Crystalline structure and its effects on the degradation of linear calcium polyphosphate bone substitute

Calcium polyphosphate (CPP) bone substitutes were prepared by gravity sintering crystal transformations. The crystalline structure of CPP was analyzed by Raman spectroscopy and in situ variable temperature XRD. In addition, the variation of CPP in SBF considering as degradation was characterized by monitoring the changes of its compressive strength and weight loss. The results revealed that CPP was inorganic condensed phosphate with linear long chain structure. Amorphous CPP (a-CPP) was initially transformed to crystalline gamma-CPP, then crystalline beta-CPP with the increase of sintering temperature. The transformation of gamma-CPP to beta-CPP occurred from 650 to 670 degrees C. Compressive strength decreased quickly at initial stage for all specimens after immersed in SBF, and thereafter, continued to decrease at a slower rate subsequently. After immersion for 15 and 30 days, the compressive strength of gamma-CPP decreased from 13.5 to 7.6 and 4.8 MPa, while beta-CPP decreased from 16 to 12 and 8 MPa, respectively. The degradation rate of a-CPP, gamma-CPP and beta-CPP decreased with time after immersed in SBF. a-CPP had highest degradation rate, which would have been completely degraded in 10 days, and the weight loss ratio of gamma-CPP was 28% for 15 days and 35% for 30 days, but the weight loss of beta-CPP was only 11% for 30 days. The results therefore revealed that CPPs with different degradation rates could be obtained by controlling crystalline structure. (C) 2008 Elsevier B. V. All rights reserved.