Mechanical energy conversion based on the piezoelectric principle has received significant attention due to its promising applications in sustainable power supply systems and sensor technology. Ferroelectric poly(vinylidene fluoride) (PVDF) combines the advantages of both good electromechanical coupling and easy processability, yet its low piezoelectric coefficient limits its output performance and it thus cannot meet the increasing requirements for power generation and sensing. Here, inorganic metal halide perovskite CsPbBr3 (CPB) nanoparticles are incorporated into PVDF fibers via an electrospinning technique, where an in situ crystallization and growth process of the CPB nanoparticles is established. Both the CPB nanoparticles and PVDF fibers are poled by the electric field during the electrospinning process, which promotes the formation of the polar phase of PVDF and distortion of the CPB lattice, resulting in greatly enhanced piezoelectric performance for the CPB/PVDF composites. The output performance under the external force of a flexible generator developed from electrospun CPB/PVDF films is significantly enhanced compared with the neat PVDF film, with an 8.4 times higher maximum open circuit voltage value. Furthermore, the measurements on the microscopic piezoelectric responses unambiguously reveal that the increased polar phase mainly contributes to the enhanced electromechanical coupling. The functions of the CPB/PVDF films as physiological signal monitoring sensors are determined and they demonstrate their potential applications as flexible piezoelectric generators and electronics for wearable health monitoring.
Additive manufacturing is an arising technology for soft materials and structures with improved complexity and functionality and has gradually become widespread in various fields, including soft robotics, flexible electronics and biomedical devices. Along with the development of material systems and fabrication techniques, mechanical design principles for additive manufactured soft materials have been greatly developed and evolved in recent years and some unique issues that are distinct from conventional manufacturing techniques have emerged. In this short review, we mainly focus on additive manufactured soft materials that are in significant need of mechanical models/simulations to provide design guidelines; therefore, topics such as soft robotics and electronics are not considered here. We first discuss the mechanical design methods for controlling shape distortions and interfacial strength, as they are directly related to the quality and reliability of additive manufactured soft materials. Design principles and manufacturing strategies for bioinspired composites, which represent a large part of current research on additive manufactured soft materials, are then summarized integrally with regards to three aspects. In addition, basic mechanical considerations for additive manufactured four-dimensional shape-changing structures are explained, together with a review of the recent theories and numerical approaches. Finally, suggestions and perspectives are given for future developments in soft material additive manufacturing.
Due to considerable progress in DNA nanotechnology, DNA is gaining significant attention as a programmable building block for the next generation of soft biomaterials. DNA has been used as either a single component to form all-DNA hydrogels or a crosslinker or functional entity to form hybrid DNA hydrogels through physical interactions or chemical reactions. The formed hydrogels exhibit adequate biocompatibility, convenient programmability, tunable multifunctionality and the capability of precise molecular recognition, making them an irreplaceable polymeric platform for interfacing with biology. Responsive DNA hydrogels that are prepared through the hybridization of DNA sticky ends, the formation of i-motifs, enzymatic ligation and enzymatic polymerization are commonly reported nowadays and can undergo disassembly induced by various triggers, including alterations in ionic strength, pH, temperature and biomolecules. These hydrogels are envisioned for applications in drug delivery and biosensing. This perspective assesses the most recent and important developments in this emerging class of biomedically useful DNA hydrogels.