2-Second In-Situ Formation of Adaptive Electronic Bio-Skin Enabled by Metal Coordination

2-Second In-Situ Formation of Adaptive Electronic Bio-Skin Enabled by Metal Coordination | 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 2-Second In-Situ Formation of Adaptive Electronic Bio-Skin Enabled by Metal Coordination Meng Gao, Xiaojuan Wang, Xiaosen Pan, Junzhi Jiang, Wanlong Song, and 7 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6344254/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Electronic skin (E-skin), a conformal human-machine interface, holds promise for healthcare monitoring and personal electronics. However, traditional fabrication methods face challenges of reliance on non-sustainable materials, intricate and time-consuming processes, and material softness-induced fragile transfer to target substrates. Inspired by "milk skin" phenomenon, we developed a rapid "dipping-dipping" molecular assembly method to in-situ fabricate cellulose-based bio-skin within seconds, exhibiting ultra-thin, high conformal, shape-customizable, degradable, and low impedance performances. This technique immerses substrates sequentially into carboxymethyl cellulose (CMC) and Cu(II) solutions, leveraging strong metal-coordination interactions. Membrane formation efficiency, influenced by the oxidation of metal ions, follows the order: Cu(II) > Fe(II) > Ca(II). CMC-Ag(I)/CMC-Cu(II) form stable membranes, whereas CMC-Fe(II) is fragmented structures, and CMC-Mg(II)/CMC-Ca(II) remain in solution. This adaptable method extends to other biomacromolecules like methylcellulose and carboxymethyl chitosan, broadening applications. The bio-skin enables real-time monitoring of electrocardiograms (ECG), electrooculograms (EOG), electroencephalograms (EEG), and electromyograms (EMG), showcasing its potential for wearable, biocompatible electronics in healthcare. Physical sciences/Materials science/Soft materials/Self-assembly Physical sciences/Materials science/Materials for devices/Electronic devices Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Electrically conductive membranes enable advanced epidermal electronics by providing flexibility and high electrical conductivity, with wide applications in medical and health monitoring, human-machine interaction, athletic performance monitoring, and personalized medicine 1 , 2 . The high-performance realization of epidermal electronic devices critically depends largely on conformal interfaces with biological tissues, high-resolution accuracy of target signal, and excellent biocompatibility 3 , 4 , 5 . However, its further development remains limited by the following challenges: (i) Multi-step and time-consuming fabrication procedure 6 , 7 ; (ii) Delicate interface design requirements such as adhesion modulation and ultra-thin membrane fabrication for matching dynamically deforming biological tissues 8 , 9 ; (iii) Limited self-standing property that hinders intact transfer onto target surface without damage 10 , 11 , 12 ; (iv) Conventional petroleum-based materials commonly used facing inherent issues with environmental friendliness and biocompatibility 13 , 14 . Therefore, there is an urgent need for a simple and time-efficient fabrication strategy to develop biomaterial-based electronic membranes that conform to living tissues, enabling accurate and high-fidelity physiological monitoring. Besides, if the electronic membrane can be formed in situ, on demand, the film could better maintain its integration since no additional transfer to the target tissue or skin is required 15 . As one of the most exciting frontiers in materials science, molecular self-assembly emerges as a promising candidate for realizing convenient and reliable production of bio-membranes due to its tunability and flexibility. It is a spontaneous process of aggregating from disorder to order, driven by non-covalent interactions, such as hydrogen bonding, van der Waals forces, electrostatic interactions, and π-π stacking, without external intervention 16 , 17 . Self-assembly is widespread in nature, exemplified by the formation of the DNA double helix and the milk-skin effect upon heating 18 , 19 . Inspired by these natural processes, precise control of intermolecular interactions enables the design and construction of materials with tailored functions and structures, providing a versatile platform for developing membrane materials across multiple scales 20 , 21 , 22 . A notable example of thermally induced molecular self-assembly is the formation of milk skin ( Fig. 1aI-II ), where heat unfolds the tertiary structure of coiled proteins, leading to the self-assembly of protein meleculars into an ordered milk lamellar membrane, driven by the synergistic effect of hydrophobic interactions, hydrogen bonding, and fat globules ( Fig. 1II ) 19 . Leveraging this natural phenomenon, the rapid fabrication of on-demand conformal bioconductive membranes employing the principles of molecular self-assembly presents a promising strategy. Here, we present a convenient and time-efficient strategy for the synthesis of biodegradable, electronic bio-membranes through strong metal coordination interactions 23 , 24 , 25 , enabling ultra-fast, in-situ, and adaptive assembly of biomacromolecules. By sequentially dipping the target substrate, regardless of its structure, first in carboxymethylcellulose (CMC) and then in a Cu(II) solution, an intact, robust bioconductive “skin” can be formed instantly within 2 seconds ( Fig. 1aIII-IV ). Research demonstrates that the capacity for instant in-situ membrane formation correlates with the oxidation state of the metal ions, following this trend: Cu(II) > Fe(II) > Ca(II). Specifically, at the same experimental conditions, CMC-Ag(I) and CMC-Cu(II) form well-defined, stable membranes, while CMC-Fe(II) exhibits a fragmented morphology, indicating incomplete formation, and CMC-Mg(II) and CMC-Ca(II) remain the solution state without significant changes. This trend also applies to other biomacromolecules, such as methylcellulose (MC) and carboxymethyl chitosan (CMCH), further extending the applicability of the method beyond CMC. The resulting CMC-based bio-membranes can serve as epidermal electronics for real-time physiological signal monitoring, including electrocardiogram (ECG), electrooculogram (EOG), electroencephalogram (EEG), and electromyography (EMG), demonstrating their potential for wearable, biocompatible electronics in healthcare applications. Results Synthesis and characterization of CMC-Cu(II) membrane The ultra-thin conductive bio-molecular skin (CMC-Cu(II) membrane) can be achieved via a facile “dipping-dipping” coordination assembly process, which only needs the target item or surface to be sequentially immersed in CMC solutions and Cu(II) salt solutions (e.g., copper chloride or copper sulfate) (Fig. 1 b, Supplementary Fig. 1 and Supplementary Video 1 ). The entire "contact and assembly" process takes 2 seconds, with each dipping step lasting 1 second. In this recipe, CMC, a derivative of cellulose that is the most abundant biopolymer on earth, is naturally biofriendly and offers realizability for biodegradability of bioelectronic skin 26 . The Cu(II) ion is the key ingredient that ensures strong coordination and a rapid assembly process, which will be discussed in detail in the later section. This simple “dipping-dipping” process enables the in-situ formation on demand of adaptive, shape-conforming conductive bio-skin on materials with arbitrary surfaces. To demonstrate its excellent conformal performance, we constructed CMC-Cu(II) surface on varied materials, including rubber model, shaped candy, polyacrylamide hydrogel, metal nut, fresh fruit (apple), and human palm skin ( Fig. 1cI ). The CMC-Cu(II) membranes adhere seamlessly to these diverse surfaces, perfectly conforming their shapes. Guided by the flexibility in the coordination assembly process, ultra-thin CMC-Cu(II) membranes can be achieved by controlling the concentration of CMC and Cu(II) ( Supplementary Fig. 2 ). The cross-sectional scanning electron microscopy (SEM) image reveals a 3.4-µm-thick CMC-Cu (II) membrane (Fig. 1 d) fabricated from a 1 wt% CMC solution and 0.5 M Cu(II) solution. The “thin” feature of the CMC-Cu(II) membrane further enhances its ability to conform to and match various interfaces 27 , 28 . The SEM demonstrates that the CMC-Cu(II) membrane on the wavy polyvinyl chloride (PVC) template closely matches its microscopic contours (Fig. 1 e and Supplementary Fig. 3 ), confirming that the proposed molecular assembly process fabricates ultra-thin CMC-Cu(II) membranes with excellent conformal adhesion, which is beneficial for the development of various applications. The CMC-Cu(II) membranes also exhibit good conductivity, serving effectively as conductive pathways or epidermal electrodes. Generally, typical CMC exhibits Na(I) ion substitution. Coordination bonds between CMC molecules and Cu(II) cause the generation of Na + owing to the displacement Na atoms. The assembly of CMC molecules induced by this robust coordination bond simultaneously accelerates the formation of a supported channel, enhancing ion transport and improving the conductivity of water-containing CMC-Cu(II) membranes ( Supplementary Fig. 4 ) 29 . This capability is demonstrated by illuminating LED lights using dumbbell-shaped CMC-Cu(II) membrane as a conductive path prepared on leaf substrates ( Supplementary Fig. 5 ). Moreover, the facile “dipping-dipping” coordination assembly process enables CMC-Cu(II) membranes to be easily fabricated into custom-shaped patterns ( Fig. 1cII ) using a mask-forming approach ( Supplementary Fig. 6 ). Unlike other conventional ways, this patterned conductive bio-skin can be formed in-situ on various 2D and 3D surfaces directly ( Fig. 1cIII and Supplementary Fig. 7 ), which eliminates the need for transfer and ensures conformal contact. Harnessing this characteristic, CMC-Cu(II) patterned microelectronic circuits are successfully integrated on human skin or other 3D interfaces (Fig. 1 f and Supplementary Fig. 8) , providing a novel and straightforward approach for in-situ flexible electronics manufacturing. Notably, while neat CMC membrane dissolves in water within 100 s, CMC-Cu(II) membrane retains its structure for up to 30 days due to the "bridging" effect of Cu(II). This facilitates long-term stability of CMC-Cu(II) membrane in aqueous solutions like human sweat, promoting both its retention and functionality ( Supplementary Fig. 9 ). Owing to the inherent biocompatibility of CMC, the biodegradability of CMC-Cu(II) membrane in natural environments is investigated. Both CMC-Cu(II) membranes and polyethylene (PE) films are placed on the soil surface. After 9 days, the CMC-Cu(II) membrane is visually degraded, whereas the PE film remains their original shape (Fig. 1 g and Supplementary Fig. 10 ). These findings suggest rapid biodegradation of CMC-Cu(II) membranes in natural environments. Coordination interactions in CMC-Cu(II) membrane by molecular assembly The Cu(II) ions, possessing strong coordination ability 30 , 31 rapidly assemble CMC macromolecules by forming planar square coordination with adjacent CMC chains, creating instantaneous CMC-Cu(II) membrane formation. Upon contact, Cu(II) initially forms a coordinated bond with the oxygen atom of C6 carboxymethyl substituent on the CMC molecule, which leads to ligand-to-metal charge transfer. Simultaneously, the partially filled d orbitals undergo energy level splitting, leading to d-d electron transitions. These changes result in new ultraviolet (UV)-visible (VIS) absorption peaks at 242 nm attributed to CMC-Cu(II), distinct from those of CMC (194 nm) and Cu(II) (192 nm). This indicates the formation of a new material state, CMC-Cu(II) (Fig. 2 a). The strong coordination between Cu(II) and CMC is supported by the pronounced reduction in intensities of C-O and C = O peaks observed in the CMC-Cu (II) membrane in the O1s and C1s fitted spectra of X-ray photoelectron spectroscopy (XPS) (Fig. 2 b, Supplementary Fig. 11 ). Furthermore, Fourier transform infrared (FTIR) spectra also confirm this through sharpened -OH peaks and shifted C-O stretching vibrations ( Supplementary Fig. 12 ). To further validate that the ultra-fast formation of CMC-Cu(II) membrane is due to strong coordination capacity of Cu(II), a series of common metal ions with varying oxidation states, including Ca(II), Mg(II), Mn(II), Zn(II), Fe(II), and Ag(I), are investigated for their molecular assembly capabilities in terms of membrane formation. It is observed that membrane-forming abilities are influenced by their oxidation properties. For instance, at the same concentration, Ag(I) forms complete and stable membranes with CMC, Fe(II) creates incomplete membrane, and Mg(II) and Ca(II) remain in solution state ( Supplementary Fig. 13 ). Among them, representative metal ions Fe(II) and Ca(II) with distinct oxidation characteristics are chosen to react with CMC for in-depth evaluating their ability for molecular assembly, obtaining materials named CMC-Fe(II) and CMC-Ca(II). At the same concentration, compared to CMC-Cu (II), which shows well-formed complete membrane peeling (Fig. 2 c insert and Supplementary Video 1 ), CMC-Fe(II) displays fragmented morphology and incomplete peeling (Fig. 2 d insert, Supplementary Video 2 ) with a novel UV absorption peak ( Supplementary Fig. 14a ); while CMC-Ca(II) remains in solution form without any discernible macroscopic changes (Fig. 2 e insert, Supplementary Video 3 ) and exhibits a negative UV absorption peak ( Supplementary Fig. 14b ). This phenomenon may be attributed to the weak electrostatic attraction or coordination between Ca(II) and CMC, resulting in the formation of certain complexes or microscopic aggregates that enhance light scattering effect and increase light transmittance, thereby manifesting a negative absorption peak. These results provide preliminary evidence