Biomimetic Exogenous "Tissue Batteries" as Artificial Power Sources for Implantable Bioelectronic Devices Manufacturing

Implantable bioelectronic devices (IBDs) have gained attention for their capacity to conformably detect physiological and pathological signals and further provide internal therapy. However, traditional power sources integrated into these IBDs possess intricate limitations such as bulkiness, rigidity, and biotoxicity. Recently, artificial "tissue batteries" (ATBs) have diffusely developed as artificial power sources for IBDs manufacturing, enabling comprehensive biological-activity monitoring, diagnosis, and therapy. ATBs are on-demand and designed to accommodate the soft and confining curved placement space of organisms, minimizing interface discrepancies, and providing ample power for clinical applications. This review presents the near-term advancements in ATBs, with a focus on their miniaturization, flexibility, biodegradability, and power density. Furthermore, it delves into material-screening, structural-design, and energy density across three distinct categories of TBs, distinguished by power supply strategies. These types encompass innovative energy storage devices (chemical batteries and supercapacitors), power conversion devices that harness power from human-body (biofuel cells, thermoelectric nanogenerators, bio-potential devices, piezoelectric harvesters, and triboelectric devices), and energy transfer devices that receive and utilize external energy (radiofrequency-ultrasound energy harvesters, ultrasound-induced energy harvesters, and photovoltaic devices). Ultimately, future challenges and prospects emphasize ATBs with the indispensability of bio-safety, flexibility, and high-volume energy density as crucial components in long-term implantable bioelectronic devices.

Engineering Self-Adaptive Multi-Response Thermochromic Hydrogel for Energy-Saving Smart Windows and Wearable Temperature-Sensing

Buildings account for ≈40% of the total energy consumption. In addition, it is challenging to control the indoor temperature in extreme weather. Therefore, energy-saving smart windows with light regulation have gained increasing attention. However, most emerging base materials for smart windows have disadvantages, including low transparency at low temperatures, ultra-high phase transition temperature, and scarce applications. Herein, a self-adaptive multi-response thermochromic hydrogel (PHC-Gel) with dual temperature and pH response is engineered through "one-pot" integration tactics. The PHC-Gel exhibits excellent mechanical, adhesion, and electrical conductivity properties. Notably, the low critical solubility temperature (LCST) of PHC-Gel can be regulated over a wide temperature range (20-35 °C). The outdoor practical testing reveals that PHC-Gel has excellent light transmittance at low temperatures and radiation cooling performances at high temperatures, indicating that PHC-Gel can be used for developing energy-saving windows. Actually, PHC-Gel-based thermochromic windows show remarkable visible light transparency (Tlum ≈ 95.2%) and solar modulation (△Tsol ≈ 57.2%). Interestingly, PHC-Gel has superior electrical conductivity, suggesting that PHC-Gel can be utilized to fabricate wearable signal-response and temperature sensors. In summary, PHC-Gel has broad application prospects in energy-saving smart windows, smart wearable sensors, temperature monitors, infant temperature detection, and thermal management.

Nature-Skin-Derived e-Skin as Versatile "Wound Therapy-Health Monitoring" Bioelectronic Skin-Scaffolds: Skin to Bio-e-Skin

Electronic skins (e-skins) have the potential to turn into breakthroughs in biomedical applications. Herein, a novel acellular dermal matrix (ADM)-based bioelectronic skin (e-ADM) is used to fabricate versatile "wound therapy-health monitoring" tissue-nanoengineered skin scaffolds via a facile "one-pot" bio-compositing strategy to incorporate the conductive carbon nanotubes and self-assembled micro-copper oxide microspheres with a cicada-wing-like rough surface and nanocone microstructure. The e-ADM exhibits robust tensile strength (22 MPa), flexibility, biodegradability, electroactivity, and antibacterial properties. Interestingly, e-ADM exhibits the pH-responsive ability for intelligent command between sterilization and wound repair . Additionally, e-ADM enables accurate real-time monitoring of human activities, providing a novel flexible e-skin sensor to record injury and motions. In vitro and in vivo experiments show that with electrical stimulation, e-ADM could prominently facilitate cell growth and proliferation and further promote full-thickness skin wound healing, providing a comprehensive therapeutic strategy for smart sensing and tissue repair, guiding the development of high-performance "wound therapy-health monitoring" bioelectronic skin-scaffolds.

