Comprehensive biocompatibility of nontoxic and high-output flexible energy harvester using lead-free piezoceramic thin film

Flexible piezoelectric energy harvesters have been regarded as an overarchingcandidate for achieving self-powered electronic systems for environmental sensors andbiomedical devicesusing the self-sufficient electrical energy. In this research, we realize a flexiblehigh-output and lead-free piezoelectric energy harvester by using the aerosol deposition methodand the laser lift-off process. We also investigated the comprehensive biocompatibility of thelead-free piezoceramic device using ex-vivo ionic elusion and invivo bioimplantation, as well as in vitrocell proliferationand histologic inspection. The fabricated LiNbO3-doped (K,Na)NbO3(KNN) thin film-based flexible energy harvester exhibited an outstanding piezoresponse,and average output performance of an open-circuit voltage of ∼130 V and a short-circuitcurrent of ∼1.3 μAunder normal bending and release deformation, which is thebest record among previously reported flexible lead-free piezoelectric energyharvesters. Although both the KNN and Pb(Zr,Ti)O3(PZT)devices showedshort-term biocompatibility in cellular and histological studies, excessivePb toxic ionswere eluted from the PZT in human serum and tap water. Moreover, the KNN-based flexibleenergy harvester was implanted into a porcine chest and generated up to ∼5 V and 700 nAfrom the heartbeat motion, comparable to the output of previously reported lead-basedflexible energy harvesters. This work can compellingly serve to advance the development ofpiezoelectric energy harvesting for actual and practical biocompatible self-poweredbiomedical applications beyond restrictions of lead-based materials in long-termphysiological and clinical aspects