supporting the assembly ability order is Cu(II) > Fe(II) > Ca(II), which is also in accordance with the oxidation sequence of these ions. In addition, the UV peak position and absorbance of CMC-Cu(II) remain unchanged with different reaction time (Fig. 2 c). In contrast, the absorbance of the CMC-Fe(II) peak increases with prolonged reaction time, accompanied by a slight redshift, suggesting that Fe(II) forms a weak complex with CMC and requiring more time to complete. ( Fig. 2 d, Supplementary Fig. 15 ). Meanwhile, CMC-Ca(II) displays no UV absorption peak (Fig. 2 e). These findings further demonstrate that Cu(II) possesses a more stable coordination interaction and molecular assembly capacity, as expectated. Furthermore, Ag(I), with a higher oxidation potential than Cu(II), forms an ultra-thin freestanding CMC-Ag(I) membrane and emerges a new UV absorption peak ( Supplementary Fig. 16 ). These results strongly support the aforementioned trend. We previously indicated that Na(I) substituents in the CMC molecule can be occupied by coordination positions of other metal ions with higher oxidation states. In Fig. 2 f, the intensity of Na elements increases as follows: CMC-Cu(II) < CMC-Fe(II) < CMC-Ca(II) < CMC, according to their ability to replace Na(I). Notably, no Na peaks are observed in CMC-Cu(II). These results confirm the consistent molecular assembly ability of these three metal ions based on their coordination energies. More attractive, we experimentally discovered that other biomacromolecules like MC and CMCH also demonstrate molecular assembly behavior triggered by metal ion coordination ( see relevant UV spectra in Supplementary Fig. 17 ). Moreover, the membrane-forming behavior of these biomacromolecules with the three metal ions (Biomacromolecule-metal ions) aligns with the CMC (Fig. 2 g ) . Similarly, Ag(I) forms membranes (CMC-Ag(I), MC-Ag(I), and CMCH-Ag(I)) with performance comparable to Cu(II) ( Supplementary Fig. 18 ). This extending ultra-fast molecular assembly strategy will facilitate the reliable generation of bio-conductive membranes from various sustainable biomass resources. Mechanism characterization and simulation of molecular assembly To reveal and elucidate the transient assembly mechanism of metal ion coordination membranes, X-ray absorption spectroscopy (XAS) is employed to analyze the Cu valence and coordination state in formed CMC-Cu(II) membrane complex. Furthermore, density functional theory (DFT) calculations are conducted to determine the most stable coordination structures. The coordinated state of copper ions in the CMC-Cu(II) membrane is verified by XAS. The results of the Cu K-edge X-ray absorption near-edge spectrum (XANES; Fig. 3 a) indicates that the electronic state of the Cu ions in CMC-Cu(II) is closer to the CuO, showing characteristic absorption peaks of Cu(II), which supports the Cu in CMC-Cu(II) is in a + 2 state without other chemical changes. Fitting of the XANES and extended X-ray absorption fine structure (EXAFS; Fig. 3 b and Supplementary Fig. 19 ) spectra reveal two Cu-O distance of 2.14 ± 0.01 Å and 2.00 ± 0.01 Å ( Supplementary Table 1 ). These distances can be attributed to the coordination of Cu(II) with the single and double bonds of oxygen atoms in the carboxyl groups of CMC. Additionally, we observe that the coordination numbers of copper in CMC-Cu(II) are 2.2 ± 0.6 and 1.8 ± 0.7, respectively ( Supplementary Table 1 ), indicating a total coordination number of approximately 4. This suggests that the carboxyl groups of CMC form a coordination structure closed to the square planar with Cu(II) by bidentate coordination mode. To support and displaying the coordination structures, CMC-Cu(II), CMC-Ag(I), MC-Cu(II), and MC-Ag(I), which exhibit excellent membrane-forming behaviors, are selected as representative examples. Two glucose units are employed as models to simulate their theoretical optimal structures using DFT theory, with consideration of the solvent effect. Figure 3 c illustrates the tetrad coordination structure of the complexes. The Cu(II) ion adopts a square planar geometry by forming bidentate coordination with four oxygen atoms from the carboxyl groups of CMC. The calculated coordination distances are 2.13 Å for the oxygen atom on the double bond and 2.01 Å for the oxygen atom on the single bond, which aligns with fitting result of the XANES and EXAFS. Additionally, the binding energies of CMC-Cu(II) and CMC-Ag(I) in their respective structures are determined to be 1.40 and 1.44 Hartree, respectively ( Supplementary Table 2 ). Similarly, MC-Cu(II) also forms a tetrad structure, but with a slightly different coordination geometry, exhibiting a square planar configuration with a coordination bond length of 1.98 Å. In contrast, MC-Ag(I) displays a tetrahedral geometry while maintaining the same tetragonal structure, with coordination bond lengths ranging from 2.34 to 2.40 Å, consistent with conventional theoretical values. Furthermore, the binding energies of MC-Cu(II) and MC-Ag are 2.28 and 2.40 Hartree, respectively ( Supplementary Table 2 ), which is consistent with the coordination binding energies order of CMC. High-fidelity physiological monitoring by CMC-Cu(II) membranes as epidermal electrodes Physiological monitoring is crucial for continuously tracking key biological signals, such as ECG, EOG, EEG, and EMG, to assess health and enable early disease detection (Fig. 4 a). For accurate monitoring, sensors must maintain conformal contact with the skin, deforming synchronously during use. Additionally, electrodes must exhibit excellent biocompatibility to avoid adverse reactions like erythema and edema. The CMC-Cu(II) membrane provides a tissue-adapting interface that causes no skin rash, unlike commercial Ag/AgCl electrodes, which induce visible redness after one hour of adhesion ( Supplementary Fig. 20 ). With its ultrafast and facile in-situ preparation, thin and conformal structure, skin-friendly compatibility, and excellent ionic conductivity, the CMC-Cu(II) membrane can serve as an ideal epidermal electrode. One crucial criterion for acquiring high-quality physiological signals is establishing a stable, low-impedance interface between electrodes and skin 32 . The CMC-Cu(II) electrodes demonstrate lower impedance than commercial Ag/AgCl electrodes (Fig. 4 b ) . Specifically, compared with the corresponding commercial electrodes (5.87×10 5 Ω), the impedance of the CMC-Cu(II) electrodes (1.87×10 5 Ω) exhibit a notable reduction by approximately 68% at 20 Hz. This reduction is attributed to its high ionic conductivity and conformal contact with the skin. Subsequently, circular CMC-Cu(II) electrodes (15 mm diameter) are applied in a classical three-lead ECG setup following the "Einthoven triangle" theory. When compared with the commercial electrodes, the CMC-Cu(II) electrodes not only capture ECG signals with identical waveforms but also achieve a higher signal-to-noise ratio (SNR) of 16.41 dB compared to 14.58 dB (Fig. 4 c). The time-frequency spectrum 33 of ECG signals (Fig. 4 d) further demonstrates the stability and precise potential extraction capability of CMC-Cu(II) electrodes, highlighting their excellent performance in physiological signal monitoring. The application of the CMC-Cu (II) electrode in EOG monitoring as horizontal unipolar leads is demonstrated in Fig. 4 e. Single CMC-Cu(II) electrodes at the outer corner of the eye capture periodic EOG signals, reflecting blinking and ocular motility. 34 For blinking, the CMC-Cu(II) electrode captures distinct voltage patterns for each blink event, with localized amplification illustrating precise signal characteristics (Fig. 4 f top ). The time-frequency spectrum further confirms signal stability and accuracy (Fig. 4 g top ). Similarly, during ocular motility tests, the CMC-Cu(II) records persistent EOG signals corresponding to eye movements, with localized amplification and time-frequency spectrum analysis revealing detailed signal patterns (Fig. 4 f bottom and Fig. 4 g bottom ). Unipolar lead EEG colection offers a simple and efficient approach for analyzing electrical activity of specific brain regions, which holds significant implications for neuroscience research and clinical applications. A CMC-Cu(II) electrode attached to a volunteer’s forehead, where it intimately associate with decision-making, attention, executive function, and other cognitive processes (Fig. 4 h), enables detection of prefrontal cortex activity by measuring potential differences between the recording and reference electrodes. Real-time EEG signals during music listening (Fig. 4 i) and mathematical calculations ( Supplementary Fig. 21a ) reveal clear neural responses to auditory stimulus and exhibit differences. The corresponding time-frequency spectrum highlights distinct oscillatory patterns, capturing the dynamic interaction between the brain and the external auditory environment (Fig. 4 j and Supplementary Fig. 21b ). Moreover, concentration and relaxation coefficients differ between tasks: music listening activity shows average coefficients of concentration and relaxation at 50.60 and 63.29, respectively (total range 0-100) (Fig. 4 k), while mathematical calculation displays 57.60 for concentration and 44.87 for relaxation ( Supplementary Fig. 21c ), which aligned with the general trend observed. A localized analysis over 20 seconds further illustrates the stability and precision of CMC-Cu(II) recordings ( Supplementary Fig. 22a and 21d ), with the time-frequency spectrum displaying well-defined frequency bands ( Supplementary Fig. 22b and 21e ) 35 , 36 . These results demonstrate the accuracy and practical application potential of CMC-Cu(II) as an electrophysiological sensor. Further, we employ CMC-Cu(II) for multi-channel and finer-scale myoelectrophysiological monitoring. A pair of circular CMC-Cu(II) electrodes, corresponding to four lead channels, are fabricated in-situ in the extensor carpi radialis longus, extensor carpi ulnaris, biceps brachii, and triceps brachii muscles, respectively (Fig. 5 a), with commercial electrodes as controls. During grip dynamometer tests, CMC-Cu (II) collects EMG signals that clearly distinguish muscle contractions across channels (Fig. 5 b), similar to commercial electrodes (Fig. 5 c), this demonstrates CMC-Cu(II)'s ability to precisely detect varying degrees of muscle activity. The SNR of CMC-Cu(II) signals (21.39 dB, 24.36 dB, 36.55 dB, and 18.63 dB) surpasses that of commercial electrodes (16.18 dB, 24.27 dB, 25.96 dB, and 10.72dB) at the corresponding site (Fig. 5 d). Similar outcomes are observed during fist clenches ( Supplementary Fig. 23 ). To monitor EMG signals of human legs, a pairs of CMC-Cu(II) electrodes are positioned on the gastrocnemius, peroneal longus, and biceps femoris muscles, corresponding to three lead channels (Fig. 5 e), and the commercial electrodes serve as control samples. During various leg activities, such as leg lift, ankle raise, standing, walking, half-squatting, jumping, landing, and sitting (Fig. 5 f top ), the CMC-Cu(II) electrodes gather physiological signals consistent with those from commercial electrodes. Specifically, distinct waveforms and amplitudes in Fig. 5 f bottom reveal varying muscle contraction levels during different movements. The precise identification of different muscle contractions and accurate transmission of electrical signals by the CMC-Cu(II) electrodes are confirmed again in human leg movements. For recognizing and transmitting electrophysiological signals during extensive motion, we further employ them for sensing microsignals. Two CMC-Cu(II) electrodes are positioned on the masseter muscle of both cheeks and throat (Fig. 5 g), endowing to obtain mouth-related movements. Attractively, when phrases like ‘Hi’, ‘Good morning’, and ‘Happy birthday’ are spoken, the CMC-Cu(II) electrodes record high-fidelity EMG signals matching their durations. Similarly, actions such as coughing or drinking water produce consistent high-quality signals. Moreover, for distinct mouth-related activities, the two channels exhibit varying EMG signals (Fig. 5 h). These findings demonstrate the ability of CMC-Cu(II) to collect and transmit electrophysiological signals by high-precision, highlighting its potential for practical applications as an epidermal electrode for monitoring human electrophysiological activity. Discussion In summary, inspired by the milk skin effect and the principle of molecular self-assembly, we have proposed a straightforward and time-efficient strategy for rapid fabrication of ultra-thin electronic bio-membranes via robust metal coordination, achieving in-situ and conformal formation of bio-skin. By employing a "dipping-dipping" process, first in a CMC solution and subsequently in a Cu(II) solution, a well-formed conductive biological "skin" can be instantaneously formed on the surface of any target substrate within seconds. This bioelectronic skin demonstrates excellent interfacial conformal contact, degradability, and low impedance. The capacity and efficiency of membrane formation relying on metal ion coordination ability follows the order: Cu(II) > Fe(II) > Ca(II). At the same experimental condition, CMC-Cu(II) and CMC-Ag(I) form complete and stable membranes, while CMC-Fe(II) shows incomplete formation, and CMC-Ca(II) and CMC-Mg(II) remains unchanged in solution. This trend is also evident in other biological macromolecules, such as MC and CMCH, further highlighting the generalization of the approach. The merits of this membrane include: (1) It is made from sustainable cellulose, the most abundant natural material on Earth, and is biodegradable within 9 days post-use; (2) The formation process is straightforward and time-efficient, requiring only 2 seconds; (3) The bio-skin's ultra-thin 3.4 µm thickness, which ensures highly conformal contact with any substrate and low impedance compared to commercial electrodes, achieving a 68% reduction at 