In situ precipitation of amorphous calcium phosphate nanoparticles within 3D porous collagen sponges for bone tissue engineering.

Amorphous calcium phosphate (ACP) plays an important role in biomineralization within the three-dimensional (3D) collagen network in human hard tissues, and exhibits osteoconductivity. Porous collagen sponges coated with ACP nanoparticles could be considered as potential scaffolds for use in bone tissue engineering. In this study, such composite materials were fabricated via homogeneous ACP precipitation using a supersaturated calcium phosphate (CaP) solution. Homogeneous ACP precipitation was induced in situ within the sponges by a temperature-controlled coating process composed of two steps. In the first step, the CaP solution was cooled to 4 °C to suppress precipitation until the solution penetrated fully into the sponge's internal pores. In the second step, the CaP solution was warmed up to 25 °C with continuous shaking to induce ACP precipitation within the sponges. The resulting sponges were therefore coated with ACP nanoparticles on their inner and outer surfaces. A simulated body fluid (SBF) test indicated osteoconductivity of the collagen sponges coated with ACP nanoparticles. Further, ACP-coated collagen sponges immobilizing basic fibroblast growth factor (bFGF) were fabricated using the CaP solution supplemented with bFGF. The fabricated sponges allowed the sustained release of bFGF in a culture medium and enhanced proliferation of osteoblastic MC3T3-E1 cells. Such ACP-coated collagen sponges have the potential to be used as scaffolds in bone tissue engineering if pursued for further in vitro and in vivo studies.