Enhancing volumetric muscle loss (VML) recovery in a rat model using super durable hydrogels derived from bacteria

Bacteria can be programmed to deliver natural materials with defined biological and mechanical properties for controlling cell growth and differentiation. Here, we present an elastic, resilient and bioactive polysaccharide derived from the extracellular matrix of Pantoea sp. BCCS 001. Specifically, it was methacrylated to generate a new photo crosslinkable hydrogel that we coined Pantoan Methacrylate or put simply PAMA. We have used it for the first time as a tissue engineering hydrogel to treat VML injuries in rats. The crosslinked PAMA hydrogel was super elastic with a recovery nearing 100 %, while mimicking the mechanical stiffness of native muscle. After inclusion of thiolated gelatin via a Michaelis reaction with acrylate groups on PAMA we could also guide muscle progenitor cells into fused and aligned tubes - something reminiscent of mature muscle cells. These results were complemented by sarcomeric alpha-actinin immunostaining studies. Importantly, the implanted hydrogels exhibited almost 2-fold more muscle formation and 50 % less fibrous tissue formation compared to untreated rat groups. In vivo inflammation and toxicity assays likewise gave rise to positive results confirming the biocompatibility of this new biomaterial system. Overall, our results demonstrate that programmable polysaccharides derived from bacteria can be used to further advance the field of tissue engineering. In greater detail, they could in the foreseeable future be used in practical therapies against VML.

Flexible solid-state Zn-air battery based on polymer-oxygen-functionalized g-C3N4 composite membrane

Personalized healthcare devices require an energy storage system that is flexible and has good mechanical strength and stability for long periods. Zn-air batteries show promise as an alternative to Li-air batteries for this purpose. Zn-air batteries with a high theoretical specific energy density of 1350 W h kg-1 have the potential to replace other metal-air batteries but faces the challenges, such as dendrite formation and Zn corrosion, hindering their successful commercialization. In this work, we report the design and performance optimization of a solid-state flexible Zn-air battery with superior performance and good mechanical property. In addition, we focused on the development of a gel-polymer composite membrane as the electrolyte. The main advantage of the flexible electrolyte is its optimum combination of good ionic conductivity and mechanical strength. Thus, we attempted to address the above-mentioned issues by modifying poly(vinyl alcohol) (PVA) with o-g-C3N4 through the in situ formation of a composite. The interaction between the functional groups of o-g-C3N4 and PVA increased the conductivity without compromising the mechanical behavior of the composite. According to the optimization of the composite composition, it was concluded that 0.32 wt% o-g-C3N4 in PVA showed the highest conductivity and excellent mechanical strength (increase from 25 MPa for pristine PVA membrane to 35 MPa for g-C3N4-PVA composite membrane). The performance of the solid-state battery was better (40 hours) than the standard PVA KOH (13 hours) membrane. Moreover, the stability of the battery was retained at various bending angles, demonstrating its potential to be used in flexible electronic devices.

Strategies Toward Stretchable Aqueous Zn-based Batteries for Wearable Electronics from Components to Devices

Recently, aqueous Zn-based batteries (AZBs) are receiving increased attention in wearable and implantable electronics due to the low cost, high safety, high eco-efficiency, and relatively high energy density. However, it is still a big challenge to develop stretchable AZBs (SAZBs) which can be conformally folded, crumpled, and stretched with human body motions. Although a lot of efforts have been dedicated to constructions of SAZBs, a comprehensive review which focuses on summarizing stretchable materials, device configurations and challenges of SAZBs is needed. Herein, this review attempts to critically review the latest developments and progress in stretchable electrodes, electrolytes, packaging materials and device configurations in detail. Furthermore, these challenges and potential future research directions in the field of SAZBs are also discussed.

Opportunities of Flexible and Portable Electrochemical Devices for Energy Storage: Expanding the Spotlight onto Semi-solid/Solid Electrolytes

The ever-increasing demand for flexible and portable electronics has stimulated research and development in building advanced electrochemical energy devices which are lightweight, ultrathin, small in size, bendable, foldable, knittable, wearable, and/or stretchable. In such flexible and portable devices, semi-solid/solid electrolytes besides anodes and cathodes are the necessary components determining the energy/power performances. By serving as the ion transport channels, such semi-solid/solid electrolytes may be beneficial to resolving the issues of leakage, electrode corrosion, and metal electrode dendrite growth. In this paper, the fundamentals of semi-solid/solid electrolytes (e.g., chemical composition, ionic conductivity, electrochemical window, mechanical strength, thermal stability, and other attractive features), the electrode-electrolyte interfacial properties, and their relationships with the performance of various energy devices (e.g., supercapacitors, secondary ion batteries, metal-sulfur batteries, and metal-air batteries) are comprehensively reviewed in terms of materials synthesis and/or characterization, functional mechanisms, and device assembling for performance validation. The most recent advancements in improving the performance of electrochemical energy devices are summarized with focuses on analyzing the existing technical challenges (e.g., solid electrolyte interphase formation, metal electrode dendrite growth, polysulfide shuttle issue, electrolyte instability in half-open battery structure) and the strategies for overcoming these challenges through modification of semi-solid/solid electrolyte materials. Several possible directions for future research and development are proposed for going beyond existing technological bottlenecks and achieving desirable flexible and portable electrochemical energy devices to fulfill their practical applications. It is expected that this review may provide the readers with a comprehensive cross-technology understanding of the semi-solid/solid electrolytes for facilitating their current and future researches on the flexible and portable electrochemical energy devices.

