Biological evaluation of pliable hydroxyapatite-ethylene vinyl acetate co-polymer composites intended for cranioplasty

Hydroxyapatite (HAP) is undoubtedly a material suitable for repairing the defective bone tissue. However, the brittleness and non-malleability of HAP limit its clinical application as a cranioplastic analogue. To improve these properties, pliable, osteoconductive composites composed of HAP and ethylene vinyl acetate co-polymer (EVA) have been developed. This study reports the biocompatibility evaluation of the newly developed composite material. Composites of two compositions, containing 40 and 50 volume percentage of HAP, were evaluated. In vitro cell culture cytotoxity studies were carried out using L929 cell line. Intracutaneous irritation studies, and intramuscular implantation studies were carried out on rabbits. Cell culture studies showed that the composite was non-cytotoxic to mouse fibroblast cell line. Intracutaneous irritation studies did not show any gross signs of tissue reaction. Histological analysis after six months of implantation in the paravertebral muscles of rabbit showed that all the implants under study were covered with a thin soft tissue capsule. On the basis of these observations, we conclude that the composite materials are biocompatible and hence are a candidate material for implantation in the cranium.