Precisely 3D printing of ultrastrong architected carbon with a bio-inspired superstructure

Precisely 3D printing of ultrastrong architected carbon with a bio-inspired superstructure | 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 Precisely 3D printing of ultrastrong architected carbon with a bio-inspired superstructure Maling Gou, Ya Ren, Li Zhang, D.L. Ma, Angxi Zhou, Haitao Peng, and 7 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6362220/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 Reducing defect is a critical challenge for developing strong metamaterials that are greatly demanded in multiple fields. Herein, we show a precisely 3D-printed ultrastrong architected carbon with a superstructure in the skeletal structure of knobby starfish. This superstructure could function as a shrinkage-adaptive structure with isotropic uniformity stress distribution to significantly reduce the defects. By pyrolyzing polymer templates that were 3D-printed using two-photon lithography, the nano-architected carbon was precisely prepared under a 99% volume shrinkage. It had a compressive strength achieving the theoretical limit of 7.23GPa, a specific strength of 10.33 GPa g − 1 cm 3 , and a fracture strain as high as 66%. It might be the strongest in specific strength among the known mechanical metamaterials. The architected carbon scaffolds, with the strength-to-weight ratio exceeding 1000000:1, were customized for bone repair. The scaffold exhibited high strength and modulus comparable to cortical bone. Animal experiments indicated that the implant could effectively repair critical-sized bone defects by inducing osteogenesis in vivo , showing great promise as a future implant for clinical bone repair. This work highlights a bio-inspired structure design cue to address the challenge of precisely fabricating strong metamaterials with little defects. Physical sciences/Materials science/Nanoscale materials/Metamaterials Physical sciences/Materials science/Biomaterials/Implants Physical sciences/Materials science/Structural materials/Mechanical properties Biomaterials Architected carbon 3D printing Bio-inspiration Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Mechanical metamaterials have promising application in multiple fields including biomedicine, aerospace and energy, in which the ultrastrong metamaterials are highly demanded 1–3 . The architected carbon is an excellent metamaterial with potential to be the strongest metamaterials with low-density 4–7 . Meanwhile, it is biocompatible, physiochemical stable and conductive, making it suitable for a wide range of applications 8 . The architected carbon is commonly prepared by the pyrolysis of polymer scaffolds. The existed methods for improving the strength of architected carbon are mainly focused on optimizing the composition and preparation process, reducing the size, and designing steady structures 9–11 . However, during the pyrolysis process, the polymer scaffolds had a severe volume shrinkage which often cause non-uniform shrinkage stress 12,13 . This process would inevitably induce severe defects into the architected carbon to severely affect the mechanical properties. Moreover, the non-uniform shrinkage stress caused defects would increase by exponential order with the increase in the size, which causes a severe size-related defects that limits the application of architected carbon 14 . The volume shrinkage or inflate in preparation also is a general challenge for others materials, including ceramics, glasses and metals, to develop mechanical metamaterials 15–17 . Despite this challenge, a shrinkage-adaptive structure would provide a design cue for ultrastrong metamaterials to address the size-defects, by achieving the proportional deformation under a dynamical uniform shrinkage stress. Natural structures can provide valuable inspiration for the design of advanced metamaterials 18–20 . The knobby starfish is an echinoderm with a calcified endoskeleton, is characterized by axial uniform development to form a five-radial symmetric structure. The skeleton of the knobby starfish can withstand environmental high pressures and dynamically adapt to the internal stress distribution to maintain its structural stability during the development 21,22 . Notably, it also has a non-catastrophic failure during the compression, which was only observed in metallic foams and polymer materials. These exceptional performances were contributed by its specifical superstructure 23 . In this work, we created architected carbons by pyrolysis of 3D-printed polymer scaffolds with the knobby starfish skeleton-mimetic superstructure. This structure was steady and could adapt the severe shrinkage process to get a precisely customized architected carbon with minimal defects. The obtained architected carbon with size features from microscopic to macroscopic had ultra-high strength, specific strength or fracture strain, which were significantly better than the known metamaterials. The improvement in mechanical properties render macroscopic architected carbon to work as qualitied implants for effective bone repair in vivo . This work demonstrated an ultrastrong metamaterial with the bioinspired shrinkage-adaptive steady superstructure, which would lead to the development of future metamaterials with novel applications. Results The bio-inspired shrinkage-adaptive steady superstructure The knobby starfish is an echinoderm with a calcified endoskeleton (Fig. 1 a). Its millimeter-sized mineral skeleton exhibited a porous superstructure structure (Fig. 1 b). High-resolution CT scan analysis revealed that the skeleton displayed a periodic arrangement of a periodic superstructure structure (Fig. 1 c, Fig. S1 and Movie.S1). This structure featured a tetrahedral geometry with the same 109.5°, similar angles as the diamond structure (Fig. S2a-c). Additionally, the structures in the [111], [1 \(\:\stackrel{-}{1}\) 0], and [11 \(\:\stackrel{-}{2}\) ] lattice directions were described as shown Fig. 1 d. To mimic the microlattice superstructure of the knobby starfish skeleton, we created a 3D digital model with its diamond-type microlattice geometry that could matched the superstructure in different lattice directions (Fig. 1 e). After a 5% strain was loaded to the superstructure model along the [111], [1 \(\:\stackrel{-}{1}\) 0], and [11 \(\:\stackrel{-}{2}\) ] lattice directions in the finite element analysis, the von Mises stress contours normalized to a uniform solid, as shown in Fig. 1 F. It was implied that the stress was dissipated through the struts of this superstructure, resulting in a uniform stress distribution rather than concentrating at the nodes. This isotropic stress uniformity was evident across all three directions. Similarly, when stress distribution models were divided along other lattice directions, the same uniform stress distribution could be observed in the ( \(\:\stackrel{-}{1}\) 11), (110), and (001) directions (Fig. 1 g). This exhibited a more uniform stress distribution compared to others micro-lattice structures 9 . This finding suggested that this structure might achieve the proportional deformation under a dynamical uniform stress. As such, it might work as a shrinkage-adaptive structure for designing carbon metamaterials, overcoming the shrinkage-associated uneven stress distribution during the pyrolysis process (Fig. 1 h). The microscopic architected carbon The microscopic architected carbon was prepared by the pyrolysis of polymer template that was precisely fabricated using the two-photon lithography (Fig. 2 a). As shown in Fig. 2 b-e, the architected carbon had the same shape and structure as the precursor polymer template. Compared to the precursor template, it exhibited a volume shrinkage rate of 99% with uniform shrinkage along the [1 \(\:\stackrel{-}{1}\) 0], [111] and [11 \(\:\stackrel{-}{2}\) ] lattice direction (Fig. 2 b-e). This finding suggested that the structure was shrinkage-adaptive which rendered the proportional shape changes in the pyrolysis process. High-resolution transmission electron microscopy (HRTEM) images revealed that the microstructure of the architected carbon composed of ultrafine curled graphene layer fragments. The crystallite size of carbon layer fragments ranged from 0.2–0.4 nm, and the interlayer spacing of approximately 0.3 nm (Fig. 2 f and S3). The crystallite size was smaller than that of previously reported glassy carbon (25). The relative volume density was 0.7 g/cm³, which was calculated based on the density of fully dense glassy carbon as 1.4 g/cm³ 6,24 . The microscopic architected carbon demonstrated a compressive strength exceeding 7.23 GPa and a fracture strain higher than 66% (Fig. 2 g). The calculated specific strength and elastic modulus were 10.33 GPa g⁻¹ cm³ and 11 GPa, respectively. During the in-situ compression, the architected carbon also exhibited high room temperature elastic deformability (Fig. 2 h, Fig.S4 and Movie.S2). The architected carbon with a compressive strain of 25% could fully recover its original shape upon unloading. When the compression test was performed with 10 cycles, the modulus and peak load unchanged with increasing compression cycles in the force–displacement dataset (Fig. 2 i and 2 j). The Ashby plots show the material property space of compressive strength (Fig. 2 k) in relation to density for the known micro/nanoscale architected materials, including carbon, ceramics and metals. Our architected carbon might have the highest specific strength among the reported materials. Its specific strength was over 5 times and more than twice of the carbon-alumina composite nanolattices 6 and carbon nanolattices (4.42 GPa g⁻¹cm³) respectively 9 . Meanwhile, our architected carbon had the highest comprehensive strength among the reported porous materials. Its compressive strength was an order of magnitude higher than that of SiOC ceramic nanolattices, with a specific strength was 9.18 times higher 24 . Its compressive strength also was significantly higher than the 1.2 GPa of gold/copper nanolattices 25 . Moreover, our architected carbon achieved a strain of over 66%, exceeding that of metamaterials with the comparable comprehensive strength, including ceramics, glasses and metals (Fig. 2 l) 9,26 . Its maximum compressive strain was higher than that of the solid Si 3 N 4 (41%), with a specific strength was 3 times higher 27 . Its maximum compressive strain was also significantly higher than that of the Mo-Co-W alloy nanolattice as 10% 28 . In summary, due to its excellent mechanical properties, our architected carbon occupied an unexplored space in the Ashby plot, where other materials are difficult to reach. We believed that the ultrahigh compressive strength, specific strength, and fracture strain of the microscopic architected