Designing a highly bioactive 3D bone-regenerative scaffold by surface immobilization of nano-hydroxyapatite

A novel approach to the fabrication of porous scaffolds with surface-immobilized nano-hydroxyapatite (N-HAp) is developed for effective bone tissue engineering. The discrete nano-level anchoring of N-HAp on the pore surface of chitosan scaffolds is achieved using surface-repellent stable colloidal N-HAp with surface phosphate functionality. Field-emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) confirm pronounced exposure of N-HAp on the surfaces of chitosan scaffolds at the nano-level, which can not be accomplished with the conventional polymer/N-HAp composite scaffolds. This rational surface engineering enables surface-anchored N-HAp to express its overall intrinsic bioactivity, since N-HAp is not phase-mixed with the polymers. The porous chitosan scaffolds with surface-immobilized N-HAp provide more favorable environments than conventional bulk phase-mixed chitosan/N-HAp scaffolds in terms of cellular interaction and growth. In vitro biological evaluation using alkaline phosphatase activity assay supports that immobilized N-HAp on pore surfaces of chitosan scaffolds contributed to the more enhanced in vitro osteogenic potential. In addition, scaffolds with surface-exposed N-HAp provide favorable environments for enhanced in vivo bone tissue growth, estimated by characteristic biomarkers of bone formation such as collagen. The results suggest that the newly developed hybrid scaffolds with surface-immobilized N-HAp may serve as useful 3D substrates with pore surfaces featuring excellent bone tissue-regenerative properties.