Geometric Effect of Matrix upon Cell Differentiation: BMP-Induced Osteogenesis Using a New Bioglass with a Feasible Structure

Abstract

A new biocompatible glass, which is composed of CaO, P₂O₅, SiO₂, and Al₂O₃ (abbreviated CPSA) and is characterized by higher elasticity than previous bioglass products, was molded into fibers with a diameter of 9μm. With CPSA fibers, two geometrically different structures, balls and bundles (each 20mg in weight), were prepared, combined with 2.2μg of rhBMP-2 (a gift from Yamanouchi Co., Japan) and implanted subcutaneously into rats. The histology showed remarkably higher bone formation in the ball-CPSA/BMP at 2 and 4 weeks than in the bundle-CPSA/BMP. The ball-CPSABMP showed 10 times higher alkaline phosphatase (ALP) activity at the second week and 5 times higher osteocalcin content at the fourth week than the bundle-CPSA/BMP. Vascular development in the implants was evaluated by mRNA expression of Flt-1 and KDR, two receptors for vascular endothelial growth factor (VEGF). Both receptors showed higher expression in the case of the ball, while they were not detected in the bundle. It is concluded that the BMP-induced bone formation depends highly upon the porous vasculature-inducing geometry of the matrix, which can be constructed with the new CPSA fibers.