Sustainable leather making - An amphoteric organic chrome-free tanning agents based on recycling waste leather

Currently, globally, 90 % of the tannery is still tanned by using chrome, resulting in chromium-containing wastewater and chromium-containing solid waste that will cause serious harm to the environment. Under the pressure of environmental protection, on the one hand, the leather manufacturing industry should to dispose the current problem of chromium pollution, especially chromium-containing solid waste (chromium-containing waste leather (CCWL)), on the other hand, to popularize chrome-free tanning agent. Organic chrome-free tanning agents are the way forward for chrome-free tanning agents. However, organic chrome-free tanning agents exhibit several limitations with respect to their preparation and applications: The preparation process is not eco-friendly, and physicochemical properties of tanned crust leather are poor. More importantly, the leather tanned by an organic chrome-free tanning agent has low absorptivity of traditional anionic wet finishing materials, resulting in high total dissolved solids in tannery wastewater, which increased the difficulty of tannery wastewater treatment, and posed a potential threat to the environment. In this study, collagen polypeptide (CP) was extracted by using in situ dechromization and industrial trypsin from CCWL, followed by modification with ethylene glycol diglycidyl ether (EGDE) to obtain an epoxy-terminated, biomass-based, amphoteric organic, chrome-free tanning agent (CP-EGDE) with a high isoelectric point of 5.16, and an epoxy value of 0.316 mol/100 g. CP-EGDE can be applied in the pickling-free and salt-free tanning processes to prepare wet white leather and the tannery wastewater with good degradability. The shrinkage temperature (T_s = 84.9 °C), grain flatness, fullness, softness, yellowing resistance, mechanical properties, absorptivity of traditional anionic fatliquor (88.4 %) and dyes (95.3 %) of CP-EGDE tanned leather exceeded those of commercial organic chrome-free tanning agents. This research considered both environmental protection and leather quality, especially greatly improving the absorptivity of traditional anionic wet finishing materials. CP-EGDE is expected to replace chrome tanning agents and has good application prospects.

Facile "Synergistic Inner-Outer Activation" Strategy for Nano-Engineering of Nature-Skin-Derived Wearable Daytime Radiation Cooling Materials

Natural skin-derived products, as traditional wearable materials are widely used in people's daily life due to the products' excellent origins. Herein, a versatile daytime-radiation cooling wearable natural skin (RC-skin) consisting of the collagen micro-nano fibers with the on-demand double-layer radiation cooling structure is nano-engineered through the proposed facile "synergistic inner-outer activation" strategy. The bottom layer (inner strategy) of the RC-skin is fabricated by filling the skin with the Mg₁₁ (HPO₃ )₈ (OH)₆ nanoparticles by soaking. The superstratum (outer strategy) is constituted by a composite coating with an irregular microporous structure. The RC-skin harvests the inherent advantages of natural building blocks including sufficient hydrophobicity, excellent mechanical properties, and friction resistance. Owing to the subtle double-layer structure design, the solar reflectance and the average emissivity in the mid-infrared band of RC-skin are ≈92.7% and ≈95%, respectively. Therefore, the RC-skin's temperature in the sub-ambient is reduced by ≈7.5 °C. Various outdoor practical application experiments further substantiate that RC-skin has superior radiation cooling performances. Collectively, RC-skin has broad-application prospects for intelligent wearing, low-carbon travel, building materials, and intelligent thermoelectric power generation, and this study also provides novel strategies for developing natural-skin-derived functional materials.