20 Hz; (4) It is formed directly on the target substrate, eliminating the need for additional transfers of the soft membrane. These attributes make the bio-skin an excellent candidate for epidermal applications and have been demonstrated for diverse electrophysiological signal monitoring, showcasing its potential for developing sustainable biological skins for various applications. Methods Materials Carboxymethylcellulose (CMC) with viscosity range of 1000–1400 mPa·s was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Copper chloride (CuCl 2 , AR, 99%) was purchased from Tianjin Damao Chemical Reagent Factory. Ferrous chloride tetrahydrate (FeCl 2 · 4H 2 O, AR, 98%), Calcium chloride (CaCl 2 , AR, 96%), methylcellulose (MC, 450 mPa.s) and carboxymethyl chitosan (CMCH) were obtained from Shanghai Macklin Biochemical Co., Ltd. The silver nitrate (AgNO 3 , AR) was acquired from Xilong Scientific Co., Ltd. Assembly of CMC-Cu(II) membrane The CMC-Cu(II) bio-membrane was synthesized through a sequential “dipping-dipping” process using different concentrations of CMC and CuCl 2 solutions. Specifically, a thin layer of CMC solution was initially dipped or coated onto the target substrate surface, followed by the coating of CuCl 2 solution after 1 s to facilitate the instantaneous coordination assembly of the CMC-Cu(II) bio-membrane. The concentrations used for all CMC-Cu(II) membranes in this study were 2 wt% for the CMC solution and 0.5 M for the CuCl 2 solution. Preparation of patterned CMC-Cu(II) membranes and microcircuits The patterned CMC-Cu(II) membranes were prepared using a laser-cut polyamide mask to define the desired pattern on the substrate. The mask was first adhered to the target surface, and then dipped in the CMC solution. After removing the mask, CuCl 2 solution was coated to form patterned CMC-Cu(II) bio-membranes. The CMC-Cu(II) microcircuit was synthesized using the same mask-forming method according to the designed circuit pattern, and subsequently, a chip LED lamp plate was positioned at its corresponding location on the circuit. Upon powering on, a complete CMC-Cu(II) microcircuit was obtained. Preparation of CMC-Fe(II), CMC-Ca(II), CMC-Ag(I) and other biomacromolecule-metal ions Solutions of MC and CMCH with a concentration of 2 wt% were prepared, along with solutions of FeCl 2 , CaCl 2 , and AgNO 3 at a concentration of 0.5 M. A thin layer of CMC solution was dipped or coated onto the desired surface, followed by subsequent coating of FeCl 2 and CaCl 2 solutions covering the CMC layer to form CMC-Fe(II) and CMC-Ca(II). The same “dipping-dipping” procedure was employed to obtain MC-Cu(II), MC-Fe(II), MC-Ca(II), MC-Ag(I), CMCH-Cu (II), CMCH-Fe(II), CMCH-Ca(II), and CMCH-Ag(I). Characterization The thickness of CMC-Cu(II) membranes was characterized using Hitachi SU-1510 SEM to obtain cross-sectional characterization data. To assess the conformal properties, a CMC-Cu(II) membrane was attached onto a wavy PVC mold and subjected to embrittle in liquid nitrogen. The samples containing 0.5 wt% of CMC, MC, and CMCH were mixed with metal salt solutions including CuCl 2 , FeCl 2 , and CaCl 2 at various concentrations respectively. The resulting mixtures were characterized using a JOSVOK UV-5600P UV-VIS spectrophotometer, which had a test range from 190 nm to 500 nm. The absorption behavior in the ultraviolet and visible regions of samples was analyzed by the characteristic absorption peak positions and intensities of the spectra. The chemical state of CMC-Cu(II) membrane was analyzed using XPS equipment (Thermo Scientific K-Alpha, USA). Fourier transform infrared (FTIR) spectra of CMC and CMC-Cu(II) membranes were obtained using the Nicolet iS5 spectrometer (Thermo Scientific, USA), covering wave numbers ranging from 4000 − 400 cm − 1 . Cu K-edge analysis of CMC-Cu(II) membrane was performed with Si(111) crystal monochromators at the BL11B beamlines at the Shanghai Synchrotron Radiation Facility (SSRF) (Shanghai, China). Before the analysis at the beamline, samples were pressed into thin sheets with 1 cm in diameter and sealed using Kapton tape film. The XAFS spectra were recorded at room temperature using a 4-channel Silicon Drift Detector (SDD) Bruker 5040. XX-edge extended X-ray absorption fine structure (EXAFS) spectra were recorded in transmission mode. Negligible changes in the line-shape and peak position of Cu K-edge XANES spectra were observed between two scans taken for a specific sample. The XAFS spectra of these standard samples (Cu foil and CuO) were recorded in transmission mode. The spectra were processed and analyzed by the software codes Athena and Artemis. The inductance-capacitance-resistance (LCR) meter (TH2838H, Tonghui) with a frequency range of 20 Hz-2 MHz, was employed to measure the intrinsic impedance of both CMC-Cu (II) skin-contact electrode and commercial electrode. Biodegradability test CMC-Cu(II) membranes and PE films were cut into a square shape with 2 cm on each side. The films were placed in natural soil surface and the photos were taken once a day. The normalized undegraded area is the mean membrane area derived from two parallel samples. Density functional theory calculations CMC-Cu(II), CMC-Ag(I), MC-Cu(II), and MC-Ag(I) models, each consisting of two carboxymethyl-substituted glucose or methyl-substituted glucose units and one metal ion, were calculated using DFT to gain the corresponding coordination structure and binding energy. The binding energy is defined as ΔE X = E 2glucose - M – E 2glucose – E M , where E 2glucose represents the energy of two glucose units substituted with carboxymethyl or methyl groups (2glucose) and E M denotes the energy of corresponding metal ions (Cu(II) or Ag(I)). E 2glucose - M refers to the energy of the linked system (2glucose-Cu(II) and 2glucose-Ag(I)) after coordination of two carboxymethyl or methyl substituted glucose units and metal ions (Cu(II) or Ag(I)), and the “X” in ΔE X corresponds to CMC-Cu(II), CMC-Ag(I), MC-Cu(II), and MC-Ag(I). DFT calculations were carried out using the Gaussian 16W, employing the M08-HX functional, the basic group 6-311 + G*, and the LANL2DZ as effective core potential for geometric optimization, energy calculation, and frequency analysis. Additionally, a continuous solvation model SMD was used to simulate solvent effects on the molecules. Electrophysiological signal monitoring For ECG monitoring, following the "Einthoven triangle" theory, a circular CMC-Cu(II) epidermal electrode with a diameter of 15 mm was applied on the subject's left and right wrists respectively. Additionally, a reference electrode was placed on the subject's left ankle. The arrangement of commercial electrodes followed the same configuration. ECG signals were recorded using an ECG sensor equipped with an integrated ADS1292R signal acquisition converter, STM32F103C8T6 microcontroller, and Bluetooth transmission device. The EOG signal was recorded using a horizontal unipolar lead. A CMC-Cu(II) epidermal electrode, with a diameter of 15 mm, was attached to the outer corner of the subject's left eye in place. The reference electrode was positioned on the left earlobe, as depicted in Fig. 4 e. The signals generated during blinking and turning eyeball movements were captured and recorded by a signal recording system equipped with an integrated bandpass filter (Neurosky TGAM EEG03, Jiangsu, China) connected to the electrodes. EEG signals were also logged using a unipolar lead configuration. A CMC-Cu(II) epidermal electrode (F4), with a diameter of 15 mm, was placed on the subject's clean forehead, while the reference electrode was positioned on the earlobe following the 10–20 international electrode placement system. The detailed arrangement of electrodes is illustrated in Fig. 4 h. All electrodes were connected to a signal recording system equipped with an integrated bandpass filter (Neurosky TGAM EEG03, Jiangsu, China). During activities involving mathematical calculations and music listening, respectively, EEG signals were detected and transmitted. For EMG signal monitoring, a six-channel system including a signal monitoring microcontroller (ZTEMG-1100 PCB, Zhituo Intelligent Technology Co., Ltd., Qingdao, China), a signal input terminal (CH-50RB), and an oscilloscope (Handyscope Model HS4, TiePie engineering, China) was utilized, and all electrodes were connected to the system. Each channel consisted of a pair of working electrodes. A pair of CMC-Cu(II) working electrodes were formed in the extensor carpi radialis longus, extensor carpi ulnaris, biceps brachii, and triceps brachii muscles respectively (Fig. 5 a), corresponding to four channels for capturing EEG signals from the arm. The reference electrode was positioned at the elbow joint. Subjects performed grip dynamometer exercises or made a fist while their resulting signals were recorded by the sensor. For collecting EEG signals from the legs, CMC-Cu(II) electrodes (Fig. 5 e) were in-situ prepared at three lead channels on the gastrocnemius, peroneus longus, and biceps femoris muscles respectively; meanwhile, a reference electrode was placed on the patella. A series of leg activities including leg lift, ankle raise, standing, walking, half-squatting, jumping, landing, and sitting were performed by subjects to elicit corresponding signals which were identified and transmitted through connected electrodes and sensors accordingly. Additionally, EEG signals generated by mouth movements of subjects were captured by sensors with two CMC-Cu(II) electrodes placed on the left and right masseter muscles and throat, respectively, with a reference electrode positioned on the earlobe (Fig. 5 g). All commercial electrodes underwent acquisition following identical procedures. Declarations Competing interests The authors declare that they have no competing interests and the manuscript is approved by all authors for publication. Data and materials availability All data are available in the main text or the supplementary materials. Additional information Supplementary information is available for this paper References Arwani RT , et al. Stretchable ionic–electronic bilayer hydrogel electronics enable in situ detection of solid-state epidermal biomarkers. Nat. Mater. 23 , 1115-1122 (2024). Yoon H , et al. Adaptive Epidermal Bioelectronics by Highly Breathable and Stretchable Metal Nanowire Bioelectrodes on Electrospun Nanofiber Membrane. Adv. Funct. Mater. 34 , 2313504 (2024). Liu S , et al. Permeable, Stretchable, and Recyclable Cellulose Aerogel On-Skin Electronics for Dual-Modal Sensing and Personal Healthcare. ACS Nano 19 , 3531-3548 (2025). Zhang L , et al. Cellulose nanofiber-mediated manifold dynamic synergy enabling adhesive and photo-detachable hydrogel for self-powered E-skin. Nat. Commun. 15 , 3859 (2024). Zou X , et al. Snail-inspired bio-based recyclable liquid-like ionic skins enabling ultra-conformal contact and elasticity recovery for epidermal electronics. Nano Today 61 , 102611 (2025). Lan L , et al. Skin-Inspired All-Natural Biogel for Bioadhesive Interface. Adv. Mater. 36 , 2401151 (2024). Lu M, Shen L, Su H, Li B, Wang L, Yu WW. Highly ionic conductive, elastic, and biocompatible double-network composite gel for epidermal biopotential monitoring and wearable sensing. J. Colloid Interface Sci. 684 , 272-282 (2025). Li C, Qian Y, Zhang X, Wang R. Robust-adhesion and high-mechanical strength hydrogel for efficient wet tissue adhesion. J. Mat. Chem. B 13 , 2469-2479 (2025). Ma P , et al. Super-Structured Wet-Adhesive Hydrogel with Ultralow Swelling, Ultrahigh Burst Pressure Tolerance, and Anti-Postoperative Adhesion Properties for Tissue Adhesion. Adv. Mater. 36 , 2305400 (2024). Namkoong M , et al. Moldable and transferrable conductive nanocomposites for epidermal electronics. npj Flex. Electron. 6 , 41 (2022). Yang C , et al. A bioinspired permeable junction approach for sustainable device microfabrication. Nat. Sustain. 7 , 1190-1203 (2024). Zhou Y, Feng B, Chen L, Fan F, Ji Z, Duan H. Wafer-Recyclable, Eco-Friendly, and Multiscale Dry Transfer Printing by Transferable Photoresist for Flexible Epidermal Electronics. ACS Appl. Mater. Interfaces 16 , 13525-13533 (2024). Qiao Y , et al. Multilayer Graphene Epidermal Electronic Skin. ACS Nano 12 , 8839-8846 (2018). Xia Q , et al. A strong, biodegradable and recyclable lignocellulosic bioplastic. Nat. Sustain. 4 , 627-635 (2021). Tang H , et al. In Situ Forming Epidermal Bioelectronics for Daily Monitoring and Comprehensive Exercise. ACS Nano 16 , 17931-17947 (2022). Pochan D, Scherman O. Introduction: Molecular Self-Assembly. Chem. Rev. 121 , 13699-13700 (2021). Zhang Z , et al. Self-adjusted aromatic cation-π binding promotes controlled self-assembly of positively charged π-electronic molecules. Chem 10 , 1279-1294 (2024). Yang L, Li Q, Ge Z, Fan C, Huang W. DNA Mechanics: From Single Stranded to Self-Assembled. Nano Lett. 24 , 11768-11778 (2024). Evans AA, Cheung E, Nyberg KD, Rowat AC. Wrinkling of milk skin is mediated by evaporation. Soft matter 13 , 1056-1062 (2017). Cha GD, Kim D-H. Toughness and elasticity from phase separation. Nat. Mater. 21 , 266-268 (2022). Li P , et al. Epidermis inspired self-assembled iontronic foam with high sensitivity and broad range. Nano Mater. Sci. , (2024). Zhu Y , et al. A general strategy for synthesizing biomacromolecular ionogel membranes via solvent-induced self-assembly. Nat. Synth. 2 , 864-872 (2023). Chen C , et al. Lightweight, Thermally Insulating, Fire-Proof Graphite-Cellulose Foam. Adv. Funct. Mater. 33 , 2204219 (2023). Khare E, Holten-Andersen N, Buehler MJ. Transition-metal coordinate bonds for bioinspired macromolecules with tunable mechanical properties. at. Rev. Mater. 6 , 421-436 (2021). Wu M , et al. A high-performance hydroxide exchange membrane enabled by Cu2+-crosslinked chitosan. Nat. Nanotechnol. 17 , 629-636 (2022). Park JS , et al. Carboxymethyl cellulose-based rotigotine nanocrystals-loaded hydrogel for increased transdermal delivery with alleviated skin irritation. Carbohydr. Polym. 