Poly(acrylic acid)-Based Composite Gel Polymer Electrolytes with High Mechanical Strength and Ionic Conductivity toward Flexible Zinc-Air Batteries with Long Cycling Lifetime

The rapid development of portable, flexible, and wearable devices motivates the requirement for flexible zinc-air batteries (FZABs) not only to provide high energy density but also to have sufficient deformability for wearer comfort. The gel polymer electrolyte (GPE) serves as the core part of the FZABs, playing a key function in the battery's practical output performance such as discharge voltage, energy density, and cycling life. Unfortunately, ascribed to its high water absorption, the GPE regularly shows comparatively poor mechanical strength, which is difficult to offer sufficient physical support between electrodes. Herein, we report an optimized poly(acrylic acid) (PAA)-based composite GPE with the aluminum oxide (Al2O3) filler and apply it for FZAB. The mechanical strength, electrolyte absorption capacity, electrolyte retention ability, and ionic conductivity of the PAA-Al2O3 gel polymers and corresponding GPEs were investigated. The results indicate that the above performances of polymers and corresponding GPEs depend to a considerable extent on the content of the addition of Al2O3 particles. When 20 wt.% Al2O3 is added to the PAA polymer, the obtained PAA-20 wt.% Al2O3 gel polymer exhibits improved mechanical strength. The corresponding PAA-20 wt.% Al2O3 GPE shows a high ionic conductivity of 186 mS cm-1 and pleasurable electrolyte retention capability. This optimized GPE enables the assembled FZAB to display a long cycling lifetime of 384 h, a large power density of 77.7 mW cm-2, and excellent discharge performance. Moreover, the integrated FZAB can power various electronic devices, demonstrating its outstanding practicability and extensibility as a flexible power source.

Wood-Derived Monolithic Catalysts with the Ability of Activating Water Molecules for Oxygen Electrocatalysis

Oxygen reduction reaction (ORR) is the key reaction on cathode of rechargeable zinc-air batteries (ZABs). However, the lack of protons in alkaline conditions limits the rate of ORR. Herein, an activating water strategy is proposed to promote oxygen electrocatalytic activity by enhancing the proton production from water dissociation. FeP nanoparticles (NPs) are coupled on N-doped wood-derived catalytically active carbon (FeP-NWCC) to associate bifunctional active sites. In alkaline, FeP-NWCC possesses outstanding catalytic activities toward ORR (E_1/2  = 0.86 V) and Oxygen evolution reaction (OER) (overpotential is 310 mV at 10 mA cm^-2 ). The liquid ZABs assembled by FeP-NWCC deliver superior peak power density (144 mW cm^-2 ) and cycle stability (over 450 h). The quasi-solid-state ZABs based on FeP-NWCC also display excellent performances. Theoretical calculation illustrates that the superb bifunctional performance of FeP-NWCC results from the elevated dissociation efficiency of water via FeP NPs to assist the oxygen catalytic process. The strategy of activating water provides a new perspective for the design of ORR/OER bifunctional catalysts. This work is a model for the application of forest biomass.

Supramolecular Gel-Derived Highly Efficient Bifunctional Catalysts for Omnidirectionally Stretchable Zn-Air Batteries with Extreme Environmental Adaptability

Most existing stretchable batteries can generally only be stretched uniaxially and suffer from poor mechanical and electrochemical robustness to withstand extreme mechanical and environmental challenges. A highly efficient bifunctional electrocatalyst is herein developed via the unique self-templated conversion of a guanosine-based supramolecular hydrogel and presents a fully integrated design strategy to successfully fabricate an omnidirectionally stretchable and extremely environment-adaptable Zn-air battery (ZAB) through the synergistic engineering of active materials and device architecture. The electrocatalyst demonstrates a very low reversible overpotential of only 0.68 V for oxygen reduction/evolution reactions (ORR/OER). This ZAB exhibits superior omnidirectional stretchability with a full-cell areal strain of >1000% and excellent durability, withstanding more than 10 000 stretching cycles. Promisingly, without any additional pre-treatment, the ZAB exhibits outstanding ultra-low temperature tolerance (down to -60 °C) and superior waterproofness, withstanding continuous water rinsing (>5 h) and immersion (>3 h). The present work offers a promising strategy for the design of omnidirectionally stretchable and high-performance energy storage devices for future on-skin wearable applications.

