Increased solubility, and consequently dissolution rate, is one of the potential advantages of metastable phases. This advantage is negated if, during dissolution, the metastable to stable transformation rate >> dissolution rate. Glancing angle XRD enabled us to quantify and thereby profile phase transformations as a function of compact depth. The technique has potential utility in monitoring surface reactions, both chemical decomposition and physical transformations, in pharmaceutical systems.
Samples of dense aluminum oxide, dense, porons, and surface-oxidized titanium of varying surface roughness and containing long cylindrical channels 95-1000 p in diameter were implant,ed in viva in dog femurs for period9 of 2-8 weeks. The depth of ingrowth of calcified tissue into t,hese channels was det,ermined as a function of time, principally by electron microprobe.The most rapid bone ingrowth was obtained with NO-, 5 2 5 , and 1000-p diameter channels in all the titanium and aluminum oxide samples. However, the fraction of any given channel cross-section filled with bone was observed to decrease as the channel diameter increased. I n these channels, ingrowth depths of more than 2000 p were oft8en achieved in 4 weeks after which the rate of ingrowth levelled off somewhat. A certain degree of surface roughness (greater than 20 p in. a.a.) appeared to be necessary for fixation and ingrowth. Ingrowth of bone into the 95-p diameter channels was neglibile even after 18 weeks. The presence of interconnecting fine porosity per se, was found not essential for bone ingrowth nor does it have a major effect on ingrowlh kinetics.
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