338 , 122197 (2024). Tan F, Zha L, Zhou Q. Assembly of AIEgen-Based Fluorescent Metal–Organic Framework Nanosheets and Seaweed Cellulose Nanofibrils for Humidity Sensing and UV-Shielding. Adv. Mater. 34 , 2201470 (2022). Zhang Z , et al. A 10-micrometer-thick nanomesh-reinforced gas-permeable hydrogel skin sensor for long-term electrophysiological monitoring. Sci. Adv. 10 , eadj5389 (2024). Dong Q , et al. A cellulose-derived supramolecule for fast ion transport. Sci. Adv. 8 , eadd2031 (2022). Qian J , et al. Highly stable, antiviral, antibacterial cotton textiles via molecular engineering. Nat. Nanotechnol. 18 , 168-176 (2023). Yang C , et al. Copper-coordinated cellulose ion conductors for solid-state batteries. Nature 598 , 590-596 (2021). Kim H , et al. Skin preparation–free, stretchable microneedle adhesive patches for reliable electrophysiological sensing and exoskeleton robot control. Sci. Adv. 10 , eadk5260 (2024). Zhang L , et al. Fully organic compliant dry electrodes self-adhesive to skin for long-term motion-robust epidermal biopotential monitoring. Nat. Commun. 11 , 4683 (2020). Debbarma S, Bhadra S. A Lightweight Flexible Wireless Electrooculogram Monitoring System With Printed Gold Electrodes. IEEE Sens. J. 21 , 20931-20942 (2021). Li X , et al. A Self-Supporting, Conductor-Exposing, Stretchable, Ultrathin, and Recyclable Kirigami-Structured Liquid Metal Paper for Multifunctional E-Skin. ACS Nano 16 , 5909-5919 (2022). Yang G , et al. Adhesive and Hydrophobic Bilayer Hydrogel Enabled On-Skin Biosensors for High-Fidelity Classification of Human Emotion. Adv. Funct. Mater. 32 , 2200457 (2022). Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryInformation.docx Supplementary Information SupplementaryvideoS1.mp4 CMC-Cu(II) membrane fabrication by “dipping-dipping” method SupplementaryvideoS2.mp4 CMC-Fe(II) membrane fabrication by “dipping-dipping” method SupplementaryvideoS3.mp4 CMC-Ca(II) membrane fabrication by “dipping-dipping” method reportingsummarynew.pdf Reporting Summary Cite Share Download PDF Status: Under Review 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. 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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-6344254","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":441810654,"identity":"c7cf7567-e576-400c-a5cc-bfd037575864","order_by":0,"name":"Meng 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characterization of CMC-Cu(II) membrane via metal ion-driven assembly strategy, mimicking the 'milk skin effect'.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Schematic illustration of the formation of milk skin and cellulose skin. (\u003cstrong\u003eI)\u003c/strong\u003e Photograph of milk source (cow) and a cup of milk. (\u003cstrong\u003eII\u003c/strong\u003e)\u003cstrong\u003e \u003c/strong\u003eThermal-induced molecular assembly during milk skin formation and a digital image of milk skin. (\u003cstrong\u003eIII\u003c/strong\u003e)\u003cstrong\u003e \u003c/strong\u003eMultilevel structure of cellulose and a photograph of CMC powder. CMC as a typical cellulosic derivative macromolecule, is derived from wood cellulose fiber. (\u003cstrong\u003eIV\u003c/strong\u003e) The molecular assembly promoted by strong coordination of Cu(II) ions and CMC molecules contributes to the rapid generation of CMC-Cu(II) ultra-thin conductive bio-membrane. \u003cstrong\u003eb\u003c/strong\u003e Digital photographs of CMC-Cu(II) membrane with Cu(II) coordination fabricated by simple “dipping-dipping” process from CMC and Cu(II) solutions. \u003cstrong\u003ec\u003c/strong\u003e The adaptable, highly conformal CMC-Cu(II) membrane assembled in-situ on irregular surfaces of multi-substrates (\u003cstrong\u003eI\u003c/strong\u003e). Digital photographs of CMC-Cu(II) patterns (\u003cstrong\u003eII\u003c/strong\u003e) on diverse 2D and 3D surfaces (\u003cstrong\u003eIII\u003c/strong\u003e). \u003cstrong\u003ed\u003c/strong\u003e Cross-sectional SEM image of ultra-thin CMC-Cu(II) membrane. \u003cstrong\u003ee\u003c/strong\u003e Cross-sectional SEM images of highly conformal CMC-Cu(II) membrane attached on PVC wavy mold. \u003cstrong\u003ef\u003c/strong\u003eDigital image of CMC-Cu(II) patterned microelectronic circuit on human skin and its ability to illuminate LED lights. \u003cstrong\u003eg\u003c/strong\u003e The degradation photographs of CMC-Cu(II) membranes and PE films.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6344254/v1/ea99a81151439eeb5bb242eb.png"},{"id":80609530,"identity":"ce31aea3-0397-4673-9b69-2c390d57723f","added_by":"auto","created_at":"2025-04-15 07:31:35","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":5468680,"visible":true,"origin":"","legend":"\u003cp\u003eMechnism validation and development of coordination interactions endowing molecular assembly to from membrane.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e UV absorption spectra of CMC, Cu(II), and CMC-Cu(II), illustrating the coordination interaction between CMC and Cu(II). \u003cstrong\u003eb\u003c/strong\u003e The O1s fitted curves of CMC and CMC-Cu(II) membranes, demonstrating a significant reduction in the C-O and C=O functional groups in the CMC-Cu(II) membrane, providing strong evidence for the robust coordination between Cu(II) and CMC. UV spectra and membrane photographs of \u003cstrong\u003ec\u003c/strong\u003e CMC-Cu(II), \u003cstrong\u003ed\u003c/strong\u003e CMC-Fe(II) and \u003cstrong\u003ee\u003c/strong\u003e CMC-Ca(II) with different reaction time. \u003cstrong\u003ef\u003c/strong\u003eXPS survey spectra of Na element in CMC, CMC-Cu(II), CMC-Fe(II) and CMC-Ca(II). \u003cstrong\u003eg \u003c/strong\u003eExtending this membrane formation strategy and rule of metal ion-induced molecular assembly to other biomacromolecules such as MC and CMCH.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6344254/v1/50e31810b8c9168bb9316e50.png"},{"id":80609533,"identity":"13660826-d535-4e5b-abb2-ac65f8e15ae7","added_by":"auto","created_at":"2025-04-15 07:31:35","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":3376541,"visible":true,"origin":"","legend":"\u003cp\u003eMechnism characterization and simulation of molecular assembly induced by coordination interactions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Cu K-edge XANES spectra of the CMC-Cu(II), CuO, and Cu foil; spectra of CuO and Cu foil standards are shown for comparison purposes. \u003cstrong\u003eb\u003c/strong\u003e R-space EXAFS spectrum of the CMC-Cu(II) and the corresponding fitting curve. FT, Fourier transform. \u003cstrong\u003ec\u003c/strong\u003e The coordination structures and electrostatic views of CMC-Cu(II), CMC-Ag(I), MC- Cu(II), and MC-Ag(I)obtained by DFT simulation.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6344254/v1/751ebb677281fc33d3bd99cc.png"},{"id":80610283,"identity":"0e3572c1-8ae3-42bd-8a88-c88d8ea60ee5","added_by":"auto","created_at":"2025-04-15 07:39:35","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":6671008,"visible":true,"origin":"","legend":"\u003cp\u003eHigh-fidelity monitoring of ECG, EOG, and EEG by the CMC-Cu(II) epidermal electrode.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Schematic diagram of ECG, EMG, EOG, and EEG monitoring.\u003cstrong\u003e b\u003c/strong\u003e Skin-contact impedance values of CMC-Cu(II) and commercial electrodes within 20 Hz to 1000 kHz. \u003cstrong\u003ec\u003c/strong\u003e The periodic ECG signals and SNR of CMC-Cu(II) and commercial electrodes. \u003cstrong\u003ed\u003c/strong\u003e Time-frequency spectrum of a single cycle of ECG signal. \u003cstrong\u003ee\u003c/strong\u003e Schematic illustration of electrode placement during EOG collection. \u003cstrong\u003ef and g\u003c/strong\u003e Periodic EOG signals captured by the CMC-Cu(II) electrodes displaying movements involving blinking and ocular motility of the subject (\u003cstrong\u003ef\u003c/strong\u003e) and corresponding time-frequency spectrum of a single cycle of EOG signal (\u003cstrong\u003eg\u003c/strong\u003e). \u003cstrong\u003eh\u003c/strong\u003e Schematic indication of electrode placement during EEG collection. \u003cstrong\u003ei \u003c/strong\u003eto\u003cstrong\u003e k\u003c/strong\u003e EEG signals (\u003cstrong\u003ei\u003c/strong\u003e), corresponding time-frequency spectrum (\u003cstrong\u003ej\u003c/strong\u003e), and coefficients of concentration and relaxation (\u003cstrong\u003ek\u003c/strong\u003e) recorded by CMC-Cu(II) electrodes during the subject's cognitive engagement in music listening.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6344254/v1/e55678d984cf1a8e4d795703.png"},{"id":80609539,"identity":"d9fcaa17-07d8-4da0-978a-8596b15a75e3","added_by":"auto","created_at":"2025-04-15 07:31:35","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":4341576,"visible":true,"origin":"","legend":"\u003cp\u003eHigh-fidelity EMG monitoring of multi-channel and finer-scale movements by the CMC-Cu(II) epidermal electrode.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Schematic illustration of electrode placement on different arm muscles during EMG collection. \u003cstrong\u003eb-c\u003c/strong\u003e The four-channel periodic EMG signals of CMC-Cu(II) (\u003cstrong\u003eb\u003c/strong\u003e) and commercial electrodes (\u003cstrong\u003ec\u003c/strong\u003e) when the subject uses the grip dynamometer. \u003cstrong\u003ed\u003c/strong\u003eSNR comparisons of EMG signals collected by CMC-Cu(II) and commercial electrodes in each channel. \u003cstrong\u003ee\u003c/strong\u003e Schematic illustration of electrode placement on different leg muscles during EMG collection. \u003cstrong\u003ef\u003c/strong\u003e A series of leg movements during the acquisition of leg EMG signals (\u003cstrong\u003etop\u003c/strong\u003e); EMG signals corresponding to the series of leg movements of the subject captured by the CMC-Cu(II) and commercial electrodes (\u003cstrong\u003ebottom\u003c/strong\u003e). \u003cstrong\u003eg\u003c/strong\u003e Schematic illustration of electrodes placed on both buccal masseters and throat to collect microsignals. \u003cstrong\u003eh\u003c/strong\u003e EMG signals when the subject speaks some common words and makes other oral movements recorded by CMC-Cu(II) and commercial electrodes.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6344254/v1/49b3ed3bc1ce8e90a1b72a4e.png"},{"id":82528344,"identity":"de737486-7ed4-447c-8728-156b8f0a3495","added_by":"auto","created_at":"2025-05-12 14:13:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":26303875,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6344254/v1/7cc070cf-0fa3-43f5-be71-83eebc402b6f.pdf"},{"id":80609552,"identity":"f30365f4-12fb-401f-8b26-1ac6b4797a6e","added_by":"auto","created_at":"2025-04-15 07:31:35","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":50961630,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-6344254/v1/df9dd375c1af2dae416e77dc.docx"},{"id":80609540,"identity":"aedeb2a2-e827-4d85-b9ca-4e0cf807fd39","added_by":"auto","created_at":"2025-04-15 07:31:35","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":31196147,"visible":true,"origin":"","legend":"CMC-Cu(II) membrane fabrication by \u0026#x201C;dipping-dipping\u0026#x201D; method","description":"","filename":"SupplementaryvideoS1.mp4","url":"https://assets-eu.researchsquare.com/files/rs-6344254/v1/c686c93e5877684705b02faa.mp4"},{"id":80610698,"identity":"4d1c424e-50e3-4079-ac0a-1ebb1ab4538e","added_by":"auto","created_at":"2025-04-15 07:47:35","extension":"mp4","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":39390011,"visible":true,"origin":"","legend":"CMC-Fe(II) membrane fabrication by \u0026#x201C;dipping-dipping\u0026#x201D; method","description":"","filename":"SupplementaryvideoS2.mp4","url":"https://assets-eu.researchsquare.com/files/rs-6344254/v1/83b9afd71ef19de75cca3c94.mp4"},{"id":80610289,"identity":"0efc8576-84e0-482b-a2e1-744bd2d4d476","added_by":"auto","created_at":"2025-04-15 07:39:35","extension":"mp4","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":26319672,"visible":true,"origin":"","legend":"CMC-Ca(II) membrane fabrication by \u0026#x201C;dipping-dipping\u0026#x201D; method","description":"","filename":"SupplementaryvideoS3.mp4","url":"https://assets-eu.researchsquare.com/files/rs-6344254/v1/3a2b2292a3270847971bc271.mp4"},{"id":80609534,"identity":"c63b0282-739d-46f3-bd8e-92e93fa89e71","added_by":"auto","created_at":"2025-04-15 07:31:35","extension":"pdf","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":1512399,"visible":true,"origin":"","legend":"Reporting Summary","description":"","filename":"reportingsummarynew.