The effect of pore size and porosity on capillary pressure in microporous hydroxyapatite samples

Abstract

Microporosity (<50μm) in hydroxyapatite (HA) scaffolds is known to improve bone ingrowth. The mechanism for the improvement is thought to be in part due to capillary forces induced by the micropores. The micropore-induced capillary forces can self load cells into the scaffolds. In this study, the effect of micropore size and porosity on capillary forces was investigated. Rectangular shaped HA samples that were either 50% or 60% porous with 5μm, 12μm, 20μm or 50μm pores were fabricated. The samples were characterized by imaging the microstructure, analyzing the composition, measuring the pore size, pore fraction, sample thickness and quantifying the defects inside and outside of the samples. Capillary rise tests were conducted on the samples and fluid height curves were obtained as a function of time. A model was implemented to determine the equilibrium heights and calculate the capillary forces. For 50% porous samples, 5μm samples had the highest equilibrium height and capillary pressure, followed by 12μm, 20μm or 50μm samples. The 60% porous 5μm samples had a faster initial rise, but a lower equilibrium height and capillary pressure than the 50% porous 5μm samples. The 60% porous 50μm samples also had a faster initial rise, a lower equilibrium height and capillary pressure than the 50% porous 50μm samples.