Integration of advanced nanogenerator technology with conventional textile processes fosters the emergence of textile-based nanogenerators (NGs), which will inevitably promote the rapid development and widespread applications of next-generation wearable electronics and multifaceted artificial intelligence systems. NGs endow smart textiles with mechanical energy harvesting and multifunctional self-powered sensing capabilities, while textiles provide a versatile flexible design carrier and extensive wearable application platform for their development. However, due to the lack of an effective interactive platform and communication channel between researchers specializing in NGs and those good at textiles, it is rather difficult to achieve fiber/fabric-based NGs with both excellent electrical output properties and outstanding textile-related performances. To this end, a critical review is presented on the current state of the arts of wearable fiber/fabric-based piezoelectric nanogenerators and triboelectric nanogenerators with respect to basic classifications, material selections, fabrication techniques, structural designs, and working principles, as well as potential applications. Furthermore, the potential difficulties and tough challenges that can impede their large-scale commercial applications are summarized and discussed. It is hoped that this review will not only deepen the ties between smart textiles and wearable NGs, but also push forward further research and applications of future wearable fiber/fabric-based NGs.

Fiber/Fabric-Based Piezoelectric and Triboelectric Nanogenerators for Flexible/Stretchable and Wearable Electronics and Artificial Intelligence.

Large-area stretchable electronics are critical for progress in wearable computing, soft robotics and inflatable structures. Recent efforts have focused on engineering electronics from soft materials-elastomers, polyelectrolyte gels and liquid metal. While these materials enable elastic compliance and deformability, they are vulnerable to tearing, puncture and other mechanical damage modes that cause electrical failure. Here, we introduce a material architecture for soft and highly deformable circuit interconnects that are electromechanically stable under typical loading conditions, while exhibiting uncompromising resilience to mechanical damage. The material is composed of liquid metal droplets suspended in a soft elastomer; when damaged, the droplets rupture to form new connections with neighbours and re-route electrical signals without interruption. Since self-healing occurs spontaneously, these materials do not require manual repair or external heat. We demonstrate this unprecedented electronic robustness in a self-repairing digital counter and self-healing soft robotic quadruped that continue to function after significant damage.

An autonomously electrically self-healing liquid metal-elastomer composite for robust soft-matter robotics and electronics.

Incorporating gold nanowires into scaffolds used to create heart patches can improve electrical communication between cells and enhance the growth of tissues.

Nanowired three-dimensional cardiac patches

Conductive MXene Nanocomposite Organohydrogel for Flexible, Healable, Low‐Temperature Tolerant Strain Sensors

Biological membranes play an essential role in living organisms by providing stable and functional compartments, preserving cell architecture, whilst supporting signalling and selective transport that are mediated by a variety of proteins embedded in the membrane. However, mimicking cell membranes – to be applied in artificial systems – is very challenging because of the vast complexity of biological structures. In this respect a highly promising strategy to designing multifunctional hybrid materials/systems is to combine biological molecules with polymer membranes or to design membranes with intrinsic stimuli-responsive properties. Here we present supramolecular polymer assemblies resulting from self-assembly of mostly amphiphilic copolymers either as 3D compartments (polymersomes, PICsomes, peptosomes), or as planar membranes (free-standing films, solid-supported membranes, membrane-mimetic brushes). In a bioinspired strategy, such synthetic assemblies decorated with biomolecules by insertion/encapsulation/attachment, serve for development of multifunctional systems. In addition, when the assemblies are stimuli-responsive, their architecture and properties change in the presence of stimuli, and release a cargo or allow “on demand” a specific in situ reaction. Relevant examples are included for an overview of bioinspired polymer compartments with nanometre sizes and membranes as candidates in applications ranging from drug delivery systems, up to artificial organelles, or active surfaces. Both the advantages of using polymer supramolecular assemblies and their present limitations are included to serve as a basis for future improvements.