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6344254/v1/3aed0e9a4fed2cca23b77838.pdf"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"2-Second In-Situ Formation of Adaptive Electronic Bio-Skin Enabled by Metal Coordination","fulltext":[{"header":"Introduction","content":"\u003cp\u003eElectrically conductive membranes enable advanced epidermal electronics by providing flexibility and high electrical conductivity, with wide applications in medical and health monitoring, human-machine interaction, athletic performance monitoring, and personalized medicine\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. The high-performance realization of epidermal electronic devices critically depends largely on conformal interfaces with biological tissues, high-resolution accuracy of target signal, and excellent biocompatibility\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. However, its further development remains limited by the following challenges: (i) Multi-step and time-consuming fabrication procedure\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e; (ii) Delicate interface design requirements such as adhesion modulation and ultra-thin membrane fabrication for matching dynamically deforming biological tissues\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e; (iii) Limited self-standing property that hinders intact transfer onto target surface without damage\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e; (iv) Conventional petroleum-based materials commonly used facing inherent issues with environmental friendliness and biocompatibility\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. Therefore, there is an urgent need for a simple and time-efficient fabrication strategy to develop biomaterial-based electronic membranes that conform to living tissues, enabling accurate and high-fidelity physiological monitoring. Besides, if the electronic membrane can be formed in situ, on demand, the film could better maintain its integration since no additional transfer to the target tissue or skin is required\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eAs one of the most exciting frontiers in materials science, molecular self-assembly emerges as a promising candidate for realizing convenient and reliable production of bio-membranes due to its tunability and flexibility. It is a spontaneous process of aggregating from disorder to order, driven by non-covalent interactions, such as hydrogen bonding, van der Waals forces, electrostatic interactions, and π-π stacking, without external intervention\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. Self-assembly is widespread in nature, exemplified by the formation of the DNA double helix and the milk-skin effect upon heating\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. Inspired by these natural processes, precise control of intermolecular interactions enables the design and construction of materials with tailored functions and structures, providing a versatile platform for developing membrane materials across multiple scales\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. A notable example of thermally induced molecular self-assembly is the formation of milk skin (\u003cb\u003eFig.\u0026nbsp;1aI-II\u003c/b\u003e), where heat unfolds the tertiary structure of coiled proteins, leading to the self-assembly of protein meleculars into an ordered milk lamellar membrane, driven by the synergistic effect of hydrophobic interactions, hydrogen bonding, and fat globules (\u003cb\u003eFig.\u0026nbsp;1II\u003c/b\u003e)\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. Leveraging this natural phenomenon, the rapid fabrication of on-demand conformal bioconductive membranes employing the principles of molecular self-assembly presents a promising strategy.\u003c/p\u003e \u003cp\u003eHere, we present a convenient and time-efficient strategy for the synthesis of biodegradable, electronic bio-membranes through strong metal coordination interactions\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e, enabling ultra-fast, in-situ, and adaptive assembly of biomacromolecules. By sequentially dipping the target substrate, regardless of its structure, first in carboxymethylcellulose (CMC) and then in a Cu(II) solution, an intact, robust bioconductive \u0026ldquo;skin\u0026rdquo; can be formed instantly within 2 seconds (\u003cb\u003eFig.\u0026nbsp;1aIII-IV\u003c/b\u003e). Research demonstrates that the capacity for instant in-situ membrane formation correlates with the oxidation state of the metal ions, following this trend: Cu(II)\u0026thinsp;\u0026gt;\u0026thinsp;Fe(II)\u0026thinsp;\u0026gt;\u0026thinsp;Ca(II). Specifically, at the same experimental conditions, CMC-Ag(I) and CMC-Cu(II) form well-defined, stable membranes, while CMC-Fe(II) exhibits a fragmented morphology, indicating incomplete formation, and CMC-Mg(II) and CMC-Ca(II) remain the solution state without significant changes. This trend also applies to other biomacromolecules, such as methylcellulose (MC) and carboxymethyl chitosan (CMCH), further extending the applicability of the method beyond CMC. The resulting CMC-based bio-membranes can serve as epidermal electronics for real-time physiological signal monitoring, including electrocardiogram (ECG), electrooculogram (EOG), electroencephalogram (EEG), and electromyography (EMG), demonstrating their potential for wearable, biocompatible electronics in healthcare applications.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eSynthesis and characterization of CMC-Cu(II) membrane\u003c/p\u003e\n\u003cp\u003eThe ultra-thin conductive bio-molecular skin (CMC-Cu(II) membrane) can be achieved via a facile \u0026ldquo;dipping-dipping\u0026rdquo; coordination assembly process, which only needs the target item or surface to be sequentially immersed in CMC solutions and Cu(II) salt solutions (e.g., copper chloride or copper sulfate) (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb, \u003cstrong\u003eSupplementary Fig.\u0026nbsp;1 and Supplementary Video 1\u003c/strong\u003e). The entire \u0026quot;contact and assembly\u0026quot; process takes 2 seconds, with each dipping step lasting 1 second. In this recipe, CMC, a derivative of cellulose that is the most abundant biopolymer on earth, is naturally biofriendly and offers realizability for biodegradability of bioelectronic skin\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. The Cu(II) ion is the key ingredient that ensures strong coordination and a rapid assembly process, which will be discussed in detail in the later section.\u003c/p\u003e\n\u003cp\u003eThis simple \u0026ldquo;dipping-dipping\u0026rdquo; process enables the in-situ formation on demand of adaptive, shape-conforming conductive bio-skin on materials with arbitrary surfaces. To demonstrate its excellent conformal performance, we constructed CMC-Cu(II) surface on varied materials, including rubber model, shaped candy, polyacrylamide hydrogel, metal nut, fresh fruit (apple), and human palm skin (\u003cstrong\u003eFig.\u0026nbsp;1cI\u003c/strong\u003e). The CMC-Cu(II) membranes adhere seamlessly to these diverse surfaces, perfectly conforming their shapes. Guided by the flexibility in the coordination assembly process, ultra-thin CMC-Cu(II) membranes can be achieved by controlling the concentration of CMC and Cu(II) (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;2\u003c/strong\u003e). The cross-sectional scanning electron microscopy (SEM) image reveals a 3.4-\u0026micro;m-thick CMC-Cu (II) membrane (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ed) fabricated from a 1 wt% CMC solution and 0.5 M Cu(II) solution. The \u0026ldquo;thin\u0026rdquo; feature of the CMC-Cu(II) membrane further enhances its ability to conform to and match various interfaces\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. The SEM demonstrates that the CMC-Cu(II) membrane on the wavy polyvinyl chloride (PVC) template closely matches its microscopic contours (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ee \u003cstrong\u003eand Supplementary Fig.\u0026nbsp;3\u003c/strong\u003e), confirming that the proposed molecular assembly process fabricates ultra-thin CMC-Cu(II) membranes with excellent conformal adhesion, which is beneficial for the development of various applications.\u003c/p\u003e\n\u003cp\u003eThe CMC-Cu(II) membranes also exhibit good conductivity, serving effectively as conductive pathways or epidermal electrodes. Generally, typical CMC exhibits Na(I) ion substitution. Coordination bonds between CMC molecules and Cu(II) cause the generation of Na\u003csup\u003e+\u003c/sup\u003e owing to the displacement Na atoms. The assembly of CMC molecules induced by this robust coordination bond simultaneously accelerates the formation of a supported channel, enhancing ion transport and improving the conductivity of water-containing CMC-Cu(II) membranes (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;4\u003c/strong\u003e)\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. This capability is demonstrated by illuminating LED lights using dumbbell-shaped CMC-Cu(II) membrane as a conductive path prepared on leaf substrates (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;5\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003eMoreover, the facile \u0026ldquo;dipping-dipping\u0026rdquo; coordination assembly process enables CMC-Cu(II) membranes to be easily fabricated into custom-shaped patterns (\u003cstrong\u003eFig.\u0026nbsp;1cII\u003c/strong\u003e) using a mask-forming approach (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;6\u003c/strong\u003e). Unlike other conventional ways, this patterned conductive bio-skin can be formed in-situ on various 2D and 3D surfaces directly (\u003cstrong\u003eFig.\u0026nbsp;1cIII and Supplementary Fig.\u0026nbsp;7\u003c/strong\u003e), which eliminates the need for transfer and ensures conformal contact. Harnessing this characteristic, CMC-Cu(II) patterned microelectronic circuits are successfully integrated on human skin or other 3D interfaces (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ef and \u003cstrong\u003eSupplementary Fig.\u0026nbsp;8)\u003c/strong\u003e, providing a novel and straightforward approach for in-situ flexible electronics manufacturing. Notably, while neat CMC membrane dissolves in water within 100 s, CMC-Cu(II) membrane retains its structure for up to 30 days due to the \u0026quot;bridging\u0026quot; effect of Cu(II). This facilitates long-term stability of CMC-Cu(II) membrane in aqueous solutions like human sweat, promoting both its retention and functionality (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;9\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003eOwing to the inherent biocompatibility of CMC, the biodegradability of CMC-Cu(II) membrane in natural environments is investigated. Both CMC-Cu(II) membranes and polyethylene (PE) films are placed on the soil surface. After 9 days, the CMC-Cu(II) membrane is visually degraded, whereas the PE film remains their original shape (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eg \u003cstrong\u003eand Supplementary Fig.\u0026nbsp;10\u003c/strong\u003e). These findings suggest rapid biodegradation of CMC-Cu(II) membranes in natural environments.\u003c/p\u003e\n\u003cp\u003eCoordination interactions in CMC-Cu(II) membrane by molecular assembly\u003c/p\u003e\n\u003cp\u003eThe Cu(II) ions, possessing strong coordination ability\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e rapidly assemble CMC macromolecules by forming planar square coordination with adjacent CMC chains, creating instantaneous CMC-Cu(II) membrane formation. Upon contact, Cu(II) initially forms a coordinated bond with the oxygen atom of C6 carboxymethyl substituent on the CMC molecule, which leads to ligand-to-metal charge transfer. Simultaneously, the partially filled d orbitals undergo energy level splitting, leading to d-d electron transitions. These changes result in new ultraviolet (UV)-visible (VIS) absorption peaks at 242 nm attributed to CMC-Cu(II), distinct from those of CMC (194 nm) and Cu(II) (192 nm). This indicates the formation of a new material state, CMC-Cu(II) (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea). The strong coordination between Cu(II) and CMC is supported by the pronounced reduction in intensities of C-O and C\u0026thinsp;=\u0026thinsp;O peaks observed in the CMC-Cu (II) membrane in the O1s and C1s fitted spectra of X-ray photoelectron spectroscopy (XPS) (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb, \u003cstrong\u003eSupplementary Fig.\u0026nbsp;11\u003c/strong\u003e). Furthermore, Fourier transform infrared (FTIR) spectra also confirm this through sharpened -OH peaks and shifted C-O stretching vibrations (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;12\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003eTo further validate that the ultra-fast formation of CMC-Cu(II) membrane is due to strong coordination capacity of Cu(II), a series of common metal ions with varying oxidation states, including Ca(II), Mg(II), Mn(II), Zn(II), Fe(II), and Ag(I), are investigated for their molecular assembly capabilities in terms of membrane formation. It is observed that membrane-forming abilities are influenced by their oxidation properties. For instance, at the same concentration, Ag(I) forms complete and stable membranes with CMC, Fe(II) creates incomplete membrane, and Mg(II) and Ca(II) remain in solution state (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;13\u003c/strong\u003e). Among them, representative metal ions Fe(II) and Ca(II) with distinct oxidation characteristics are chosen to react with CMC for in-depth evaluating their ability for molecular assembly, obtaining materials named CMC-Fe(II) and CMC-Ca(II). At the same concentration, compared to CMC-Cu (II), which shows well-formed complete membrane peeling (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec \u003cstrong\u003einsert and Supplementary Video 1\u003c/strong\u003e), CMC-Fe(II) displays fragmented morphology and incomplete peeling (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ed \u003cstrong\u003einsert, Supplementary Video 2\u003c/strong\u003e) with a novel UV absorption peak (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;14a\u003c/strong\u003e); while CMC-Ca(II) remains in solution form without any discernible macroscopic changes (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ee \u003cstrong\u003einsert, Supplementary Video 3\u003c/strong\u003e) and exhibits a negative UV absorption peak (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;14b\u003c/strong\u003e). This phenomenon may be attributed to the weak electrostatic attraction or coordination between Ca(II) and CMC, resulting in the formation of certain complexes or microscopic aggregates that enhance light scattering effect and increase light transmittance, thereby manifesting a negative absorption peak. These results provide preliminary evidence supporting the assembly ability order is Cu(II)\u0026thinsp;\u0026gt;\u0026thinsp;Fe(II)\u0026thinsp;\u0026gt;\u0026thinsp;Ca(II), which is also in accordance with the oxidation sequence of these ions. In addition, the UV peak position and absorbance of CMC-Cu(II) remain unchanged with different reaction time (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec). In contrast, the absorbance of the CMC-Fe(II) peak increases with prolonged reaction time, accompanied by a slight redshift, suggesting that Fe(II) forms a weak complex with CMC and requiring more time to complete. \u003cstrong\u003e(\u003c/strong\u003eFig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ed, \u003cstrong\u003eSupplementary Fig.