Influence of hydroxyapatite crystallization temperature and concentration on stress transfer in wet-spun nanohydroxyapatite-chitosan composite fibres

Hydroxyapatite possesses appropriate osteoconductivity and biocompatibility for hard-tissue replacement implants but suffers from brittleness. One approach to overcome this problem is to incorporate nanometre hydroxyapatite (nHA) into a polymer matrix, such as chitosan, to yield a hydroxyapatite-chitosan (HC) composite. Here, a novel HC composite was synthesized and its elastic properties were investigated by varying (1) nHA concentration and (2) crystallization temperature (T), where T is a parameter which influences the morphology of the crystals. Crystals of nHA were precipitated at T = 40 degrees C and 100 degrees C, blended in a chitosan matrix, and wet-spun to yield fibres of HC composites at 5, 15, 20 and 40% concentrations (mass fraction of nHA). Scanning electron microscopy and energy-dispersive x-ray spectroscopy revealed a uniform distribution of nanocrystallites within the fibre. Tensile testing revealed that HC fibres, which comprised nHA treated at T = 100 degrees C, possessed low tensile strength, sigma(0), and stiffness, E, at low nHA concentrations but high sigma(0) and E at higher concentrations, i.e. beyond a 15% mass fraction of nHA. However, with nHA treated at T = 40 degrees C, the fibres yielded high sigma(0) and E at low nHA concentrations but low sigma(0) and E at high concentrations. The results strongly implicate the underlying effect of crystallite morphology on stress transfer at different concentrations.