Stretchable, tough and elastic nanofibrous hydrogels with dermis-mimicking network structure

Breathable, Adhesive, and Biomimetic Skin-Like Super Tattoo

Electronic tattoo, capable of imperceivably acquiring bio-electrical signals from the body, is broadly applied in healthcare and human-machine interface. Tattoo substrate, the foundation of electronic tattoo, is expected to be mechanically mimetic to skin, adhesive, and breathable, and yet remains highly challenging to achieve. Herein, the study mimics human skin and design a breathable, adhesive, and mechanically skin-like super tattoo substrate based on an ultra-thin film (≈2 µm). Similar to skin, super tattoo demonstrates strain-adaptive stiffening properties with high tear energy (5.4 kJ·m-2) and toughness (1.3 MJ·m-3). Superior to skin, it exhibits high adhesion, ionic conductivity, and permeability. A variety of conductive electrodes can be processed on it, showing the universality toward an ideal platform for electronic tattoo with stable and low contact impedance. Super tattoo-based electrodes can imperceivably and accurately monitor weak electromyography (EMG) of swallowing on the junction, providing effective guidance for rehabilitation training of dysphagia.

Strong, tough and anisotropic bioinspired hydrogels

Soft materials are widely used in tissue engineering, soft robots, wearable electronics, etc. However, it remains a challenge to fabricate soft materials, such as hydrogels, with both high strength and toughness that are comparable to biological tissues. Inspired by the anisotropic structure of biological tissues, a novel solvent-exchange-assisted wet-stretching strategy is proposed to prepare anisotropic polyvinyl alcohol (PVA) hydrogels by tuning the macromolecular chain movement and optimizing the polymer network. The reinforcing and toughening mechanisms are found to be "macromolecule crystallization and nanofibril formation". These hydrogels exhibit excellent mechanical properties, such as extremely high fracture stress (12.8 ± 0.7 MPa) and fracture strain (1719 ± 77%), excellent modulus (4.51 ± 0.76 MPa), high work of fracture (134.47 ± 9.29 MJ m-3), and fracture toughness (305.04 kJ m-2) compared with other strong hydrogels and even natural tendons. In addition, excellent conductivity, strain sensing capability, water retention, freezing resistance, swelling resistance, and biocompatibility can also be achieved. This work provides a new and effective method to fabricate multifunctional anisotropic hydrogels with high tunable strength and toughness with potential applications in the fields of regenerative medicine, flexible sensors, and soft robotics.

Polysaccharides, proteins, and synthetic polymers based multimodal hydrogels for various biomedical applications: A review

Nature-derived or biologically encouraged hydrogels have attracted considerable interest in numerous biomedical applications owing to their multidimensional utility and effectiveness. The internal architecture of a hydrogel network, the chemistry of the raw materials involved, interaction across the interface of counter ions, and the ability to mimic the extracellular matrix (ECM) govern the clinical efficacy of the designed hydrogels. This review focuses on the mechanistic viewpoint of different biologically driven/inspired biomacromolecules that encourages the architectural development of hydrogel networks. In addition, the advantage of hydrogels by mimicking the ECM and the significance of the raw material selection as an indicator of bioinertness is deeply elaborated in the review. Furthermore, the article reviews and describes the application of polysaccharides, proteins, and synthetic polymer-based multimodal hydrogels inspired by or derived from nature in different biomedical areas. The review discusses the challenges and opportunities in biomaterials along with future prospects in terms of their applications in biodevices or functional components for human health issues. This review provides information on the strategy and inspiration from nature that can be used to develop a link between multimodal hydrogels as the main frame and its utility in biomedical applications as the primary target.

Highly Elastic and Strain Sensing Corn Protein Electrospun Fibers for Monitoring of Wound Healing

Due to the lack of sufficient elasticity and strain sensing capability, protein-based ultrafine fibrous tissue engineering scaffolds, though favorable for skin repair, can hardly fulfill on-spot wound monitoring during healing. Herein, we designed highly elastic corn protein ultrafine fibrous smart scaffolds with a three-layer structure for motion tracking at an unpackaged state. The densely cross-linked protein networks were efficiently established by introducing a highly reactive epoxy and provided the fiber substrates with wide-range stretchability (360% stretching range) and ultrahigh elasticity (99.91% recovery rate) at a wet state. With the assistance of the polydopamine bonding layer, a silver conductive sensing layer was built on the protein fibers and endowed the scaffolds with wide strain sensing range (264%), high sensitivity (gauge factor up to 210.55), short response time (<70 ms), reliable cycling stability, and long-lasting duration (up to 30 days). The unpackaged smart scaffolds could not only support cell growth and accelerate wound closure but also track motions on skin and in vivo and trigger alarms once excessive wound deformations occurred. These features not only confirmed the great potential of these smart scaffolds for applications in tissue reconstruction and wound monitoring but also proved the possibility of employing various plant protein ultrafine fibers as flexible bioelectronics.

