Hydroxyapatite (HA) is a natural compound (Ca10 (PO4)6(OH) 2) found in human bone and clinical research has shown that HA coated orthopaedic implants improve the ingrowth and outgrowth of bone and reduce patients recovery time. Residual stress plays a critical role in the life of these implants. Cold spray coating technology is a newer development in thermal spray coatings which is designed to minimise the residual stress and phase transformations in HA coatings. The aim of this proposal is to measure through thickness residual strain profile in cold sprayed HA coatings for use in orthopaedic implants. A patent has already been filed in this area by the Principal Investigator and this investigation will provide urgent data for modelling the residual stress behaviour of these next generation implant coatings.