The rhBMP-2 release experiment showed that the degree of osteoinductivity is difficult to ascertain because less than 20 % of the total rhBMP-2 in the composite was released after seven days. While both of the components in the composite used in this study could act as carriers of rhBMP-2, the β-TCP microspheres are considered to have combined more strongly with rhBMP-2. Because the rhBMP-2 release was relatively small in this study, when compared to rhBMP-2 release kinetics using a hyaluronic acid-based hydrogel which were previously reported [32, 33]. Moreover, the authors have observed that the rhBMP-2 release pattern of the β-TCP microsphere in the present data seemed similar to the pattern in our previous unpublished data. Thus, this indicates that β-TCP binds more strongly with rhBMP-2 and β-TCP is the rate limiting step of the rhBMP-2 kinetic release.