\u0026nbsp;15\u003c/strong\u003e). Meanwhile, CMC-Ca(II) displays no UV absorption peak (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ee). These findings further demonstrate that Cu(II) possesses a more stable coordination interaction and molecular assembly capacity, as expectated. Furthermore, Ag(I), with a higher oxidation potential than Cu(II), forms an ultra-thin freestanding CMC-Ag(I) membrane and emerges a new UV absorption peak (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;16\u003c/strong\u003e). These results strongly support the aforementioned trend.\u003c/p\u003e\n\u003cp\u003eWe previously indicated that Na(I) substituents in the CMC molecule can be occupied by coordination positions of other metal ions with higher oxidation states. In Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ef, the intensity of Na elements increases as follows: CMC-Cu(II)\u0026thinsp;\u0026lt;\u0026thinsp;CMC-Fe(II)\u0026thinsp;\u0026lt;\u0026thinsp;CMC-Ca(II)\u0026thinsp;\u0026lt;\u0026thinsp;CMC, according to their ability to replace Na(I). Notably, no Na peaks are observed in CMC-Cu(II). These results confirm the consistent molecular assembly ability of these three metal ions based on their coordination energies.\u003c/p\u003e\n\u003cp\u003eMore attractive, we experimentally discovered that other biomacromolecules like MC and CMCH also demonstrate molecular assembly behavior triggered by metal ion coordination (\u003cstrong\u003esee relevant UV spectra in Supplementary Fig.\u0026nbsp;17\u003c/strong\u003e). Moreover, the membrane-forming behavior of these biomacromolecules with the three metal ions (Biomacromolecule-metal ions) aligns with the CMC (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eg\u003cstrong\u003e)\u003c/strong\u003e. Similarly, Ag(I) forms membranes (CMC-Ag(I), MC-Ag(I), and CMCH-Ag(I)) with performance comparable to Cu(II) (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;18\u003c/strong\u003e). This extending ultra-fast molecular assembly strategy will facilitate the reliable generation of bio-conductive membranes from various sustainable biomass resources.\u003c/p\u003e\n\u003cp\u003eMechanism characterization and simulation of molecular assembly\u003c/p\u003e\n\u003cp\u003eTo reveal and elucidate the transient assembly mechanism of metal ion coordination membranes, X-ray absorption spectroscopy (XAS) is employed to analyze the Cu valence and coordination state in formed CMC-Cu(II) membrane complex. Furthermore, density functional theory (DFT) calculations are conducted to determine the most stable coordination structures. The coordinated state of copper ions in the CMC-Cu(II) membrane is verified by XAS. The results of the Cu K-edge X-ray absorption near-edge spectrum (XANES; Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea) indicates that the electronic state of the Cu ions in CMC-Cu(II) is closer to the CuO, showing characteristic absorption peaks of Cu(II), which supports the Cu in CMC-Cu(II) is in a\u0026thinsp;+\u0026thinsp;2 state without other chemical changes. Fitting of the XANES and extended X-ray absorption fine structure (EXAFS; Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb \u003cstrong\u003eand Supplementary Fig.\u0026nbsp;19\u003c/strong\u003e) spectra reveal two Cu-O distance of 2.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 \u0026Aring; and 2.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 \u0026Aring; (\u003cstrong\u003eSupplementary Table\u0026nbsp;1\u003c/strong\u003e). These distances can be attributed to the coordination of Cu(II) with the single and double bonds of oxygen atoms in the carboxyl groups of CMC. Additionally, we observe that the coordination numbers of copper in CMC-Cu(II) are 2.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6 and 1.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7, respectively (\u003cstrong\u003eSupplementary Table\u0026nbsp;1\u003c/strong\u003e), indicating a total coordination number of approximately 4. This suggests that the carboxyl groups of CMC form a coordination structure closed to the square planar with Cu(II) by bidentate coordination mode.\u003c/p\u003e\n\u003cp\u003eTo support and displaying the coordination structures, CMC-Cu(II), CMC-Ag(I), MC-Cu(II), and MC-Ag(I), which exhibit excellent membrane-forming behaviors, are selected as representative examples. Two glucose units are employed as models to simulate their theoretical optimal structures using DFT theory, with consideration of the solvent effect. Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec illustrates the tetrad coordination structure of the complexes. The Cu(II) ion adopts a square planar geometry by forming bidentate coordination with four oxygen atoms from the carboxyl groups of CMC. The calculated coordination distances are 2.13 \u0026Aring; for the oxygen atom on the double bond and 2.01 \u0026Aring; for the oxygen atom on the single bond, which aligns with fitting result of the XANES and EXAFS. Additionally, the binding energies of CMC-Cu(II) and CMC-Ag(I) in their respective structures are determined to be 1.40 and 1.44 Hartree, respectively (\u003cstrong\u003eSupplementary Table\u0026nbsp;2\u003c/strong\u003e). Similarly, MC-Cu(II) also forms a tetrad structure, but with a slightly different coordination geometry, exhibiting a square planar configuration with a coordination bond length of 1.98 \u0026Aring;. In contrast, MC-Ag(I) displays a tetrahedral geometry while maintaining the same tetragonal structure, with coordination bond lengths ranging from 2.34 to 2.40 \u0026Aring;, consistent with conventional theoretical values. Furthermore, the binding energies of MC-Cu(II) and MC-Ag are 2.28 and 2.40 Hartree, respectively (\u003cstrong\u003eSupplementary Table\u0026nbsp;2\u003c/strong\u003e), which is consistent with the coordination binding energies order of CMC.\u003c/p\u003e\n\u003cp\u003eHigh-fidelity physiological monitoring by CMC-Cu(II) membranes as epidermal electrodes\u003c/p\u003e\n\u003cp\u003ePhysiological monitoring is crucial for continuously tracking key biological signals, such as ECG, EOG, EEG, and EMG, to assess health and enable early disease detection (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea). For accurate monitoring, sensors must maintain conformal contact with the skin, deforming synchronously during use. Additionally, electrodes must exhibit excellent biocompatibility to avoid adverse reactions like erythema and edema. The CMC-Cu(II) membrane provides a tissue-adapting interface that causes no skin rash, unlike commercial Ag/AgCl electrodes, which induce visible redness after one hour of adhesion (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;20\u003c/strong\u003e). With its ultrafast and facile in-situ preparation, thin and conformal structure, skin-friendly compatibility, and excellent ionic conductivity, the CMC-Cu(II) membrane can serve as an ideal epidermal electrode.\u003c/p\u003e\n\u003cp\u003eOne crucial criterion for acquiring high-quality physiological signals is establishing a stable, low-impedance interface between electrodes and skin\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. The CMC-Cu(II) electrodes demonstrate lower impedance than commercial Ag/AgCl electrodes (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb\u003cstrong\u003e)\u003c/strong\u003e. Specifically, compared with the corresponding commercial electrodes (5.87\u0026times;10\u003csup\u003e5\u003c/sup\u003e Ω), the impedance of the CMC-Cu(II) electrodes (1.87\u0026times;10\u003csup\u003e5\u003c/sup\u003e Ω) exhibit a notable reduction by approximately 68% at 20 Hz. This reduction is attributed to its high ionic conductivity and conformal contact with the skin. Subsequently, circular CMC-Cu(II) electrodes (15 mm diameter) are applied in a classical three-lead ECG setup following the \u0026quot;Einthoven triangle\u0026quot; theory. When compared with the commercial electrodes, the CMC-Cu(II) electrodes not only capture ECG signals with identical waveforms but also achieve a higher signal-to-noise ratio (SNR) of 16.41 dB compared to 14.58 dB (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec). The time-frequency spectrum\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e of ECG signals (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed) further demonstrates the stability and precise potential extraction capability of CMC-Cu(II) electrodes, highlighting their excellent performance in physiological signal monitoring.\u003c/p\u003e\n\u003cp\u003eThe application of the CMC-Cu (II) electrode in EOG monitoring as horizontal unipolar leads is demonstrated in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ee. Single CMC-Cu(II) electrodes at the outer corner of the eye capture periodic EOG signals, reflecting blinking and ocular motility.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e For blinking, the CMC-Cu(II) electrode captures distinct voltage patterns for each blink event, with localized amplification illustrating precise signal characteristics (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ef \u003cstrong\u003etop\u003c/strong\u003e). The time-frequency spectrum further confirms signal stability and accuracy (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eg \u003cstrong\u003etop\u003c/strong\u003e). Similarly, during ocular motility tests, the CMC-Cu(II) records persistent EOG signals corresponding to eye movements, with localized amplification and time-frequency spectrum analysis revealing detailed signal patterns (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ef \u003cstrong\u003ebottom and\u003c/strong\u003e Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eg \u003cstrong\u003ebottom\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003eUnipolar lead EEG colection offers a simple and efficient approach for analyzing electrical activity of specific brain regions, which holds significant implications for neuroscience research and clinical applications. A CMC-Cu(II) electrode attached to a volunteer\u0026rsquo;s forehead, where it intimately associate with decision-making, attention, executive function, and other cognitive processes (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eh), enables detection of prefrontal cortex activity by measuring potential differences between the recording and reference electrodes. Real-time EEG signals during music listening (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ei) and mathematical calculations (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;21a\u003c/strong\u003e) reveal clear neural responses to auditory stimulus and exhibit differences. The corresponding time-frequency spectrum highlights distinct oscillatory patterns, capturing the dynamic interaction between the brain and the external auditory environment (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ej \u003cstrong\u003eand Supplementary Fig.\u0026nbsp;21b\u003c/strong\u003e). Moreover, concentration and relaxation coefficients differ between tasks: music listening activity shows average coefficients of concentration and relaxation at 50.60 and 63.29, respectively (total range 0-100) (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ek), while mathematical calculation displays 57.60 for concentration and 44.87 for relaxation (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;21c\u003c/strong\u003e), which aligned with the general trend observed. A localized analysis over 20 seconds further illustrates the stability and precision of CMC-Cu(II) recordings (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;22a and 21d\u003c/strong\u003e), with the time-frequency spectrum displaying well-defined frequency bands (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;22b and 21e\u003c/strong\u003e)\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. These results demonstrate the accuracy and practical application potential of CMC-Cu(II) as an electrophysiological sensor.\u003c/p\u003e\n\u003cp\u003eFurther, we employ CMC-Cu(II) for multi-channel and finer-scale myoelectrophysiological monitoring. A pair of circular CMC-Cu(II) electrodes, corresponding to four lead channels, are fabricated in-situ in the extensor carpi radialis longus, extensor carpi ulnaris, biceps brachii, and triceps brachii muscles, respectively (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea), with commercial electrodes as controls. During grip dynamometer tests, CMC-Cu (II) collects EMG signals that clearly distinguish muscle contractions across channels (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb), similar to commercial electrodes (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ec), this demonstrates CMC-Cu(II)\u0026apos;s ability to precisely detect varying degrees of muscle activity. The SNR of CMC-Cu(II) signals (21.39 dB, 24.36 dB, 36.55 dB, and 18.63 dB) surpasses that of commercial electrodes (16.18 dB, 24.27 dB, 25.96 dB, and 10.72dB) at the corresponding site (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ed). Similar outcomes are observed during fist clenches (\u003cstrong\u003eSupplementary Fig.