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 patient¿s recovery time. The aim of this proposal is to measure through thickness residual strain profile in thermally sprayed HA coatings for use in orthopaedic implant applications. Research has shown that residual stress at the coating substrate interface can initiate the failure of implant. Hence, data is required to model the generation of residual stress in HA coated orthopaedic implants to optimise their design and prolong implant¿s expected life. The novelty of this proposal is in the use of future generation nano-structured HA powders. The z-scan technique with partly submerged gauge volume will be used to measure the through thickness residual strain in HA coatings.