carbon were attributed to its shrinkage-adaptive steady superstructure. During the pyrolysis possess, the structure-leaded dynamically uniform stress distribution enabled architected carbon to have the precisely controlled shape and the ultrafine crystallites. Meanwhile, the smaller size always means stronger mechanical properties of the carbon 29 . Our architected carbon also benefited from its nano-sized feature in reducing internal defects, to have the ultrastrong mechanical properties. Furthermore, the stress-uniform steady structure prevents crack propagation and catastrophic failure during compression. These factors collectively contribute to the enhanced mechanical properties of the microscopic architected carbon. The macroscopic architected carbon The shrinkage-adaptive steady superstructure also was also used to improve the mechanical properties of macroscopic architected carbon. Polymer scaffolds with the superstructure was precisely fabricated by the DLP-based fast 3D printing technology (Fig. 3 a). The pyrolysis process was optimized according to the thermogravimetric analysis results (Fig. S5). Architected carbons measuring 2 x 2 x 2mm, 5 x 5 x 5mm, and 10 x 10 x 10 mm architected carbons were prepared. During the pyrolysis process, the polymer scaffolds with different sizes exhibited uniform shrinkage in various lattice directions including [111], [1 \(\:\stackrel{-}{1}\) 0] and [11 \(\:\stackrel{-}{2}\) ]. In the [111] direction, the shrinkage rates were 58.33%, 56.2%, and 51.91% for the 2mm, 5mm, and 10mm samples, respectively. In the [1 \(\:\stackrel{-}{1}\) 0] direction, the shrinkage rates were 57.93%, 56.46%, and51.37%. In the [11 \(\:\stackrel{-}{2}\) ] direction, the shrinkage rates were 57.7%, 56.18%, and 51.91% (Fig. S6). However, the different size of architected carbon had different shrinkage rates. The larger size means the lower shrinkage rates, which implies more defects in the architected carbon with larger size. The isotropic proportional shrinkage allowed the precise preparation of digitally designed macroscopic architected carbon with complex geometric shapes (Fig. 3 a and 3 b). The obtained carbon even had a metallic sheen (Movie.S3). The precisely customized architected carbon also could be combined with others blocks of nylon and polylactic acid (PLA) to get a more complex products (Fig. S7), thereby extending the potential applications of architected carbons. The Raman spectroscopy results showed that the G band centered at 1580 cm⁻¹ and the D band centered at 1360 cm⁻¹, indicating the internal defects in the amorphous carbon and graphitic crystalline structures, respectively (Fig. S8). The broad 2D band at approximately 2700 cm⁻¹ also implied the presence of highly disordered and randomly arranged graphene layers. Moreover, the broad peaks at approximately 23.5° and 43.5° in the XRD spectra were corresponded to the (002) and (1 \(\:\stackrel{-}{1}\) 0), which identified the composition as carbon materials (Fig. S9). The disappearance of polymer-associated peaks in the Fourier-transform infrared (FTIR) spectra implied that the polymer was completely converted into carbon material (Fig. S10). The obtained macroscopic carbon had a carbon content of over 98% (Fig. S11). The macroscopic architected carbon exhibited excellent mechanical properties. A small architected carbon sample weighting only of 0.1g could easily support a person weighing over 100 kg. The strength-to-weight ratio exceeded 1,000,000:1 (Fig. 3 d), significantly surpassing that of previously reported macroscopic architected carbons 10 . The macroscopic architected carbon with an average density of 0.62g/cm³, had a compressive strength of 204 MPa and a Yong's modulus of 39 GPa (Fig. 3 e, Movie S4). The HRTEM results revealed that the macroscopic architected carbon was consisted of curled graphene layer fragments, with the crystallite size of 1.8–2.7 nm and the interlayer spacing of about 0.35 nm (Fig. 3 f). The macroscopic architected carbon had the similar microscopic structure to previously reported macroscopic carbons 4 . The SEM image of the cross-sections revealed no obvious defects (Fig. 3 g and S11a). The TEM image, uniform pores with size of about 50 nm were found (Fig. 3 h and S16). These nanopores might work as reinforcement phases to enhance the strength and reduce the density 30 . In contrast, the severe shape deformation and micron-scale defects were observed in the commonly architected carbon with the severe stress concentration (Fig. S14). The stress concentration caused defects also increased with increase in the size (Fig. S15). It was suggested that the shrinkage-adaptive steady structure rendered the precise preparation of macroscopic carbon with minimal structural defects and excellent mechanical properties. Typically, the larger size often means the lower mechanical properties of metamaterials, due to the size effects 34–36 . Nevertheless, the strength of our architected carbon was 2–3 times higher than that of the previously reported materials with the same density 29 . It had a higher specific strength than the known macroscopic architected materials such as titanium-based metamaterials 33 , boron carbide ceramic metamaterials( 34 ) and the previously reported macroscopic architected carbon (Fig. 3 i) 8–11,35,36 . Notably, its Young's modulus was higher than 21.56GPa (0.73g/cm³) of previous reported carbon micro/nanolattices (Fig. 3 j) 9 . By using the shrinkage-adaptive steady structure, the macroscopic architected carbon was significantly improved in mechanical properties, which would lead to the wider application of architected carbon. The architected carbon implants for bone repair in vivo In this study, the architected carbon was used as an implant for bone repair. After co-culturing for 2 days, the bone marrow mesenchymal stem cells (BMSCs) uniformly covered the architected carbon without affecting cell viability (Fig. 4a). Following the implantation of the architected carbon into healthy rats for three months, the architected carbon did not cause obvious systemic toxicity (Fig. S17). These results implied that the architected carbon was biocompatible. A critical-sized bone defect model in the rat cranial was employed to evaluate the efficacy of the architected carbon for bone repair in vivo (Fig. 4b and 4c). After the customized φ5mm x 1mm architected carbon were implanted in the defects for 3 months, the bone formation was directly observed via micro-CT, taking advantages of its no-imaging artifacts and being nearly radiolucent. The results indicated that the architected carbon treated defects were efficiently filled with new bone tissue, while the control defect area showed minimal new bone tissue formation (Fig. 4d). According to the cross-sectional、sagittal and reconstructive imaging, the interior of the defects was fully filled with new bone tissues (Fig. 4e and 4f). We also employed H&E staining to further evaluate the impact of the architected carbon on bone repair. As shown in Fig. 4g and 4h, obvious mature bone tissue ingrowth was observed in the area with the implanted architected carbon compared to the control defect area, also demonstrating superior osteogenesis capability. Additionally, there was no inflammation or necrosis was observed around the bone defect areas with the implanted architected carbon, further confirming its biocompatible in vivo . Current clinical bone implants materials are primarily titanium alloys, which suffer from high density, poor bone integration, and stress shielding, affecting bone healing 37 . As mentioned earlier, the macroscopic architected carbon demonstrated strength and modulus comparable to mechanical properties of bone 38 . Additionally, the architected carbon showed superior biocompatibility, and better bone integration, making it more beneficial for bone healing compared to titanium alloys 39 . Moreover, micro-CT scans of the architected carbon implants revealed no imaging artifacts and being nearly radiolucent, in contrast to titanium alloy implants, which exhibited significant metal artifacts that severely hindered clinical diagnosis (Fig. 4d-f). Currently, the pyrolysis carbon has been used in clinic for coating implants to improve their biocompatibility. However, due to the limitations in precisely controlling the shapes and mechanical properties, it remains challenging to use pyrolysis carbon scaffolds for clinical applications 14 . In this study, we also customized a macroscopic architected carbon implant with high strength and modulus which were comparable to that of the bone. The architected carbon implants demonstrated superior osteogenesis capability compared to traditionally used titanium alloys scaffolds in vivo . The 3D printed architected carbon implants hold promise as the next generation of bone repair materials. Discussion Architected carbon, as an excellent metamaterial, has the potential to be the strongest metamaterial with low-density 4 . In this study, we demonstrated a method for precisely 3D printing ultrastrong architected carbon. Commonly, smaller feature sizes correlate with stronger mechanical properties 29 . Some attempts have been made to create strong material by preparing nano-sized architected carbon 6 . However, precisely fabricating architected carbon with nano-sized structure remains a challenge due to non-uniform shrinkage during the pyrolysis process 40 . In this work, we discovered a shrinkage-adaptive steady structure in the skeleton of knobby starfish that addresses this issue. The nano-sized architected carbon maintained its precise structure of the 3D-printed polymer templates despite a 99% volume shrinkage. The obtained architected carbon had a compressive strength of 7.23 GPa, achieving the theoretical limit. It also had a specific strength of 10.33 GPa g − 1 cm 3 , surpassing previously reported metamaterials. Moreover, it had a fracture strain of 66%, which was unattainable for conventional glassy carbon and ceramics. This work represents the first attempt to employ a shrinkage-adaptive steady superstructure design to overcome the challenge of precisely fabricating nano-sized metamaterials with ultrastrong mechanical properties. Architected carbon has potential applications in biomedicine, aerospace, and energy, where macro-sized architected carbon is often required 2,3 . For pyrolytic carbon, larger sizes typically lead to more severe defects 14 . Precisely controlling the shrinkage process is therefore important for preparing macroscopic architected carbon with designed structure and size. Some attempts have been made to address this issue by adjusting the composition of polymer templates to reduce the volume shrinkage rate 10,11,35 . However, such approaches often lead to a reduction in mechanical properties. In this work, we precisely fabricated macroscopic architected carbon using a shrinkage-adaptive steady superstructure design, without reducing the volume shrinkage rate during pyrolysis. The obtained architected carbon exhibited a compressive strength of 204 MPa and a Young’s modulus of 39 GPa, significantly exceedingly previously reported architected carbon with the same size 10,35 . Moreover, its strength-to-weight ratio > 1000000:1 was two orders of magnitude higher than that of titanium alloys 33 higher than the any reported metamaterial of comparable size. Therefore, this work provides a new method for precisely fabricating macroscopic architected carbon with ultrastrong mechanical properties, which would solidly support the wider applications of architected carbon in multiple fields. Advanced bone repair materials are in high demanded in clinical applications 31 . 