Preparation of 3DP Hydroxyapatite Composite by Single and Double Pass Poly(ε-caprolactone) Infiltration

Abstract

Recently, porous hydroxyapatite was fabricated by three dimensional printing (3DP) in coupled with low temperature phosphorization to yield nanosized and low crystalline structure. However, brittleness was an intrinsic drawback for some foreseen applications. Polymer infiltration aiming to improve the toughness and mechanical integrity was thus carried out using biodegradable poly(ε-caprolactone) (PCL) as an infiltrant since it has shown good biocompatibility together with a high elongation and energy to failure as compared to other medical polymers. Three routes of infiltration were performed including melt infiltration of low molecular weight PCL (Mw ˜ 10,000), solution infiltration by 10 % high molecular weight PCL (Mw ˜ 80,000) and the combination of both melt and solution infiltration of low and high molecular weight PCL. The combination of low and high MW infiltration yielded the greatest increase in the mechanical properties and followed by the melt infiltration of low molecular weight PCL while the use of high MW infiltration yielded limited enhancement. After immersing in simulated body fluid (SBF), no significant changes in flexural properties were seen for both hydroxyapatite and high molecular weight infiltrated sample. However, flexural strength and strain at break of low molecular weight infiltrated sample largely dropped after 7 days of immersion to be closed to those of hydroxyapatite and high molecular weight infiltrated sample. The flexural properties of high-low infiltrated sample also decreased after immersion, but to a less degree and still maintained the greatest values amongst all samples. This could be associated to the difference in degradation of different molecular weight of PCL and the content of polymer infiltration induced by different infiltration routes. Calcium and phosphorus ions in the SBF were quantified and observed to be consumed continuously during immersion for all samples. Newly formed apatite crystals were observed to form on the surface of the infiltrated composites signifying that infiltration did not hinder the bioactivity of the composites.