Silk Fibroin Improves the Release of Nerve Growth Factor from Hydroxyapatite Particles Maintaining its Bioactivity

Background: Hydroxyapatite (HA) was emerging as the most promising biomaterial owing to its excellent bioactivity, biocompatibility, and high compressive strength for segmental bone defects. However, due to the lack of synergistic signals of osteogenic cells or growth factors, attempts concerning HA have not achieved an ideal therapeutical effect. Objective: This work was intended to combine HA particles with nerve growth factor (NGF) to co-accelerate the bone repair. Method: To deal with the strong absorption on HA particles and short half-life of exogenous NGF, bovine serum albumin (BSA) and silk fibroin (SF) were introduced. Result: Protected with SF, maximum release rate was 49.8% at 48 h for 2 mg/ml SF used group while the release rate was less than 5% without SF. PC-12 cells cultured in the NGF release fluid quit proliferation and differentiated to neural phenotype, and approximately 9.5% of NGF loading released from the particles within 48 h. Conclusion: Protected with BSA, in vitro release showed no obvious effect on strong absorption for the surface of HA particles, however, the drug loading of model protein decreased. Fortunately, SF demonstrated the capacity of adjusting the release profile of protein by varying the amount of SF embedded with no influence on drug loading and maintaining the bioactivity of NGF absorbed on HA particles.