3D printing technology enables the customization of complex scaffolds to improve bone repair. Currently, 3D-printed titanium alloy scaffolds are the most commonly used bone repair implants. However, traditional titanium alloy implants suffer from poor oxidation resistance, X-ray artifacts, and MRI incompatibility 38 . Additionally, stress shielding is a critical factor affecting bone healing in titanium alloy implants 39,40 . Moreover, it is difficult to significantly improve the resolution of titanium alloy scaffolds that are often 3D printed using SLM 40 . Due to these drawbacks, we aimed to develop architected carbon-based implants for bone repair. Pyrolytic carbon has already been clinically used as a coating material for implants due to its biocompatibility, chemical stability, and radiolucency 14 . However, due to challenges in precisely fabricating strong architected carbon, such scaffolds have not yet been independently used for bone repair in clinical practice 41 . In this work, architected carbon was precisely prepared by pyrolyzing polymer templates that were rapidly 3D printed via digital light process. Compared to conventional titanium alloy scaffolds, polymer-based scaffolds have higher resolution, and the resolution of architected carbon was further improved by volume shrinkage during pyrolysis. The strength and modulus of the architected carbon were comparable to those of cortical bone 39 . The customized architected carbon scaffolds could effectively repair critical-sized bone defects. With this advanced precision fabrication method, the obtained architected carbon scaffolds with superior mechanical properties show great promise as future bone repair implants in clinical applications. Conclusion This work demonstrates a method for precisely 3D printing of ultrastrong architected carbon with a superstructure in knobby starfish. This superstructure as a shrinkage-adaptive steady structure rendered the polymer scaffold to uniformly shrink during the pyrolysis process, to create the architected carbon with minimal defects. The obtained architected carbon had a compressive strength achieving the theoretical strength of 7.23GPa, a specific strength of 10.33 GPa g − 1 cm 3 and a fracture strain of as high as 66%. The macroscopic architected carbon implant had the strength and modulus comparable to bone, showing potential applications for efficient bone repair in vivo . This study would inspire the development of future mechanical metamaterials. Materials and Methods Design and preparation of superstructure The superstructure design was inspired by the spatial structural analysis of the knobby starfish skeleton. High-resolution micro-CT was used to perform precise scans of the starfish skeleton. The scan results were then processed through 3D reconstruction analysis to create a digital three-dimensional model. Preparation of architected carbon The micro-size superstructured polymer was fabricated using TPL DLW (Nanoscribe, GmbH) with IP-Dip2 photoresist. The resulting microscopic superstructured polymer was then heated in a vacuum at a rate of 3°C per second to 900°C, held at 900°C for one hour, and then allowed to cool naturally to room temperature, yielding the microscopic architected carbon. The macro-size superstructured polymer lattices were fabricated using a DLP printer (Vortex6 DLP Matrix, GouLab), with ordinary rigid resin, and a 405nm light source. The slice distance was set to 50µm, and each two-dimensional layer was cured for 5 seconds. The superstructured polymer lattices were then heat-treated under argon protection. Microstructure and composition characterization The surface morphology and microstructure of the architected carbon were observed using field emission scanning electron microscopy (FESEM; FEI Quanta FEG450). Transmission electron microscopy (TEM; JEOL JEM 2100) equipped with selected area electron diffraction (SAED) was used to detect the presence of graphene sheets and fullerene-like spheroidal curled graphene structures formed during carbonization. TEM samples were prepared using a focused ion beam (FIB; FEI Scios DualBeam). Thermogravimetric analysis (TGA; Mettler-Toledo, TGA/DSC 3+) was conducted to assess the transition temperatures at high temperatures, with the experiments carried out in an argon atmosphere and a heating rate of 3°C/min. Fourier-transform infrared spectroscopy (FTIR; PE Spectrum One) was performed to identify the presence of functional groups in the fabricated architected carbon. Additionally, Raman spectroscopy (Renishaw RM-2000) and X-ray diffraction (XRD;) were carried out to further analyze the microstructure of the carbon atoms in the samples. Mechanical property characterization. The microscopic carbon was subjected to uniaxial micro-pillar compression testing at a constant strain rate of 10⁻³/s. The tests were conducted using a nano-mechanical testing instrument equipped with a 10µm flat diamond punch. The mechanical properties were calibrated prior to testing. Stress and strain values were obtained by normalizing the recorded load and displacement according to the cross-sectional area and initial height, respectively. Compression tests on macroscopic architected carbon were conducted using an electromechanical testing frame (Instron 5569). The load was applied to the sample surface at a rate of 0.2 mm/min until failure (Supplementary Movie 3), and the load-displacement curve was obtained. By normalizing the measured force to the cross-sectional area of the architected carbon and the compressive displacement to the sample height, the stress-strain curve was calculated. The Young's modulus of the architected carbon was determined from the linear-elastic portion of the stress-strain curve (after the initial toe region), while the compressive strength represented the maximum stress achieved before brittle failure. Cell isolation、culture and cell adhesion experiment Six-week-old male Sprague-Dawley (SD) rats were euthanized following excessive anesthesia with 3% sodium pentobarbital. The rats were then soaked in 75% ethanol for 15 minutes. Using sterilized tools after high-temperature autoclaving, bone marrow was extracted from the femurs and tibias of the rats. Bone marrow mesenchymal stem cells (BMSCs) were collected and cultured in a medium containing α-MEM (Gibco, USA), 10% FBS (YEASEN, China), and 1% PS (Biosharp, China) at 37°C in a 5% CO2 incubator. The medium was partially changed on the third day and fully replaced on the fifth day. When the BMSCs in the culture dish reached 80% confluence, they were passaged. Subsequent experiments used cells between passages three and five. BMSCs were further co-cultured with the architected carbon. After two days, the carbon scaffolds were soaked in 4% paraformaldehyde for 15 minutes, fixed, treated with 0.2% (v/v) Triton X-100 for 10 minutes, and then washed three times with PBS. The actin of the cells was labeled with 200 µL of FITC, respectively. Finally, a laser scanning confocal microscope (TCS SP8 STED 3X, Germany) was used to locate the labeled cells. Microstructure and composition characterization The surface morphology and microstructure of the architected carbon were observed using field emission scanning electron microscopy (FESEM; FEI Quanta FEG450). Transmission electron microscopy (TEM; JEOL JEM 2100) equipped with selected area electron diffraction (SAED) was used to detect the presence of graphene sheets and fullerene-like spheroidal curled graphene structures formed during carbonization. TEM samples were prepared using a focused ion beam (FIB; FEI Scios DualBeam). Thermogravimetric analysis (TGA; Mettler-Toledo, TGA/DSC 3+) was conducted to assess the transition temperatures at high temperatures, with the experiments carried out in an argon atmosphere and a heating rate of 3°C/min. Fourier-transform infrared spectroscopy (FTIR; PE Spectrum One) was performed to identify the presence of functional groups in the fabricated architected carbon. Additionally, Raman spectroscopy (Renishaw RM-2000) and X-ray diffraction (XRD;) were carried out to further analyze the microstructure of the carbon atoms in the samples. Determination of theoretical limits for young’s modulus and strength versus density The modulus-density theoretical limit was taken from the literature and was determined by the bound of many data of real materials based on Granta Design, which is a standard software for materials selection and graphical analysis of materials properties. More information regarding Granta Design can be found on its webpage ( https://www.grantadesign.com/ ) and in relevant software documentation. The strength-density limit is defined in the literature and is only a specific range based on measurements for all materials that have been made to date. The lower bound of this range is defined by diamond, which has the highest specific strength of all bulk materials, whereas the upper bound is determined by graphene, which holds the highest strength in all materials so far. In vivo bone implantation and bone repair efficacy analysis A rat cranial defect model was used to evaluate the bone repair efficacy of the architected carbon implant. Five male Sprague-Dawley (SD) rats (200–250 g, 8 weeks old) were selected, with each rat having two cranial defects: the left defect served as the blank control group, and the right defect was treated with the architected carbon implant. After anesthetizing the rats, their skulls were shaved and disinfected. A 2 cm incision was made along the sagittal suture of the skull, and the subcutaneous tissue was carefully dissected. A trephine was then used to create bilateral cranial defects with a diameter of 5 mm. The implants were placed in the defects at a depth of 1 mm and a diameter of 5 mm. The skin incision was closed with 4 − 0 sutures. The experimental procedures were approved by the Animal Care and Use Committee of West China Hospital, Sichuan University. At