Fabrication of Flexible Porous Calcium-Deficient Apatite -Alginate Composite and Its Evaluation

Abstract

The calcium-deficient apatite (Ca9.36(HPO4)0.74(PO4)5.26(OH)1.26·nH2O (Ca/P ratio=1.56): DAp) – alginate (AG) composite was fabricated by the ice crystal sublimation technique. The starting whisker-like calcium-deficient apatite (w-DAp) powder with long-axis length of 62.6 μm and short-axis length of 2.85 μm was prepared by the homogeneous precipitation technique. After mixing the w-DAp with AG paste (DAp/AG ratio: 10), the mixture was flash frozen at a temperature between −5 and −196°C. The frozen materials were further lyophilized at -50°C for 24 h under reduced pressure and put into 1 mol-dm−3 CaCl2 solution at room temperature for 24 h The microscopic observation showed that the pore size of w-DAp-AG composite increased from ~20 to ~100 μm with decreasing concentration of starting AG paste from 7.5 to 2.5 mass% and with decreasing freezing temperature from −196°C down to −5°C. The maximum porosity of w-DAp-AG composite, which was fabricated using 2.5 mass% AG at the freezing temperature of -5°C, attained 92.3%.