Frontiers and Structural Engineering for Building Flexible Zinc-Air Batteries

With the development of flexible devices, the demand for wearable power sources has increased and gradually become imperative. Zinc-air batteries (ZABs) have attracted lots of research interest due to their high theoretical energy density and excellent safety properties, which can meet the wearable energy supply requirements. Here, the flexibility of energy storage devices is discussed first, followed by the chemistries and development of flexible ZABs. The design of flexible electrodes, the properties of solid-state electrolytes (SSEs), and the construction of deformable structures are discussed in depth. The researchers working on flexible energy storage devices will benefit from the work.

Advanced Multifunctional Aqueous Rechargeable Batteries Design: From Materials and Devices to Systems

Multifunctional aqueous rechargeable batteries (MARBs) are regarded as safe, cost-effective, and scalable electrochemical energy storage devices, which offer additional functionalities that conventional batteries cannot achieve, which ideally leads to unprecedented applications. Although MARBs are among the most exciting and rapidly growing topics in scientific research and industrial development nowadays, a systematic summary of the evolution and advances in the field of MARBs is still not available. Therefore, the review presented comprehensively and systematically summarizes the design principles and the recent advances of MARBs by categories of smart ARBs and integrated systems, together with an analysis of their device design and configuration, electrochemical performance, and diverse smart functions. The two most promising strategies to construct novel MARBs may be A) the introduction of functional materials into ARB components, and B) integration of ARBs with other functional devices. The ongoing challenges and future perspectives in this research and development field are outlined to foster the future development of MARBs. Finally, the most important upcoming research directions in this rapidly developing field are highlighted that may be most promising to lead to the commercialization of MARBs and to a further broadening of their range of applications.

Stretchable Energy Storage Devices Based on Carbon Materials

Stretchable energy storage devices are essential for developing stretchable electronics and have thus attracted extensive attention in a variety of fields including wearable devices and bioelectronics. Carbon materials, e.g., carbon nanotube and graphene, are widely investigated as electrode materials for energy storage devices due to their large specific surface areas and combined remarkable electrical and electrochemical properties. They can also be effectively composited with many other functional materials or designed into different microstructures for fabricating stretchable energy storage devices. This review summarizes recent advances toward the development of carbon-material-based stretchable energy storage devices. An overview of common carbon materials' fundamental properties and general strategies to enable the stretchability of carbon-material-based electrodes are presented. The performances of the as-fabricated stretchable energy storage devices including supercapacitors, lithium-ion batteries, metal-air batteries, and other batteries are then carefully discussed. Challenges and perspectives in this emerging field are finally highlighted for future studies.

Battery-Sensor Hybrid: A New Gas Sensing Paradigm with Complete Energy Self-Sufficiency

Fully autonomous operation has long been an ultimate goal in environmental sensing. Although self-powered gas sensors based on energy harvesting have been widely reported to provide power for autonomous operation, these sensors rely on external sources of harvestable energy, thus are not completely self-sufficient. Herein, a battery-sensor hybrid device that can simultaneously function as both a power source and a gas sensor is presented. The battery-sensor consists of a cathode that reduces NO₂ to NO₂^- via a catalyst with Fe-N_x species distributed on highly graphitic porous nitrogen-doped carbon. On the basis of the efficient and selective electrocatalytic activity of the catalyst, the battery-sensor is capable of sensing NO₂ and does so without any external power, overcoming the long-standing grand challenge to achieve complete energy self-sufficiency. Furthermore, through controlling the working current the sensing range can be significantly expanded and electronically tuned, which is not only unprecedented for gas sensors but also of remarkable commercial practicality. The proposed battery-sensor hybrid architecture represents a new paradigm toward sensors with complete energy self-sufficiency.

Energy Harvesting and Storage with Soft and Stretchable Materials

This review highlights various modes of converting ambient sources of energy into electricity using soft and stretchable materials. These mechanical properties are useful for emerging classes of stretchable electronics, e-skins, bio-integrated wearables, and soft robotics. The ability to harness energy from the environment allows these types of devices to be tetherless, thereby leading to a greater range of motion (in the case of robotics), better compliance (in the case of wearables and e-skins), and increased application space (in the case of electronics). A variety of energy sources are available including mechanical (vibrations, human motion, wind/fluid motion), electromagnetic (radio frequency (RF), solar), and thermodynamic (chemical or thermal energy). This review briefly summarizes harvesting mechanisms and focuses on the materials' strategies to render such devices into soft or stretchable embodiments.

A hierarchical porous P-doped carbon electrode through hydrothermal carbonization of pomelo valves for high-performance supercapacitors

Porous carbon materials are synthesized from pomelo valves by the hydrothermal activation of H3PO4 followed by simple carbonization. The as-synthesized hierarchically porous carbon electrode exhibits a high specific capacitance of 966.4 F g-1 at 1 A g-1 and an ultra-high stability of 95.6% even after 10 000 cycles. Moreover, the supercapacitor also demonstrates a maximum energy of 36.39 W h kg-1 and a maximum power of 33.33 kW kg-1 with an energy retention of 25.56 W h kg-1, which paves the way for the development of high-performance, green supercapacitors for advanced energy storage systems.