Biodegradable piezoelectric PHB-BT nanofiber scaffolds combined with ultrasound stimulation to accelerate bone regeneration by regulating Ca ²⁺ /CaN/NFAT

<b>Rationale:</b> Bone defects pose a persistent challenge in orthopedic medicine due to their limited self-repair capacity. Although guided bone regeneration scaffolds have shown therapeutic potential, their clinical efficacy remains constrained by their suboptimal osteoinductive capability. <b>Methods:</b> Herein, we developed biodegradable piezoelectric polyhydroxybutyrate-barium titanate (PHB-BT) nanofiber scaffolds capable of generating synergistic piezoelectric stimulation for bone repair when integrated with low-intensity pulsed ultrasound (LIPUS). <b>Results:</b> Compared with conventional PHB scaffolds, ​PHB-BT nanofiber scaffolds​ ​showed enhanced piezoelectric properties​ and ​excellent biocompatibility, ​thereby facilitating​ sustained osteogenic activity. ​<i>In vitro</i>​ studies revealed that these scaffolds ​significantly promoted​ the osteogenic differentiation of bone marrow mesenchymal stem cells under LIPUS stimulation. ​Notably, ​<i>in vivo</i>​ evaluations ​demonstrated​ that these scaffolds ​substantially accelerated bone defect repair​, with complete scaffold degradation observed after eight weeks. Mechanistically, PHB-BT nanofibers improved osteogenesis via activating the Ca²⁺/calcineurin/nuclear factor of activated T-cells signaling pathway in response to ultrasound stimulation. <b>Conclusions:</b> These findings have significant implications for the design of next-generation, implantable electrical stimulators capable of providing sustained electromechanical cues for personalized bone tissue engineering applications.