Leather for flexible multifunctional bio-based materials: a review

Nowadays, diverse leather usage conditions and increasing demands from consumers challenge the leather industry. Traditional leather manufacturing is facing long-term challenges, including low-value threshold, confined application fields, and environmental issues. Leather inherits all the biomimetic properties of natural skin such as flexibility, sanitation, cold resistance, biocompatibility, biodegradability, and other cross-domain functions, achieving unremitting attention in multi-functional bio-based materials. Series of researches have been devoted to creating and developing leather-based flexible multi-functional bio-materials, including antibacterial leather, conductive leather, flame-retardant leather, self-cleaning leather, aromatic leather, and electromagnetic shielding leather. In this review, we provide a comprehensive overview of the commonly used leather-based functional materials. Furthermore, the possible challenges for the development of functional leathers are proposed, and expected development directions of leather-based functional materials are discussed. This review may promote and inspire the emerging preparation and applications of leather for flexible functional bio-based materials.

Graphical Abstract

Development of a multifunctional injectable temperature-sensitive gelatin-based adhesive double-network hydrogel

Gelatin-based bioadhesives are suitable for the treatment of wounds due to their inherent biocompatibility, lack of immunogenicity, and potential for modification. However, common limitations with such adhesives include their adhesive strength and versatility. In the present study, a multifunctional injectable temperature-sensitive gelatin-based adhesive double-network hydrogel (DNGel) was engineered using facile dual-syringe methodology. An integrative crosslinking strategy utilized the complexation of catechol-Fe³⁺ and NIPAAm-methacryloyl. As anticipated, the DNGel exhibited multifunctional therapeutic properties, namely temperature-sensitivity, mechanical flexibility, good adhesive strength, injectability, self-healing capability, antibacterial activity, and the capability to enable hemostasis and wound healing. The bioinspired dynamic double-network was stabilized by a number of molecular interactions between components in the DNGel, providing multifunctional therapeutic performance. In addition, comprehensive in vitro and in vivo testing confirmed that the adhesive hydrogel exhibited effective antihemorrhagic properties and accelerated wound healing by the promotion of revascularization, representing considerable potential as a next-generation multifunctional smart adhesive patch.

Self-Healable, High-Strength Hydrogel Electrode for Flexible Sensors and Supercapacitors

Flexible energy storage materials and sensors have become the key equipment of human-machine interface technology. For the preparation of these devices, hydrogel electrodes are relevant because of their unique porous structure, high capacitance, flexibility, small size, and lightweight. In this paper, regular polypyrrole (PPy) is synthesized on a heat-induced phase-separated gel (H-Gel/AS) by the template degradation method, and a gelatin-based PPy hydrogel with high strength, high strain rate, and high conductivity is prepared. Moreover, by adding multiwalled carbon nanotubes (MWCNTs) into a gelatin solution according to the H-Gel/AS method, the electrochemical performance of the resulting H-Gel/AS-MWCNTs-PPy electrode is greatly improved. When the H-Gel/AS-MWCNTs-PPy gel is immersed in an ammonium sulfate solution, wrinkles appear on the surface, resulting in further enhancement of the capacitance. On this basis, a flexible sensor and a solid-state supercapacitor are assembled, and their performance is tested. The sensor can detect tensile, bending, and twisting strains with high sensitivity. Meanwhile, as a flexible solid-state supercapacitor, the specific capacitance is 75 F g^-1, and the capacitance retention rate after 5000 cycles is 98.1% under bending conditions. More importantly, the gelatin-based hydrogel shows great potential for application in wearable devices.

Spider-Web and Ant-Tentacle Doubly Bio-Inspired Multifunctional Self-Powered Electronic Skin with Hierarchical Nanostructure

For the practical applications of wearable electronic skin (e-skin), the multifunctional, self-powered, biodegradable, biocompatible, and breathable materials are needed to be assessed and tailored simultaneously. Integration of these features in flexible e-skin is highly desirable; however, it is challenging to construct an e-skin to meet the requirements of practical applications. Herein, a bio-inspired multifunctional e-skin with a multilayer nanostructure based on spider web and ant tentacle is constructed, which can collect biological energy through a triboelectric nanogenerator for the simultaneous detection of pressure, humidity, and temperature. Owing to the poly(vinyl alcohol)/poly(vinylidene fluoride) nanofibers spider web structure, internal bead-chain structure, and the collagen aggregate nanofibers based positive friction material, e-skin exhibits the highest pressure sensitivity (0.48 V kPa-1 ) and high detection range (0-135 kPa). Synchronously, the nanofibers imitating the antennae of ants provide e-skin with short response and recovery time (16 and 25 s, respectively) to a wide humidity range (25-85% RH). The e-skin is demonstrated to exhibit temperature coefficient of resistance (TCR = 0.0075 °C-1 ) in a range of the surrounding temperature (27-55 °C). Moreover, the natural collagen aggregate and the all-nanofibers structure ensure the biodegradability, biocompatibility, and breathability of the e-skin, showing great promise for practicability.