\u0026nbsp;23\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003eTo monitor EMG signals of human legs, a pairs of CMC-Cu(II) electrodes are positioned on the gastrocnemius, peroneal longus, and biceps femoris muscles, corresponding to three lead channels (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ee), and the commercial electrodes serve as control samples. During various leg activities, such as leg lift, ankle raise, standing, walking, half-squatting, jumping, landing, and sitting (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ef \u003cstrong\u003etop\u003c/strong\u003e), the CMC-Cu(II) electrodes gather physiological signals consistent with those from commercial electrodes. Specifically, distinct waveforms and amplitudes in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ef \u003cstrong\u003ebottom\u003c/strong\u003e reveal varying muscle contraction levels during different movements. The precise identification of different muscle contractions and accurate transmission of electrical signals by the CMC-Cu(II) electrodes are confirmed again in human leg movements.\u003c/p\u003e\n\u003cp\u003eFor recognizing and transmitting electrophysiological signals during extensive motion, we further employ them for sensing microsignals. Two CMC-Cu(II) electrodes are positioned on the masseter muscle of both cheeks and throat (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eg), endowing to obtain mouth-related movements. Attractively, when phrases like \u0026lsquo;Hi\u0026rsquo;, \u0026lsquo;Good morning\u0026rsquo;, and \u0026lsquo;Happy birthday\u0026rsquo; are spoken, the CMC-Cu(II) electrodes record high-fidelity EMG signals matching their durations. Similarly, actions such as coughing or drinking water produce consistent high-quality signals. Moreover, for distinct mouth-related activities, the two channels exhibit varying EMG signals (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eh). These findings demonstrate the ability of CMC-Cu(II) to collect and transmit electrophysiological signals by high-precision, highlighting its potential for practical applications as an epidermal electrode for monitoring human electrophysiological activity.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn summary, inspired by the milk skin effect and the principle of molecular self-assembly, we have proposed a straightforward and time-efficient strategy for rapid fabrication of ultra-thin electronic bio-membranes via robust metal coordination, achieving in-situ and conformal formation of bio-skin. By employing a \"dipping-dipping\" process, first in a CMC solution and subsequently in a Cu(II) solution, a well-formed conductive biological \"skin\" can be instantaneously formed on the surface of any target substrate within seconds. This bioelectronic skin demonstrates excellent interfacial conformal contact, degradability, and low impedance. The capacity and efficiency of membrane formation relying on metal ion coordination ability follows the order: Cu(II)\u0026thinsp;\u0026gt;\u0026thinsp;Fe(II)\u0026thinsp;\u0026gt;\u0026thinsp;Ca(II). At the same experimental condition, CMC-Cu(II) and CMC-Ag(I) form complete and stable membranes, while CMC-Fe(II) shows incomplete formation, and CMC-Ca(II) and CMC-Mg(II) remains unchanged in solution. This trend is also evident in other biological macromolecules, such as MC and CMCH, further highlighting the generalization of the approach. The merits of this membrane include: (1) It is made from sustainable cellulose, the most abundant natural material on Earth, and is biodegradable within 9 days post-use; (2) The formation process is straightforward and time-efficient, requiring only 2 seconds; (3) The bio-skin's ultra-thin 3.4 \u0026micro;m thickness, which ensures highly conformal contact with any substrate and low impedance compared to commercial electrodes, achieving a 68% reduction at 20 Hz; (4) It is formed directly on the target substrate, eliminating the need for additional transfers of the soft membrane. These attributes make the bio-skin an excellent candidate for epidermal applications and have been demonstrated for diverse electrophysiological signal monitoring, showcasing its potential for developing sustainable biological skins for various applications.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eMaterials\u003c/p\u003e \u003cp\u003eCarboxymethylcellulose (CMC) with viscosity range of 1000\u0026ndash;1400 mPa\u0026middot;s was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Copper chloride (CuCl\u003csub\u003e2\u003c/sub\u003e, AR, 99%) was purchased from Tianjin Damao Chemical Reagent Factory. Ferrous chloride tetrahydrate (FeCl\u003csub\u003e2\u003c/sub\u003e\u0026middot; 4H\u003csub\u003e2\u003c/sub\u003eO, AR, 98%), Calcium chloride (CaCl\u003csub\u003e2\u003c/sub\u003e, AR, 96%), methylcellulose (MC, 450 mPa.s) and carboxymethyl chitosan (CMCH) were obtained from Shanghai Macklin Biochemical Co., Ltd. The silver nitrate (AgNO\u003csub\u003e3\u003c/sub\u003e, AR) was acquired from Xilong Scientific Co., Ltd.\u003c/p\u003e \u003cp\u003eAssembly of CMC-Cu(II) membrane\u003c/p\u003e \u003cp\u003eThe CMC-Cu(II) bio-membrane was synthesized through a sequential \u0026ldquo;dipping-dipping\u0026rdquo; process using different concentrations of CMC and CuCl\u003csub\u003e2\u003c/sub\u003e solutions. Specifically, a thin layer of CMC solution was initially dipped or coated onto the target substrate surface, followed by the coating of CuCl\u003csub\u003e2\u003c/sub\u003e solution after 1 s to facilitate the instantaneous coordination assembly of the CMC-Cu(II) bio-membrane. The concentrations used for all CMC-Cu(II) membranes in this study were 2 wt% for the CMC solution and 0.5 M for the CuCl\u003csub\u003e2\u003c/sub\u003e solution.\u003c/p\u003e \u003cp\u003ePreparation of patterned CMC-Cu(II) membranes and microcircuits\u003c/p\u003e \u003cp\u003eThe patterned CMC-Cu(II) membranes were prepared using a laser-cut polyamide mask to define the desired pattern on the substrate. The mask was first adhered to the target surface, and then dipped in the CMC solution. After removing the mask, CuCl\u003csub\u003e2\u003c/sub\u003e solution was coated to form patterned CMC-Cu(II) bio-membranes. The CMC-Cu(II) microcircuit was synthesized using the same mask-forming method according to the designed circuit pattern, and subsequently, a chip LED lamp plate was positioned at its corresponding location on the circuit. Upon powering on, a complete CMC-Cu(II) microcircuit was obtained.\u003c/p\u003e \u003cp\u003ePreparation of CMC-Fe(II), CMC-Ca(II), CMC-Ag(I) and other biomacromolecule-metal ions\u003c/p\u003e \u003cp\u003eSolutions of MC and CMCH with a concentration of 2 wt% were prepared, along with solutions of FeCl\u003csub\u003e2\u003c/sub\u003e, CaCl\u003csub\u003e2\u003c/sub\u003e, and AgNO\u003csub\u003e3\u003c/sub\u003e at a concentration of 0.5 M. A thin layer of CMC solution was dipped or coated onto the desired surface, followed by subsequent coating of FeCl\u003csub\u003e2\u003c/sub\u003e and CaCl\u003csub\u003e2\u003c/sub\u003e solutions covering the CMC layer to form CMC-Fe(II) and CMC-Ca(II). The same \u0026ldquo;dipping-dipping\u0026rdquo; procedure was employed to obtain MC-Cu(II), MC-Fe(II), MC-Ca(II), MC-Ag(I), CMCH-Cu (II), CMCH-Fe(II), CMCH-Ca(II), and CMCH-Ag(I).\u003c/p\u003e \u003cp\u003eCharacterization\u003c/p\u003e \u003cp\u003eThe thickness of CMC-Cu(II) membranes was characterized using Hitachi SU-1510 SEM to obtain cross-sectional characterization data. To assess the conformal properties, a CMC-Cu(II) membrane was attached onto a wavy PVC mold and subjected to embrittle in liquid nitrogen. The samples containing 0.5 wt% of CMC, MC, and CMCH were mixed with metal salt solutions including CuCl\u003csub\u003e2\u003c/sub\u003e, FeCl\u003csub\u003e2\u003c/sub\u003e, and CaCl\u003csub\u003e2\u003c/sub\u003e at various concentrations respectively. The resulting mixtures were characterized using a JOSVOK UV-5600P UV-VIS spectrophotometer, which had a test range from 190 nm to 500 nm. The absorption behavior in the ultraviolet and visible regions of samples was analyzed by the characteristic absorption peak positions and intensities of the spectra. The chemical state of CMC-Cu(II) membrane was analyzed using XPS equipment (Thermo Scientific K-Alpha, USA). Fourier transform infrared (FTIR) spectra of CMC and CMC-Cu(II) membranes were obtained using the Nicolet iS5 spectrometer (Thermo Scientific, USA), covering wave numbers ranging from 4000\u0026thinsp;\u0026minus;\u0026thinsp;400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eCu K-edge analysis of CMC-Cu(II) membrane was performed with Si(111) crystal monochromators at the BL11B beamlines at the Shanghai Synchrotron Radiation Facility (SSRF) (Shanghai, China). Before the analysis at the beamline, samples were pressed into thin sheets with 1 cm in diameter and sealed using Kapton tape film. The XAFS spectra were recorded at room temperature using a 4-channel Silicon Drift Detector (SDD) Bruker 5040. XX-edge extended X-ray absorption fine structure (EXAFS) spectra were recorded in transmission mode. Negligible changes in the line-shape and peak position of Cu K-edge XANES spectra were observed between two scans taken for a specific sample. The XAFS spectra of these standard samples (Cu foil and CuO) were recorded in transmission mode. The spectra were processed and analyzed by the software codes Athena and Artemis. The inductance-capacitance-resistance (LCR) meter (TH2838H, Tonghui) with a frequency range of 20 Hz-2 MHz, was employed to measure the intrinsic impedance of both CMC-Cu (II) skin-contact electrode and commercial electrode.\u003c/p\u003e \u003cp\u003eBiodegradability test\u003c/p\u003e \u003cp\u003eCMC-Cu(II) membranes and PE films were cut into a square shape with 2 cm on each side. The films were placed in natural soil surface and the photos were taken once a day. The normalized undegraded area is the mean membrane area derived from two parallel samples.\u003c/p\u003e \u003cp\u003eDensity functional theory calculations\u003c/p\u003e \u003cp\u003eCMC-Cu(II), CMC-Ag(I), MC-Cu(II), and MC-Ag(I) models, each consisting of two carboxymethyl-substituted glucose or methyl-substituted glucose units and one metal ion, were calculated using DFT to gain the corresponding coordination structure and binding energy. The binding energy is defined as ΔE\u003csub\u003eX\u003c/sub\u003e= E\u003csub\u003e2glucose\u003c/sub\u003e-\u003csub\u003eM\u003c/sub\u003e \u0026ndash; E\u003csub\u003e2glucose\u003c/sub\u003e \u0026ndash; E\u003csub\u003eM\u003c/sub\u003e, where E\u003csub\u003e2glucose\u003c/sub\u003e represents the energy of two glucose units substituted with carboxymethyl or methyl groups (2glucose) and E\u003csub\u003eM\u003c/sub\u003e denotes the energy of corresponding metal ions (Cu(II) or Ag(I)). E\u003csub\u003e2glucose\u003c/sub\u003e-\u003csub\u003eM\u003c/sub\u003e refers to the energy of the linked system (2glucose-Cu(II) and 2glucose-Ag(I)) after coordination of two carboxymethyl or methyl substituted glucose units and metal ions (Cu(II) or Ag(I)), and the \u0026ldquo;X\u0026rdquo; in ΔE\u003csub\u003eX\u003c/sub\u003e corresponds to CMC-Cu(II), CMC-Ag(I), MC-Cu(II), and MC-Ag(I).\u003c/p\u003e \u003cp\u003eDFT calculations were carried out using the Gaussian 16W, employing the M08-HX functional, the basic group 6-311\u0026thinsp;+\u0026thinsp;G*, and the LANL2DZ as effective core potential for geometric optimization, energy calculation, and frequency analysis. Additionally, a continuous solvation model SMD was used to simulate solvent effects on the molecules.\u003c/p\u003e \u003cp\u003eElectrophysiological signal monitoring\u003c/p\u003e \u003cp\u003eFor ECG monitoring, following the \"Einthoven triangle\" theory, a circular CMC-Cu(II) epidermal electrode with a diameter of 15 mm was applied on the subject's left and right wrists respectively. Additionally, a reference electrode was placed on the subject's left ankle. The arrangement of commercial electrodes followed the same configuration. ECG signals were recorded using an ECG sensor equipped with an integrated ADS1292R signal acquisition converter, STM32F103C8T6 microcontroller, and Bluetooth transmission device.\u003c/p\u003e \u003cp\u003eThe EOG signal was recorded using a horizontal unipolar lead. A CMC-Cu(II) epidermal electrode, with a diameter of 15 mm, was attached to the outer corner of the subject's left eye in place. The reference electrode was positioned on the left earlobe, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee. The signals generated during blinking and turning eyeball movements were captured and recorded by a signal recording system equipped with an integrated bandpass filter (Neurosky TGAM EEG03, Jiangsu, China) connected to the electrodes.\u003c/p\u003e \u003cp\u003eEEG signals were also logged using a unipolar lead configuration. A CMC-Cu(II) epidermal electrode (F4), with a diameter of 15 mm, was placed on the subject's clean forehead, while the reference electrode was positioned on the earlobe following the 10\u0026ndash;20 international electrode placement system. The detailed arrangement of electrodes is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh. All electrodes were connected to a signal recording system equipped with an integrated bandpass filter (Neurosky TGAM EEG03, Jiangsu, China). During activities involving mathematical calculations and music listening, respectively, EEG signals were detected and transmitted.