Ultrastructural study of mineralization of a strontium-containing hydroxyapatite (Sr-HA) cement in vivo

The purpose of this study was to investigate the mineralization leading to osseointegration of strontium‐containing hydroxyapatite (Sr‐HA) bioactive bone cement injected into cancellous bone in vivo. Sr‐HA cement was injected into the ilium of rabbits for 1, 3, and 6 months. The bone mineralization area was found to be largest at 3 months, then at 1 month, and smallest at 6 months (p < 0.01) measured with tetracycline labeling. Osseointegration of Sr‐HA cement was achieved at 3 months as observed by scanning electron microscopy. A high calcium and phosphorus area was observed at the interface of bone–Sr‐HA cement determined by energy‐dispersive X‐ray analysis. Transmission electron microscopy gave evidence of the mechanism of bone formation. Dissolution of Sr‐HA into debris by the bone remodeling process was thought to increase the concentration of calcium and phosphorus at the interface of bone–Sr‐HA cement and stimulate bone formation. Crystalline Sr‐HA formed an amorphous layer and dissolved into the surrounding solution, then apatite crystallites were precipitated and formed new bone at 3 months. This young bone then becomes mature bone, which bonds tightly to the Sr‐HA cement with collagen fibers inserted perpendicularly after 6 months. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 70A: 428–435, 2004