Freeze casting of porous hydroxyapatite scaffolds. I. Processing and general microstructure.
Freeze casting of aqueous suspensions on a cold substrate was investigated as a method for preparing hydroxyapatite (HA) scaffolds with unidirectional porosity. In the present paper, we report on the ability to manipulate the microstructure of freeze-cast constructs by controlling the processing parameters. Constructs prepared from aqueous suspensions (5-20 volume percent particles) on a steel substrate at -20 degrees C had a lamellar-type microstructure, consisting of plate-like HA and unidirectional pores oriented in the direction of freezing. Sintering for 3 h at 1350 degrees C produced constructs with dense HA lamellas, porosity of approximately 50%, and inter-lamellar pore widths of 5-30 microm. The thickness of the HA lamellas decreased but the width of the pores increased with decreasing particle concentration. Decreasing the substrate temperature from -20 degrees C to -196 degrees C produced a finer lamellar microstructure. The use of water-glycerol mixtures (20 wt % glycerol) as the solvent in the suspension resulted in the production of finer pores (1-10 microm) and a larger number of dendritic growth connecting the HA lamellas. On the other hand, the use of water-dioxane mixtures (60 wt % dioxane) produced a cellular-type microstructure with larger pores (90-110 microm). The ability to produce a uniaxial microstructure and its manipulation by controlling the processing parameters indicate the potential of the present freeze casting route for the production of scaffolds for bone tissue engineering applications.
D001672:Biocompatible Materials / Q000737:chemistry*; D001842:Bone and Bones / Q000473:pathology; D002516:Ceramics / Q000737:chemistry*; D004146:Dioxanes / Q000737:chemistry; D017886:Durapatite / Q000737:chemistry*; D005615:Freezing; D005990:Glycerol / Q000737:chemistry; D008422:Materials Testing; D016062:Porosity; D012212:Rheology / Q000379:methods; D012997:Solvents / Q000737:chemistry; D013314:Stress, Mechanical; D013696:Temperature; D023822:Tissue Engineering / Q000379:methods; D014945:Wound Healing
D001672:Biocompatible Materials; D004146:Dioxanes; D012997:Solvents; D017886:Durapatite; C025223:1,4-dioxane; D005990:Glycerol