Nacre-Mimetic, Mechanically Flexible, and Electrically Conductive Silk Fibroin-MXene Composite Foams as Piezoresistive Pressure Sensors

What Exactly Can Bionic Strategies Achieve for Flexible Sensors?

Flexible sensors have attracted great attention in the field of wearable electronic devices due to their deformability, lightness, and versatility. However, property improvement remains a key challenge. Fortunately, natural organisms exhibit many unique response mechanisms to various stimuli, and the corresponding structures and compositions provide advanced design ideas for the development of flexible sensors. Therefore, this Review highlights recent advances in sensing performance and functional characteristics of flexible sensors from the perspective of bionics for the first time. First, the "twins" of bionics and flexible sensors are introduced. Second, the enhancements in electrical and mechanical performance through bionic strategies are summarized according to the prototypes of humans, plants, and animals. Third, the functional characteristics of bionic strategies for flexible sensors are discussed in detail, including self-healing, color-changing, tangential force, strain redistribution, and interfacial resistance. Finally, we summarize the challenges and development trends of bioinspired flexible sensors. This Review aims to deepen the understanding of bionic strategies and provide innovative ideas and references for the design and manufacture of next-generation flexible sensors.

Biopolymer-Based Biomimetic Aerogel for Biomedical Applications

Aerogels are lightweight and highly porous materials that have been found to have great potential in biomedical research because of some of their unique properties, such as their high surface area, tunable porosity, and biocompatibility. Researchers have been exploring ways to use aerogels to create biomimetic scaffolds inspired by natural extracellular matrices (ECMs) for various biomedical applications. Aerogel scaffolds can serve as three-dimensional (3D) templates for cell growth and tissue regeneration, promoting wound healing and tissue repair. Additionally, aerogel-based scaffolds have great potential in controlled drug delivery systems, where their high surface area and porosity enable the efficient loading and release of therapeutic agents. In this review, we discuss biopolymer-based biomimetic aerogel scaffolds for tissue engineering, drug delivery, and biosensors. Finally, we also discuss the potential directions in the development of aerogel-based biomimetic scaffolds.

Machine intelligence accelerated design of conductive MXene aerogels with programmable properties

Designing ultralight conductive aerogels with tailored electrical and mechanical properties is critical for various applications. Conventional approaches rely on iterative, time-consuming experiments across a vast parameter space. Herein, an integrated workflow is developed to combine collaborative robotics with machine learning to accelerate the design of conductive aerogels with programmable properties. An automated pipetting robot is operated to prepare 264 mixtures of Ti3C2Tx MXene, cellulose, gelatin, and glutaraldehyde at different ratios/loadings. After freeze-drying, the aerogels' structural integrity is evaluated to train a support vector machine classifier. Through 8 active learning cycles with data augmentation, 162 unique conductive aerogels are fabricated/characterized via robotics-automated platforms, enabling the construction of an artificial neural network prediction model. The prediction model conducts two-way design tasks: (1) predicting the aerogels' physicochemical properties from fabrication parameters and (2) automating the inverse design of aerogels for specific property requirements. The combined use of model interpretation and finite element simulations validates a pronounced correlation between aerogel density and compressive strength. The model-suggested aerogels with high conductivity, customized strength, and pressure insensitivity allow for compression-stable Joule heating for wearable thermal management.

MXene-Based Soft Humidity-Driven Actuator with High Sensitivity and Fast Response

Soft actuators possessing notable mechanical deformations, high sensitivity, and fast response speed play a crucial role in various applications, such as artificial muscles, soft robots, and intelligent devices. In this study, a smart humidity-driven actuator was successfully fabricated by utilizing MXene/cellulose nanofiber (CNF)/LiCl (MCL) through vacuum-assisted filtration with fast response speed and high sensitivity. Utilizing the excellent humidity responsiveness of MXene/CNF and the robust hygroscopicity of LiCl, the synergistic effect of these materials enhances the hygroscopic properties and response speed of the actuator. The MCL actuator demonstrates excellent actuation performance, fast deformation, and reliable cyclic stability. To illustrate the extensive potential of the soft actuator, a range of applications, from bionic devices to soft grippers and crawling actuators, are showcased. Remarkably, the crawling actuator demonstrates sustained crawling motion without necessitating a humidity switch, relying on the humidity gradient from water droplets, and exhibits spontaneous directional motions within a certain range, which makes it a promising prospect in the field of soft robotics.

