Modeling and Simulation of Microporous Titanium: Effects of Morphology with Application to Orthopaedic Implants

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Effective and reliable material and structure as bone implant have been a continuing challenge for scientists from bioengineering, material science and mechanical engineering. Porous titanium has reduced stiffness comparable to bone and open pores to allow complete bone infiltration, thus making it attractive for bone-replacement implants in biomedical engineering. To facilitate the design and application of the material, it is necessary to develop an understanding of the relationship between the morphology of porous microstructure and the mechanical properties of the material. 2D finite element (FE) models based on simulate microstructures of different porosities are initially set up to investigate the effects of pore morphology and bone infiltration on the mechanical response of titanium foam in vivo. It is proved that several microstructural features and bone ingrowth have significant influence on the mechanical properties of porous titanium. Inspired by these results, a factorial design of experiment methodology (DOE) is therefore used to systematically compare the effect that these features have on the mechanical responses via 2D and 3D models based on simulate microstructures of titanium wire foam of 12% porosity. Five microstructural features, including pore shape, size, orientation, and arrangement, and bone infiltration, are varied to create test microstructures. The quantitative effects of the features are used to screen their relative importance for elastic moduli, yield stress and stress concentration factor. Finally, 2D FE models based on real microstructures at various porosities are compared with 2D and 3D FE models based on simulate microstructures at same or similar porosities. The results of these studies indicate that bone infiltration into the pores serves as the most dominant factor and is the key to improve mechanical performance of microporous titanium. Compared to other morphological factors, the orientation and arrangement of pores have relative more important effects on the mechanical response of titanium foam. 3D FE models based on simulate microstructures have been proved to predict more accurate results than 2D FE models based either on real or simulate microstructures. However, based on the DOE study, 2D and 3D FE models at low porosity (12%) have similar estimations on the effects of most factors on the macroscopic and microscopic responses. This implies the possible use of 2D models to observe the impact of microstructural features on mechanical responses.

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  • 05/10/2018
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