(TLA/LA) and DELA. \u003cstrong\u003eL\u003c/strong\u003e, Sealing of the leaked porcine intestines and stomachs. \u003cstrong\u003eM\u003c/strong\u003e, Bursting pressure of the DELA under nature light for 3 days and P(TLA/LA)@DELA band-aid.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7750130/v1/21ef878d965f5f1a2c648f7e.png"},{"id":100547702,"identity":"452492b1-62cb-4982-bc46-c0191186b15a","added_by":"auto","created_at":"2026-01-19 08:16:23","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2990071,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7750130/v1/999d3da0-464b-416d-befa-5d4e957daffd.pdf"},{"id":97856555,"identity":"fca9ab6c-c6f0-4ca1-a1ce-3cf1259b7620","added_by":"auto","created_at":"2025-12-10 07:56:23","extension":"mp4","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":829825,"visible":true,"origin":"","legend":"The liquidity of the ELA-LA","description":"","filename":"TheliquidityoftheELALA.mp4","url":"https://assets-eu.researchsquare.com/files/rs-7750130/v1/9521956f5aee8867d7fc1c72.mp4"},{"id":97899615,"identity":"b5d8528c-35c0-4f41-8cfe-0d3144fb6044","added_by":"auto","created_at":"2025-12-10 15:44:45","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":12361641,"visible":true,"origin":"","legend":"The Preparation of the ELA-LA deep eutectic bioadhensives","description":"","filename":"ThePreparationoftheELALAdeepeutecticbioadhensives.mp4","url":"https://assets-eu.researchsquare.com/files/rs-7750130/v1/a1a7752870c86df83781e8a1.mp4"},{"id":97856569,"identity":"496210b5-402e-4ad3-9abd-2813289a2a8b","added_by":"auto","created_at":"2025-12-10 07:56:23","extension":"docx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":14633139,"visible":true,"origin":"","legend":"supporting information","description":"","filename":"supportinginformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-7750130/v1/4a07dd5cbc91e706fbe4af68.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Developing α-lipoic acid-derived solvent-free bioadhesives via deep eutectic melting","fulltext":[{"header":"Introduction","content":"\u003cp\u003eContemporary wound closure strategies in clinical practice primarily utilize sutures and staples\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. These conventional approaches present notable limitations such as iatrogenic tissue trauma caused by surgical trauma, along with heightened susceptibility to microbial contamination and compromised wound integrity and require professional skills and equipment\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Bioadhesives has received widespread attention in recent years, because there is an urgent need for bioadhesives in both outpatient trauma treatment and intraoperative procedures\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. Skin trauma, visceral trauma (especially those that cannot be sutured), tissue transplantation (corneal transplantation), and other treatments all require the use of bioadhesives\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. However, there are currently few products in clinical application. Due to the need to ensure biological safety, the adhesive strength of bioadhesives is much lower than that of industrial adhesives, and is greatly affected by the water/oil interface on the tissue surface, which often leads to the inability of bioadhesives to meet adhesive requirements in practical applications\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. Therefore, the development of bioadhesives that do not rely on tissue surface pretreatment and can form strong adhesion properties on water/oil tissue surfaces is of great significance.\u003c/p\u003e\u003cp\u003eNormally, adhesives achieve firm adhesion by undergoing interface wetting, diffusion permeation, and solidification\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. In industrial applications, considering the environmentally unfriendly drawbacks of adhesives containing organic solvents, solvent-free hot-melt adhesives are receiving more and more attention\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Most of the traditional hot-melt adhesives are solid thermoplastic materials that can be heated to a liquid molten state, which is easy to apply onto surfaces. Upon cooling, they are solidified, forming strong bonding with the target surface. Furthermore, the solidification of solvent-free adhesives can also rely on polymerization or cross-linking. Solvent-free molten adhesives usually exhibit strong adhesion strength\u003csup\u003e\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. Adhesives based on the heat-triggered melting and polymerization of α-lipoic acid (LA) are an example of solvent-free adhesive that has received widespread attention in recent years\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. LA is a crystalline small molecule with a melting point of approximately 63 \u003csup\u003eo\u003c/sup\u003eC. The dithiolane structure in LA can undergo ring-opening polymerization (ROP) under heating or UV irradiation to from poly(\u003cem\u003eα\u003c/em\u003e-lipoic acid) (PLA), which has been widely reported to possess adhesion performance\u003csup\u003e\u003cspan additionalcitationids=\"CR18 CR19 CR20 CR21 CR22 CR23 CR24 CR25 CR26 CR27 CR28 CR29 CR30 CR31 CR32 CR33 CR34 CR35 CR36 CR37 CR38\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e. It is worth noting that the adhesive strength of the LA solvent-free adhesive prepared by melting thermal polymerization of LA is far higher than that of the PLA hydrogel adhesives prepared by thermal polymerization of LA dissolved in water \u003csup\u003e\u003cspan additionalcitationids=\"CR41 CR42 CR43 CR44\" citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eAs a small molecule coenzyme necessary for the aerobic metabolism of mitochondria, LA can eliminate superoxide and peroxide free radicals and has been applied in clinics\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e. LA-derived bioadhesives have received more and more attention recently\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e. Although the solvent-free PLA has significantly higher adhesive strength, like traditional hot-melt adhesives, the adhesion of solvent-free PLA depends on the melting-solidification process. Once PLA is formed, it is a non-adhesive elastomer. Therefore, its application in the biomedical field is limited because the melting point (\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e) of LA and the temperature required for its ROP (over 70 \u003csup\u003eo\u003c/sup\u003eC) are much higher than body temperature. In addition, the heat-triggered ROP usually costs long duration. Besides heating, UV can also trigger the ROP of dithiolane and is gentler than heating. In addition, UV-triggered LA-polymerization was reported to yield circular PLA, which possessed better stability.\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e However, UV is rarely reported in PLA-based adhesives preparation. Because UV still needs to act on transparent molten LA, while it is powerless for non-molten LA powder. Therefore, to explore the application of solvent-free PLA adhesives in biomedical application, obtaining molten LA at or below body temperature is crucial.