The repair of bone defects with biomaterials depends on a sufficient vascularization of the implantation site. We analyzed the effect of pore size on the vascularization and osseointegration of biphasic calcium phosphate particles, which were implanted into critical-sized cranial defects in Balb/c mice. Dense particles and particles with pore sizes in the ranges 40-70, 70-140, 140-210, and 210-280 microm were tested (n = 6 animals per group). Angiogenesis, vascularization, and leukocyte-endothelium interactions were monitored for 28 days by intravital microscopy. The formation of new bone and the bone-interface contact (BIC) were determined histomorphometrically. Twenty-eight days after implantation, the functional capillary density was significantly higher with ceramic particles whose pore sizes exceeded 140 microm [140-210 microm: 6.6 (+/-0.8) mm/mm(2); 210-280 microm: 7.3 (+/-0.6) mm/mm(2)] than with those whose pore sizes were lesser than 140 microm [40-70 microm: 5.3 (+/-0.4) mm/mm(2); 70-140 microm: 5.6 (+/-0.3) mm/mm(2)] or with dense particles [5.7 (+/-0.8) mm/mm(2)]. The volume of newly-formed bone deposited within the implants increased as the pore size increased [40-70 microm: 0.07 (+/-0.02) mm(3); 70-140 microm: 0.10 (+/-0.06) mm(3); 140-210 microm: 0.13 (+/-0.05) mm(3); 210-280 microm: 0.15 (+/-0.06) mm(3)]. Similar results were observed for the BIC. The data demonstrates pore size to be a critical parameter governing the dynamic processes of vascularization and osseointegration of bone substitutes.

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Titanium alloy implants were precoated biomimetically with a thin and dense layer of calcium phosphate and then incubated either in a supersaturated solution of calcium phosphate or in phosphate-buffered saline, each containing bovine serum albumin (BSA) at various concentrations, under physiological conditions for 48 h. Coated implants then underwent scanning electron microscopy, immunohistochemical evaluation, Fourier transform infrared spectroscopy, and X-ray diffraction. The quantity of BSA taken up by coatings and the kinetics of protein release were monitored colorimetrically. In coatings prepared by the coprecipitation of calcium phosphate and BSA, protein had become incorporated into the mineral crystal latticework. With increasing BSA concentration, matrices decreased in thickness, became more dense, showed lower crystallinity, and underwent a change in crystal geometry. The octacalcium phosphate structure manifested in the absence of protein was gradually transformed into a carbonated apatite form. Preformed mineral coatings became only superficially mantled with a layer of BSA, and the morphology of the mineral matrices themselves remained unchanged. At equivalent protein concentrations, coatings prepared by the coprecipitation of calcium phosphate released only a minute fraction of its protein component under physiological conditions, whereas preformed mineral matrices showed a "burst" release of their associated protein within a single 2-h period. The biomimetic coating can be a carrier for osteoinductive agents.