Fiber Actuators Based on Reversible Thermal Responsive Liquid Crystal Elastomer.

Soft actuators inspired by the movement of organisms have attracted extensive attention in the fields of soft robotics, electronic skin, artificial intelligence, and healthcare due to their excellent adaptability and operational safety. Liquid crystal elastomer fiber actuators (LCEFAs) are considered as one of the most promising soft actuators since they can provide reversible linear motion and are easily integrated or woven into complex structures to perform pre-programmed movements such as stretching, rotating, bending, and expanding. The research on LCEFAs mainly focuses on controllable preparation, structural design, and functional applications. This review, for the first time, provides a comprehensive and systematic review of recent advances in this important field by focusing on reversible thermal response LCEFAs. First, the thermal driving mechanism, and direct and indirect heating strategies of LCEFAs are systematically summarized and analyzed. Then, the fabrication methods and functional applications of LCEFAs are summarized and discussed. Finally, the challenges and technical difficulties that may hinder the performance improvement and large-scale production of LCEFAs are proposed, and the development opportunities of LCEFAs are prospected.

Continuous Rapid Fabrication of Ceramic Fiber Sponge Aerogels with High Thermomechanical Properties via a Green and Low-Cost Electrospinning Technique.

Ceramic aerogel is an appealing fireproof and heat-insulation material, but synchronously improving its mechanical and thermal properties is a challenge. Moreover, the expensive discontinuous processing techniques inhibit the large-scale fabrication of ceramic aerogels. Here, we propose a water-based electrospinning method, based on the hydrolysis and condensation reactions of ceramic precursor salts themselves, for the continuous and rapid (0.025 m3/min) fabrication of ceramic fiber sponge aerogels with dual micronano fiber networks, which show synchronous enhanced fireproof, thermal insulation, and resilience performance. The elastic ceramic micro/nano fiber sponge aerogels contain robust silica-based microfibers as a firm skeleton and alumina-based nanofibers as elastic thermal insulation filler. The sponges have a high porosity of >99.8%, a low mass density (6.21 mg/cm3), a small thermal conductivity (0.022 W/m·K), and a large compression strength (21.15 kPa at 80% strain). The ceramic fiber sponges can effectively prevent the propagation of thermal runaway when a lithium battery experiences catastrophic thermal shock (>1000 °C) in the power battery packs. The proposed strategy is feasible for low-cost and rapid synthesizing ceramic aerogels toward effective battery thermal management.

Biomimetic three-layer hierarchical scaffolds for efficient water management and cell recruitment.

Taking inspiration from the structures of roots, stems and leaves of trees in nature, a biomimetic three-layered scaffold was designed for efficient water management and cell recruitment. Using polycaprolactone (PCL) and polyacrylonitrile (PAN) as raw materials, radially oriented nanofiber films and multistage adjustable nanofiber films were prepared through electrospinning technology as the base skin-friendly layer (roots) and middle unidirectional moisture conductive material (stems), the porous polyurethane foam was integrated as the outer moisturizing layer (leaves). Among which, radially oriented nanofiber films could promote the directional migration of fibroblasts and induce cell morphological changes. For the spatially hierarchically nanofiber films, the unidirectional transport of liquid was effectively realized. While the porous polyurethane foam membrane could absorb 9 times its weight in biofluid and retain moisture for up to 10 h. As a result, the biomimetic three-layered scaffolds with different structures can promote wound epithelization and drain biofluid while avoiding wound inflammation caused by excessive biofluid, which is expected to be applied in the field of skin wounds.

Platelet-rich plasma-loaded bioactive chitosan@sodium alginate@gelatin shell-core fibrous hydrogels with enhanced sustained release of growth factors for diabetic foot ulcer healing.

The ability of autologous platelet-rich plasma (PRP) gel to promote rapid wound healing without immunological rejection has opened new avenues for the treatment of diabetic foot wounds. However, PRP gel still suffers from the quick release of growth factors (GFs) and requires frequent administration, thus resulting in decreased wound healing efficiency, higher cost as well as greater pain and suffering for the patients. In this study, the flow-assisted dynamic physical cross-linked coaxial microfluidic three-dimensional (3D) bio-printing technology, combined with the calcium ion chemical dual cross-linking method was developed to design PRP-loaded bioactive multi-layer shell-core fibrous hydrogels. The prepared hydrogels exhibited outstanding water absorption-retention capacity, good biocompatibility as well as a broad-spectrum antibacterial effect. Compared with clinical PRP gel, these bioactive fibrous hydrogels displayed a sustained release of GFs, reducing the administration frequency by 33 % availably during the wound treatment, but more prominent therapeutic effects such as effective reduced inflammation, in addition to promoting the growth of granulation tissue and angiogenesis, the formation of high-density hair follicles, and the generation of regular ordered and high-density collagen fiber network, which suggested great promise as exceptional candidates for treatment of diabetic foot ulcer in clinical settings.

A multifunctional 3D dressing unit based on the core-shell hydrogel microfiber for diabetic foot wound healing.

The healing mechanism of diabetic foot wounds is very complicated, and it is difficult for a single-function medical dressing to achieve good therapeutic effects. We propose a simple coaxial biological 3D printing technology, which uses one-step 3D deposition to continuously produce multifunctional medical dressings on the basis of core-shell hydrogel fibers. These dressings have good biocompatibility, controlled drug-release performance, excellent water absorption and retention, and antibacterial and anti-inflammatory functions. In vivo experiments with type 2 diabetic rats were performed over a 14-day period to compare the performance of the multifunctional 3D dressing with a gauze control; the multifunctional 3D dressing reduced inflammation, effectively increased the post-healing thickness of granulation tissue, and promoted the formation of blood vessels, hair follicles, and highly oriented collagen fiber networks. Therefore, the proposed multifunctional dressing is expected to be suitable for clinical applications for healing diabetic foot wounds.

Microfluidic-directed biomimetic Bulbine torta-like microfibers based on inhomogeneous viscosity rope-coil effect.

Helical structures are attracting increasing attention owing to their unique typical physical and chemical properties. However, it remains a challenge to construct atypical helical structures at the microscale. This paper proposes a continuous spinning method with a microfluidic-chip-based spinning device to engineer atypical helical microfibers. The strategy causes polymer fluid to form the biomimetic Bulbine torta (BT)-like shape with the aid of the inhomogeneous viscosity rope-coil effect. In particular, the structure parameter of the BT microfibers could be optimized through the synchronous regulation of the microfluidic flow and reaction kinetics, and the obtained microfibers exhibit ultrahigh strain sensitivity, indicating great promise as exceptional candidates for constructing ideal strain sensors. In addition, single- and double-hollow BT microfibers are also prepared by introducing the core flow channel into the microfluidic chip and demonstrate high structural similarity to irregular blood vessels (e.g. varicose veins), which is promising for the actual application of blood vessel tissue engineering.