\u003c/p\u003e\u003cp\u003eA deep eutectic melting is a mixture composed of hydrogen bond donors and acceptors, characterized by a melting point significantly lower than that of any individual component, typically remaining liquid at room temperature\u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e. LA also has the potential in forming deep eutectic melting mixture. Cui et al. have reported the deep eutectic phenomenon between LA and sodium lipoate (LA-Na). However, the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e of LA/LA-Na mixture (the ratio is 3) is 42.3 \u003csup\u003eo\u003c/sup\u003eC, and still higher than body temperature\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. Given that it cannot form a molten state at body temperature, it cannot use milder and more efficient UV to achieve solidification. Based on deep eutectic melting principle, by exploring hydrogen bond donors to match with LA to establish deep eutectic melting system, a kind of molten LA-based deep eutectic adhesives that can be UV-cured will be greatly attractive in biomedical application.\u003c/p\u003e\u003cp\u003eIn the present study, we propose to use LA as the hydrogen bond acceptor and synthesize LA derivatives as hydrogen bond donors to develop LA-based deep eutectic adhesives. By reducing \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e through deep eutectic melting, LA can be transformed into a flowing and transparent molten state at body temperature or even room temperature. The deep eutectic adhesives are molten at body temperature and can be injected or spread directly onto living tissue surfaces and subsequently cured via photo-initiated ROP of dithiolane. The amphiphilicity of LA and its derivative molecules allows the adhesive to fully penetrate the water or oil interface before curing, and form a strong interlocking structure after UV curing. This kind of adhesives is anticipated to achieve strong and durable adhesion to oily, wet, dynamic, and complex biological tissues.\u003c/p\u003e"},{"header":"Result and discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Study of the deep eutectic behavior between LA and its derivatives\u003c/h2\u003e\u003cp\u003eLA undergoes amidation reactions with ethanolamine (EA), aminopropanediol (AP), diethanolamine (DEA) and tris(hydroxymethyl)amino-methane (Tris) respectively to yield its derivatives, including 5-(1,2-dithiolan-3-yl)-N-(2-hydroxyethyl)pentanamide (ELA), N-(2,3-dihydroxypropyl)-5-(1,2-dithiolan-3-yl)pentanamide (APLA), 5-(1,2-dithiolan-3-yl)-N,N-bis(2-hydroxyethyl)pentanamide (DELA), N-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl)-5-(1,2-dithiolan-3-yl)-pentanamide (TLA) (\u003cb\u003eFig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e-S4\u003c/b\u003e). \u003csup\u003e1\u003c/sup\u003eH-NMR spectra, FT-IR spectra and Mass spectra confirm the synthesis of the derivatives and their structures. ELA, APLA and TLA are solids with crystallization, while the DELA is liquid at room temperature (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe structure and binding energies between LA and its derivatives are studied based on density functional theory (DFT). The bonding energy of the hydrogen bond between LA dimer is -0.61 eV, while the bonding energies of the hydrogen bonds between LA and ELA, APLA, DELA, TLA are \u0026minus;\u0026thinsp;0.65 eV, -0.51 eV, -0.62 eV, -0.63 eV, respectively. The results show that the hydrogen bond between LA and ELA, DELA, TLA is stronger than the hydrogen bond between LA dimer, the hydrogen bond between LA and APLA is weaker than the hydrogen bond between LA dimer (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB), but its energies are negative, which are conducive to form the hydrogen bonds.\u003c/p\u003e\u003cp\u003eSubsequently, the deep eutectic systems are prepared and characterized by simply mixing LA with its derivatives in different molar ratios (\u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e-S4\u003c/b\u003e). The thermal performances of LA, its derivatives, and their mixtures are measured by differential scanning calorimetry (DSC) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC). For ELA/LA, the molar ratios of ELA to LA are 6:1, 4:1, 2:1, 1:1 and 1:2, which are named as ELA/LA\u003csub\u003e6:1\u003c/sub\u003e, ELA/LA\u003csub\u003e4:1\u003c/sub\u003e, ELA/LA\u003csub\u003e2:1\u003c/sub\u003e, ELA/LA\u003csub\u003e1:1\u003c/sub\u003e and ELA/LA\u003csub\u003e1:2\u003c/sub\u003e. The melting point (\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e) of ELA and LA are 39.51\u0026deg;C and 63.54\u0026deg;C, respectively. The \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e of ELA/LA\u003csub\u003e6:1\u003c/sub\u003e, ELA/LA\u003csub\u003e4:1\u003c/sub\u003e, ELA/LA\u003csub\u003e1:1\u003c/sub\u003e and ELA/LA\u003csub\u003e1:2\u003c/sub\u003e is 29.38\u0026deg;C, 14.17\u0026deg;C, 47.22\u0026deg;C and 54.20\u0026deg;C, mirroring a typical eutectic phenomenon. Interestingly, when the molar ratio of ELA to LA is 2:1, the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e is undetectable within the detection range of -75\u0026deg;C to 90\u0026deg;C. Similarly, APLA/LA mixtures show a typical deep eutectic phenomenon. The \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e of APLA is 59.15\u0026deg;C. When the molar ratios of APLA to LA are 4:1, 2:1, 1:1 and 1:2, the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e of the APLA/LA\u003csub\u003e4:1\u003c/sub\u003e, APLA/LA\u003csub\u003e2:1\u003c/sub\u003e, APLA/LA\u003csub\u003e1:1\u003c/sub\u003e and APLA/LA\u003csub\u003e1:2\u003c/sub\u003e mixture are 45.22\u0026deg;C, 43.00\u0026deg;C, 45.11\u0026deg;C and 50.19\u0026deg;C. When the molar ratio of APLA to LA is 1.5:1, the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e of the mixture is undetectable within the detection range of -75\u0026deg;C to 90\u0026deg;C. For TLA/LA, the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e of TLA powder is 109.46\u0026deg;C, while the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e of the TLA/LA mixture decreases with the increasing addition of LA into TLA. When the ratios of TLA to LA are from 5:1 to 1:2, the mixtures have two \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e. With further increasing TLA/LA ratio to 1:3 and 1:4, the mixture has one melting point and is reduced to 60.59\u0026deg;C and 61.82\u0026deg;C, which are lower than that of pristine TLA and LA, mirroring a typical eutectic phenomenon.\u003c/p\u003e\u003cp\u003eDifferently, DELA is a liquid at room temperature, the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e of which is undetectable within the detection range of -75\u0026deg;C to 90\u0026deg;C. When the molar ratios of DELA to LA is 2:1, the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e of the DELA/LA\u003csub\u003e2:1\u003c/sub\u003e is also undetectable within the detection range of -75\u0026deg;C to 90\u0026deg;C. When the molar ratios of DELA to LA are 1:1 and 1:2, the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e of the DELA/LA\u003csub\u003e1:1\u003c/sub\u003e and DELA/LA\u003csub\u003e1:2\u003c/sub\u003e are 38.13\u0026deg;C and 43.86\u0026deg;C.