Guidelines derived from biomineralized tissues for design and construction of high-performance biomimetic materials: from weak to strong

Living organisms in nature have undergone continuous evolution over billions of years, resulting in the formation of high-performance fracture-resistant biomineralized tissues such as bones and teeth to fulfill mechanical and biological functions, despite the fact that most inorganic biominerals that constitute biomineralized tissues are weak and brittle. During the long-period evolution process, nature has evolved a number of highly effective and smart strategies to design chemical compositions and structures of biomineralized tissues to enable superior properties and to adapt to surrounding environments. Most biomineralized tissues have hierarchically ordered structures consisting of very small building blocks on the nanometer scale (nanoparticles, nanofibers or nanoflakes) to reduce the inherent weaknesses and brittleness of corresponding inorganic biominerals, to prevent crack initiation and propagation, and to allow high defect tolerance. The bioinspired principles derived from biomineralized tissues are indispensable for designing and constructing high-performance biomimetic materials. In recent years, a large number of high-performance biomimetic materials have been prepared based on these bioinspired principles with a large volume of literature covering this topic. Therefore, a timely and comprehensive review on this hot topic is highly important and contributes to the future development of this rapidly evolving research field. This review article aims to be comprehensive, authoritative, and critical with wide general interest to the science community, summarizing recent advances in revealing the formation processes, composition, and structures of biomineralized tissues, providing in-depth insights into guidelines derived from biomineralized tissues for the design and construction of high-performance biomimetic materials, and discussing recent progress, current research trends, key problems, future main research directions and challenges, and future perspectives in this exciting and rapidly evolving research field.

Bioinspired Macroporous Materials of MXene Nanosheets: Ice-Templated Assembly and Multifunctional Applications

Biological macroporous materials, such as stems of the plants and bone of the animals, possess outstanding properties for powerful guarantee of creatures' survival through the well-aligned architecture constructed from limited components. Transition metal carbides or nitrides (MXenes), as novel 2D assemblies, have attracted numerous attentions in various applications due to their unique properties. Therefore, mimicking the bioinspired architecture with MXenes will boost the development of human-made materials with unparalleled properties. Freeze casting has been widely applied to fabricate bioinspired MXene-based materials and achieve the assembly of MXene nanosheets into 3D forms. This process solves the inherent restacking problems of MXenes, simultaneously preserving the unique properties of MXenes with a physical process. Here, the ice-templated assembly of MXene in terms of the freezing processes and their potential mechanisms is summarized. In addition, applications of MXene-based materials in electromagnetic interference shielding and absorption, energy storage and conversion, as well as piezoresistive pressure sensors are also reviewed. Finally, the current challenges and bottlenecks of ice-templated assembly of MXene are further discussed to guide the development of bioinspired MXene-based materials.

MXene-Based Elastomer Mimetic Stretchable Sensors: Design, Properties, and Applications

Flexible sensors based on MXene-polymer composites are highly prospective for next-generation wearable electronics used in human-machine interfaces. One of the motivating factors behind the progress of flexible sensors is the steady arrival of new conductive materials. MXenes, a new family of 2D nanomaterials, have been drawing attention since the last decade due to their high electronic conductivity, processability, mechanical robustness and chemical tunability. In this review, we encompass the fabrication of MXene-based polymeric nanocomposites, their structure-property relationship, and applications in the flexible sensor domain. Moreover, our discussion is not only limited to sensor design, their mechanism, and various modes of sensing platform, but also their future perspective and market throughout the world. With our article, we intend to fortify the bond between flexible matrices and MXenes thus promoting the swift advancement of flexible MXene-sensors for wearable technologies.

