Surface potential modulation for improved mechanical energy harvesting and sensing in 3D printed biopolymer thermoelectret

This study presents the development of a special class of electret known as thermoelectret, made with polylactic acid (PLA), prepared via 3D printing technology followed by a heat-assisted corona discharged technique. We show that the bimodal surface polarity (i.e., ± 1 kV) is possible to achieve over the top and bottom surfaces of 3D printed PLA thermoelectret that enable a wide range of potential applications, such as mechanical energy harvesting to wearable biomedical sensors. Besides this, the enhanced surface potential leads to a giant longitudinal piezoelectric coefficient (d33) of 350 ± 15 pC/N, which is typically 10 times higher than the best-known piezoelectric polymer, polyvinylidene fluoride-trifluoro ethylene (PVDF-TrFE). To utilize this benefit, a 3D-printed thermoelectret-based mechanical energy harvester (3D-TEH) has been developed that delivers an outstanding power density of ⁓ 25 mW/m2, which makes it a suitable candidate for the self-power pressure sensor. As a proof of concept, we have demonstrated that 3D-TEH is capable of recording the bone-joints motions, coughing action, and human foot-pressure distribution that signify its potential application as a self-powered bio-medical sensor.