Effect of hydroxyapatite size on properties of PBS-DLS/HAp composites obtained by twin-screw extrusion and injection moulding techniques

The aim of this work is to develop new polymer-ceramic composites based on poly(butylene succinate-dilinoleic succinate) (PBS-DLS) and hydroxyapatites (HAp) of different sizes. Irregularly shaped nano-hydroxyapatite (nHAp) and whisker-shaped micro-hydroxyapatite (μHAp) were used as fillers. For each of the hydroxyapatites, composites with copolymer:filler weight ratios of 9:1 and 8:2 were prepared by co-rotating twin-screw extrusion combined with injection moulding techniques. The investigations carried out allowed the characterisation of the specific behaviour of both fillers during processing, such as the tendency of nanoparticles to agglomerate or the breaking of whisker microparticles leading to a significant change in their aspect ratio (from about 4 to less than 3). A comprehensive characterisation of the produced materials was carried out and a comparison was made of the effect of filler particle size on the physicochemical and mechanical properties of the composites. A series of mechanical tests were carried out, such as dynamic thermo-mechanical analysis, quasi-static tensile test, quasi-static flexural test, impact strength and Brinell hardness, showing the reinforcing effect of the fillers used, with a predominance of whiskered micro-hydroxyapatite. The developed materials also showed good processability, thermal stability, bioactivity and biocompatibility towards the mouse fibroblast L929 cell line. The results presented in this work certainly provide useful information for the design and fabrication of effective polymer-ceramic biocomposites for bone tissue engineering applications.