Uncovering Key Factors in Graphene Aerogel-Based Electrocatalysts for Sustainable Hydrogen Production: An Unsupervised Machine Learning Approach

The application of principal component analysis (PCA) as an unsupervised learning method has been used in uncovering correlations among diverse features of aerogel-based electrocatalysts. This analytical approach facilitates a comprehensive exploration of catalytic activity, revealing intricate relationships with various physical and electrochemical properties. The first two principal components (PCs), collectively capturing nearly 70% of the total variance, attested the reliability and efficacy of PCA in unveiling meaningful patterns. This study challenges the conventional understanding that a material's reactivity is solely dictated by the quantity of catalyst loaded. Instead, it unveils a complex perspective, highlighting that reactivity is intricately influenced by the material's overall design and structure. The PCA bi-plot uncovers correlations between pH and Tafel slope, suggesting an interdependence between these variables and providing valuable insights into the complex interactions among physical and electrochemical properties. Tafel slope stands to be positively correlated with PC1 and PC2, showing an evident positive correlation with the pH. These findings showed that the pH can have a positive correlation with the Tafel slope, however, it does not necessarily reflect a direct positive correlation with the overpotential. The impact of pH on current density (j)and Tafel slope underscores the importance of adjusting pH to lower overpotential effectively, enhancing catalytic activity. Surface area (from 30 to 533 m2 g-1) emerges as a key physical property, inclusively inverse correlation with overpotential, indicating its direct role in lowering overpotential and increasing catalytic activity. The introduction of PC3, in conjunction with PC1, enriches the analysis by revealing consistent trends despite a slightly lower variance (60%). This reinforces the robustness of PCA in delineating distinct characteristics of graphene aerogels, affirming their potential implications in diverse electrocatalytic applications. In summary, PCA proves to be a valuable tool for unraveling complex relationships within aerogel-based electrocatalysts, extending insights beyond catalytic sites to emphasize the broader spectrum of material properties. This approach enhances comprehension of dataset intricacies and holds promise for guiding the development of more effective and versatile electrocatalytic materials.

Nacre-like ceramic composites: Properties, functions and fabrication in the context of dental restorations

Dental restorations are in increasing demand, yet their success rate strongly decreases after 5-10 years post-implantation, attributed in part to mismatching properties with the surrounding buccal environment that causes failures and wear. Among current research to address this issue, biomimetic approaches are promising. Nacre-like ceramic composites are particularly interesting because they combine multiple antagonistic properties making them more resistant to failure in harsh environment than other materials. With the rapid progress in 3D printing producing nacre-like structures has open up new opportunities not yet realised. In this paper, nacre-like composites of various compositions are reviewed in the context of hypothetical biomimetic dental restorations. Their structural, functional and biological properties are compared with those of dentin, enamel, and bone to determine which composition would be the most suitable for each of the 3 mineralized regions found in teeth. The role of complex microstructures and mineral orientations are discussed as well as 3D printing methods that allow the design and fabrication of such complex architectures. Finally, usage of these processes and anticipated prospects for next generation biomimetic dental replacements are discussed to suggest future research directions in this area. STATEMENT OF SIGNIFICANCE: With the current ageing population, dental health is a major issue and current dental restorations still have shortcomings. For the next generation of dental restorations, more biomimetic approaches would be desirable to increase their durability. Among current materials, nacre-like ceramic composites are interesting because they can approach the various structural properties found in the different parts of our teeth. Furthermore, it is also possible to embed self-sensing functionalities to enable monitoring of oral health. Finally, new recent 3D printing technologies now permit the fabrication of complex shapes with local compositions and local microstructures. With this current status of the research, we anticipate new dental restorations designs and highlight the remaining gaps and issues to address.

Multifunctional nacre-like materials

Nacre, the iridescent inner layer of seashells, displays an exceptional combination of strength and toughness due to its 'brick-wall' architecture. Significant research has been devoted to replicating nacre's architecture and its associated deformation and failure mechanisms. Using the resulting materials in applications necessitates adding functionalities such as self-healing, force sensing, bioactivity, heat conductivity and resistance, transparency, and electromagnetic interference shielding. Herein, progress in the fabrication, mechanics, and multi-functionality of nacre-like materials, particularly over the past three years is systematically and critically reviewed. The fabrication techniques reviewed include 3D printing, freeze-casting, mixing/coating-assembling, and laser engraving. The mechanical properties of the resulting materials are discussed in comparison with their constituents and previously developed nacre mimics. Subsequently, the progress in incorporating multifunctionalities and the resulting physical, chemical, and biological properties are evaluated. We finally provide suggestions based on 3D/4D printing, advanced modelling techniques, and machine elements to make reprogrammable nacre-like components with complex shapes and small building blocks, tackling some of the main challenges in the science and translation of these materials.