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Bioinspired polymer vesicles and membranes for biological and medical applications

Tough hydrogels, polymeric network structures with excellent mechanical properties (such as high stretchability and toughness), are emerging soft materials. Despite their remarkably mechanical features, tough hydrogels exhibit two flaws (freezing around the icing temperatures of water and drying under arid conditions). Inspired by cryoprotectants (CPAs) used in the inhibition of the icing of water in biological samples, a versatile and straightforward method is reported to fabricate extreme anti-freezing, non-drying CPA-based organohydrogels with long-term stability by partially displacing water molecules within the pre-fabricated hydrogels. CPA-based Ca-alginate/polyacrylamide (PAAm) tough hydrogels were successfully fabricated with glycerol, glycol, and sorbitol. The CPA-based organohydrogels remain unfrozen and mechanically flexible even up to -70 °C and are stable under ambient conditions or even vacuum.

Rational Fabrication of Anti-Freezing, Non-Drying Tough Organohydrogels by One-Pot Solvent Displacement.

Liquid Metal‐Based Transient Circuits for Flexible and Recyclable Electronics

As one of the most outstanding materials, the analysis of the structure and function of hydrogels has been extensively carried out to tailor and adapt them to various fields of application. The high water content, which is beneficial for plenty of applications in the biomedical setting, prevents the adoption of hydrogels in flexible electronics and sensors in real life applications, because hydrogels lose their excellent properties, including conductivity, transparency, flexibility, etc., upon freezing at sub-zero temperatures. Therefore, depressing the liquid–solid phase transition temperature is a powerful means to expand the application scope of hydrogels, and will benefit the chemical engineering and materials science communities. This review summarizes the recent research progress of anti-freezing hydrogels. At first, approaches for the generation of anti-freezing (hydro)gels are introduced and their anti-freezing mechanisms and performances are briefly discussed. These approaches are either based on addition of salts, alcohols (cryoprotectants and organohydrogels), and ionic liquids (ionogels), modification of the polymer network or a combination of several techniques. Then, a concise overview of applications leveraged by the widened temperature resistance is provided and future research areas and developments are envisaged.

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Biomimetic anti-freezing polymeric hydrogels: keeping soft-wet materials active in cold environments

Owing to their structural advantages in comparison with bulk polydimethylsiloxane (PDMS), porous 3D substrates, which are also known as PDMS sponges, possess immense potential in energy generation, transport and storage, absorption, separation, photocatalysis, wearable electronics and life science applications. Extensive effort has therefore been devoted to the design and synthesis of porous PDMS sponges. The key to excellent performance in high-value applications is a deep knowledge of the beneficial aspects of their porosity, structure and morphology for a specific application. Several new routes for the fabrication of PDMS sponges, as well as novel applications, have been developed recently. Therefore, this review focuses on advances in the field of the fabrication and application of PDMS sponges since 2011. After a concise introduction, which includes remarks on the benefits of PDMS in comparison with other materials, strategies for the synthesis/fabrication of PDMS sponges are presented and their advantages and drawbacks are concisely discussed. A summary of the potential fabrication procedures will be beneficial for those entering the field, as it gives a quick overview of the feasible applications of a PDMS sponge fabricated via a specific method. Afterwards, different high-value applications of PDMS sponges are described in conjunction with specific and detailed examples of all the abovementioned applications. In this regard, suggestions are also made regarding which fabrication method is most beneficial for the application being discussed. Finally, recent advances in the fabrication and application of PDMS sponges are summarized, as well as issues, such as surface functionalization and pore size limitations, which are impeding reasonable future applications. We envision that this review will be helpful to those entering the field, as well as experienced researchers who need rapid access to recent literature, and will give new stimuli for the development of novel porous materials.

Recent progress in fabrication and application of polydimethylsiloxane sponges

Liquid metal sponges were developed by loading liquid metals (GaInSn) into elastomer sponges. The elasticity of 3D-interconnected networks and the fluidic nature of liquid metals led to the formation of all-soft structures for electrical conductors with high electrical conductivity and mechanical flexibility.

Stephan Handschuh-Wang

Papers

Rational Fabrication of Anti-Freezing, Non-Drying Tough Organohydrogels by One-Pot Solvent Displacement.

Liquid Metal‐Based Transient Circuits for Flexible and Recyclable Electronics

Biomimetic anti-freezing polymeric hydrogels: keeping soft-wet materials active in cold environments

Recent progress in fabrication and application of polydimethylsiloxane sponges

Liquid metal sponges for mechanically durable, all-soft, electrical conductors