Development of superporous hydroxyapatites and their examination with a culture of primary rat osteoblasts.

When the usage of hydroxyapatite (HAp) was first approved at clinics by the Kouseishou (Japanese FDA) as a bone substitute (APACERAM), the upper limit of pore content was set at 60%. Cells play an important role in bone repair, especially in regeneration therapy, but on using these HAps, the cells cannot penetrate deeply into them because their inside pores rarely connect. To promote cell penetration into the inside of the HAps, we have developed superporous HAps (HAp-Ss). First, phosphoric acid was added to a calcium hydroxide solution, and the mixture was dried by the spray-dry method to produce fine primary particles. Then, two kinds of surfactants were used to form a large amount of pores. These two HAp-Ss have 85% porosity and interconnected pores in the inside. They were tested with a culture of primary rat osteoblasts, which showed good penetration therein. The penetrated osteoblasts maintained high alkaline phosphatase activity during the culture period. This indicates that the developed HAp-Ss are very good bone substitutes and also useful scaffolds in bone regeneration therapy.