week 12, the target animals were euthanized to evaluate the bone repair efficacy of the implants. The skulls were collected and fixed in 4% paraformaldehyde for 24 hours. Micro-CT scans of the cranial defect areas were performed, followed by three-dimensional reconstruction. Further analysis of new bone tissue infiltration into the scaffold and collagen fiber deposition in the defect areas was conducted out using histological sections with H&E staining. This comprehensive evaluation aimed to assess the bone integration capacity of the architected carbon scaffold. Declarations Acknowledgments: We thank Boya. Li for the writing and language. We thank H. Wang from the Analytical and Testing Center, Sichuan University, P. R. China for the SEM observation and analysis of the data. Funding: This work was supported by the National Natural Science Foundation（32271468）; 1·3·5 project for disciplines of excellence, West China Hospital, Sichuan University（ZYYC23005). Author contributions: Maling Gou. and Ya Ren. conceptualized the research. Ya Ren. and Li Zhang. synthesized the raw material, and Donglin Ma. developed the manufacturing process steps. Angxi Zho. and Haitao Pen. designed the manufactured specimens, and Haofan Liu. carried out fabrication efforts. Jiamei Zhang. conducted TEM analyses and the optical lens design and optimization. Yinchu Dong. performed all other experimental characterizations. Shuwei Ye, Tao Li., and Ya Ren. interpreted results, Ya Ren. and Maling Gou. wrote the manuscript. Competing interests: The authors declare no other competing interests. Data and materials availability: All data are available in the main text or the supplementary materials. References Liu, W., Janbaz, S., Dykstra, D., Ennis, B. & Coulais, C. Harnessing plasticity in sequential metamaterials for ideal shock absorption. Nature (2024) Zheng, X. et al. Ultralight, ultrastiff mechanical metamaterials. Science 344 , 1373–1377 (2014). Cui, H. et al. 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Adv Healthc Mater 13 , 2302132 (2024). Koons, G. L., Diba, M. & Mikos, A. G. Materials design for bone-tissue engineering. Nat Rev Mater 5 , 584–603 (2020). Xiao, F. et al. Gradient gyroid Ti6Al4V scaffolds with TiO2 surface modification: Promising approach for large bone defect repair. Biomaterials Advances 161 , 213899 (2024). Eggeler, Y. M. et al. A Review on 3D Architected Pyrolytic Carbon Produced by Additive Micro/Nanomanufacturing. Adv Funct Materials 2302068 (2023). Additional Declarations There is NO Competing Interest. Supplementary Files Movie.S1.MP4.mp4 High-resolution CT scan image of knobby starfish skeleton Movie.S2.mp4 In situ compression testing of nano-architected carbon. MovieS3.mp4 Fabrication of macro-sized architected carbon. Movie.S4.mp4 Compression test of macro-sized architected carbon. 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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-6362220","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":440687092,"identity":"f47b25d2-a406-410b-a663-5cbfbbed9ce2","order_by":0,"name":"Maling Gou","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3ElEQVRIiWNgGAWjYNCCAgkGBvYGMJOxgTgtBkAtPAdI0wLEEglEapF37zHd8MPAIk8+8vnDzzwMNrIbDjA/e4BPi+GZM2Y3ewwkig1v5xhL8zCkGW84wGZugFfLjByzGzwGEokbZ+ewMfMwHE7ccICHTYKQlpt/QFpmHn8G1PKfsBZ5iRyz2yBb5kswmAG1HCCsxYDnWNltGaCWDTw5xpJzDJKNZx5mM8NvS3vztptvKuoS57cff/jhTYWdbN/x5mf4bTmAwgAFFTM+9SBbGtAZo2AUjIJRMArQAQA55kb1BDpDyAAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0003-0431-0340","institution":"Sichuan University,China","correspondingAuthor":true,"prefix":"","firstName":"Maling","middleName":"","lastName":"Gou","suffix":""},{"id":440687093,"identity":"88648962-750f-4209-aca8-fea2a17f8248","order_by":1,"name":"Ya Ren","email":"","orcid":"","institution":"Sichaun university","correspondingAuthor":false,"prefix":"","firstName":"Ya","middleName":"","lastName":"Ren","suffix":""},{"id":440687094,"identity":"f49bd39c-6e41-44a4-8049-4f00ae0234de","order_by":2,"name":"Li Zhang","email":"","orcid":"","institution":"West China Hospital, Sichuan University,China","correspondingAuthor":false,"prefix":"","firstName":"Li","middleName":"","lastName":"Zhang","suffix":""},{"id":440687095,"identity":"d2a1e4c2-545a-4cf2-bacd-ba52457fb912","order_by":3,"name":"D.L. Ma","email":"","orcid":"","institution":"Chengdu Normal University","correspondingAuthor":false,"prefix":"","firstName":"D.L.","middleName":"","lastName":"Ma","suffix":""},{"id":440687096,"identity":"e8dbef80-c87e-4057-a937-d5cbb3771957","order_by":4,"name":"Angxi Zhou","email":"","orcid":"","institution":"Department of Biotherapy, Cancer Center and State Key Laboratory of Biotherapy","correspondingAuthor":false,"prefix":"","firstName":"Angxi","middleName":"","lastName":"Zhou","suffix":""},{"id":440687097,"identity":"76e93751-9cc6-4382-8913-1620b18b8bee","order_by":5,"name":"Haitao Peng","email":"","orcid":"","institution":"Sichaun university","correspondingAuthor":false,"prefix":"","firstName":"Haitao","middleName":"","lastName":"Peng","suffix":""},{"id":440687098,"identity":"2013b20a-1fb8-4ceb-98f8-8212b1939164","order_by":6,"name":"Boya Li","email":"","orcid":"","institution":"West China Hospital, Sichuan University,China","correspondingAuthor":false,"prefix":"","firstName":"Boya","middleName":"","lastName":"Li","suffix":""},{"id":440687099,"identity":"c17ae831-238d-45dc-ad93-d53855fd4abf","order_by":7,"name":"Haofan Liu","email":"","orcid":"","institution":"West China Hospital, Sichuan University,China","correspondingAuthor":false,"prefix":"","firstName":"Haofan","middleName":"","lastName":"Liu","suffix":""},{"id":440687100,"identity":"09aa62c2-5bfa-4473-8257-8a35cd7f6de4","order_by":8,"name":"Jiamei Zhang","email":"","orcid":"","institution":"Department of Biotherapy, Cancer Center and State Key Laboratory of Biotherapy","correspondingAuthor":false,"prefix":"","firstName":"Jiamei","middleName":"","lastName":"Zhang","suffix":""},{"id":440687101,"identity":"cfc5aa6d-1aa5-4833-89fe-ff26b1ebef6b","order_by":9,"name":"Yinchu Dong","email":"","orcid":"","institution":"West China Hospital, Sichuan University,China","correspondingAuthor":false,"prefix":"","firstName":"Yinchu","middleName":"","lastName":"Dong","suffix":""},{"id":440687102,"identity":"21cc44c5-c9af-4d62-8e5f-7ab262df7cb2","order_by":10,"name":"Shuwei Ye","email":"","orcid":"","institution":"Department of Orthopedic Surgery, West China Hospital, Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"Shuwei","middleName":"","lastName":"Ye","suffix":""},{"id":440687103,"identity":"62e1b554-af55-497b-9007-356640777763","order_by":11,"name":"Tao Li","email":"","orcid":"","institution":"Department of Biotherapy, Cancer Center and State Key Laboratory of Biotherapy","correspondingAuthor":false,"prefix":"","firstName":"Tao","middleName":"","lastName":"Li","suffix":""},{"id":440687104,"identity":"bb7b6f85-40e3-459b-b4f0-5275876c4769","order_by":12,"name":"Xide Dai","email":"","orcid":"","institution":"Department of Biotherapy, Cancer Center and State Key Laboratory of Biotherapy","correspondingAuthor":false,"prefix":"","firstName":"Xide","middleName":"","lastName":"Dai","suffix":""}],"badges":[],"createdAt":"2025-04-02 14:30:38","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6362220/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6362220/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":80405768,"identity":"40103c36-1de9-4f85-937c-31f3d6f4da0a","added_by":"auto","created_at":"2025-04-11 14:39:21","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1027040,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-6362220/v1/7451812acb045a748087775c.png"},{"id":80405766,"identity":"bff8e7e8-0794-4fa4-9c25-0145aa9aba78","added_by":"auto","created_at":"2025-04-11 14:39:21","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1548908,"visible":true,"origin":"","legend":"\u003cp\u003eMicro-scale carbon preparation. (a)Schematic diagram showing nanoarchitected carbon preparation via two-photon lithography. (b-c) High-precision printing of polymer structure and their pyrolyzed structures. (d-e) Construction of complex polymer structures and their pyrolyzed structures. (f) TEM image of nanoarchitected carbon after pyrolysis. (g)Stress-strain curve of nanoarchitected carbon. (h) SEM images of nanoarchitected carbon during in-situ compression. (i) Force-displacement curve of nanoarchitected carbon under cyclic in-situ compression. (j)SEM images showing the elastic recovery of nanoarchitected carbon after 25% strain. \u0026nbsp;(k)Compressive strength–density Ashby map. (l)Specific strength–Compressive strain Ashby map.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-6362220/v1/410574044e0b846f557cfcf4.png"},{"id":80405767,"identity":"ff2cec5f-8c74-4f06-91b0-f3d5e8639d09","added_by":"auto","created_at":"2025-04-11 14:39:21","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1145292,"visible":true,"origin":"","legend":"\u003cp\u003eMacroscopic architected carbon preparation. (a) Schematic diagram showing the preparation of macroscopic architected carbon via fast 3D printing. (b-c) Precision preparation of macroscopic architected carbon with complex structure. (d)0.1g architected carbon can support a human body of over 100kg. (e) Stress-strain curve of macroscopic architected carbon. (f)TEM images of macroscopic architected carbon.\u003c/p\u003e\n\u003cp\u003e(g) SEM images showing fracture surface defect analysis of architected carbon. \u0026nbsp;(h)TEM images showing fracture surface defect analysis of architected carbon. (i) Compressive strength–density Ashby map. (j) Compressive modulus–density Ashby map.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-6362220/v1/b060ca4a0f258468dd58f28b.png"},{"id":80406257,"identity":"b10d12cb-4419-41bd-a83d-236f2deca0d7","added_by":"auto","created_at":"2025-04-11 14:47:21","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1180201,"visible":true,"origin":"","legend":"\u003cp\u003eBone repair analysis of architected carbon. (a) Confocal images of bone marrow mesenchymal stem cells co-cultured with architected carbon. (b-c) Implantation of architected carbon into critical cranial defects in rats. (d-f) CT scan results and 3D reconstruction of the \u003cem\u003ein viv\u003c/em\u003eo repair efficacy of architected carbon. (g-h) H\u0026amp;E staining of tissue sections.