An Experimentally Validated Micromechanical Model for Elasticity and Strength of Hydroxyapatite Biomaterials
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1132-Z06-03
An Experimentally Validated Micromechanical Model for Elasticity and Strength of Hydroxyapatite Biomaterials Andreas Fritsch1,2, Luc Dormieux2, Christian Hellmich1 and Julien Sanahuja3 1
Vienna University of Technology (TU Wien), Karlsplatz 13, A-1040 Wien, Austria Ecole Nationale des Ponts et Chaussess, 6-8 av. Blaise Pascal, 77455 Marne-la-Vallee, France 3 Électricité de France, Route de Sens, Ecuelles, 77818 Moret sur Loing, France
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ABSTRACT Hydroxyapatite biomaterials production has been a major field in biomaterials science and biomechanical engineering. As concerns prediction of their stiffness and strength, we propose to go beyond statistical correlations with porosity or empirical structure-property relationships, as to resolve the material-immanent microstructures governing the overall mechanical behavior. The macroscopic mechanical properties are estimated from the microstructures of the materials and their composition, in a homogenization process based on continuum micromechanics. Thereby, biomaterials are envisioned as porous polycrystals consisting of hydroxyapatite needles and spherical pores. Validation of respective micromechanical models relies on two independent experimental sets: Biomaterial-specific macroscopic (homogenized) stiffness and uniaxial (tensile and compressive) strength predicted from biomaterial-specific porosities, on the basis of biomaterial-independent (‘universal’) elastic and strength properties of hydroxyapatite, are compared to corresponding biomaterial-specific experimentally determined (acoustic and mechanical) stiffness and strength values. The good agreement between model predictions and the corresponding experiments underlines the potential of micromechanical modeling in improving biomaterial design, through optimization of key parameters such as porosities or geometries of microstructures, in order to reach desired values for biomaterial stiffness or strength. INTRODUCTION Hydroxyapatite [HA, with chemical formula Ca10(PO4)6(OH)2 in its pure (‘stoichiometric’) form] biomaterials production has been a major field in biomaterials science and biomechanical engineering due to their excellent biocompatibility, and since their chemical composition, structure, and mechanical properties are similar to bone mineral [1]. Aiming at mimicking the bone mineral and its important biological and mechanical properties within bone tissues, HA is widely used for biomedical applications: They encompass coating of orthopedic and dental implants [2], artificial hard tissue replacement implants in orthopedics, maxillofacial and dental implant surgery [3]. Thereby, HA is used either in a pure state [4, 5] or as composite, with ceramic, metallic or polymer inclusions as reinforcing component [6]. Typical examples of powder-based porous HA biomaterials encompass sintered ceramics [7, 8, 9, 10, 11, 14], HA monoliths prepared at physiological temperature [12] and HA cement [3]. An overview of the processing routes is given elsewhere [13]. The mechanical and microstructural properti
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