Nanofibrous hemostatic materials: Structural design, fabrication methods, and hemostatic mechanisms

Development of rapid and effective hemostatic materials has always been the focus of research in the healthcare field. Nanofibrous materials which recapitulate the delicate nano-topography feature of fibrin fibers produced during natural hemostatic process, offer large length-to-diameter ratio and surface area, tunable porous structure, and precise control in architecture, showing great potential for staunching bleeding. Here we present a comprehensive review of advances in nanofibrous hemostatic materials, focusing on the following three important parts: structural design, fabrication methods, and hemostatic mechanisms. This review begins with an introduction to the physiological hemostatic mechanism and current commercial hemostatic agents. Then, it focuses on recent progress in electrospun nanofibrous hemostatic materials in terms of composition and structure control, surface modification, and in-situ deposition. The article emphasizes the development of three-dimensional (3D) electrospun nanofibrous materials and their emerging evolution for improving hemostatic function. Next, it discusses the fabrication of self-assembling peptide or protein-mimetic peptide nanofibers, co-assembling supramolecular nanofibers, as well as other nanofibrous hemostatic agents. Further, the article highlights the external and intracavitary hemostatic management based on various nanofiber aggregates. In the end, this review concludes with the current challenges and future perspectives of nanofibrous hemostatic materials. STATEMENT OF SIGNIFICANCE: This article reviews recent advances in nanofibrous hemostatic materials including fabrication methods, composition and structural control, performance improvement, and hemostatic mechanisms. A variety of methods including electrospinning, self-assembly, grinding and refining, template synthesis, and chemical vapor deposition, have been developed to prepare nanofibrous materials. These methods provide robustness in control of the nanofiber architecture in the forms of hydrogels, two-dimensional (2D) membranes, 3D sponges, or composites, showing promising potential in the external and intracavitary hemostasis and wound healing applications. This review will be of great interest to the broad readers in the field of hemostatic materials and multifunctional biomaterials.

Electro-Blown Spun Silk/Graphene Nanoionotronic Skin for Multifunctional Fire Protection and Alarm

Artificial protective skins are widely used in artificial intelligence robots, such as humanoid robots, mobile manipulation robots, and automatic probe robots, but their safety in use, especially flame retardancy, is rarely considered. As many artificial skins are designed for use in flammable or even explosive environments, flammability is a significant concern. Herein, a flame-retardant silk/graphene nanoionotronic (SGNI) skin is developed by using a rationally designed high-throughput electro-blown spinning technique, with a more efficient production efficiency than electrospinning. These flame retardant SGNI skins combine the advantages of nanofibrous and ionotronic materials, and they are sustainable, conductive, highly porous, mechanically robust, highly stretchable, self-adhesive, and humidity- and temperature-sensitive. These merits support the assembly of SGNI skins into a fire alarm system, with real-time alarm (response in 2 s) to mobile phones, clouds, and a central control system. The concept that combines a flame retardant and fire alarm material into an intelligent skin may provide potential solutions toward the design of protective skins for robotics and human-machine interactions.

Skin-inspired nanofibrillated cellulose-reinforced hydrogels with high mechanical strength, long-term antibacterial, and self-recovery ability for wearable strain/pressure sensors

The advent of electric skins (E-skin) with tactile sensation, flexibility, and human affinity characteristics have attracted considerable attention in extensive research fields, including intelligent robots and health monitoring, etc. To improve the intrinsic brittleness of hydrogels, a multifunctional E-skin was fabricated involving a TEMPO-NFC and a covalently cross-linked polyacrylamide (PAM) network. In this work, silver nanoparticles (AgNPs) as long-term antibacterial agent and conductive fillers were coated onto NFC nanofibers. Subsequently, this nanocomposite hydrogel was synthesized by free radical copolymerization of AM monomers with PNAg fibers as interpenetrating fibers network. Importantly with NFC present, the nanocomposite hydrogel exhibited superior mechanical performance and excellent self-recovery ability. The obtained sensor with excellent mechanical stability and sensing performance could detect mechanotransduction signal of human movements. This work provides a practicable method to prepare high antibacterial efficiency, excellent mechanical performance, and dual-modal nanocellulose-based hydrogel sensor for the broad-range application in human-motion detection and intelligence skins.