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-6362220/v1/c00a5837abb92d4bc996cb2e.png"},{"id":104402519,"identity":"99089e5d-af55-45d6-8615-64573c25d608","added_by":"auto","created_at":"2026-03-11 12:15:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5719654,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6362220/v1/b9f5fc6e-a60c-48c2-afaf-7ef46d503d9e.pdf"},{"id":80405781,"identity":"3786c7c8-6219-4445-a29a-2a5e5acd6bb4","added_by":"auto","created_at":"2025-04-11 14:39:21","extension":"mp4","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":47471600,"visible":true,"origin":"","legend":"High-resolution CT scan image of knobby starfish skeleton","description":"","filename":"Movie.S1.MP4.mp4","url":"https://assets-eu.researchsquare.com/files/rs-6362220/v1/d688414fa0e485fc4349df4c.mp4"},{"id":80405774,"identity":"f0e6d563-002e-4791-862b-72aa98a67e88","added_by":"auto","created_at":"2025-04-11 14:39:21","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":22295003,"visible":true,"origin":"","legend":"In situ compression testing of nano-architected carbon.","description":"","filename":"Movie.S2.mp4","url":"https://assets-eu.researchsquare.com/files/rs-6362220/v1/71e7d6e7fa69bbd5aec35589.mp4"},{"id":80406258,"identity":"8d0201f0-d1f1-413d-9625-6ce510a4d743","added_by":"auto","created_at":"2025-04-11 14:47:21","extension":"mp4","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":2600659,"visible":true,"origin":"","legend":"Fabrication of macro-sized architected carbon.","description":"","filename":"MovieS3.mp4","url":"https://assets-eu.researchsquare.com/files/rs-6362220/v1/ae21435977af12504a75a53e.mp4"},{"id":80405779,"identity":"e5608387-9840-4798-b1cc-3f87e0129773","added_by":"auto","created_at":"2025-04-11 14:39:21","extension":"mp4","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":36003846,"visible":true,"origin":"","legend":"Compression test of macro-sized architected carbon.","description":"","filename":"Movie.S4.mp4","url":"https://assets-eu.researchsquare.com/files/rs-6362220/v1/128a43801218f398c117d495.mp4"},{"id":80405782,"identity":"13137859-f9fd-4cd8-873a-1bdf6fe30e68","added_by":"auto","created_at":"2025-04-11 14:39:22","extension":"docx","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":45870921,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMaterialsNC.docx","url":"https://assets-eu.researchsquare.com/files/rs-6362220/v1/c1c2ca163181859201698202.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Precisely 3D printing of ultrastrong architected carbon with a bio-inspired superstructure","fulltext":[{"header":"Introduction","content":"\u003cp\u003eMechanical metamaterials have promising application in multiple fields including biomedicine, aerospace and energy, in which the ultrastrong metamaterials are highly demanded\u003csup\u003e1–3\u003c/sup\u003e. The architected carbon is an excellent metamaterial with potential to be the strongest metamaterials with low-density\u003csup\u003e4–7\u003c/sup\u003e. Meanwhile, it is biocompatible, physiochemical stable and conductive, making it suitable for a wide range of applications\u003csup\u003e8\u003c/sup\u003e. The architected carbon is commonly prepared by the pyrolysis of polymer scaffolds. The existed methods for improving the strength of architected carbon are mainly focused on optimizing the composition and preparation process, reducing the size, and designing steady structures\u003csup\u003e9–11\u003c/sup\u003e. However, during the pyrolysis process, the polymer scaffolds had a severe volume shrinkage which often cause non-uniform shrinkage stress\u003csup\u003e12,13\u003c/sup\u003e. This process would inevitably induce severe defects into the architected carbon to severely affect the mechanical properties. Moreover, the non-uniform shrinkage stress caused defects would increase by exponential order with the increase in the size, which causes a severe size-related defects that limits the application of architected carbon\u003csup\u003e14\u003c/sup\u003e. The volume shrinkage or inflate in preparation also is a general challenge for others materials, including ceramics, glasses and metals, to develop mechanical metamaterials\u003csup\u003e15–17\u003c/sup\u003e. Despite this challenge, a shrinkage-adaptive structure would provide a design cue for ultrastrong metamaterials to address the size-defects, by achieving the proportional deformation under a dynamical uniform shrinkage stress.\u003c/p\u003e \u003cp\u003eNatural structures can provide valuable inspiration for the design of advanced metamaterials\u003csup\u003e18–20\u003c/sup\u003e. The knobby starfish is an echinoderm with a calcified endoskeleton, is characterized by axial uniform development to form a five-radial symmetric structure. The skeleton of the knobby starfish can withstand environmental high pressures and dynamically adapt to the internal stress distribution to maintain its structural stability during the development\u003csup\u003e21,22\u003c/sup\u003e. Notably, it also has a non-catastrophic failure during the compression, which was only observed in metallic foams and polymer materials. These exceptional performances were contributed by its specifical superstructure\u003csup\u003e23\u003c/sup\u003e. In this work, we created architected carbons by pyrolysis of 3D-printed polymer scaffolds with the knobby starfish skeleton-mimetic superstructure. This structure was steady and could adapt the severe shrinkage process to get a precisely customized architected carbon with minimal defects. The obtained architected carbon with size features from microscopic to macroscopic had ultra-high strength, specific strength or fracture strain, which were significantly better than the known metamaterials. The improvement in mechanical properties render macroscopic architected carbon to work as qualitied implants for effective bone repair \u003cem\u003ein vivo\u003c/em\u003e. This work demonstrated an ultrastrong metamaterial with the bioinspired shrinkage-adaptive steady superstructure, which would lead to the development of future metamaterials with novel applications.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eThe bio-inspired shrinkage-adaptive steady superstructure\u003c/h2\u003e \u003cp\u003eThe knobby starfish is an echinoderm with a calcified endoskeleton (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). Its millimeter-sized mineral skeleton exhibited a porous superstructure structure (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). High-resolution CT scan analysis revealed that the skeleton displayed a periodic arrangement of a periodic superstructure structure (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec, Fig.\u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e and Movie.S1). This structure featured a tetrahedral geometry with the same 109.5\u0026deg;, similar angles as the diamond structure (Fig. S2a-c). Additionally, the structures in the [111], [1\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{1}\\)\u003c/span\u003e\u003c/span\u003e0], and [11\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{2}\\)\u003c/span\u003e\u003c/span\u003e] lattice directions were described as shown Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed. To mimic the microlattice superstructure of the knobby starfish skeleton, we created a 3D digital model with its diamond-type microlattice geometry that could matched the superstructure in different lattice directions (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee). After a 5% strain was loaded to the superstructure model along the [111], [1\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{1}\\)\u003c/span\u003e\u003c/span\u003e0], and [11\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{2}\\)\u003c/span\u003e\u003c/span\u003e] lattice directions in the finite element analysis, the von Mises stress contours normalized to a uniform solid, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eF. It was implied that the stress was dissipated through the struts of this superstructure, resulting in a uniform stress distribution rather than concentrating at the nodes. This isotropic stress uniformity was evident across all three directions. Similarly, when stress distribution models were divided along other lattice directions, the same uniform stress distribution could be observed in the (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{1}\\)\u003c/span\u003e\u003c/span\u003e11), (110), and (001) directions (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg). This exhibited a more uniform stress distribution compared to others micro-lattice structures\u003csup\u003e9\u003c/sup\u003e. This finding suggested that this structure might achieve the proportional deformation under a dynamical uniform stress. As such, it might work as a shrinkage-adaptive structure for designing carbon metamaterials, overcoming the shrinkage-associated uneven stress distribution during the pyrolysis process (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eh).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eThe microscopic architected carbon\u003c/h3\u003e\n\u003cp\u003eThe microscopic architected carbon was prepared by the pyrolysis of polymer template that was precisely fabricated using the two-photon lithography (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb-e, the architected carbon had the same shape and structure as the precursor polymer template. Compared to the precursor template, it exhibited a volume shrinkage rate of 99% with uniform shrinkage along the [1\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{1}\\)\u003c/span\u003e\u003c/span\u003e0], [111] and [11\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{2}\\)\u003c/span\u003e\u003c/span\u003e] lattice direction (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb-e). This finding suggested that the structure was shrinkage-adaptive which rendered the proportional shape changes in the pyrolysis process. High-resolution transmission electron microscopy (HRTEM) images revealed that the microstructure of the architected carbon composed of ultrafine curled graphene layer fragments. The crystallite size of carbon layer fragments ranged from 0.2\u0026ndash;0.4 nm, and the interlayer spacing of approximately 0.3 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef and S3). The crystallite size was smaller than that of previously reported glassy carbon (25). The relative volume density was 0.7 g/cm\u0026sup3;, which was calculated based on the density of fully dense glassy carbon as 1.4 g/cm\u0026sup3;\u003csup\u003e6,24\u003c/sup\u003e. The microscopic architected carbon demonstrated a compressive strength exceeding 7.23 GPa and a fracture strain higher than 66% (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg). The calculated specific strength and elastic modulus were 10.33 GPa g⁻\u0026sup1; cm\u0026sup3; and 11 GPa, respectively. During the in-situ compression, the architected carbon also exhibited high room temperature elastic deformability (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh, Fig.S4 and Movie.S2). The architected carbon with a compressive strain of 25% could fully recover its original shape upon unloading. When the compression test was performed with 10 cycles, the modulus and peak load unchanged with increasing compression cycles in the force\u0026ndash;displacement dataset (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ei and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ej).