\u003c/p\u003e \u003cp\u003eFor EMG signal monitoring, a six-channel system including a signal monitoring microcontroller (ZTEMG-1100 PCB, Zhituo Intelligent Technology Co., Ltd., Qingdao, China), a signal input terminal (CH-50RB), and an oscilloscope (Handyscope Model HS4, TiePie engineering, China) was utilized, and all electrodes were connected to the system. Each channel consisted of a pair of working electrodes. A pair of CMC-Cu(II) working electrodes were formed in the extensor carpi radialis longus, extensor carpi ulnaris, biceps brachii, and triceps brachii muscles respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea), corresponding to four channels for capturing EEG signals from the arm. The reference electrode was positioned at the elbow joint. Subjects performed grip dynamometer exercises or made a fist while their resulting signals were recorded by the sensor. For collecting EEG signals from the legs, CMC-Cu(II) electrodes (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee) were in-situ prepared at three lead channels on the gastrocnemius, peroneus longus, and biceps femoris muscles respectively; meanwhile, a reference electrode was placed on the patella. A series of leg activities including leg lift, ankle raise, standing, walking, half-squatting, jumping, landing, and sitting were performed by subjects to elicit corresponding signals which were identified and transmitted through connected electrodes and sensors accordingly. Additionally, EEG signals generated by mouth movements of subjects were captured by sensors with two CMC-Cu(II) electrodes placed on the left and right masseter muscles and throat, respectively, with a reference electrode positioned on the earlobe (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eg). All commercial electrodes underwent acquisition following identical procedures.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eCompeting interests\u003c/h2\u003e\n\u003cp\u003eThe authors declare that they have no competing interests and the manuscript is approved by all authors for publication.\u003c/p\u003e\n\u003ch2\u003eData and materials availability\u003c/h2\u003e\n\u003cp\u003eAll data are available in the main text or the supplementary materials.\u003c/p\u003e\n\u003ch2\u003eAdditional information\u003c/h2\u003e\n\u003cp\u003eSupplementary information is available for this paper\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eArwani RT\u003cem\u003e, et al.\u003c/em\u003e Stretchable ionic\u0026ndash;electronic bilayer hydrogel electronics enable in situ detection of solid-state epidermal biomarkers. \u003cem\u003eNat. Mater.\u003c/em\u003e \u003cstrong\u003e23\u003c/strong\u003e, 1115-1122 (2024).\u003c/li\u003e\n\u003cli\u003eYoon H\u003cem\u003e, et al.\u003c/em\u003e Adaptive Epidermal Bioelectronics by Highly Breathable and Stretchable Metal Nanowire Bioelectrodes on Electrospun Nanofiber Membrane. \u003cem\u003eAdv. Funct. Mater.\u003c/em\u003e \u003cstrong\u003e34\u003c/strong\u003e, 2313504 (2024).\u003c/li\u003e\n\u003cli\u003eLiu S\u003cem\u003e, et al.\u003c/em\u003e Permeable, Stretchable, and Recyclable Cellulose Aerogel On-Skin Electronics for Dual-Modal Sensing and Personal Healthcare. \u003cem\u003eACS Nano\u003c/em\u003e \u003cstrong\u003e19\u003c/strong\u003e, 3531-3548 (2025).\u003c/li\u003e\n\u003cli\u003eZhang L\u003cem\u003e, et al.\u003c/em\u003e Cellulose nanofiber-mediated manifold dynamic synergy enabling adhesive and photo-detachable hydrogel for self-powered E-skin. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cstrong\u003e15\u003c/strong\u003e, 3859 (2024).\u003c/li\u003e\n\u003cli\u003eZou X\u003cem\u003e, et al.\u003c/em\u003e Snail-inspired bio-based recyclable liquid-like ionic skins enabling ultra-conformal contact and elasticity recovery for epidermal electronics. \u003cem\u003eNano Today\u003c/em\u003e \u003cstrong\u003e61\u003c/strong\u003e, 102611 (2025).\u003c/li\u003e\n\u003cli\u003eLan L\u003cem\u003e, et al.\u003c/em\u003e Skin-Inspired All-Natural Biogel for Bioadhesive Interface. \u003cem\u003eAdv. Mater.\u003c/em\u003e \u003cstrong\u003e36\u003c/strong\u003e, 2401151 (2024).\u003c/li\u003e\n\u003cli\u003eLu M, Shen L, Su H, Li B, Wang L, Yu WW. Highly ionic conductive, elastic, and biocompatible double-network composite gel for epidermal biopotential monitoring and wearable sensing. \u003cem\u003eJ. Colloid Interface Sci.\u003c/em\u003e \u003cstrong\u003e684\u003c/strong\u003e, 272-282 (2025).\u003c/li\u003e\n\u003cli\u003eLi C, Qian Y, Zhang X, Wang R. Robust-adhesion and high-mechanical strength hydrogel for efficient wet tissue adhesion. \u003cem\u003eJ. Mat. Chem. B\u003c/em\u003e \u003cstrong\u003e13\u003c/strong\u003e, 2469-2479 (2025).\u003c/li\u003e\n\u003cli\u003eMa P\u003cem\u003e, et al.\u003c/em\u003e Super-Structured Wet-Adhesive Hydrogel with Ultralow Swelling, Ultrahigh Burst Pressure Tolerance, and Anti-Postoperative Adhesion Properties for Tissue Adhesion. \u003cem\u003eAdv. Mater.\u003c/em\u003e \u003cstrong\u003e36\u003c/strong\u003e, 2305400 (2024).\u003c/li\u003e\n\u003cli\u003eNamkoong M\u003cem\u003e, et al.\u003c/em\u003e Moldable and transferrable conductive nanocomposites for epidermal electronics. \u003cem\u003enpj Flex. Electron.\u003c/em\u003e \u003cstrong\u003e6\u003c/strong\u003e, 41 (2022).\u003c/li\u003e\n\u003cli\u003eYang C\u003cem\u003e, et al.\u003c/em\u003e A bioinspired permeable junction approach for sustainable device microfabrication. \u003cem\u003eNat. Sustain.\u003c/em\u003e \u003cstrong\u003e7\u003c/strong\u003e, 1190-1203 (2024).\u003c/li\u003e\n\u003cli\u003eZhou Y, Feng B, Chen L, Fan F, Ji Z, Duan H. Wafer-Recyclable, Eco-Friendly, and Multiscale Dry Transfer Printing by Transferable Photoresist for Flexible Epidermal Electronics. \u003cem\u003eACS Appl. Mater. Interfaces\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, 13525-13533 (2024).\u003c/li\u003e\n\u003cli\u003eQiao Y\u003cem\u003e, et al.\u003c/em\u003e Multilayer Graphene Epidermal Electronic Skin. \u003cem\u003eACS Nano\u003c/em\u003e \u003cstrong\u003e12\u003c/strong\u003e, 8839-8846 (2018).\u003c/li\u003e\n\u003cli\u003eXia Q\u003cem\u003e, et al.\u003c/em\u003e A strong, biodegradable and recyclable lignocellulosic bioplastic. \u003cem\u003eNat. Sustain.\u003c/em\u003e \u003cstrong\u003e4\u003c/strong\u003e, 627-635 (2021).\u003c/li\u003e\n\u003cli\u003eTang H\u003cem\u003e, et al.\u003c/em\u003e In Situ Forming Epidermal Bioelectronics for Daily Monitoring and Comprehensive Exercise. \u003cem\u003eACS Nano\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, 17931-17947 (2022).\u003c/li\u003e\n\u003cli\u003ePochan D, Scherman O. Introduction: Molecular Self-Assembly. \u003cem\u003eChem. Rev.\u003c/em\u003e \u003cstrong\u003e121\u003c/strong\u003e, 13699-13700 (2021).\u003c/li\u003e\n\u003cli\u003eZhang Z\u003cem\u003e, et al.\u003c/em\u003e Self-adjusted aromatic cation-\u0026pi; binding promotes controlled self-assembly of positively charged \u0026pi;-electronic molecules. \u003cem\u003eChem\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, 1279-1294 (2024).\u003c/li\u003e\n\u003cli\u003eYang L, Li Q, Ge Z, Fan C, Huang W. DNA Mechanics: From Single Stranded to Self-Assembled. \u003cem\u003eNano Lett.\u003c/em\u003e \u003cstrong\u003e24\u003c/strong\u003e, 11768-11778 (2024).\u003c/li\u003e\n\u003cli\u003eEvans AA, Cheung E, Nyberg KD, Rowat AC. Wrinkling of milk skin is mediated by evaporation. \u003cem\u003eSoft matter\u003c/em\u003e \u003cstrong\u003e13\u003c/strong\u003e, 1056-1062 (2017).\u003c/li\u003e\n\u003cli\u003eCha GD, Kim D-H. Toughness and elasticity from phase separation. \u003cem\u003eNat. Mater.\u003c/em\u003e \u003cstrong\u003e21\u003c/strong\u003e, 266-268 (2022).\u003c/li\u003e\n\u003cli\u003eLi P\u003cem\u003e, et al.\u003c/em\u003e Epidermis inspired self-assembled iontronic foam with high sensitivity and broad range. \u003cem\u003eNano Mater. Sci.\u003c/em\u003e, (2024).\u003c/li\u003e\n\u003cli\u003eZhu Y\u003cem\u003e, et al.\u003c/em\u003e A general strategy for synthesizing biomacromolecular ionogel membranes via solvent-induced self-assembly. \u003cem\u003eNat. Synth.\u003c/em\u003e \u003cstrong\u003e2\u003c/strong\u003e, 864-872 (2023).\u003c/li\u003e\n\u003cli\u003eChen C\u003cem\u003e, et al.\u003c/em\u003e Lightweight, Thermally Insulating, Fire-Proof Graphite-Cellulose Foam. \u003cem\u003eAdv. Funct. Mater.\u003c/em\u003e \u003cstrong\u003e33\u003c/strong\u003e, 2204219 (2023).\u003c/li\u003e\n\u003cli\u003eKhare E, Holten-Andersen N, Buehler MJ. Transition-metal coordinate bonds for bioinspired macromolecules with tunable mechanical properties. \u003cem\u003eat. Rev. Mater.\u003c/em\u003e \u003cstrong\u003e6\u003c/strong\u003e, 421-436 (2021).\u003c/li\u003e\n\u003cli\u003eWu M\u003cem\u003e, et al.\u003c/em\u003e A high-performance hydroxide exchange membrane enabled by Cu2+-crosslinked chitosan. \u003cem\u003eNat. Nanotechnol.\u003c/em\u003e \u003cstrong\u003e17\u003c/strong\u003e, 629-636 (2022).\u003c/li\u003e\n\u003cli\u003ePark JS\u003cem\u003e, et al.\u003c/em\u003e Carboxymethyl cellulose-based rotigotine nanocrystals-loaded hydrogel for increased transdermal delivery with alleviated skin irritation. \u003cem\u003eCarbohydr. Polym.\u003c/em\u003e \u003cstrong\u003e338\u003c/strong\u003e, 122197 (2024).\u003c/li\u003e\n\u003cli\u003eTan F, Zha L, Zhou Q. Assembly of AIEgen-Based Fluorescent Metal\u0026ndash;Organic Framework Nanosheets and Seaweed Cellulose Nanofibrils for Humidity Sensing and UV-Shielding. \u003cem\u003eAdv. Mater.\u003c/em\u003e \u003cstrong\u003e34\u003c/strong\u003e, 2201470 (2022).\u003c/li\u003e\n\u003cli\u003eZhang Z\u003cem\u003e, et al.\u003c/em\u003e A 10-micrometer-thick nanomesh-reinforced gas-permeable hydrogel skin sensor for long-term electrophysiological monitoring. \u003cem\u003eSci. Adv.\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, eadj5389 (2024).\u003c/li\u003e\n\u003cli\u003eDong Q\u003cem\u003e, et al.\u003c/em\u003e A cellulose-derived supramolecule for fast ion transport. \u003cem\u003eSci. Adv.\u003c/em\u003e \u003cstrong\u003e8\u003c/strong\u003e, eadd2031 (2022).\u003c/li\u003e\n\u003cli\u003eQian J\u003cem\u003e, et al.\u003c/em\u003e Highly stable, antiviral, antibacterial cotton textiles via molecular engineering. \u003cem\u003eNat. Nanotechnol.\u003c/em\u003e \u003cstrong\u003e18\u003c/strong\u003e, 168-176 (2023).\u003c/li\u003e\n\u003cli\u003eYang C\u003cem\u003e, et al.\u003c/em\u003e Copper-coordinated cellulose ion conductors for solid-state batteries. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e598\u003c/strong\u003e, 590-596 (2021).\u003c/li\u003e\n\u003cli\u003eKim H\u003cem\u003e, et al.\u003c/em\u003e Skin preparation\u0026ndash;free, stretchable microneedle adhesive patches for reliable electrophysiological sensing and exoskeleton robot control. \u003cem\u003eSci. Adv.\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, eadk5260 (2024).\u003c/li\u003e\n\u003cli\u003eZhang L\u003cem\u003e, et al.\u003c/em\u003e Fully organic compliant dry electrodes self-adhesive to skin for long-term motion-robust epidermal biopotential monitoring. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cstrong\u003e11\u003c/strong\u003e, 4683 (2020).\u003c/li\u003e\n\u003cli\u003eDebbarma S, Bhadra S. A Lightweight Flexible Wireless Electrooculogram Monitoring System With Printed Gold Electrodes. \u003cem\u003eIEEE Sens. J.\u003c/em\u003e \u003cstrong\u003e21\u003c/strong\u003e, 20931-20942 (2021).\u003c/li\u003e\n\u003cli\u003eLi X\u003cem\u003e, et al.\u003c/em\u003e A Self-Supporting, Conductor-Exposing, Stretchable, Ultrathin, and Recyclable Kirigami-Structured Liquid Metal Paper for Multifunctional E-Skin. \u003cem\u003eACS Nano\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, 5909-5919 (2022).\u003c/li\u003e\n\u003cli\u003eYang G\u003cem\u003e, et al.\u003c/em\u003e Adhesive and Hydrophobic Bilayer Hydrogel Enabled On-Skin Biosensors for High-Fidelity Classification of Human Emotion. \u003cem\u003eAdv. Funct. Mater.\u003c/em\u003e \u003cstrong\u003e32\u003c/strong\u003e, 2200457 (2022).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6344254/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6344254/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eElectronic skin (E-skin), a conformal human-machine interface, holds promise for healthcare monitoring and personal electronics. However, traditional fabrication methods face challenges of reliance on non-sustainable materials, intricate and time-consuming processes, and material softness-induced fragile transfer to target substrates. Inspired by \"milk skin\" phenomenon, we developed a rapid \"dipping-dipping\" molecular assembly method to in-situ fabricate cellulose-based bio-skin within seconds, exhibiting ultra-thin, high conformal, shape-customizable, degradable, and low impedance performances. This technique immerses substrates sequentially into carboxymethyl cellulose (CMC) and Cu(II) solutions, leveraging strong metal-coordination interactions. Membrane formation efficiency, influenced by the oxidation of metal ions, follows the order: Cu(II)\u0026thinsp;\u0026gt;\u0026thinsp;Fe(II)\u0026thinsp;\u0026gt;\u0026thinsp;Ca(II). CMC-Ag(I)/CMC-Cu(II) form stable membranes, whereas CMC-Fe(II) is fragmented structures, and CMC-Mg(II)/CMC-Ca(II) remain in solution. This adaptable method extends to other biomacromolecules like methylcellulose and carboxymethyl chitosan, broadening applications. The bio-skin enables real-time monitoring of electrocardiograms (ECG), electrooculograms (EOG), electroencephalograms (EEG), and electromyograms (EMG), showcasing its potential for wearable, biocompatible electronics in healthcare.\u003c/p\u003e","manuscriptTitle":"2-Second In-Situ Formation of Adaptive Electronic Bio-Skin Enabled by Metal Coordination","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-15 07:31:30","doi":"10.21203/rs.3.rs-6344254/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"455fec6c-bbca-45cb-9e5c-9a350fb473ac","owner":[],"postedDate":"April 15th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":47045816,"name":"Physical sciences/Materials science/Soft materials/Self-assembly"},{"id":47045817,"name":"Physical sciences/Materials science/Materials for devices/Electronic devices"}],"tags":[],"updatedAt":"2026-05-06T16:11:41+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-15 07:31:30","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6344254","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6344254","identity":"rs-6344254","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}