One Year Chemical Degradation of HA/TCP Scaffolds for Bone Regeneration

Methods: Scaffolds of HA and/or TCP were chemically synthesized to ensure homogenous distribution of the two phases. Porosity was 90% with interconnected pores of 100-500 microns in diameter. The HA/TCP ratios varied from 100/0, 80/20, 60/40, 20/80 to 0/100. From the 5 HA/TCP materials tested 10 samples of each were weighted and suspended with 7 ml tris-buffer solution (10 mmol tris-(hydroxy-methyl)aminomethan, 150 mmol sodiumchloride, pH 7.4) in 15 ml PP screw cap vials. The vials were shaken in an incubator at 37 °C with an overhead-mixer for 15 minutes at 30 rpm every 6 hours. Buffer solutions were exchanged after 1, 4, 7, 14, 21 and so forth days. The elements P and Ca were analysed using an ICP-OES spectrometer (PE 4300DV). The amount of released P was converted into PO₄. Mean values and standard deviations were calculated as a function of time.

Results: The in vitro degradation rate is depending on the HA/TCP ratio, with a higher degradation rate the lower the HA content. The substance loss after 1 year of chemical degradation varied between 0.3% (HA/TCP=100/0), 1.2% (HA/TCP=80/20), 1.3% (HA/TCP=60/40), 1.4% (HA/TCP=20/80) and 2.5% (HA/TCP=0/100).

Conclusion: The HA/TCP ratio had an influence on the chemical degradation. Because of the slow chemical degradation rate of HA preventing excessive resorption, the augmentate volume is maintained providing mechanical stability. Through the selection of suitable HA/TCP mixtures the chemical degradation can be adapted to the clinical indication.