\u003c/p\u003e \u003cp\u003eThe Ashby plots show the material property space of compressive strength (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ek) in relation to density for the known micro/nanoscale architected materials, including carbon, ceramics and metals. Our architected carbon might have the highest specific strength among the reported materials. Its specific strength was over 5 times and more than twice of the carbon-alumina composite nanolattices\u003csup\u003e6\u003c/sup\u003e and carbon nanolattices (4.42 GPa g⁻\u0026sup1;cm\u0026sup3;) respectively\u003csup\u003e9\u003c/sup\u003e. Meanwhile, our architected carbon had the highest comprehensive strength among the reported porous materials. Its compressive strength was an order of magnitude higher than that of SiOC ceramic nanolattices, with a specific strength was 9.18 times higher \u003csup\u003e24\u003c/sup\u003e. Its compressive strength also was significantly higher than the 1.2 GPa of gold/copper nanolattices \u003csup\u003e25\u003c/sup\u003e. Moreover, our architected carbon achieved a strain of over 66%, exceeding that of metamaterials with the comparable comprehensive strength, including ceramics, glasses and metals (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003el)\u003csup\u003e9,26\u003c/sup\u003e. Its maximum compressive strain was higher than that of the solid Si\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e (41%), with a specific strength was 3 times higher\u003csup\u003e27\u003c/sup\u003e. Its maximum compressive strain was also significantly higher than that of the Mo-Co-W alloy nanolattice as 10%\u003csup\u003e28\u003c/sup\u003e. In summary, due to its excellent mechanical properties, our architected carbon occupied an unexplored space in the Ashby plot, where other materials are difficult to reach. We believed that the ultrahigh compressive strength, specific strength, and fracture strain of the microscopic architected carbon were attributed to its shrinkage-adaptive steady superstructure. During the pyrolysis possess, the structure-leaded dynamically uniform stress distribution enabled architected carbon to have the precisely controlled shape and the ultrafine crystallites. Meanwhile, the smaller size always means stronger mechanical properties of the carbon\u003csup\u003e\u003cem\u003e29\u003c/em\u003e\u003c/sup\u003e. Our architected carbon also benefited from its nano-sized feature in reducing internal defects, to have the ultrastrong mechanical properties. Furthermore, the stress-uniform steady structure prevents crack propagation and catastrophic failure during compression. These factors collectively contribute to the enhanced mechanical properties of the microscopic architected carbon.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eThe macroscopic architected carbon\u003c/h3\u003e\n\u003cp\u003eThe shrinkage-adaptive steady superstructure also was also used to improve the mechanical properties of macroscopic architected carbon. Polymer scaffolds with the superstructure was precisely fabricated by the DLP-based fast 3D printing technology (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). The pyrolysis process was optimized according to the thermogravimetric analysis results (Fig. S5). Architected carbons measuring 2 x 2 x 2mm, 5 x 5 x 5mm, and 10 x 10 x 10 mm architected carbons were prepared. During the pyrolysis process, the polymer scaffolds with different sizes exhibited uniform shrinkage in various lattice directions including [111], [1\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{1}\\)\u003c/span\u003e\u003c/span\u003e0] and [11\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{2}\\)\u003c/span\u003e\u003c/span\u003e]. In the [111] direction, the shrinkage rates were 58.33%, 56.2%, and 51.91% for the 2mm, 5mm, and 10mm samples, respectively. In the [1\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{1}\\)\u003c/span\u003e\u003c/span\u003e0] direction, the shrinkage rates were 57.93%, 56.46%, and51.37%. In the [11\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{2}\\)\u003c/span\u003e\u003c/span\u003e] direction, the shrinkage rates were 57.7%, 56.18%, and 51.91% (Fig. S6). However, the different size of architected carbon had different shrinkage rates. The larger size means the lower shrinkage rates, which implies more defects in the architected carbon with larger size. The isotropic proportional shrinkage allowed the precise preparation of digitally designed macroscopic architected carbon with complex geometric shapes (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). The obtained carbon even had a metallic sheen (Movie.S3). The precisely customized architected carbon also could be combined with others blocks of nylon and polylactic acid (PLA) to get a more complex products (Fig. S7), thereby extending the potential applications of architected carbons. The Raman spectroscopy results showed that the G band centered at 1580 cm⁻\u0026sup1; and the D band centered at 1360 cm⁻\u0026sup1;, indicating the internal defects in the amorphous carbon and graphitic crystalline structures, respectively (Fig. S8). The broad 2D band at approximately 2700 cm⁻\u0026sup1; also implied the presence of highly disordered and randomly arranged graphene layers. Moreover, the broad peaks at approximately 23.5\u0026deg; and 43.5\u0026deg; in the XRD spectra were corresponded to the (002) and (1\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{1}\\)\u003c/span\u003e\u003c/span\u003e0), which identified the composition as carbon materials (Fig. S9). The disappearance of polymer-associated peaks in the Fourier-transform infrared (FTIR) spectra implied that the polymer was completely converted into carbon material (Fig. S10). The obtained macroscopic carbon had a carbon content of over 98% (Fig. S11).\u003c/p\u003e \u003cp\u003eThe macroscopic architected carbon exhibited excellent mechanical properties. A small architected carbon sample weighting only of 0.1g could easily support a person weighing over 100 kg. The strength-to-weight ratio exceeded 1,000,000:1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed), significantly surpassing that of previously reported macroscopic architected carbons\u003csup\u003e10\u003c/sup\u003e. The macroscopic architected carbon with an average density of 0.62g/cm\u0026sup3;, had a compressive strength of 204 MPa and a Yong's modulus of 39 GPa (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, Movie S4). The HRTEM results revealed that the macroscopic architected carbon was consisted of curled graphene layer fragments, with the crystallite size of 1.8\u0026ndash;2.7 nm and the interlayer spacing of about 0.35 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef). The macroscopic architected carbon had the similar microscopic structure to previously reported macroscopic carbons\u003csup\u003e4\u003c/sup\u003e. The SEM image of the cross-sections revealed no obvious defects (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg and S11a). The TEM image, uniform pores with size of about 50 nm were found (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh and S16). These nanopores might work as reinforcement phases to enhance the strength and reduce the density\u003csup\u003e30\u003c/sup\u003e. In contrast, the severe shape deformation and micron-scale defects were observed in the commonly architected carbon with the severe stress concentration (Fig. S14). The stress concentration caused defects also increased with increase in the size (Fig. S15). It was suggested that the shrinkage-adaptive steady structure rendered the precise preparation of macroscopic carbon with minimal structural defects and excellent mechanical properties. Typically, the larger size often means the lower mechanical properties of metamaterials, due to the size effects\u003csup\u003e34\u0026ndash;36\u003c/sup\u003e. Nevertheless, the strength of our architected carbon was 2\u0026ndash;3 times higher than that of the previously reported materials with the same density\u003csup\u003e29\u003c/sup\u003e. It had a higher specific strength than the known macroscopic architected materials such as titanium-based metamaterials\u003csup\u003e33\u003c/sup\u003e, boron carbide ceramic metamaterials(\u003cem\u003e34\u003c/em\u003e) and the previously reported macroscopic architected carbon (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei)\u003csup\u003e8\u0026ndash;11,35,36\u003c/sup\u003e. Notably, its Young's modulus was higher than 21.56GPa (0.73g/cm\u0026sup3;) of previous reported carbon micro/nanolattices (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ej)\u003csup\u003e9\u003c/sup\u003e. By using the shrinkage-adaptive steady structure, the macroscopic architected carbon was significantly improved in mechanical properties, which would lead to the wider application of architected carbon.\u003c/p\u003e \u003cp\u003e \u003cb\u003eThe architected carbon implants for bone repair\u003c/b\u003e \u003cb\u003ein vivo\u003c/b\u003e\u003c/p\u003e \u003cp\u003eIn this study, the architected carbon was used as an implant for bone repair. After co-culturing for 2 days, the bone marrow mesenchymal stem cells (BMSCs) uniformly covered the architected carbon without affecting cell viability (Fig.\u0026nbsp;4a). Following the implantation of the architected carbon into healthy rats for three months, the architected carbon did not cause obvious systemic toxicity (Fig. S17). These results implied that the architected carbon was biocompatible. A critical-sized bone defect model in the rat cranial was employed to evaluate the efficacy of the architected carbon for bone repair \u003cem\u003ein vivo\u003c/em\u003e (Fig.\u0026nbsp;4b and 4c). After the customized φ5mm x 1mm architected carbon were implanted in the defects for 3 months, the bone formation was directly observed via micro-CT, taking advantages of its no-imaging artifacts and being nearly radiolucent. The results indicated that the architected carbon treated defects were efficiently filled with new bone tissue, while the control defect area showed minimal new bone tissue formation (Fig.\u0026nbsp;4d). According to the cross-sectional、sagittal and reconstructive imaging, the interior of the defects was fully filled with new bone tissues (Fig.\u0026nbsp;4e and 4f). We also employed H\u0026amp;E staining to further evaluate the impact of the architected carbon on bone repair. As shown in Fig.