Materials Design and Osteoinduction Characteristics of Biomimetic and Functionally Graded Apatites

Abstract

Bioabsorbable and functionally graded apatites (fg-HAp) were designed using bovine bone by the calcination and partial dissolution-precipitation methods. The fg-HAp ceramics had the specified surface structure and pore size distribution derived from living body. The pore structure of the ceramics with specific surface areas of 30-40 m 2 ¥g -1 and porosities of 60-80 % was divided into a macro-pore originating from spongy bone and a micro-pore related to body fluid permeation and blood permeability. Recombinant human bone morphogenetic protein-2 (rhBMP-2) solution was added to fg-HAp ceramics to obtain rhBMP-2-loaded fg- HAp (rhBMP-2/fg-HAp) ceramics exhibiting osteoinduction. The fg-HAp and rhBMP-2/fg-HAp ceramics were implanted to the subcutaneous tissue of rats. At 4 weeks after the implantation, for the fg-HAp, body fluid and albumin permeated the bulk region of the ceramics through the micro-pores, and surface- and bulk-degradations of the HAp grains proceeded. At 12 weeks, the fg-HAp ceramics were completely biodegraded and bioabsorbed. For the rhBMP-2/ fg-HAp, at 4 weeks after the implantation, some pieces of fg-HAp were incorporated into the induced bone and fatty marrow, suggesting that osteoinduction occurred in conjunction with bone remodeling. The rhBMP-2/fg-HAp ceramics would be newly biomimetic materials with excellent blood permeability and osteoinduction.