Hybrid lead-free polymer-based nanocomposites with improved piezoelectric response for biomedical energy-harvesting applications: A review

Lead-free alternative materials for converting mechanical energy into electrical energy through piezoelectric transduction are of significant value in a diverse range of technological applications. This review describes novel approaches to the fabrication of hybrid piezoelectric polymer-based materials with enhanced piezoelectric responses for biomedical energy-harvesting applications. The most promising routes toward significant improvements in the piezoelectric response and energy-harvesting performance of such materials are discussed. Background information, including definitions of increases in the piezoelectric charge coefficients, generated open circuit voltage, short circuit current, and power density are presented. The effects of the presence of various lead-free components in the structure of the piezoelectric polymers on their piezoresponse or energy-harvesting performance are reviewed. The piezocomposites described are mostly based on poly-(vinylidene fluoride) (PVDF), or its copolymer, poly-(vinylidene fluoride)-trifluoroethylene PVDF-TrFE, loaded with various nanofillers such as reduced graphene oxide (rGO), inorganic compounds (nanoparticles such as barium titanate BaTiO3, and potassium sodium niobate (KNaNbO3)), salts (LaCl3, ErCl3, GdCl3, etc), metal oxides (ZnO, MgO, TiO2), metallic nanoparticles (Ag, Pt), and carbon nanotubes (CNTs). Non-biodegradable hybrid piezocomposites developed with potential or actually demonstrated applications in biomedical devices and sensors, including implantable nanogenerators and stimulatory materials for wound healing and tissue regeneration form the focus of the current research. Based on a literature survey, it is concluded that novel piezoelectric material systems and device architectures can support the development of flexible, self-powered, multifunctional e-skin for detecting of the rate of motion in humans, for degrading many kinds of organic pollutants, and for sterilizing bacteria on its surface. Various implantable devices that require no external energy input for biomedical energy-harvesting or bone defect repair applications in vivo, as well as sensors or detectors for human motion, health monitoring, independent temperature monitoring, and pressure control that can be prepared based on piezoelectric polymer materials are also discussed.