Studies On Crystal Morphology Transformation, In Vitro Degradation And Cellular Biocompatibility Of Porous Calcium Polyphosphate Scaffolds For Bone Substitute Applications

The research on bone substitute materials is one of the most attractive aspects of biomaterials. Composite materials and new bone substitute are widely researched because of the defects of traditional bone substitute materials. Porous calcium polyphospahte (CPP) scaffolds, which has good mechanical property and suitable biodegradation, is one of the new kind of bone substitute materials. A great number of experiments in vivo and in vitro have confirmed the potential of CPP as a bone substitute.Firstly, study on preparation and characterization of CPP frit were carried out. According to TG data, CPP was synthesized at 500℃. Chemical structure and average chain length were determined by IR and 3IPNMR. Results showed that CPP had a long chain structure and average chain length was about 26. Noncrystal structure of CPP frit was determined by XRD. Morphology and particle size distribution of CPP frit were characterized by SEM and laser particle size analysis. Results indicated that the Particle size of CPP frit was between 0μm-30μm, but most was less than 10μm.Phase transformation of CPP during sintering processing was investigated byX-ray diffraction (XRD) and Differential thermal analysis (DTA). From thermo-dynamic aspect, the result of DTA showed that CPP underwent three phase transformations during 0℃-1000℃. CPP sintered at 500, 585, 600, 650, 700, 800, 900, 960, and 980℃ were characterized by XRD. The results demonstrated that the transformation of amorphous CPP to semi-crystalline CPP occurred below 585℃, and semi-crystalline CPP to γ -CPP at temperature of 585℃-600℃; γ -CPP to β-CPP at 600℃-700℃, CPP sintered between 600℃-700℃ were composed of both γ -CPP and β-CPP; between 700℃-900℃, the sintered CPP only contained β-CPP; β -CPP to α-CPP at 900℃-960℃.In vitro degradation of Porous CPP scaffolds with different crystal structures in 0.1M Tris-buffered solution (pH=7.4) and simulated body fluid (SBF) at 37℃ for periods up to 30 days was carried out. Results indicated that, in both solutions, the loss of weight and compression strength of CPP scaffolds with different crystal structure was different. The sequence was a-CPP < P-CPP < y-CPP. SEM pictures showed that, after degradation in Tris-buffered solution, more small apertures and pores appeared on the surface of samples, while after degradation in SBF, new substance deposited on the surface of samples. The amount of new substance on samples with different crystal structure was different, the sequence was a-CPP < P-CPP < y-CPP. IR showed that there was OH and CO32" in the new substance on P-CPP and y-CPP scaffolds. In both solutions, the initial loss of weight and compression strength of CPP scaffolds was rapid, but with elapse of degradation time, the loss became slower. CPP scaffolds in SBF degraded faster than those in Tris-buffered solution.Cellular biocompatibility of CPP scaffolds with different crystal structure was investigated by culturing ROS 17/2.8 cell on the samples. Results indicated that osteoblastic cell could attach, spread, and proliferate on all samples, keeping with normal shape and functionality. This confirmed good cellular biocompatibility of CPP scaffolds. Cells on P -CPP scaffolds showed the strongest proliferation capability which indicated that crystal structure may affect the growth of osteoblastic cell.