Solid titration was used to explore the solubility isotherms of partially (Srx-HAp, x=1, 5, 10, 40, 60 mol.%) and fully substituted strontium hydroxyapatite (Sr-HAp). Solubility increased with increasing strontium content. No phase other than strontium-substituted HAp, corresponding to the original titrant, was detected in the solid present at equilibrium; in particular, dicalcium hydrogen phosphate was not detected at low pH. The increase in solubility with strontium content is interpreted as a destabilization of the crystal structure by the larger strontium ion. Carbonated HAp was formed in simulated body fluid containing carbonate on seeding with Sr10-HAp, but the precipitate was strontium-substituted on seeding with Sr-HAp. Strontium-substituted HAp might be usable as a template for the growth of new bone, since nucleation appears to be facilitated.
The purpose of this study was to investigate the in vivo bone response to the strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement injected into the cancellous bone. Sr-HA cement was injected into the iliac crest of rabbits for 1, 3, and 6 months. Active bone formation and remodeling were observed after 1 month. Newly formed bone was observed to grow onto the bone cement after 3 months. Thick osteoid layer with osteoblasts formed along the bone and guided over the bone cement surface reflected the stimulating effect of Sr-HA. From scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis, high calcium and phosphorus levels were detected at the interface with a thick layer of 70 microm in width, and fusion of Sr-HA with the bone was observed. Blood vessels were found developing in remodeling sites. The affinity of bone on Sr-HA cement was increased from 73.55 +/- 3.50% after 3 months up to 85.15 +/- 2.74% after 6 months (p < 0.01). In contrast to Sr-HA cement, poly(methyl methacrylate) (PMMA) bone cement was neither osteoconductive nor bioresorbable. Results show that the Sr-HA cement is biocompatible and osteoconductive, which is suitable for use in treating osteoporotic vertebral fractures.
The purpose of this study was to evaluate the strontium-containing hydroxyapatite (Sr-HA) cement in primary hip replacement, using a rabbit model, and to investigate the histological findings at the cement-implant and bone-cement interfaces under weight-bearing conditions. Unilateral hip replacement was performed with Sr-HA cement or polymethylmethacrylate (PMMA) cement in rabbits and observations were made after 6 months. Good fixation between the Sr-HA cement and implant was observed. Osseointegration of the Sr-HA cement with cancellous bone was widespread. Many multinucleus cells covered the surface of the cement, and resorbed the superficial layer of the cement. By scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis, high calcium and phosphorus levels were detected at the interface with a thickness of about 10 microm. Intimate contact was also observed between the Sr-HA cement and cortical bone without fibrous layer intervening. The overall affinity index of bone on Sr-HA cement was (85.06 +/- 5.40)%, which is significantly higher than that on PMMA cement (2.77%+/- 0.49%). On the contrary, a fibrous layer was consistently observed between PMMA cement and bone, and PMMA cement evoked an inflammatory response and foreign body reaction in the surrounding bony tissues. Results suggested good bioactivity and bone-bonding ability of the Sr-HA cement under weight-bearing conditions.
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