Multimodal extracellular osteogenic microenvironment orchestrating with piezoelectric collagen fibrils for promoting bone regeneration.

Bone defects, especially critical-sized bone defects, still remain a major challenge due to limited intrinsic regenerative capacity. Limitations in biomimetic structure and functional performance in existing bone repair materials motivate the development of multifunctional osteogenic scaffolds. Herein, hierarchical topological nanofibrous mats (HTNFMs) functionalized with triple-helical piezoelectric collagen fibrils (PECFs, d33 = 9.92 pm V-1) were fabricated, with gradient PECF loadings of 5, 10, and 20 wt‰. Quantitative cellular assays verify that the 10 wt‰ PECF-modified group (HTNFM-10) achieves the optimal osteogenic performance, with alkaline phosphatase activity and extracellular mineral deposition reaching 1.82-fold and 2.16-fold of pure polycaprolactone (PCL) substrates, respectively. This unique structural design enables HTNFMs to create a multimodal extracellular osteogenic microenvironment with synergistic structural, mechanical, and electrical cues. Benefiting from their intrinsic piezoelectricity, HTNFMs can effectively convert endogenous cell traction forces and physiological external mechanical stimuli into bioelectric signals in situ, independent of external power sources, while providing biomimetic mechanical support for cell adhesion and tissue regeneration. The synergistic regulation of multiple microenvironmental cues significantly promotes osteogenic differentiation of bone marrow mesenchymal stem cells in vitro and accelerates bone regeneration in vivo. Furthermore, transcriptomic analysis revealed that the multimodal extracellular osteogenic microenvironment constructed by HTNFMs activates intracellular calcium signaling cascades to mediate the upregulation of osteogenic-related genes. This work proposes a self-stimulating novel piezoelectric biomimetic design strategy and validates HTNFMs as a promising platform for complex bone defect repair.