\u0026nbsp;4g and 4h, obvious mature bone tissue ingrowth was observed in the area with the implanted architected carbon compared to the control defect area, also demonstrating superior osteogenesis capability. Additionally, there was no inflammation or necrosis was observed around the bone defect areas with the implanted architected carbon, further confirming its biocompatible \u003cem\u003ein vivo\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eCurrent clinical bone implants materials are primarily titanium alloys, which suffer from high density, poor bone integration, and stress shielding, affecting bone healing\u003csup\u003e37\u003c/sup\u003e. As mentioned earlier, the macroscopic architected carbon demonstrated strength and modulus comparable to mechanical properties of bone\u003csup\u003e38\u003c/sup\u003e. Additionally, the architected carbon showed superior biocompatibility, and better bone integration, making it more beneficial for bone healing compared to titanium alloys\u003csup\u003e39\u003c/sup\u003e. Moreover, micro-CT scans of the architected carbon implants revealed no imaging artifacts and being nearly radiolucent, in contrast to titanium alloy implants, which exhibited significant metal artifacts that severely hindered clinical diagnosis (Fig.\u0026nbsp;4d-f). Currently, the pyrolysis carbon has been used in clinic for coating implants to improve their biocompatibility. However, due to the limitations in precisely controlling the shapes and mechanical properties, it remains challenging to use pyrolysis carbon scaffolds for clinical applications\u003csup\u003e14\u003c/sup\u003e. In this study, we also customized a macroscopic architected carbon implant with high strength and modulus which were comparable to that of the bone. The architected carbon implants demonstrated superior osteogenesis capability compared to traditionally used titanium alloys scaffolds \u003cem\u003ein vivo\u003c/em\u003e. The 3D printed architected carbon implants hold promise as the next generation of bone repair materials.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eArchitected carbon, as an excellent metamaterial, has the potential to be the strongest metamaterial with low-density\u003csup\u003e4\u003c/sup\u003e. In this study, we demonstrated a method for precisely 3D printing ultrastrong architected carbon. Commonly, smaller feature sizes correlate with stronger mechanical properties\u003csup\u003e29\u003c/sup\u003e. Some attempts have been made to create strong material by preparing nano-sized architected carbon\u003csup\u003e6\u003c/sup\u003e. However, precisely fabricating architected carbon with nano-sized structure remains a challenge due to non-uniform shrinkage during the pyrolysis process\u003csup\u003e40\u003c/sup\u003e. In this work, we discovered a shrinkage-adaptive steady structure in the skeleton of knobby starfish that addresses this issue. The nano-sized architected carbon maintained its precise structure of the 3D-printed polymer templates despite a 99% volume shrinkage. The obtained architected carbon had a compressive strength of 7.23 GPa, achieving the theoretical limit. It also had a specific strength of 10.33 GPa g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e3\u003c/sup\u003e, surpassing previously reported metamaterials. Moreover, it had a fracture strain of 66%, which was unattainable for conventional glassy carbon and ceramics. This work represents the first attempt to employ a shrinkage-adaptive steady superstructure design to overcome the challenge of precisely fabricating nano-sized metamaterials with ultrastrong mechanical properties.\u003c/p\u003e \u003cp\u003eArchitected carbon has potential applications in biomedicine, aerospace, and energy, where macro-sized architected carbon is often required\u003csup\u003e2,3\u003c/sup\u003e. For pyrolytic carbon, larger sizes typically lead to more severe defects\u003csup\u003e14\u003c/sup\u003e. Precisely controlling the shrinkage process is therefore important for preparing macroscopic architected carbon with designed structure and size. Some attempts have been made to address this issue by adjusting the composition of polymer templates to reduce the volume shrinkage rate \u003csup\u003e10,11,35\u003c/sup\u003e. However, such approaches often lead to a reduction in mechanical properties. In this work, we precisely fabricated macroscopic architected carbon using a shrinkage-adaptive steady superstructure design, without reducing the volume shrinkage rate during pyrolysis. The obtained architected carbon exhibited a compressive strength of 204 MPa and a Young\u0026rsquo;s modulus of 39 GPa, significantly exceedingly previously reported architected carbon with the same size\u003csup\u003e10,35\u003c/sup\u003e. Moreover, its strength-to-weight ratio\u0026thinsp;\u0026gt;\u0026thinsp;1000000:1 was two orders of magnitude higher than that of titanium alloys\u003csup\u003e33\u003c/sup\u003e higher than the any reported metamaterial of comparable size. Therefore, this work provides a new method for precisely fabricating macroscopic architected carbon with ultrastrong mechanical properties, which would solidly support the wider applications of architected carbon in multiple fields.\u003c/p\u003e \u003cp\u003eAdvanced bone repair materials are in high demanded in clinical applications\u003csup\u003e31\u003c/sup\u003e. 3D printing technology enables the customization of complex scaffolds to improve bone repair. Currently, 3D-printed titanium alloy scaffolds are the most commonly used bone repair implants. However, traditional titanium alloy implants suffer from poor oxidation resistance, X-ray artifacts, and MRI incompatibility\u003csup\u003e38\u003c/sup\u003e. Additionally, stress shielding is a critical factor affecting bone healing in titanium alloy implants\u003csup\u003e39,40\u003c/sup\u003e. Moreover, it is difficult to significantly improve the resolution of titanium alloy scaffolds that are often 3D printed using SLM\u003csup\u003e40\u003c/sup\u003e. Due to these drawbacks, we aimed to develop architected carbon-based implants for bone repair. Pyrolytic carbon has already been clinically used as a coating material for implants due to its biocompatibility, chemical stability, and radiolucency\u003csup\u003e14\u003c/sup\u003e. However, due to challenges in precisely fabricating strong architected carbon, such scaffolds have not yet been independently used for bone repair in clinical practice\u003csup\u003e41\u003c/sup\u003e. In this work, architected carbon was precisely prepared by pyrolyzing polymer templates that were rapidly 3D printed via digital light process. Compared to conventional titanium alloy scaffolds, polymer-based scaffolds have higher resolution, and the resolution of architected carbon was further improved by volume shrinkage during pyrolysis. The strength and modulus of the architected carbon were comparable to those of cortical bone\u003csup\u003e39\u003c/sup\u003e. The customized architected carbon scaffolds could effectively repair critical-sized bone defects. With this advanced precision fabrication method, the obtained architected carbon scaffolds with superior mechanical properties show great promise as future bone repair implants in clinical applications.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis work demonstrates a method for precisely 3D printing of ultrastrong architected carbon with a superstructure in knobby starfish. This superstructure as a shrinkage-adaptive steady structure rendered the polymer scaffold to uniformly shrink during the pyrolysis process, to create the architected carbon with minimal defects. The obtained architected carbon had a compressive strength achieving the theoretical strength of 7.23GPa, a specific strength of 10.33 GPa g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e3\u003c/sup\u003e and a fracture strain of as high as 66%. The macroscopic architected carbon implant had the strength and modulus comparable to bone, showing potential applications for efficient bone repair \u003cem\u003ein vivo\u003c/em\u003e. This study would inspire the development of future mechanical metamaterials.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eDesign and preparation of superstructure\u003c/span\u003e \u003c/p\u003e\u003cp\u003eThe superstructure design was inspired by the spatial structural analysis of the knobby starfish skeleton. High-resolution micro-CT was used to perform precise scans of the starfish skeleton. The scan results were then processed through 3D reconstruction analysis to create a digital three-dimensional model.\u003c/p\u003e\u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003ePreparation of architected carbon\u003c/span\u003e \u003c/p\u003e\u003cp\u003eThe micro-size superstructured polymer was fabricated using TPL DLW (Nanoscribe, GmbH) with IP-Dip2 photoresist. The resulting microscopic superstructured polymer was then heated in a vacuum at a rate of 3°C per second to 900°C, held at 900°C for one hour, and then allowed to cool naturally to room temperature, yielding the microscopic architected carbon.\u003c/p\u003e\u003cp\u003eThe macro-size superstructured polymer lattices were fabricated using a DLP printer (Vortex6 DLP Matrix, GouLab), with ordinary rigid resin, and a 405nm light source. The slice distance was set to 50µm, and each two-dimensional layer was cured for 5 seconds. The superstructured polymer lattices were then heat-treated under argon protection.\u003c/p\u003e\u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eMicrostructure and composition characterization\u003c/span\u003e \u003c/p\u003e\u003cp\u003eThe surface morphology and microstructure of the architected carbon were observed using field emission scanning electron microscopy (FESEM; FEI Quanta FEG450). Transmission electron microscopy (TEM; JEOL JEM 2100) equipped with selected area electron diffraction (SAED) was used to detect the presence of graphene sheets and fullerene-like spheroidal curled graphene structures formed during carbonization. TEM samples were prepared using a focused ion beam (FIB; FEI Scios DualBeam). Thermogravimetric analysis (TGA; Mettler-Toledo, TGA/DSC 3+) was conducted to assess the transition temperatures at high temperatures, with the experiments carried out in an argon atmosphere and a heating rate of 3°C/min. Fourier-transform infrared spectroscopy (FTIR; PE Spectrum One) was performed to identify the presence of functional groups in the fabricated architected carbon. Additionally, Raman spectroscopy (Renishaw RM-2000) and X-ray diffraction (XRD;) were carried out to further analyze the microstructure of the carbon atoms in the samples.\u003c/p\u003e\u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eMechanical property characterization.