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Preparation and characterizes of the ELA/LA deep eutectic adhesive\u003c/h2\u003e\u003cp\u003eIn the ELA/LA deep eutectic mixture, ELA/LA\u003csub\u003e2:1\u003c/sub\u003e is unique. When the molar ratio of ELA to LA is 2:1, the mixture of the two solid powders quickly transforms into a yellow transparent liquid, which possesses thin fluidity and could be easily injected (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). Therefore, unlike most reported deep eutectic solvents, this ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic mixture does not require heating. Rheological testing shows the liquid feature of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e (\u003cb\u003eFig. S5\u003c/b\u003e). Through polarizing microscope observation, it is found that the eutectic mixture of ELA/LA at different molar ratios has liquefying phenomenon at room temperature (\u003cb\u003eFig. S6\u003c/b\u003e). When the molar ratio of ELA to LA is 6:1 and 4:1, there is more ELA in the ELA/LA\u003csub\u003e6:1\u003c/sub\u003e with small ELA crystals. The deep eutectic ELA/LA\u003csub\u003e2:1\u003c/sub\u003e is a flowing yellow liquid at room temperature without crystal structure observed. X-ray diffraction (XRD) is employed to illustrate structural changes of the ELA, LA and ELA/LA\u003csub\u003e2:1\u003c/sub\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB shows that there are highly ordered nanoscale crystal structures in ELA and LA, while the diffraction peaks in ELA/LA\u003csub\u003e2:1\u003c/sub\u003e totally disappeared, indicating the formation of amorphous phase. With the LA ratio continues to increase, LA gradually becomes more abundant in ELA/LA\u003csub\u003e1:1\u003c/sub\u003e and ELA/LA\u003csub\u003e1:2\u003c/sub\u003e. LA crystals are clearly observed (\u003cb\u003eFig. S6\u003c/b\u003e). The existence of the crystal structure also affects the penetrability of visible light. The transmittance of the ELA/LA deep eutectic system is tested by UV-Vis absorption spectroscopy. The results show that the transmittances of the ELA/LA\u003csub\u003e2:1\u003c/sub\u003e, ELA/LA\u003csub\u003e4:1\u003c/sub\u003e and ELA/LA\u003csub\u003e6:1\u003c/sub\u003e are 98.8%, 98.2% and 92.3%, while the transmittances of the ELA/LA\u003csub\u003e1:1\u003c/sub\u003e and ELA/LA\u003csub\u003e1:2\u003c/sub\u003e are 18.6% and 10.3% (\u003cb\u003eFig. S7\u003c/b\u003e).\u003c/p\u003e\u003cp\u003eThe formation mechanism of the deep eutectic mixture between ELA and LA is investigated by FT-IR (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC). Compared with the stretching vibration peak of O-H and N-H groups at 3301 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in ELA, as well as the stretching vibration peak of O-H groups at 3436 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in LA, the stretching vibration peak of O-H and N-H groups at 3325 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in ELA/LA\u003csub\u003e2:1\u003c/sub\u003e is significantly strengthened and broadened, indicating that there are clear intermolecular hydrogen bonding between ELA and LA. In ELA/LA\u003csub\u003e2:1\u003c/sub\u003e, the stretching vibration peak of C═O group in LA shifts from 1700 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 1720 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and the bending vibration of O-H group in LA shifts from 946 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 888 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the bending vibration of O-H group in ELA shifts from 1056 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 1068 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the in-plane bending vibration of the N-H bond at 611 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in ELA/LA\u003csub\u003e2:1\u003c/sub\u003e is significantly enhanced, suggesting that the formation of intermolecular hydrogen bonds affect their vibration absorption. In other molar ratios of ELA/LA deep eutectic mixtures, the intermolecular hydrogen bonds are also formed and detected (\u003cb\u003eFig. S8\u003c/b\u003e). To further investigate the formation mechanism of the ELA/LA deep eutectic system, molecular simulation calculations are conducted on the ELA/LA\u003csub\u003e2:1\u003c/sub\u003e to explore the interaction between ELA and LA small molecules in the molar ratio of 2:1. The results show that there are a large number of hydrogen bonds in the ELA/LA deep eutectic mixture. The O-H group of ELA forms a strong hydrogen bond with the -COOH group of LA. There are also electrostatic interaction forces in other parts. In the process of mixing ELA and LA, the number of hydrogen bonds increases and the total energy value of the system decreases (\u003cb\u003eFig. S9\u003c/b\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eNormally, the fluidity of hydrogels and their initial adhesion to the tissues surface require special attention. Because the flowing hydrogels without initial adhesion before curing often suffer from unintended leakage to surrounding tissues\u003csup\u003e\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e. The deep eutectic mixtures of ELA/LA have adhesive ability based on its abundant adhesive groups. They can adhere on gelatin-coated glass slides, exhibiting well-performed initial adhesion that may prevent the loss of the adhesive. The adhesion strengths of ELA/LA\u003csub\u003e6:1\u003c/sub\u003e, ELA/LA\u003csub\u003e4:1\u003c/sub\u003e, ELA/LA\u003csub\u003e2:1\u003c/sub\u003e, ELA/LA\u003csub\u003e1:1\u003c/sub\u003e and ELA/LA\u003csub\u003e1:2\u003c/sub\u003e are ~\u0026thinsp;2.29 kPa, ~\u0026thinsp;0.76 kPa, ~\u0026thinsp;0.93 kPa, ~\u0026thinsp;1.47 kPa and ~\u0026thinsp;3.17 kPa (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD, S10). For adhesive derived from LA, it is usually achieved by heating to trigger LA polymerization to obtain sufficiently high adhesive strength. But this requires high temperature and longer heating duration. Dithiolane can easily achieve the ring-opening polymerization (ROP) under 365 nm UV light without any initiator. However, this is rarely used for the preparation of LA adhesives, mainly because UV cannot effectively act on LA solid powders. In the present study, the melting of ELA and LA solid powders into transparent melt is achieved through deep eutectic melting, which exhibits sensitive and rapid UV responsiveness (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eE). As shown in UV spectra, initially, the ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic mixture mainly consists of small molecule monomers, and the absorption peak of dithiolane at 338 nm can be clearly observed. As the UV-irradiation duration increases, the dithiolane of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e undergoes ring-opening polymerization. The absorption peak at 338 nm gradually decreases, while the absorption of linear disulfide in the 250 nm \u0026minus;\u0026thinsp;300 nm range increases (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eF)\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. As shown in Raman spectra, a distinctive Raman peak of the linear disulfide bonds appears at 525 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e as the radiation time increases\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. This characteristic change solidly proved the successful conversion of monomers into polymers by ROP (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eG). According to Mass spectra results in \u003cb\u003eFig. S11\u003c/b\u003e, there are small molecules and oligomers in ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic mixture, while polymers in ELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV with obvious MS signal in a larger m/z range. As well, the cyclic topology of the ELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV after photopolymerization is proved (\u003cb\u003eFig. S11\u003c/b\u003e). Density functional theory (DFT) is used to study the polymerization process of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e eutectic system, including the possibility of chain segment combination of ELA and LA, and the changes of Gibbs free energy. The results show that in the ELA/LA\u003csub\u003e2:1\u003c/sub\u003e eutectic system, five types of polymerization segments, namely ELA/ELA, LA/LA, ELA/LA, ELA/ELA/LA and ELA/LA/ELA, may occur during the polymerization process, with corresponding Gibbs free energies of -1.811 eV, -1.762 eV, -1.680 eV, -3.807 eV and \u0026minus;\u0026thinsp;4.047 eV respectively. All five Gibbs free energies are negative, indicating that the polymerization reaction can proceed in the forward direction, and the polymer chain is mostly composed of ELA/LA/ELA polymer segments (\u003cb\u003eFig. S12\u003c/b\u003e). Moreover, according to rheological testing results in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eH, the photo-curing duration of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic mixture is about at 43 s. Meanwhile, UV light triggered the ring-opening polymerization of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic mixture in a short time can produce stronger cohesion, leading to the significantly enhanced adhesive strength. The adhesive strength of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV are ~\u0026thinsp;1120.2 kPa and ~\u0026thinsp;1698.5 kPa after being exposed to irradiation for 5 min and 10 min (\u003cb\u003eFig. S13\u003c/b\u003e).