MXene-Integrated Silk Fibroin-Based Self-Assembly-Driven 3D-Printed Theragenerative Scaffolds for Remotely Photothermal Anti-Osteosarcoma Ablation and Bone Regeneration

Aiming to address the bone regeneration and cancer therapy functionalities in one single material, in this study, we developed a dual-functional theragenerative three-dimensional (3D) aerogel-based composite scaffold from hybridization of photo-cross-linked silk fibroin (SF) biopolymer with MXene (Ti3C2) two-dimensional (2D) nanosheets. To fabricate the scaffold, we first develop a dual-cross-linked SF-based aerogel scaffold through 3D printing and photo-cross-linking of the self-assembly-driven methacrylate-modified SF (SF-MA) gel with controlled pore size, macroscopic geometry, and mechanical stability. In the next step, to endow a remotely controlled photothermal antiosteosarcoma ablation function to fabricated aerogel scaffold, MXene 2D nanosheets with strong near-infrared (NIR) photon absorption properties were integrated into the 3D-printed scaffolds. While 3D-printed MXene-modified dual-cross-linked SF composite scaffolds can mediate the in vitro growth and proliferation of preosteoblastic cell lines, they also endow a strong photothermal effect upon remote irradiation with NIR laser but also significantly stimulate bone mineral deposition on the scaffold surface. Additionally, besides the local release of the anticancer model drug, the generated heat (45-53 °C) mediated the photothermal ablation of cancer cells. The developed aerogel-based composites and chosen therapeutic techniques are thought to render a significant breakthrough in biomaterials' future clinical applications.

Graphene oxide nanosheets augment silk fibroin aerogels for enhanced water stability and oil adsorption

Nanocomposite aerogels exhibit high porosity and large interfacial surface areas, enabling enhanced chemical transport and reactivity. Such mesoporous architectures can be prepared by freeze-casting naturally-derived biopolymers such as silk fibroin, but often form mechanically weak structures that degrade in water, which limits their performance under ambient conditions. Adding 2D material fillers such as graphene oxide (GO) or transition metal carbides (e.g. MXene) could potentially reinforce these aerogels via stronger intermolecular interactions with the polymeric binder. Here, we show that freeze-casting of GO nanosheets with silk fibroin results in a highly water-stable, mechanically robust aerogel, with considerably enhanced properties relative to silk-only or silk-MXene aerogels. These silk-GO aerogels exhibit high contact angles with water and are highly water stable. Moreover, aerogels can adsorb up 25-35 times their mass in oil, and can be used robustly for selective oil separation from water. This increased stability may occur due to strengthened intermolecular interactions such as hydrogen bonding, despite the random coil and α-helix conformation of silk fibroin, which is typically more soluble in water. Finally, we show these aerogels can be prepared at scale by freeze-casting on a copper mesh. Ultimately, we envision that these multicomponent aerogels could be widely utilized for molecular separations and environmental sensing, as well as for thermal insulation and electrical conductivity.

Robust and flexible smart silk/PEDOT conductive fibers as wearable sensor for personal health management and information transmission

Flexible highly conductive fibers have attracted much attention due to their great potential in the field of wearable electronic devices. In this work, silk/PEDOT conductive fibers with a resistivity of 1.73 Ω·cm were obtained by oxidizing Ce3+ with H2O2 under alkaline conditions to produce CeO2 and further promote the in-situ polymerization of 3,4-ethylenedioxythiophene (EDOT) on the surface of silk fibers. The morphology and chemical composition of the silk/PEDOT conductive fibers were characterized and the results confirmed that a large amount of polythiophene was synthesized and deposited on the surface of silk fibers. The conductivity and electrochemical property stability of the silk/PEDOT conductive fibers were evaluated by soaping and organic solvent immersion, and the conductive silk fibers exhibited excellent environmental stability and durability. The silk/PEDOT conductive fibers show good pressure sensing and strain sensing performance, which exhibits high sensitivity, fast response and cyclability, and have excellent applications in personal health monitoring, human-machine information transmission, etc.