\u003c/span\u003e \u003c/p\u003e\u003cp\u003eThe microscopic carbon was subjected to uniaxial micro-pillar compression testing at a constant strain rate of 10⁻³/s. The tests were conducted using a nano-mechanical testing instrument equipped with a 10µm flat diamond punch. The mechanical properties were calibrated prior to testing. Stress and strain values were obtained by normalizing the recorded load and displacement according to the cross-sectional area and initial height, respectively.\u003c/p\u003e\u003cp\u003eCompression tests on macroscopic architected carbon were conducted using an electromechanical testing frame (Instron 5569). The load was applied to the sample surface at a rate of 0.2 mm/min until failure (Supplementary Movie 3), and the load-displacement curve was obtained. By normalizing the measured force to the cross-sectional area of the architected carbon and the compressive displacement to the sample height, the stress-strain curve was calculated. The Young's modulus of the architected carbon was determined from the linear-elastic portion of the stress-strain curve (after the initial toe region), while the compressive strength represented the maximum stress achieved before brittle failure.\u003c/p\u003e\u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eCell isolation、culture and cell adhesion experiment\u003c/span\u003e \u003c/p\u003e\u003cp\u003eSix-week-old male Sprague-Dawley (SD) rats were euthanized following excessive anesthesia with 3% sodium pentobarbital. The rats were then soaked in 75% ethanol for 15 minutes. Using sterilized tools after high-temperature autoclaving, bone marrow was extracted from the femurs and tibias of the rats. Bone marrow mesenchymal stem cells (BMSCs) were collected and cultured in a medium containing α-MEM (Gibco, USA), 10% FBS (YEASEN, China), and 1% PS (Biosharp, China) at 37°C in a 5% CO2 incubator. The medium was partially changed on the third day and fully replaced on the fifth day. When the BMSCs in the culture dish reached 80% confluence, they were passaged. Subsequent experiments used cells between passages three and five. BMSCs were further co-cultured with the architected carbon. After two days, the carbon scaffolds were soaked in 4% paraformaldehyde for 15 minutes, fixed, treated with 0.2% (v/v) Triton X-100 for 10 minutes, and then washed three times with PBS. The actin of the cells was labeled with 200 µL of FITC, respectively. Finally, a laser scanning confocal microscope (TCS SP8 STED 3X, Germany) was used to locate the labeled cells.\u003c/p\u003e\u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eMicrostructure and composition characterization\u003c/span\u003e \u003c/p\u003e\u003cp\u003eThe surface morphology and microstructure of the architected carbon were observed using field emission scanning electron microscopy (FESEM; FEI Quanta FEG450). Transmission electron microscopy (TEM; JEOL JEM 2100) equipped with selected area electron diffraction (SAED) was used to detect the presence of graphene sheets and fullerene-like spheroidal curled graphene structures formed during carbonization. TEM samples were prepared using a focused ion beam (FIB; FEI Scios DualBeam). Thermogravimetric analysis (TGA; Mettler-Toledo, TGA/DSC 3+) was conducted to assess the transition temperatures at high temperatures, with the experiments carried out in an argon atmosphere and a heating rate of 3°C/min. Fourier-transform infrared spectroscopy (FTIR; PE Spectrum One) was performed to identify the presence of functional groups in the fabricated architected carbon. Additionally, Raman spectroscopy (Renishaw RM-2000) and X-ray diffraction (XRD;) were carried out to further analyze the microstructure of the carbon atoms in the samples.\u003c/p\u003e\u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eDetermination of theoretical limits for young’s modulus and strength versus density\u003c/span\u003e \u003c/p\u003e\u003cp\u003eThe modulus-density theoretical limit was taken from the literature and was determined by the bound of many data of real materials based on Granta Design, which is a standard software for materials selection and graphical analysis of materials properties. More information regarding Granta Design can be found on its webpage (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.grantadesign.com/\u003c/span\u003e\u003cspan address=\"https://www.grantadesign.com/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e) and in relevant software documentation. The strength-density limit is defined in the literature and is only a specific range based on measurements for all materials that have been made to date. The lower bound of this range is defined by diamond, which has the highest specific strength of all bulk materials, whereas the upper bound is determined by graphene, which holds the highest strength in all materials so far.\u003c/p\u003e\u003cp\u003e \u003cspan type=\"ItalicUnderline\" class=\"ItalicUnderline\" name=\"Emphasis\"\u003eIn vivo\u003c/span\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003ebone implantation and bone repair efficacy analysis\u003c/span\u003e\u003c/p\u003e\u003cp\u003eA rat cranial defect model was used to evaluate the bone repair efficacy of the architected carbon implant. Five male Sprague-Dawley (SD) rats (200–250 g, 8 weeks old) were selected, with each rat having two cranial defects: the left defect served as the blank control group, and the right defect was treated with the architected carbon implant. After anesthetizing the rats, their skulls were shaved and disinfected. A 2 cm incision was made along the sagittal suture of the skull, and the subcutaneous tissue was carefully dissected. A trephine was then used to create bilateral cranial defects with a diameter of 5 mm. The implants were placed in the defects at a depth of 1 mm and a diameter of 5 mm. The skin incision was closed with 4 − 0 sutures. The experimental procedures were approved by the Animal Care and Use Committee of West China Hospital, Sichuan University.\u003c/p\u003e\u003cp\u003eAt week 12, the target animals were euthanized to evaluate the bone repair efficacy of the implants. The skulls were collected and fixed in 4% paraformaldehyde for 24 hours. Micro-CT scans of the cranial defect areas were performed, followed by three-dimensional reconstruction. Further analysis of new bone tissue infiltration into the scaffold and collagen fiber deposition in the defect areas was conducted out using histological sections with H\u0026amp;E staining. This comprehensive evaluation aimed to assess the bone integration capacity of the architected carbon scaffold.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank Boya. Li for the writing and language. We thank H. Wang from the Analytical and Testing Center, Sichuan University, P. R. China for the SEM observation and analysis of the data.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Natural Science Foundation（32271468）; \u0026nbsp;1\u0026middot;3\u0026middot;5 project for disciplines of excellence, West China Hospital, Sichuan University（ZYYC23005).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMaling Gou. and Ya Ren. conceptualized the research. Ya Ren. and Li Zhang. synthesized the raw material, and Donglin Ma. developed the manufacturing process steps. Angxi Zho. and Haitao Pen. designed the manufactured specimens, and Haofan Liu. carried out fabrication efforts. Jiamei Zhang. conducted TEM analyses and the optical lens design and optimization. Yinchu Dong. performed all other experimental characterizations. Shuwei Ye, Tao Li., and Ya Ren. interpreted results, Ya Ren. and Maling Gou. wrote the manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no other competing interests.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData and materials availability:\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data are available in the main text or the supplementary materials.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLiu, W., Janbaz, S., Dykstra, D., Ennis, B. \u0026amp; Coulais, C. 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Adv Funct Materials 2302068 (2023).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"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":"Biomaterials, Architected carbon, 3D printing, Bio-inspiration","lastPublishedDoi":"10.21203/rs.3.rs-6362220/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6362220/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eReducing defect is a critical challenge for developing strong metamaterials that are greatly demanded in multiple fields. Herein, we show a precisely 3D-printed ultrastrong architected carbon with a superstructure in the skeletal structure of knobby starfish. This superstructure could function as a shrinkage-adaptive structure with isotropic uniformity stress distribution to significantly reduce the defects. By pyrolyzing polymer templates that were 3D-printed using two-photon lithography, the nano-architected carbon was precisely prepared under a 99% volume shrinkage. It had a compressive strength achieving the theoretical limit of 7.23GPa, a specific strength of 10.33 GPa g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e3\u003c/sup\u003e, and a fracture strain as high as 66%. It might be the strongest in specific strength among the known mechanical metamaterials. The architected carbon scaffolds, with the strength-to-weight ratio exceeding 1000000:1, were customized for bone repair. The scaffold exhibited high strength and modulus comparable to cortical bone. Animal experiments indicated that the implant could effectively repair critical-sized bone defects by inducing osteogenesis \u003cem\u003ein vivo\u003c/em\u003e, showing great promise as a future implant for clinical bone repair. This work highlights a bio-inspired structure design cue to address the challenge of precisely fabricating strong metamaterials with little defects.\u003c/p\u003e","manuscriptTitle":"Precisely 3D printing of ultrastrong architected carbon with a bio-inspired superstructure","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-11 14:39:16","doi":"10.21203/rs.3.rs-6362220/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":"ad52c56b-156e-4044-9c63-99a64871da3b","owner":[],"postedDate":"April 11th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":46919370,"name":"Physical sciences/Materials science/Nanoscale materials/Metamaterials"},{"id":46919371,"name":"Physical sciences/Materials science/Biomaterials/Implants"},{"id":46919372,"name":"Physical sciences/Materials science/Structural materials/Mechanical properties"}],"tags":[],"updatedAt":"2026-05-07T15:26:58+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-11 14:39:16","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6362220","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6362220","identity":"rs-6362220","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}