\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eI and \u003cb\u003eFig. S14\u003c/b\u003e show the UV exposure process of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e eutectic mixture and its ability to withstand a weight of 5 kg in the vertical direction and 400 g in the horizontal direction, manifesting a reliable adhesion ability. In addition, ELA/LA\u003csub\u003e2:1\u003c/sub\u003e can adhere to different substances such as PE, rubber, ceramic, wood and steel, etc. Interesting, after UV exposure, the color of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e eutectic system changes from yellow to colorless, which is different with heat-triggered polymerization (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eI, S15). The influence of UV irradiation on the adhesion performance of ELA/LA with different molar ratios is evaluated in the Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eJ. After 5 min of UV irradiation, the maximum adhesive force of ELA/LA\u003csub\u003e6:1\u003c/sub\u003e@UV, ELA/LA\u003csub\u003e4:1\u003c/sub\u003e@UV, ELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV, ELA/LA\u003csub\u003e1:1\u003c/sub\u003e@UV and ELA/LA\u003csub\u003e1:2\u003c/sub\u003e@UV is ~\u0026thinsp;213.60 N, ~\u0026thinsp;261.67 N, ~\u0026thinsp;335.67 N, ~\u0026thinsp;140.57 N and ~\u0026thinsp;72.67 N, respectively. Their adhesion strength is 766.50 kPa, ~\u0026thinsp;976.57 kPa, ~\u0026thinsp;1120.20 kPa, ~\u0026thinsp;437.60 kPa and ~\u0026thinsp;236.27 kPa, respectively. ELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV has the highest adhesion strength, possibly because ELA/LA\u003csub\u003e2:1\u003c/sub\u003e has the best liquefaction degree, possessing more small molecules participate in the polymerization under UV irradiation. Meanwhile, the ELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV will continue to polymerize under natural light, with the cohesion further enhanced, leading to the gradually increased adhesion strength (\u003cb\u003eFig. S16\u003c/b\u003e).\u003c/p\u003e\u003cp\u003eTrauma can cause bleeding and exudation of tissue fluid, etc. Underwater adhesion is an important criterion for evaluating biological adhesives\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan additionalcitationids=\"CR51 CR52 CR53 CR54 CR55 CR56 CR57\" citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u003c/sup\u003e. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eK and \u003cb\u003eFig. S17\u003c/b\u003e, the wet adhesion test of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive is carried out. ELA/LA\u003csub\u003e2:1\u003c/sub\u003e could be injected and adhered onto the surfaces of substrates such as glass, plastic and metal respectively in water. After being exposed to UV for 5 min, ELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV could adhere firmly for lifting substrates. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eL, the glass sheets adhered with ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive that exposed to UV light for 5 min are immersed in water. The maximum adhesive force of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV immersed in water for 0 day, 1 day, 3 days, 5 days and 7 days, is ~\u0026thinsp;336.05 N, ~\u0026thinsp;273.82 N, ~\u0026thinsp;316.60 N, ~\u0026thinsp;276.39 N and ~\u0026thinsp;246.33 N, respectively. Their adhesion strength is ~\u0026thinsp;1120.20 kPa, ~\u0026thinsp;1057.99 kPa, ~\u0026thinsp;1087.15 kPa, ~\u0026thinsp;1060.64 kPa and ~\u0026thinsp;951.52 kPa, respectively. During the immersion duration of 5 days, the adhesion strength of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV does not decrease significantly, suggesting that it has a relatively stable underwater adhesion ability.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Preparation and characterizes of the APLA/LA deep eutectic adhesive\u003c/h2\u003e\u003cp\u003eThe similar deep eutectic phenomenon also occurs in the APLA/LA. When the molar ratio of APLA to LA is 1.5:1, the two solid powders mixed at room temperature within 10 min will transform into a viscous liquid that is injectable (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA, \u003cb\u003eFig. S18\u003c/b\u003e). Other molar ratios of APLA to LA is set as 4:1, 2:1, 1:1 and 1:2. The appearance and polarized microscope observation are showed in \u003cb\u003eFig. S19\u003c/b\u003e. The APLA/LA\u003csub\u003e4:1\u003c/sub\u003e and APLA/LA\u003csub\u003e1:2\u003c/sub\u003e are semisolid. When APLA or LA is in excess, APLA or LA crystals exist in the APLA/LA. XRD is also employed to illustrate structural changes in APLA/LA\u003csub\u003e1.5:1\u003c/sub\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB shows that there are highly ordered nanoscale crystal structures in APLA and LA, while the diffraction peaks in APLA/LA\u003csub\u003e1.5:1\u003c/sub\u003e disappeared, indicating the formation of amorphous phase.\u003c/p\u003e\u003cp\u003eThe formation mechanism of the deep eutectic system between APLA and LA is investigated by FT-IR (\u003cb\u003eFig. S20\u003c/b\u003e). Compared with the stretching vibration peak of O-H and N-H groups at 3343 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in APLA, and the stretching vibration peak of O-H groups at 3436 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in LA, the stretching vibration peaks of O-H and N-H groups at 3346 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in APLA/LA\u003csub\u003e1.5:1\u003c/sub\u003e are significantly broadened and strengthened, indicating the intermolecular hydrogen bond interactions between APLA and LA. For APLA/LA\u003csub\u003e1.5:1\u003c/sub\u003e, the stretching vibration peak of C═O group in LA shifts from 1700 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 1719 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and the bending vibration of O-H group in LA shifts from 946 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 880 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The bending vibration of O-H group in APLA at 1113 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1049 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is significantly weakened, suggesting that the formation of intermolecular hydrogen bonds that affect their vibration absorption. In other molar ratios of APLA/LA deep eutectic systems, the intermolecular hydrogen bonds are also detected (\u003cb\u003eFig. S20\u003c/b\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eMeanwhile, the APLA/LA deep eutectic mixture also exhibits UV responsiveness, the photo-curing time of APLA/LA\u003csub\u003e1.5:1\u003c/sub\u003e deep eutectic system is about at 124 s, which is slower than ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC). Moreover, compared with ELA/LA\u003csub\u003e2:1\u003c/sub\u003e, the viscosity of APLA/LA\u003csub\u003e1.5:1\u003c/sub\u003e is higher (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD).\u003c/p\u003e\u003cp\u003eThe adhesive properties of APLA/LA deep eutectic mixture before and after UV irradiation are evaluated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eE and \u003cb\u003eFig. S21\u003c/b\u003e. The adhesion strengths of APLA/LA\u003csub\u003e4:1\u003c/sub\u003e, APLA/LA\u003csub\u003e2:1\u003c/sub\u003e, APLA/LA\u003csub\u003e1.5:1\u003c/sub\u003e, APLA/LA\u003csub\u003e1:1\u003c/sub\u003e and APLA/LA\u003csub\u003e1:2\u003c/sub\u003e are ~\u0026thinsp;9.80 kPa, ~\u0026thinsp;6.77 kPa, ~\u0026thinsp;5.24 kPa, ~\u0026thinsp;7.40 kPa and ~\u0026thinsp;7.95 kPa. After UV irradiation, the adhesion strengths of APLA/LA\u003csub\u003e4:1\u003c/sub\u003e@UV, APLA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV, APLA/LA\u003csub\u003e1.5:1\u003c/sub\u003e@UV, APLA/LA\u003csub\u003e1:1\u003c/sub\u003e@UV and APLA/LA\u003csub\u003e1:2\u003c/sub\u003e@UV are ~\u0026thinsp;41.20 kPa, ~\u0026thinsp;78.15 kPa, ~\u0026thinsp;133.40 kPa, ~\u0026thinsp;127.84 kPa and ~\u0026thinsp;102.34 kPa. Of note, the adhesive strength of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV is 1120.20 kPa, which is significantly higher than that of APLA/LA\u003csub\u003e1.5:1\u003c/sub\u003e@UV. Therefore, ELA/LA\u003csub\u003e2:1\u003c/sub\u003e is selected as a representative adhesive for in vitro and in vivo tissue adhesion and repair.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Wet/oil tissue adhesion and application of ELA/LA deep eutectic adhesive\u003c/h2\u003e\u003cp\u003eBased on the unique feature of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive, it is used as a new type of photo-curing molten adhesive. Through mixing ELA and LA powder at room temperature, a molten adhesive is quickly formed. After applying or injecting the molten adhesive onto the surfaces of the tissues, significant interfacial adhesion can be immediately formed. Further UV irradiation to trigger polymerization for curing to achieve reliable adhesion (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA).\u003c/p\u003e\u003cp\u003eThe ability to effectively adhere to various biological tissues and its effect for tissue healing are further evaluated. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB and \u003cb\u003eFig. S22\u003c/b\u003e, ELA/LA\u003csub\u003e2:1\u003c/sub\u003e applied onto the surfaces of fresh chicken kidneys, lungs, livers and hearts can effectively adhere to the tissues without loss due to random flow. After being exposed to UV light, it can firmly bond biological tissues. After UV irradiation, the adhesion is strong enough to bear stretching, bending and distorting, as well as PBS and water flushing (\u003cb\u003eFig. S23\u003c/b\u003e). The lap-shear tests confirm that the maximum adhesive force of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV on porcine skin is ~\u0026thinsp;3.56 N and the adhesion strength is ~\u0026thinsp;52.24 kPa. The maximum adhesive force of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV on porcine lean meat is ~\u0026thinsp;2.29 N, and the adhesion strength is ~\u0026thinsp;37.17 kPa. The 90-degree peel tests confirm that the maximum peel force of ELA/LA\u003csub\u003e2:1\u003c/sub\u003e on pigskin is ~\u0026thinsp;3.45 N and the peel strength is ~\u0026thinsp;443.33 N/m, which is significantly higher than that of fibrin glue (~\u0026thinsp;45.41 N/m) (\u003cb\u003eFig. S24\u003c/b\u003e).\u003c/p\u003e\u003cp\u003eIt should be emphasized that these fresh tissues have not undergone any processing before adhesion, indicating the convenience of the application. In practical in vivo applications, in addition to the challenge of adhesion brought by moist environments, the oil on the tissue surface is more challenging\u003csup\u003e\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e. To verify the adhesive's response to this challenge, ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive is applied into the inner section of fresh porcine fat. It is observed that the ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive effectively forms adhesion to the surfaces of the fat (\u003cb\u003eFig. S25\u003c/b\u003e). After UV irradiation, the fat is firmly adhered (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC). The adhesion mechanism belongs to typical topological adhesion, which requires the adhesive to penetrate into the tissue and form an interlocking structure. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eD, because ELA and LA are small molecule in the deep eutectic mixture, they are more likely to penetrate tissues compared to macromolecules. Therefore, after UV-triggered polymerization, the polymer chains form a strong interlocking structure with the tissue. Similarly, adhesives can also penetrate wet tissues rich in water to form strong topological adhesion. To illustrate this point, corneal tissue is used for adhesion test. ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive is applied to two separated corneas and exposed to UV light, the two corneas are firmly adhered together (\u003cb\u003eFig. S26-27\u003c/b\u003e). Therefore, whether it is a wet tissue surface rich in water or a tissue surface rich in oil, ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive can form effective adhesion. There is no need to pre-treat the tissue surface during application, which is very convenient for surgical application.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn vivo evaluation was further carried out. As one of the important organs of the human body, liver is easy to cause massive bleeding after injury. In severe cases, it will lead to shock. Unlike other organs, liver is soft and brittle. When traditional suture is performed on the wound, it is not only difficult to operate, but also prone to secondary tears and pinhole bleeding, which is difficult to achieve effective hemostasis. Therefore, a new type of biological adhesive that combines highly efficient hemostatic function with excellent wet adhesion is needed in improving the clinical treatment of liver injury. ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive is used to verify their liver hemostatic ability. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eE, a wound is created on the liver with an 18G needle. ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive is injected at the site of liver injury, followed by UV irradiation. The liver bleeding is observed. The amount of bleeding in the blank group and the ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive group is tracked using filter paper. The results show that compared with the blank group, the ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive group has a significant hemostatic effect. Within 3 minutes, the bleeding volume in the blank group is 30.6 mg, while that in the ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive group is 1.8 mg.