Self-Assembled Multilayered Coatings with Multiple Cyclic Self-Healing Capability, Bacteria Killing, Osteogenesis, and Angiogenesis Properties on Magnesium Alloys

Self-healing coatings improve the durability of magnesium (Mg) implants, but rapid corrosion still poses a challenge in the healing stage. Moreover, Mg-based materials with acceptable bacteria killing, osteogenic and angiogenic properties are challenging in biomedical applications. Herein, the self-healing polymeric coatings are fabricated on Mg alloys using the spin-assisted layer-by-layer (SLbL) assembly of hyaluronic acid (HA) and branched polyethyleneimine (bPEI) followed by chemical crosslinking treatment. The self-healing coatings show excellent adhesion strength and structure stability. The corrosion resistance is improved due to the physical barrier of polymer coatings, which also promotes the formation of hydroxyapatite (HAp) during degradation for further protection of Mg substrate. Owing to the dynamic reversible hydrogen bonds existing between HA and bPEI, the crosslinked multilayered coatings possess fast, substantial, and cyclic self-healing capabilities leading to restoration of the original structure and functions. In vitro investigations reveal that the self-healing coatings have multiple functionalities pertaining to bacteria killing, cytocompatibility, osteogenesis, as well as angiogenesis. In addition, the self-healing coatings stimulate alkaline phosphatase activity (ALP), extracellular matrix (ECM) mineralization, and the expression of osteogenesis-related genes of mBMSCs and HUVECs. This study reveals a feasible strategy to design and prepare versatile self-healing coatings on Mg implants for biomedical applications.

Unleashing the Potential of MXene-Based Flexible Materials for High-Performance Energy Storage Devices

Since the initial discovery of Ti3 C2 a decade ago, there has been a significant surge of interest in 2D MXenes and MXene-based composites. This can be attributed to the remarkable intrinsic properties exhibited by MXenes, including metallic conductivity, abundant functional groups, unique layered microstructure, and the ability to control interlayer spacing. These properties contribute to the exceptional electrical and mechanical performance of MXenes, rendering them highly suitable for implementation as candidate materials in flexible and wearable energy storage devices. Recently, a substantial number of novel research has been dedicated to exploring MXene-based flexible materials with diverse functionalities and specifically designed structures, aiming to enhance the efficiency of energy storage systems. In this review, a comprehensive overview of the synthesis and fabrication strategies employed in the development of these diverse MXene-based materials is provided. Furthermore, an in-depth analysis of the energy storage applications exhibited by these innovative flexible materials, encompassing supercapacitors, Li-ion batteries, Li-S batteries, and other potential avenues, is conducted. In addition to presenting the current state of the field, the challenges encountered in the implementation of MXene-based flexible materials are also highlighted and insights are provided into future research directions and prospects.

Interfacial Engineering Enables Perovskite Heteroepitaxial Growth on Black Phosphorus for Flexible X-ray Detectors

2D materials with atomic-scale thickness and mechanical robustness are required for flexible devices. The superior optoelectronic properties and high-Z atoms in metal halide perovskites render them desirable for X-ray detection, but the intrinsic brittleness is an obstacle hampering the applications in flexible detectors. Herein, an interfacial engineering strategy is demonstrated for the epitaxial growth of methylammonium lead bromide (MAPbBr3 ) on black phosphorus (BP) for flexible X-ray detectors. The mechanically robust, high-quality heterostructure consisting of a Pb transition layer is synthesized for the two-way bridging of BP and MAPbBr3 . Excellent optoelectronic properties such as a high X-ray sensitivity of 1,609 ± 122 µC Gy-1  cm-2 (80 times higher than that of the commercial amorphous Se), a fast response time of 40 ± 5 ms, as well as a low detection limit of 3 µGys-1 (about a fifteenth of the medical chest X-ray dose rate) are achieved from the simple and planar direct X-ray detector fabricated on an organic filter membrane. More importantly, these flat and simple devices are bendable and mechanically durable by exhibiting only 10% photocurrent degradation after 200 bending cycles. The novel heterostructure has great potential in large-area, flexible, and sensitive X-ray detection applications.

Cross-Link-Dependent Ionogel-Based Triboelectric Nanogenerators with Slippery and Antireflective Properties

Given the ability to convert various ambient unused mechanical energies into useful electricity, triboelectric nanogenerators (TENGs) are gaining interest since their inception. Recently, ionogel-based TENGs (I-TENGs) have attracted increasing attention because of their excellent thermal stability and adjustable ionic conductivity. However, previous studies on ionogels mainly pursued the device performance or applications under harsh conditions, whereas few have investigated the structure-property relationships of components to performance. The results indicate that the ionogel formulation-composed of a crosslinking monomer with an ionic liquid-affects the conductivity of the ionogel by modulating the cross-link density. In addition, the ratio of cross-linker to ionic liquid is important to ensure the formation of efficient charge channels, yet increasing ionic liquid content delivers diminishing returns. The ionogels are then used in I-TENGs to harvest water droplet energy and the performance is correlated to the ionogels structure-property relationships. Improvement of the energy harvesting is further explored by the introduction of surface polymer brushes on I-TENGs via a facile and universal method, which enhances droplet sliding by means of ideal surface contact angle hysteresis and improves its anti-reflective properties by employing the I-TENG as a surface covering for solar cells.

Flexible All-Inorganic Perovskite Photodetector with a Combined Soft-Hard Layer Produced by Ligand Cross-Linking

Although perovskite nanocrystals have attracted considerable interests as emerging semiconductors in optoelectronic devices, design and fabrication of a deformable structure with high stability and flexibility while meeting the charge transport requirements remain a huge challenge. Herein, a combined soft-hard strategy is demonstrated to fabricate intrinsically flexible all-inorganic perovskite layers for photodetection via ligand cross-linking. Perfluorodecyltrichlorosilane (FDTS) is employed as the capping ligand and passivating agent bound to the CsPbBr₃ surface via Pb-F and Br-F interactions. The SiCl head groups of FDTS are hydrolyzed to produce SiOH groups which subsequently condense to form the SiOSi network. The CsPbBr₃ @FDTS nanocrystals (NCs) are monodispersed cubes with an average particle size of 13.03 nm and exhibit excellent optical stability. Furthermore, the residual hydroxyl groups on the surface of the CsPbBr₃ @FDTS render the NCs tightly packed and cross-linked to each other to form a dense and elastic CsPbBr₃ @FDTS film with soft and hard components. The photodetector based on the flexible CsPbBr₃ @FDTS film exhibits outstanding mechanical flexibility and robust stability after 5000 bending cycles.