Aerogel-Based Biomaterials for Biomedical Applications: From Fabrication Methods to Disease-Targeting Applications

Aerogel-based biomaterials are increasingly being considered for biomedical applications due to their unique properties such as high porosity, hierarchical porous network, and large specific pore surface area. Depending on the pore size of the aerogel, biological effects such as cell adhesion, fluid absorption, oxygen permeability, and metabolite exchange can be altered. Based on the diverse potential of aerogels in biomedical applications, this paper provides a comprehensive review of fabrication processes including sol-gel, aging, drying, and self-assembly along with the materials that can be used to form aerogels. In addition to the technology utilizing aerogel itself, it also provides insight into the applicability of aerogel based on additive manufacturing technology. To this end, how microfluidic-based technologies and 3D printing can be combined with aerogel-based materials for biomedical applications is discussed. Furthermore, previously reported examples of aerogels for regenerative medicine and biomedical applications are thoroughly reviewed. A wide range of applications with aerogels including wound healing, drug delivery, tissue engineering, and diagnostics are demonstrated. Finally, the prospects for aerogel-based biomedical applications are presented. The understanding of the fabrication, modification, and applicability of aerogels through this study is expected to shed light on the biomedical utilization of aerogels.

Preparation of High-k Polymeric Composites Based on Low-k Boron Nitride Nanosheets with High-Connectivity Lamellar Structure

Typically, the basic method to enhance the dielectric response of polymer-based composites is to fill giant dielectric ceramic fillers, such as BaTiO₃ and CaCu₃Ti₄O₁₂, into the polymer matrix. Here, by using low-k boron nitride (BN) with well-controlled microstructure and surface, we successfully prepared a high-k polymeric composite, where the improvement in the dielectric constant of the composite even exceeds that of composites containing BaTiO₃ and CaCu₃Ti₄O₁₂ particles at the same weight percent. First, a lamellar boron nitride nanosheet (BNNS) aerogel was prepared by bidirectional freezing and freeze drying, respectively, and then the aerogel was calcined at 1000 °C to obtain the lamellar BNNS skeleton with some hydroxyl groups. Finally, the epoxy resin (EP) was vacuum impregnated into the BNNS skeleton and cured inside to prepare the lamellar-structured BNNSs/EP (LBE) composites. Interestingly, the dielectric constants of LBE with a 10 wt % BNNS content reached 8.5 at 10³ Hz, which was higher by 2.7 times than that of pure EP. The experimental data and the finite element simulations suggested that the increased dielectric constants of LBE resulted from the combination of two factors, namely, the lamellar microstructure and the hydroxyl groups. The stacking of the BNNS phase into a highly connected lamellar skeleton significantly increased the internal electric field and the polarization intensity, while the introduction of hydroxyl groups on the BNNS surface further improved the polarization of the composite, resulting in a significant increase in the dielectric constant of the LBE. This work provides a new strategy for improving the dielectric constant through the microstructure design of composites.

Flexible Pressure Sensor with an Excellent Linear Response in a Broad Detection Range for Human Motion Monitoring

Pressure sensing is highly demanding in wearable devices, robotics, and artificial intelligence, whereas it is still a big challenge to develop a pressure sensor with an excellent linear response in a broad detection range. Herein, a flexible and porous carbon nanotube (CNT)/carbon black (CB)/carbonyl iron powder (CIP)/silicone composite is proposed by a simple strategy of mixing, curing, and washing. Due to the porous structure induced by the sacrifice of sugar particles, an excellent linear response (R² = 0.999) is achieved for the composite sensor by manipulating the contributions of contact resistance and tunnel resistance to the sensing performance via the alternation of CB and CNT contents. Moreover, the porous structure donates the composite sensor a low compressive modulus at a low pressure level, while the CIPs introduced lead to a high compressive modulus at a high pressure level with the assistance of an external magnetic field. As a result, the sensor produced has a wide linear response range of 80 Pa to 220 kPa, much wider than most of the linear response pressure sensors reported previously. The wide detection range is demonstrated by cyclic pressure tests in the frequency range of 0.1-5 Hz, durability tests, and monitoring human or robot motions including breathing, walking, lifting, and boxing, etc. Taking the advantages of low cost, high sensitivity, and excellent linear response in a wide pressure range, the current composite sensor is promising for precise monitoring of human motions and delicate controlling of robots.

