Freeze casting of porous bioactive glass and bioceramics

Abstract

Highly porous network structures of hydroxyapatite, tricalcium phosphates, a bioactive glass as well as their composites have been fabricated using variations of camphene-, glycerol-, and ice-based freeze-casting techniques. The ball-milled slurries containing 10%-60% solid loading were cast at ambient temperature, followed by sublimation at temperatures between -70° and 60°C. The green body was sintered in air to a maximum temperature of 1100°C for 4 h, which produced excellent three-dimensionally (3-D) interconnected structures with open pores. The nature of the pore channels varied from dendritic, columnar, and cellular to mixed geometry, with dense outer shells in some cases, depending on the particular method used. A monotonic increase in porosity with loading was observed with a decrease in the loading volume. Microstructural analysis was used for porous structures to extract information on geometry, porosity, and pore size distribution. This proved particularly useful to assess whether some of the 3-D structures produced by these methods are suitable for tissue engineering applications. Differential thermal analysis-thermogravimetry, scanning electron microscopy, X-ray diffraction, and density were used to characterize precursor powders, slurry, and sintered products. © 2008 The American Ceramic Society.