Effects of degradation and porosity on the load bearing properties of model hydroxyapatite bone scaffolds

Abstract

Degradation of three types of model hydroxyapatite (HA) scaffolds was studied after in vitro degradation in a sodium acetate buffer (pH 4). Degradation was evaluated using compression testing, scanning electron microscopy (SEM), inductively coupled plasma (ICP) analysis, and weight measurements. Scaffolds were fabricated with a solid freeform fabrication (SFF) technique based on the robotic deposition of colloidal pastes. Scaffolds had a macrostructure resembling a lattice of rods. Scaffolds contained either macropores (270 or 680 microm in the x-y direction and 280 microm in the z-direction) and micropores (1-30-microm pores and pores <1 microm) or only macropores pores (270 microm in the x-y direction and 280 microm in the z-direction). A computer-aided design (CAD) program controlled the size and distribution of macropores; micropores were created by polymethylmethacrylate (PMMA) microsphere porogens (1-30-microm pore diameter) and controlled sintering (pores <1 microm). Percent weight loss of the scaffolds and calcium and phosphorus ion concentrations in solution increased as the degradation period increased for all scaffold types. After degradation, compressive strength and compressive modulus decreased significantly for those scaffolds with microporosity. For scaffolds without microporosity, the changes in strength and modulus after degradation were not statistically significant. The compressive strength of scaffolds without microporosity was significantly greater than the scaffolds with microporosity.