Thesis (Ph.D.)--Chulalongkorn University, 2010

The objectives of this research were to (1) develop the production process of porous hydroxyapatite (HA) ceramics with controllable porosity and (2) study key forming factors affecting on porosity and mechanical strength of porous HA scaffolds. The HA powder was synthesized through a precipitation reaction between calcium hydroxide and orthophosphoric acid. The porous samples were prepared from HA powder without and with 1wt% surfactant (agar powder) through three methods; including (1) sacrificial template technique using polymethyl methacrylate (PMMA) granule ranging from 5 to 50wt% in content, (2) direct foaming technique using hydrogen peroxide solution ranging from 1 to 30wt% in concentration, and (3) combination technique between sacrificial template and direct foaming techniques using PMMA and hydrogen peroxide, at liquid to powder ratio of 1.3 ml/g and 1.5 ml/g. Afterwards, the porous samples were sintered at 1,100℃ for 2 hours and then cooled in the furnace. Moreover, the HA powder was characterized by X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), Particle Size Analysis (PSA) and Scanning Electron Microscope (SEM). The porous samples were investigated for porosity, microstructure, compressive and flexural strength, and stiffness. The study found that (1) sacrificial template technique using PMMA provided pore sizes ranging between 100-300 µm, porosity ranging between 52-74%, compressive and flexural strengths ranging between 0.5-36 MPa and 0.6-7 MPa, respectively, compressive and flexural stiffness ranging between 33-5,530 kN/m2 and 8-730 MN/sq.m, respectively; (2) direct foaming technique using hydrogen peroxide provided pore sizes ranging between 100-1,000 µm, porosity ranging between 80-85%, compressive and flexural strengths ranging between 0.07-0.7 MPa and 0.1-1.1 MPa, respectively, and compressive and flexural stiffness ranging between 60-550 kN/sq.m. and 2-75 MN/sq.m, respectively; (3) combination technique using PMMA and hydrogen peroxide provided pore sizes ranging between 100-1,000 µm, porosity ranging between 82-90%, compressive and flexural strengths ranging between 0.03-0.5 MPa and 0.1-0.7 MPa, respectively, and compressive and flexural stiffness ranging between 13-440 KN/sq.m. and 0.5-45 MN/sq.m, respectively; (4) the combination technique provided the interconnected pores, while the sacrificial template and the direct foaming techniques performed the closed pores; (5) the sacrificial template technique was the best method to control the porosity; (6) Increasing PMMA content, hydrogen peroxide concentration and L/P ratio affected an increase of porosity and a decrease of mechanical strength; and (7) addition of surfactant was a significant effect on an increasing compressive strength of the porous samples prepared via direct foaming technique using hydrogen peroxide, at 95% confident interval. At the hydrogen peroxide concentration between 5wt% and 20wt%, the compressive strength increased from approximately 0.29 to 0.46 MPa (increased about 60%).