Piezoelectricity in chalcogenide perovskites.

Piezoelectric materials show potential to harvest the ubiquitous, abundant, and renewable energy associated with mechanical vibrations. However, the best performing piezoelectric materials typically contain lead which is a carcinogen. Such lead-containing materials are hazardous and are being increasingly curtailed by environmental regulations. In this study, we report that the lead-free chalcogenide perovskite family of materials exhibits piezoelectricity. First-principles calculations indicate that even though these materials are centrosymmetric, they are readily polarizable when deformed. The reason for this is shown to be a loosely packed unit cell, containing a significant volume of vacant space. This allows for an extended displacement of the ions, enabling symmetry reduction, and resulting in an enhanced displacement-mediated dipole moment. Piezoresponse force microscopy performed on BaZrS3 confirmed that the material is piezoelectric. Composites of BaZrS3 particles dispersed in polycaprolactone were developed to harvest energy from human body motion for the purposes of powering electrochemical and electronic devices.

Centrifugally spun alginate-poly(lactic acid) microbeads: A promising carrier for drug delivery and tissue engineering.

A facile and high yield centrifugal spinning technique known as Forcespinning® (FS) was used to develop unique microstructures consisting of PLA microbeads along alginate fibers. Morphological variation and structural features appeared in the field-emission scanning electron micrographs for the PLA-alginate composites and dried PLA-alginate films from precursor emulsions at constant PLA and varied alginate contents. Shrunk and deflated microbeads were observed for composites whilst spherical beads were evident for the PLA control. Furthermore, PLA was found surrounding the alginate when the alginate was present at 0.24 wt% or lower, while alginate (mushroom-like structures), were seen protruding through the PLA layer at ≥0.34 wt% alginate. Rheological characterization of the composite emulsions revealed that the filler (alginate) provided shear thinning properties including pseudoplasticity, desirable for printing and other related applications in contrast to the Newtonian flow shown by the PLA control. Along with infra-red spectroscopy, the nanocomposites were further characterized using thermal gravimetry and differential scanning calorimetry featuring reversible events influenced by heat capacity and irreversible kinetic/thermodynamic counterparts. The work provides a comprehensive investigation of biocompatible networks of PLA-alginate microbeads embedded in nano-sized fibers and the prospective application of these microbeads as a drug delivery system.

Nanofiber-Based Substrate for a Triboelectric Nanogenerator: High-Performance Flexible Energy Fiber Mats.

Flexible and stretchable triboelectric nanogenerators (TENGs) are the next-generation systems for wearable and portable electronics. In this study, we have demonstrated an all nanofiber-based TENG for energy harvesting and biomechanical sensing applications. The TENG was prepared using the Forcespinning (FS) method to produce poly(vinylidene fluoride) (PVDF) and thermoplastic polyurethane (TPU) nanofiber (NF) membranes. The TPU nanofiber membranes were interfaced with a homogeneously sputtered gold nanofilm. The experimental characterization of the PVDF-TPU/Au NF-TENG revealed that surface interfaced with dispersed gold in a TPU fiber membrane produced a maximum open-circuit voltage of 254 V and a short-circuit current of 86 µA output at a 240 bpm load frequency, which was, respectively, 112 and 87% greater than bare PVDF-TPU NF-based TENG. All systems were composed of an active contact surface area of 3.2 × 2.5 cm2. Furthermore, the TENG was able to light up 75 LEDs (1.5 V of each) by the hand-tapping motion. The resistive load and capacitor test results exemplified a TENG offering a simple and high-performance self-chargeable device. Furthermore, we have tested the TENG's response for biomechanical movements at different frequencies, suggesting the TENG's potential to be also used as a cost-effective self-powered flexible body motion sensor.