Behavior of dense and porous hydroxyapatite implants and tissue response in rat femoral defects.

Porous and dense hydroxyapatite cylinders (PHA and DHA) were implanted into cavities produced in rat femora and the sites of implantation were examined at different times over a period of 24 weeks by microradiologic and histological techniques. Microradiographs showed the presence of a layer of trabecular bone around the implants, which became more radiopaque and thinner along the experimental time. The microradiologic methodology used was suitable for the evaluation of the interface between hydroxyapatite and newly formed bone in nondecalcified materials. Microscopic observations showed that young bone grew over the surface of both types of implants after 1 and 2 weeks of surgery and that bone also grew inside PHA implants. Progressive bone absorption was observed in both types of implants after the fourth week. A layer of fibrous tissue was formed in the interface between new bone and DHA. Mature bone with haversian systems surrounded DHA implants and filled the pores of PHA implants throughout the experimental period. The pores of PHA implants were smaller than those commonly reported, which should have been a disadvantage, although it was observed that the extra cellular fluid induced disintegration of the ceramic granules, allowing the gradual growth of bone tissue into the spaces among them, without the interposition of fibrous tissue.

Interface potential of calcium phosphate in simulated body fluid.

Calcium phosphate ceramics are used in the substitution of injured or damaged bones. Nevertheless, the behaviour of these materials, and in particular, the mechanisms guiding their interface response in physiological environment is still unknown. This work describes the construction of hydroxyapatite and tricalcium phosphate electrodes used to determine the interface potential behaviour of these materials in a simulated body fluid, in a pH range corresponding to the variation observed in human body injuries, at ambient and physiological temperatures. These measurements are associated with the adsorption/desorption of ions from the materials. The results show that hydroxyapatite and tricalcium phosphate have similar behaviour in that they reach an interface potential equilibrium state faster when the solution pH is decreased and the temperature increased. This behaviour may be attributed to their ability to form a calcium-rich layer and is relevant to their quality as implantable materials.