Skin-inspired gelatin-based flexible bio-electronic hydrogel for wound healing promotion and motion sensing

Next generation tissue-engineered skin scaffolds promise to provide sensory restoration through electrical stimulation in addition to effectively rebuilding and repairing skin. The integration of real-time monitoring of the injury motion activities can fundamentally improve the therapeutic efficacy by providing detailed data to guide the clinical practice. Herein, a mechanically-flexible, electroactive, and self-healable hydrogels (MESGel) was engineered for the combinational function of electrically-stimulated accelerated wound healing and motion sensing. MESGel shows outstanding biocompatibility and multifunctional therapeutic properties including flexibility, self-healing characteristics, biodegradability, and bioelectroactivity. Moreover, MESGel shows its potential of being a novel flexible electronic skin sensor to record the injury motion activities. Comprehensive in vitro and in vivo experiments prove that MESGel can facilitate effective electrical stimulation, actively promoting proliferation in Chinese hamster lung epithelial cells and therefore can accelerate favorable epithelial biology during skin wound healing, demonstrating an effective therapeutic strategy for a full-thickness skin defect model and leading to new-type flexible bioelectronics.

Feasibility Study of Gelatin Preparation from the Bioinspired Collagen Aggregates by a "Two-step" Facile Degradation Method

Gelatin is the putative research hotspot of natural products, but gelatin prepared by traditional alkali methods has seriously affected its applications due to the worryingly low molecular weight and poor gel strength. Herein, we took the lead to extract the distinct gelatin from a kind of bioinspired collagen aggregate (CA) by a two-step controlled degradation method. Structural analysis suggested that the CA better preserves the natural aggregated structure of nature collagen (typical D-periodic cross-striated pattern). Compared with the gelatin gelatinized by the conventional alkali method (G-Al) and commercial gelatin (CG), the gelatin (G-CA) from CA had a wide molecular weight distribution range, high transparency, high viscosity, and strong gel strength as expected. Meanwhile, the G-CA film exhibited better mechanical performance and thermostability than CG and G-Al films, and water vapor permeability was also higher in the G-CA film, whereas water solubility was higher in the CG and G-Al films. Thus, the G-CA film is more conducive to the use of food packaging or edible films, exhibiting more potential market application prospects. Notably, G-CA based on CA from waste hide offal provides a way to reuse leather waste resources and further realize green and clean production in leather industry.

A novel eco-friendly imidazole ionic liquids based amphoteric polymers for high performance fatliquoring in chromium-free tanned leather production

The potential environmental pollution of chrome tanned leather results in the development of ecological chromium-free leather tanning production in leather industry. However, with weakly positive charge, chromium-free tanned leather cannot strongly bind to anionic dyes, thus causing low quality of finished leather. Herein, p(DM-co-[DDVIM]Br)PS was synthesized by free radical polymerization method. The structure and properties of the targeted products were synthetically characterized. The results indicated that the use of p(DM-co-[DDVIM]Br)PS fatliquoring agent can not only make leather fibers become loose, but also improve the binding affinity between leather and anionic dye during the fatliquoring process. The fatliquoring agent adsorption rates and the dye absorption rate of the leather were as high as 99.26% and 99.01%, respectively; the fatliquoring and dye solutions were clear, so they can be used as clean materials in the fatliquoring process of chromium-free tanned leather. Leather treated with p(DM-co-[DDVIM]Br)PS fatliquoring agent had higher K/S value (12.80) and is softer than those treated with commercial fatliquoring agent. Consequently, this study can not only help improve the absorption rate of anionic wet finishing materials, but also reduce the pollution caused by chrome tanning agents, thus providing a new way for the cleaner production in leather industry.