\u003c/p\u003e\u003cp\u003eAt the same time, ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive used as sealants to treat gastrointestinal perforation is evaluated in a rat gastric perforation model (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eF). A 3.5-mm vertical perforation is made at the gastric antrum using a scalpel, allowing the gastric lumen to open into the abdominal cavity. The gastric perforations are closed by using a non-absorbable suture, or ELA/LA\u003csub\u003e2:1\u003c/sub\u003e deep eutectic adhesive (0.1 mL). The untreated wound is the blank group. On day 7 after the treatment, general examination on the stomach tissues reveals a significantly smaller wound area in the adhesive treated group (11.65\u0026thinsp;\u0026plusmn;\u0026thinsp;1.68 mm\u003csup\u003e2\u003c/sup\u003e) than that in the suture group (16.95\u0026thinsp;\u0026plusmn;\u0026thinsp;1.66 mm\u003csup\u003e2\u003c/sup\u003e) and the blank group (68.86\u0026thinsp;\u0026plusmn;\u0026thinsp;5.50 mm\u003csup\u003e2\u003c/sup\u003e), indicating better wound healing in the adhesive treated group (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eF, \u003cb\u003eFig. S28\u003c/b\u003e). Histological staining further shows that the serum muscle layer around the wounds in the three groups had a certain degree of regeneration on day 7. Among the three groups, only the gastric perforations sealed with adhesives are completely bridged with the regenerated mucosa. In contrast, the perforations in the blank group and the suture group showed larger and clearer gaps on the mucosa (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eG).\u003c/p\u003e\u003cp\u003eAbove all, both the ELA/LA and APLA/LA eutectic systems possess the ability to form a molten adhesive simply by mixing two solid components at room temperature. This molten adhesive can be applied or injected onto tissue surfaces. Following UV irradiation, significant interfacial adhesion is immediately formed. These molten adhesives hold promise for applications in tissue dressings for wound healing, injectable adhesives or sealants for tissue repair, UV light-shielding adhesives, drug delivery adhesives, as well as flexible wearables and electronics.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5 Preparation and characterizes of the DELA/LA deep eutectic adhesive\u003c/h2\u003e\u003cp\u003eDifferent from ELA and APLA, DELA is a yellow transparent thin liquid that possesses fluidity (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA). It also has UV responsiveness. Under UV irradiation, the dithiolane gradually undergoes ring-opening polymerization reaction, the absorption peak at 338 nm gradually decreases, while the absorption of linear disulfide in the 250\u0026ndash;300 nm range increases (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB). Meanwhile, UV triggers the ring-opening polymerization of DELA in a short time can produce strong cohesion, which greatly enhances the adhesive strength of DELA@UV. The adhesive strength of DELA@UV after being exposed for 5 min is ~\u0026thinsp;477.50 kPa, which is significantly higher than that of DELA without UV irradiation (~\u0026thinsp;1.13 kPa) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC, \u003cb\u003eFig. S29\u003c/b\u003e).\u003c/p\u003e\u003cp\u003eOf note, DELA can undergo ring-opening self-polymerization under natural light. When DELA is exposed to natural light for 3 days, its viscosity increases significantly, showing no flowing down after inversion (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eD). Its adhesion performance also increases significantly (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eE). MS signals after 3 day\u0026rsquo;s self-polymerization of DELA is concentrated between 600 and 3000 m/z, which is higher than the monomer of 293.97 m/z (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eF, \u003cb\u003eFig. S30\u003c/b\u003e). G\u0026rsquo;\u0026rsquo; and G\u0026rsquo; of DELA after 3 days are ~\u0026thinsp;24644.5 Pa and ~\u0026thinsp;17616.9 Pa (angular frequency at 10 rad/s), which are significantly higher than those of DELA at day 0 (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eG). The viscosity of DELA after 3 days is ~\u0026thinsp;9821.81 Pa.s (shear rate at 10 1/s), which is significantly higher than that of DELA (~\u0026thinsp;16.69 Pa.s) at 0 day (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eH). The degree of self-polymerization of DELA under different natural light exposure duration for 0 day, 1 day, 3 days, 5 days and 7 days is monitored by UV-Vis spectra. With the increase of irradiation duration, the absorption peak at 338 nm gradually decreases, while the absorption of linear disulfide in the 250\u0026ndash;300 nm range increases (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eI). Meanwhile, nature light triggers the ring-opening polymerization of DELA in different days also produce enhanced cohesion, leading to the promoted adhesive strength. The maximum adhesive force of DELA@nature light at 0 day, 1 day, 3 day, 5 day and 7 day is ~\u0026thinsp;0.37 N, ~\u0026thinsp;23.20 N, ~\u0026thinsp;158.90 N, ~\u0026thinsp;141.58 N and ~\u0026thinsp;114.65 N respectively. Their adhesion strength is ~\u0026thinsp;1.13 kPa, ~\u0026thinsp;65.27 kPa, ~\u0026thinsp;611.87 kPa, ~\u0026thinsp;594.30 kPa and ~\u0026thinsp;446.73 kPa, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eJ, \u003cb\u003eFig. S31\u003c/b\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eDELA and LA also exhibit deep eutectic phenomena. When the molar ratio of DELA to LA is 2:1, the LA powder can be dissolved in DELA at room temperature within ~\u0026thinsp;1 min, producing a thin and transparent liquid (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eK, \u003cb\u003eFig. S32\u003c/b\u003e). It is found from the polarizing microscope that the complete liquefaction occurs at DELA/LA\u003csub\u003e2:1\u003c/sub\u003e mixture. LA crystals exist in the DELA/LA\u003csub\u003e1:1\u003c/sub\u003e and DELA/LA\u003csub\u003e1:2\u003c/sub\u003e mixture (\u003cb\u003eFig. S33\u003c/b\u003e). XRD curves show that DELA and DELA/LA\u003csub\u003e2:1\u003c/sub\u003e mixture are amorphous phases, while the diffraction peaks of LA appeared in DELA/LA\u003csub\u003e1:1\u003c/sub\u003e and DELA/LA\u003csub\u003e1:2\u003c/sub\u003e mixture. The presence of LA crystals also affects the transparency (\u003cb\u003eFig. S34\u003c/b\u003e). The formation mechanism of the deep eutectic mixture between DELA and LA is investigated by FT-IR (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eL). Compared with the stretching vibration peak of O-H and N-H groups at 3393 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in DELA, as well as the stretching vibration peak of O-H groups at 3436 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in LA, the stretching vibration peak of O-H and N-H groups at 3395 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in DELA/LA\u003csub\u003e2:1\u003c/sub\u003e is significantly broadened and strengthen, indicating that there are intermolecular hydrogen bond interactions between DELA and LA. In DELA/LA\u003csub\u003e2:1\u003c/sub\u003e, the stretching vibration peak of C═O group in LA shifted from 1700 to 1723 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and the bending vibration of O-H group in LA shifted from 946 to 860 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, suggesting that the formation of intermolecular hydrogen bonds affected their vibration absorption. In other molar ratios of DELA/LA mixture, the intermolecular hydrogen bonds are also formed (\u003cb\u003eFig. S35\u003c/b\u003e).\u003c/p\u003e\u003cp\u003eDELA/LA deep eutectic mixture possesses UV responsiveness. The ROP reaction of the dithiolane occurs under UV irradiation (\u003cb\u003eFig. S36\u003c/b\u003e). As shown in Raman spectra, a distinctive Raman peak of the linear disulfide bonds appears at 526 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. As the radiation time increases, the absorption peak of the dithiolane at 338 nm gradually decreases, while the absorption of linear disulfide in the 250\u0026ndash;300 nm range increases. These characteristic changes proved the successful conversion of monomers into polymers by ROP. The polymerization reaction increases the cohesion of DELA/LA deep eutectic adhesive. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eM and \u003cb\u003eFig. S37\u003c/b\u003e, the adhesion strength of DELA/LA\u003csub\u003e2:1\u003c/sub\u003e, DELA/LA\u003csub\u003e1:1\u003c/sub\u003e and DELA/LA\u003csub\u003e1:2\u003c/sub\u003e is ~\u0026thinsp;1.18 kPa, ~\u0026thinsp;2.23 kPa, ~\u0026thinsp;3.25 kPa. After UV irradiation for 5 min, the adhesion strengths of DELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV, DELA/LA\u003csub\u003e1:1\u003c/sub\u003e@UV and DELA/LA\u003csub\u003e1:2\u003c/sub\u003e@UV is ~\u0026thinsp;1546.89 kPa, ~\u0026thinsp;1362.30 kPa, ~\u0026thinsp;618.62 kPa. Meanwhile, the DELA/LA\u003csub\u003e2:1\u003c/sub\u003e@UV will continue to polymerize under natural light, with the cohesion further enhanced, leading to the gradually increased adhesion force and adhesion strength (\u003cb\u003eFig. S38\u003c/b\u003e). In addition, the DELA/LA\u003csub\u003e2:1\u003c/sub\u003e can adhere to different substrates and tissues after UV irradiation to withstand a high separation force (\u003cb\u003eFig. S39\u003c/b\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e2.6 Preparation and characterizes of the TLA/LA deep eutectic adhesives\u003c/h2\u003e\u003cp\u003eSimilar to ELA and APLA, TLA is a solid powder, which, however, possessing higher \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e (109.46 ℃). Although there is no liquefaction phenomenon after mixing TLA with LA powder with different molar ratios at room temperature, the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e of the TLA/LA\u003csub\u003e1:3\u003c/sub\u003e is reduced to 60.59 ℃, which is also a typical deep eutectic mixture. Heating the TLA/LA deep eutectic mixtures above their \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e, will yield a series of light-yellow viscous liquids of TLA/LA mixtures. At the same time, the ring-opening polymerization of dithiolane is also triggered during heating, resulting in a light-yellow and transparent P(TLA/LA) patch after cooling to room temperature (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA, \u003cb\u003eFig. S40\u003c/b\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe formation mechanism of TLA/LA deep eutectic systems is monitored by FT-IR spectra. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eB and \u003cb\u003eFig. S41\u003c/b\u003e, TLA/LA\u003csub\u003e1:3\u003c/sub\u003e solid powder is obtained by simply mixing TLA and LA powders. The FT-IR spectra of TLA/LA\u003csub\u003e1:3\u003c/sub\u003e powder without heating is a simple superposition of the FT-IR spectra of TLA and LA, with no obvious shift of each characteristic peak. PTLA and PLA are obtained by the polymerization of small molecule monomers TLA and LA, respectively. In their FT-IR spectra, the peak shapes have changed, but the peak displacements have not changed (\u003cb\u003eFig. S42\u003c/b\u003e). While in P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e), the stretching vibration peak of C═O group in LA shifts from 1700 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 1706 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and the bending vibration of O-H group in LA shifts from 946 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 893 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the bending vibration of O-H group in TLA shifts from 1020 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 1058 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, indicating that the intermolecular hydrogen bond interactions. In other molar ratios of TLA/LA deep eutectic mixtures, the intermolecular hydrogen bonds are also detected (\u003cb\u003eFig. S43\u003c/b\u003e).\u003c/p\u003e\u003cp\u003eThe tunable melting temperature, abundant adhesive groups, and in situ curing ability after cooling make TLA/LA deep eutectic mixtures excellent hot melt adhesives. The adhesion ability of TLA/LA deep eutectic adhesives to various substrates is investigated by lap-shear testes. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eC, the adhesion strength of P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e) to glass and stainless steel is higher than that of to PC, PMMA and PTFE. It is worth noting that the adhesion strength of P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e) to glass is about 4.33 MPa, which is higher than that of ELA/LA, APLA/LA and TLA/LA eutectic adhesives.\u003c/p\u003e\u003cp\u003eThe long-lasting adhesion of adhesives is one of the important indicators of adhesives. Lap-shear tests are conducted at different time. The results show that with the increase of duration, the adhesion strength becomes significantly stronger. After 2 days, the adhesion strength of P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e) to stainless steel and glass increases to more than 9 MPa (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eD, S44). TLA with more quantity of terminal hydroxyl groups afforded a structural P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e) adhesive with strength equivalent to that of conventional industrial adhesives\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e\u003c/sup\u003e. Remarkably, the P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e) adhered stainless steels with an adhesion area of 2 \u0026times;1 cm could easily lift a weight of person with 65 kg in the vertical direction (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eE). Such a powerful adhesive force is not only due to the introduction of the more hydroxyl group, but also the increased cohesion from thermal polymerization. As shown in Raman spectra, the Raman peak shapes of LA and TLA are relatively sharp. After heating, the peak shape of PTA, PTLA and P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e) becomes rounded. A distinctive Raman peak of the linear disulfide bonds appears at 523 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, confirming the successful conversion of monomers into polymers by heating-triggered ROP (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eF).\u003c/p\u003e\u003cp\u003eNext, the water-resistance adhesion capabilities of P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e) adhesives are examined by soaking the P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e) -adhered stainless steels into water for 4 days (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eG). The results show that the adhesion strength of P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e) do not decrease significantly compared with dry state. The adhesive strength is always maintained at a relatively high level (~\u0026thinsp;3 MPa). Remarkably, the soaked P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e) -adhered stainless steels with an adhesion area of 2 \u0026times;1 cm could easily lift a weight of 30 kg in the vertical direction and 400 g in the horizontal direction (\u003cb\u003eFig. S45\u003c/b\u003e). The adhesion strength of P(TLA/LA\u003csub\u003e1:3\u003c/sub\u003e) deep eutectic adhesives compared with the LA-based adhesives reported in the representative literatures is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eH. It is worth noting that the adhesive strength of the deep eutectic adhesives used in this study is the highest in the UV-triggered preparation of LA-derivatives. In the hot-melt adhesives, the adhesion strength of the deep eutectic adhesives in this study also exceeded that of most reports. Although its adhesive strength is not the highest, the components used in this study are the simplest compared to other adhesives. It is rare to report achieving such high adhesion strength and stability solely through two components with no chemical crosslinking units.