The Degradation Behavior And Surface Modification Of Calcium Phosphate Based Porous Bioglass-ceramic Scaffolds

Calcium phosphate bioglass-ceramics have been used as bone substitutes mainly due to their chemical similarity to the mineral component of mammalian bones. Also, calcium phosphate bioglass-ceramics can dissolve over time in physiological fluids, being eventually replaced by natural tissue, which made them the ideal materials used as degradable temporary implants or drug delivery device. Moreover, the solubility of calcium phosphate bioglass-ceramics can be easily governed by changing the chemical components, heat treatment temperature, or the crystalline phases to suit their end applications.In this paper, the porous scaffolds were manufactured by coating polyurethane foams with sol-gel derived bioglass-ceramic slurry in the system of CaO-P₂O₅-Na₂O-SrO-MgO-HA. Three conditions with different pH at 1.0, 3.0, and 10.0 were selected to study their solubility and surface modification. The role of HA precursor on the crystallization and microstructure of the bioglass-ceramics was investigated by XRD and SEM. The influence of heat treatment temperature on compressive strength was also studied. The degradation behavior of the scaffolds was carried out by soaking in stimulated body fluid (SBF) for different periods. The effect of pH values on surface modification of the scaffolds was described, and the impact of surface modification on the degradation and cell culture was also studied.The result implied that HA precursor incorporated into the initial component as nucleation agent could induce the emergence of Ca₇Sr₃(PO₄)₆(OH)₂ phase, and promote the substitution of Ca²⁺ by Sr²⁺ in Ca₄P₆O₁₉ structure, while the major crystalline phase Ca₄P₆O₁₉ resulted from the reaction ofβ-Ca₂P₂O₇ and HA precursor. The maximum compressive strength of the porous scaffolds was 8.46 MPa while the porosity was 72.2%. The solubility of Sr-doped Ca₄P₆O₁₉ was proved to be largely higher than that of pure Ca₄P₆O₁₉, and the dissolution of minor phase Ca₇Sr₃(PO₄)₆(OH)₂ provided nucleation sites for apatite formation, which can improve the bioactivity of the scaffolds.The new CaP2O6 layer was precipitated on the sample surface after tested at pH 3.0, while the amorphous tricalcium phosphate Ca3(PO4)2·nH2O layer was also formed on the surface after immersed at pH 10.0. The new-formed layers increased the level of surface roughness, and promoted the formation of apatite layer in SBF, which improved the degradation of the scaffolds. In vitro cell culture, the bioglass-ceramic scaffolds with the main phase Ca₄P₆O₁₉ showed good biocompatibility and bioactivity, and the amorphous Ca₃(PO₄)₂·nH₂O layer was proved to be beneficial to for cell adhesion after surface modification at pH 10.0.