Silk and its composites for humidity and gas sensing applications

Silk fibroin (SF) is a natural protein largely used in the textile industry with applications in bio-medicine, catalysis as well as in sensing materials. SF is a fiber material which is bio-compatible, biodegradable, and possesses high tensile strength. The incorporation of nanosized particles into SF allows the development of a variety of composites with tailored properties and functions. Silk and its composites are being explored for a wide range of sensing applications like strain, proximity, humidity, glucose, pH and hazardous/toxic gases. Most studies aim at improving the mechanical strength of SF by preparing hybrids with metal-based nanoparticles, polymers and 2D materials. Studies have been conducted by introducing semiconducting metal oxides into SF to tailor its properties like conductivity for use as a gas sensing material, where SF acts as a conductive path as well as a substrate for the incorporated nanoparticles. We have reviewed gas and humidity sensing properties of silk, silk with 0D (i.e., metal oxide), 2D (e.g., graphene, MXenes) composites. The nanostructured metal oxides are generally used in sensing applications, which use its semiconducting properties to show variation in the measured properties (e.g., resistivity, impedance) due to analyte gas adsorption on its surface. For example, vanadium oxides (i.e., V₂O₅) have been shown as candidates for sensing nitrogen containing gases and doped vanadium oxides for sensing CO gas. In this review article we provide latest and important results in the gas and humidity sensing of SF and its composites.

CaCO3 Crystals with Unique Morphologies Controlled by the Hydrogen-Bonded Supramolecular Assemblies of Ureido-Pyrimidinone-Amino Acid Derivatives

Biomineral materials such as nacre of shells exhibit high mechanical strength and toughness on account of their unique "brick-mortar" multilayer structure. 2-Ureido-4[1H]-pyrimidinone (UPy) derivatives with different types of end groups, due to the self-complementary quadruple hydrogen bonds and abundant Ca²⁺ binding sites, can easily self-assemble into supramolecular aggregates and act as templates and skeleton in the process of inducing mineral crystallization. In this work, UPy derivatives were used as templates to induce the mineralization and growth of CaCO₃ through a CO₂ diffusion method. The morphology of CaCO₃ crystals was modulated and analyzed by adjusting the synthesizing parameters including Ca²⁺ concentration, pH, and end groups. The results showed that, by the regulatory role of the mineralization template, it was easier to realize the multilayer crystal structure at a lower concentration of Ca²⁺ (less than 0.01 mol L^-1). Under alkaline regulation, the quadruple hydrogen bonds would be destroyed, and the template's regulation effect on the morphology of CaCO₃ crystals would be weakened. Moreover, by comparing different types of end groups, it was proven that the UPy derivatives with carboxylic acid groups (-COOH) played a crucial role in the process of CaCO₃ crystallization with unique morphologies.

Interfused core-shell heterogeneous graphene/MXene fiber aerogel for high-performance and durable electromagnetic interference shielding

Flexible, lightweight, and durable electromagnetic interference (EMI) shielding materials are urgently required to solve the increasingly serious electromagnetic radiation pollution. Transition metal carbides/nitrides (MXenes) are promising candidates for EMI shielding materials because of their excellent metallic electrical conductivity. However, MXenes are highly susceptible to oxidization when exposed to wet environments, leading to the loss of their functional properties and degradation of reliability and stability. Herein, an interfused core-shell heterogeneous reduced graphene oxide (rGO)/MXene aerogel (GMA) is designed for the first time via coaxial wet spinning and freeze-drying. The fabricated GMAs exhibit excellent EMI shielding performance, and the EMI shielding effectiveness (SE) and specific EMI SE can be up to 83.3 dB and 3119 dB·cm³/g, respectively, which is higher than most carbon-based and MXene-based aerogels and foams. More importantly, GMAs have only a 17.4 % degradation in EMI shielding performance after 120 days due to the protection of hydrophobic graphene sheath, exhibiting superior EMI shielding durability to its MXene film counterpart. Moreover, the hydrophobic GMAs exhibit good oil/water separation and thermal insulation performance. The interfused core-shell GMAs are highly promising for applications in durable EMI shielding, thermal insulation, oil/water separation and sensors, etc.

