Novel hydroxyapatite ceramics with an interconnective porous structure exhibit superior osteoconduction in vivo

Calcium hydroxyapatite ceramics (CHA) are nontoxic materials, provoke littl e reaction from tissues, and by virtue of these properties represent a good starting point for creating bone substitutes. Although several porous CHAs have been used clinically, there have been few reports that CHA is fully r eplaced by newly formed bone, which may be due to its structure and the lim ited connectivity between pores. We recently developed a fully interconnect ed porous CHA (IP-CHA) by adopting a "foam-gel" technique. Structural analy sis by scanning electron microscopy revealed that IP-CHA had spherical pore s of uniform size that were interconnected by window-like holes. The surfac e of the wall structure was smooth, and hydroxyapatite particles were bound tightly to one another. Most of the interpore connections of IP-CHA ranged from 10 to 80 mum in diameter (average, 40 mum). When the cylindrical IP-C HA (diameter, 6 mm; height, 15 mm) was implanted into a rabbit femoral cond yle, bone, and bone marrow with abundant vessels formed deep in the pores t hrough the interpore connections. Within a period of 6 weeks, new bone had formed and penetrated to a distance of 3 mm from the surface of the IP-CHA implant. Furthermore, a compression test at 9 weeks revealed that the impla nted IP-CHA steadily increased in strength to more than double the value of the initial test. These results indicate that the IP-CHA may have clinical utility as a superior bone substitute. (C) 2001 John Wiley & Sons, Inc.