Bone-derived bioactive substrates promote axonal sprouting but elicit astrocyte reactivity: Implications for CNS-repair scaffold design.

Abstract

Mineralized bone is increasingly considered as a functional substrate for regenerative applications, yet its impact on neuron-glia remodeling remains insufficiently defined. We cultured ex vivo injured rat hippocampal tissue on glass coverslips either uncoated or coated with micron-scale mouse skull bone particles and quantified neurite architecture and astrocyte morphology. Bone-particle substrates supported robust adhesion and selectively modulated process development. Axons on bone displayed a 2.8-fold increase in varicosity-like expansion size and 2.2-fold higher neurofilament-M expression relative to glass, indicating potentiated axonal sprouting. In contrast, dendrites exhibited 20% shorter mean length and 73% lower branching. Astrocytes on bone showed 21% shorter processes with 34% fewer processes per cell; total cell area and GFAP levels were unchanged. However, astrocytes displayed increased circularity, decreased roundness, and elevated solidity-morphologies consistent with a reactive, potentially chronic, state. Together, these data identify mineralized bone as a bioactive osseous substrate that enhances axonogenesis while biasing astrocytes toward reactivity. This divergence suggests design trade-offs for osseous or mineral-hybrid scaffolds aimed at central nervous system repair. Our findings provide quantitative guidance for engineering bone-derived or mineral-composite scaffolds that differentially control neuronal and glial outcomes in neural repair strategies.