Human Skin-Inspired Electrospun Patterned Robust Strain-Insensitive Pressure Sensors and Wearable Flexible Light-Emitting Diodes

Wearable skin-inspired electronic skins present remarkable outgrowth in recent years because their promising comfort device integration, lightweight, and mechanically robust durable characteristics led to significant progresses in wearable sensors and optoelectronics. Wearable electronic devices demand real-time applicability and factors such as complex fabrication steps, manufacturing cost, and reliable and durable performances, severely limiting the utilization. Herein, we nominate a scalable solution-processable electrospun patterned candidate capable of forming ultralong mechanically robust nano-microdimensional fibers with higher uniformity. Nanofibrous patterned substrates present surface energy and silver nanoparticle crystallization shifts, contributing to strain-sensitive and -insensitive conductive electrodes (10 000 cycles of 50% strain). Synergistic robust stress releasing and durable electromechanical behavior engenders stretchable durable health sensors, strain-insensitive pressure sensors (sensitivity of ∼83 kPa^-1 and 5000 durable cycles), robust alternating current electroluminescent displays, and flexible organic light-emitting diodes (20% improved luminescence and 300 flex endurance of 2 mm bend radius).

Silk-based bioinspired structural and functional materials

Natural biological materials provide a rich source of inspiration for building high-performance materials with extensive applications. By mimicking their chemical compositions and hierarchical architectures, the past decades have witnessed the rapid development of bioinspired materials. As a very promising biosourced raw material, silk is drawing increasing attention due to excellent mechanical properties, favorable versatility, and good biocompatibility. In this review, we provide an overview of the recent progress in silk-based bioinspired structural and functional materials. We first give a brief introduction of silk, covering its sources, features, extraction, and forms. We then summarize the preparation and application of silk-based materials mimicking four typical biological materials including bone, nacre, skin, and polar bear hair. Finally, we discuss the current challenges and future prospects of this field.

Pistachio-Inspired Bulk Graphene Oxide-Based Materials with Shapeability and Recyclability

Nowadays, despite the fact that recent progress has been reported to mimic natural structural materials (especially nacre), designing bioinspired ultrastrong composites in a universal, viable, and scalable manner still remains a long-standing challenge. In particular, pistachio shells show high tissue strength attributed to the cellulose sheet laminated microstructures. Compared with nacre, pistachio shells own interlocking mortise-tenon joints in their structure, which offer higher energy dissipation and deformability. Here we present a strategy to produce nanocomposites with pistachio-mimetic structures through repeated kneading of graphene oxide (GO) in a dynamic covalent and supramolecular poly(sodium thioctic) (pST) system. The dynamic nature of the polymeric backbones endows the resultant GO-based composite with full recyclability and three-dimensional shapeability. The superior mechanical properties of the pistachio-mimetic composite can be attributed to the mortise-tenon joints design in the structure, which has not been achieved in the nacre-mimetic composite. The resulting composite also exhibits high thermal conductivity (15.6 W/(m·K)), yielding an alternative approach to design in engineered and thermal management materials.

Fabrication of Antibacterial, Osteo-Inductor 3D Printed Aerogel-Based Scaffolds by Incorporation of Drug Laden Hollow Mesoporous Silica Microparticles into the Self-Assembled Silk Fibroin Biopolymer

In this study, the novel biomimetic aerogel-based composite scaffolds through a synergistic combination of wet chemical synthesis and advanced engineering approaches have successfully designed. To this aim, initially the photo-crosslinkable methacrylated silk fibroin (SF-MA) biopolymer and methacrylated hollow mesoporous silica microcapsules (HMSC-MA) as the main constituents of the novel composite aerogels were synthesized. Afterward, by incorporation of drug-loaded HMSC-MA into the self-assembled SF-MA, printable gel-based composite inks are developed. By exploiting micro-extrusion-based three-dimensional (3D) printing, SF-MA-HMSC composite gels are printed by careful controlling their viscosity to provide a means to control the shape fidelity of the resulted printed gel constructs. The developed scaffold has shown a multitude of interesting biophysical and biological performances. Namely, thanks to the photo-crosslinking of the gel components during the 3D printing, the scaffolds become mechanically more stable than the pristine SF scaffolds. Also, freeze-casting the printed constructs generates further interconnectivity in the printed pore struts resulting in the scaffolds with hierarchically organized porosities necessary for cell infiltration and growth. Importantly, HMSC incorporated scaffolds promote antibacterial drug delivery, cellular ingrowth and proliferation, promoting osteoblastic differentiation by inducing the expression of osteogenic markers and matrix mineralization. Finally, the osteoconductive, -inductive, and anti-infective composite aerogels are expected to act as excellent bone implanting materials with an extra feature of local and sustained release of drug for efficient therapy of bone-related diseases.