title: Evaluation of commercial implants with nanoindentation defines future development needs for hydroxyapatite coatings.
abstract: The performance of biomedical implants relies on the ability to assess and refine the microstructure of biomaterials. Instrumented nanoindentation was applied to determine the mechanical properties of plasma sprayed hydroxyapatite-coated implants from different commercial vendors. All biomedical devices contained both amorphous and crystalline phases. Nanoindentation of the amorphous phase revealed a hardness of 1.5 + or - 0.3 GPa and an elastic modulus of 48 + or - 6 GPa. The crystalline phase revealed a range in hardness of 3.0-7.7 GPa. The large range is attributed to the presence of porosity, surrounding amorphous areas, and hydroxyapatite (unmolten particle cores and recrystallized hydroxyapatite). A selection of the powder type (spray-dried or sintered) leads to different mechanical properties within the coating. A spray-dried powder provides a lower hardness and elastic modulus when unmolten particle cores are included in the coating. Meanwhile recrystallized areas are intermediate in hardness. The combination of a polished cross-section and nanoindentation offers the ability to determine a range of quality control tests including hardness, elastic modulus, bond strength, fracture toughness, substrate and coating roughness, crystallinity, and coating thickness. Property maps determined from nanoindentation will provide a graphical representation of the mechanical property distribution within the coating and provide a basis for coating property refinements. The assessment of commercial coatings is used a basis for discussion of future developments for hydroxyapatite coatings.
authors.affiliation: Department of Mechanical Engineering, University of Melbourne, VIC 3010, Australia. kgross@unimelb.edu.au
authors.forename: Kārlis A
authors.initials: KA
authors.lastname: Gross
authors.forename: Saeed
authors.initials: S
authors.lastname: Saber-Samandari
authors.forename: Karina S
authors.initials: KS
authors.lastname: Heemann
mesh_terms: D001696:Biomechanical Phenomena; D002130:Calcium Phosphates; D020099:Coated Materials, Biocompatible; D003460:Crystallization; D017886:Durapatite; D004548:Elasticity; D006622:Hip Prosthesis; D006801:Humans; D066298:In Vitro Techniques; D008422:Materials Testing; D036103:Nanotechnology; D019736:Prostheses and Implants; D013499:Surface Properties
chemical_list: D002130:Calcium Phosphates; D020099:Coated Materials, Biocompatible; D017886:Durapatite; C020243:calcium phosphate