Date of Graduation

5-2018

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering (MSME)

Degree Level

Graduate

Department

Mechanical Engineering

Advisor/Mentor

Arun Nair

Committee Member

Wenchao Zhou

Second Committee Member

Paul Millett

Keywords

Bio-inspired Scaffold, Finite Element Analysis, Multiscale Modeling, Substitution, Surface Texture

Abstract

Synthetic scaffolds are widely used as implants to repair bone fracture. Without a proper design, scaffolds could pose significant health risks to the patient and fail to heal the bone properly. A good synthetic scaffold needs to have high porosity and large pore size to allow new bone cells to form on it. However, a scaffold with higher porosity and larger pore size tends to have reduced mechanical strength. Thus, it is important to find a structural design which allows the implant to have a high porosity and large pore size while retaining high strength. In this research, a 3D-printable bio-inspired structure based on the unit cell of hydroxyapatite (HAp), along with several other common scaffold structures, were designed and tested using a multiscale approach. Those structures are tested under different loading conditions to find the stress levels. HAp material properties are extracted from the density functional theory calculations, and the effect of porosity on the material properties are modeled based on empirical relations by utilizing the density as the scaling factor. The results show that the HAp-inspired scaffold could have up to 70% lower stress level when compared to other common scaffold designs，such as round or square pores scaffolds, under the same loading condition. Due to substitutions during aging, the scaffolds made of apatite can be significantly different from stoichiometric HAp. Hence, this study is also extended to test the HAp-inspired scaffold with varying anionic and cationic substitutions, including Mg2+, Zn2+, and CO32-. Furthermore, the surface texture of synthetic scaffolds has also become an important research subject in the last decade. Studies have found that surface texture can alter surface properties, such as cell adhesion, protein adsorption, and coefficient of friction, of a biomaterial. In this study, two of very promising 3D-printable bio-inspired surface textures are studied for their stress reaction under a loading condition. Some advice that could lead to a structurally stronger surface texture design is concluded. This study will provide an insight into a better scaffold design based on bio-inspired structures and the effects of substitutions on HAp scaffolds.

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