\u003c/p\u003e\u003cp\u003eMore importantly, heat-induced LA-based adhesives inevitably have the problem of de-polymerization. It has been reported in the literature that the researches on anti-depolymerization of LA-based adhesives is conducted by end-capping, introducing halogens or steric hindrance, and intermolecular hydrogen bonding\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e,\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e\u003c/sup\u003e. Similarly, the interactions between TLA and LA endow the TLA/LA deep eutectic adhesives with well performed anti-depolymerization property, cause by intermolecular hydrogen bonding and steric hindrance. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eI and \u003cb\u003eFig. S40\u003c/b\u003e, LA, TLA/LA\u003csub\u003e1:2\u003c/sub\u003e, TLA/LA\u003csub\u003e1:1\u003c/sub\u003e, TLA/TLA\u003csub\u003e1:2\u003c/sub\u003e, TLA/LA\u003csub\u003e1:3\u003c/sub\u003e and TLA/LA\u003csub\u003e1:4\u003c/sub\u003e after heating and polymerization are monitored for 3 days. Obvious de-polymerization of PLA is observed after 3 days later. However, no de-polymerization is observed in the TLA/LA deep eutectic mixtures (\u003cb\u003eFig. S46\u003c/b\u003e). XRD spectra confirm that no small molecule crystallization peaks of P(TLA/LA) are observed after 3 days (\u003cb\u003eFig. S47\u003c/b\u003e). Raman spectra confirm that the linear disulfide bonds in PLA are significantly weakened due to the de-polymerization of PLA. However, the intensity of the Raman peaks of linear disulfide bonds in P(TLA/LA) show no significant weakening, indicating that P(TLA/LA) does not undergo obvious de-polymerization (\u003cb\u003eFig. S48\u003c/b\u003e). In conclusion, the introduction of TLA with only a relatively small amount has a significant inhibitory effect on the depolymerization of TLA/LA deep eutectic mixture.\u003c/p\u003e\u003cp\u003eOf note, similar to most adhesives formed by LA thermal polymerization, the application of TLA/LA adhesives requires placing them on the surface of the substrate and then heating them to achieve a firm adhesion. But if the P(TLA/LA) patch is obtained by heating first, it does not have adhesion ability to the substrate. Because the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e of the TLA/LA mixtures is much higher than body temperature, they are not suitable for tissue adhesion applications through is-situ heating. They also cannot be in-situ cured by UV like ELA/LA, APLA/LA and DELA/LA. However, according to its robust mechanical feature (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eJ), P(TLA/LA) patch can be used to combine with other deep eutectic adhesives in this study such as DELA to prepare a band-aid. DELA can form tight binding to P(TLA/LA) patch because of the disulfide exchange on their interface during dithiolane ROP. Such Janus structure combines the high cohesion of P(TLA/LA) and the high interfacial adhesion strength of DELA. This band-aid can effectively achieve the sealing of the leaked porcine intestines and stomachs (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eK, \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eL). The bursting pressure is ~\u0026thinsp;0.094 MPa (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eM, S49). This combination implies that LA derivatives and their deep eutectics can be cross-combined to suit different applications.\u003c/p\u003e\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this work, a kind of UV-triggered, solvent-free, LA-based room-temperature molten adhesive has been reported for the first time. The critical discovery is that functionally modified LA (ELA, APLA and DELA) can mix with LA powders to produces a molten adhesive at room temperature via deep eutectic melting. The UV-triggered polymerization of dithiolane in the molten adhesives enables rapid, robust and stable tissue bonding upon contact with wet/oil tissue. These LA-based molten adhesives demonstrate superior mechanical and biological properties compared to conventional medical-grade fibrin glue. Meanwhile, TLA with three terminal hydroxyl groups can also form deep eutectic mixture, which, however, needs heating. TLA mix with LA powders after heating can impart resistance to depolymerization in the resulting polymer. The performances of stabilized P(TLA/LA) polymers are competitive with or exceed commercially available alternatives, thus opening the door to a diverse family of LA-based adhesives.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information files or from the corresponding author upon request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eTaboada, G. M. et al. Overcoming the translational barriers of tissue adhesives. \u003cem\u003eNat. Rev. 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A novel dynamic polymer synthesis via chlorinated solvent quenched depolymerization. \u003cem\u003eCCS Chem\u003c/em\u003e. \u003cstrong\u003e5,\u003c/strong\u003e 1841\u0026ndash;1853 (2023).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"α-lipoic acid, bioadhesives, solvent-free molten adhesives, deep eutectic melting, topological adhesion","lastPublishedDoi":"10.21203/rs.3.rs-7750130/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7750130/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSolvent-free molten adhesives normally have high adhesion strength, which are widely used in industry but rare in medicine. Developing molten adhesives with medical potential is attractive. Herein, based on the positive therapy effect of \u003cem\u003eα\u003c/em\u003e-lipoic acid (LA) and its significant feature of producing adhesives, a family of LA-derivatives containing terminal hydroxyl groups are synthesized and used to establish a serious of room-temperature molten LA-derived adhesives via deep eutectic strategy. The number of hydroxyl groups and molecular structure significantly affect the deep eutectic behavior and further affect the solidification and subsequent mechanical properties of the molten adhesives. The molten deep eutectic LA-derived adhesives can be applied to wounds and quickly cured under ultraviolet irradiation, forming tight and stable adhesion on moist or greasy tissue surfaces without the need for additional surface pretreatment. In vivo evaluation shows the deep eutectic adhesive successfully sealed gastric perforation that bridged by the regenerated mucosa. Besides the room temperature molten adhesives, LA-derivative with more quantity of terminal hydroxyl groups afforded a structural adhesive with strength equivalent to that of conventional adhesives. The deep eutectic behavior of LA and its derivatives provides a new perspective for the development of various types of LA-based adhesives.\u003c/p\u003e","manuscriptTitle":"Developing α-lipoic acid-derived solvent-free bioadhesives via deep eutectic melting","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-10 07:56:12","doi":"10.21203/rs.3.rs-7750130/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ed0de919-3520-4ac5-bde9-2d2bba1fd715","owner":[],"postedDate":"December 10th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":58998254,"name":"Physical sciences/Materials science/Biomaterials/Biomedical materials"},{"id":58998255,"name":"Physical sciences/Chemistry/Materials chemistry/Biomaterials/Biomedical materials"}],"tags":[],"updatedAt":"2026-01-16T17:01:53+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-10 07:56:12","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7750130","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7750130","identity":"rs-7750130","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}