Dissolution behavior of calcium phosphate nanocrystals deposited on titanium alloy surfaces.

We have recently shown that a new implant surface design, achieved by the deposition of discrete nanocrystals of calcium phosphate on microtopographically complex titanium-based substrates, accelerates osteoconduction and also renders the implant surface bone bonding. Thus, we wished to examine the elution behavior of these calcium phosphate nanocrystals and their modulation in vivo. We first compared the total amount of calcium phosphate on these implants with that of plasma-sprayed implants, by measuring the eluted calcium using atomic absorption spectrophotometry. We then plotted their dissolution behavior in vitro as a function of pH relevant to physiological conditions. To assess their structural stability in vivo for periods of up to 1 month, we placed samples in diffusion chambers, implanted them in the abdominal cavity of rats, and examined their surfaces by scanning electron microscopy following retrieval. Our results show that these nanocrystals are stable at normal pH but, as expected, dissolve at acidic pH, and that they remain unchanged when exposed to body fluid in vivo for up to 1 month.