In-situ electret scaffolds with controllable electric fields printed by MEW for bone tissue regeneration

•In-situ electret scaffolds with adjustable electric field were fabricated.•Explain and prove the effect of electrical stimulation on cells and particles.•Verify the effect of electrical stimulation on promoting bone differentiation in vitro.•Clarify that electrical stimulation can improve the immune micro-environment.•Verify the osteogenic effect of the scaffolds in vivo and explore its mechanism. Physiologically relevant electrical microenvironments play an integral role in manipulating bone metabolism. Although implanted biomaterials using conductive or piezoelectric materials to mimic natural tissue electrical properties have been introduced into the field of bone regeneration, the use of electret materials to provide stable and durable electrical stimulation has rarely been studied in biomaterial design. In this study, the ZnO/PCL composite scaffolds with in-situ electret were fabricated using melt electro-writing to explore its efficacy in bone regeneration. By adjusting the electret concentration, the surface potential of the composite scaffolds could be tuned to the biopotential for promoting bone regeneration, and the prepared scaffolds exhibited good electrical stability over an observation period of up to 42 days. In vitro biological experiments showed that the in-situ electret scaffolds promoted the cell viability and osteogenic differentiation of mesenchymal stem cells. At the same time, the in-situ electret composite scaffolds can induce the phenotype transformation of RAW 264.7 cells from M1 to M2, creating a favorable microenvironment for bone tissue regeneration. The composite scaffolds significantly promoted bone regeneration in vivo through sustained endogenous electrical stimulation. These findings suggest that the in-situ electret scaffolds that maintain a stable and physiological electrical microenvironment are promising candidates for enhanced bone regeneration.