Date of Graduation

5-2018

Document Type

Thesis

Degree Name

Master of Science in Microelectronics-Photonics (MS)

Degree Level

Graduate

Department

Microelectronics-Photonics

Advisor/Mentor

Nair, Arun K.

Committee Member

Wejinya, Uche C.

Second Committee Member

Chen, Jingyi

Third Committee Member

Wise, Rick L.

Keywords

Mechanisms Of Deformation; Mineralization In Bone; Molecular Modeling Of Bone

Abstract

Bone is a composite biomaterial with a structural load-bearing function. Understanding the biomechanics of bone is important for characterizing factors such as age, trauma, or disease, and in the development of scaffolds for tissue engineering and bioinspired materials. At the nanoscale, bone is primarily composed of collagen protein, apatite crystals, and water. Though several studies have characterized nanoscale bone mechanics as the mineral content changes, the effect of water, mineral, and carbon nanotube (CNT) content and distribution in fibril gap and overlap regions is unexplored. This study used molecular dynamics to investigate the change in collagen fibril deformation mechanisms as a function of mineral, water, and CNT content. Collagen fibrils with 0 wt%, 20 wt%, and 40 wt% intrafibrillar mineralization and 0 wt%, 2 wt%, and 4 wt% hydration were studied under tension and compression. Non-mineralized fibrils with 43 wt% water and 5 wt%, 10 wt%, and 15 wt% CNTs were studied under compression.

An increase in mineral content for hydrated fibrils was found to reduce the nonlinear stress versus strain behavior caused by hydration, and the Young’s modulus of non-mineralized and mineralized fibrils decreased as the water content increased. At low water contents, it was found in non-mineralized fibrils that water primarily occupied voids in the gap regions, while in mineralized fibrils water primarily occupied voids in the overlap regions. Mineral and water content were found to affect the distribution of water in fibrils in tension and compression, which changed the deformation behavior of the gap and overlap regions. An increase in water content was found to increase the gap/overlap ratio by approximately 40% in non-mineralized fibrils and 16% in mineralized fibrils. For non-mineralized fibrils it was found that the gap/overlap ratio increased with an increase in tensile or compressive stress, while in mineralized fibrils the gap/overlap ratio decreased with an increase in stress. CNTs in non-mineralized fibril gap region voids reduced the decrease in the gap/overlap ratio as stress increased. CNTs increased the non-mineralized fibril elastic modulus from 0.43 GPa to approximately 1.74 GPa to 2.83 GPa, which was comparable to the elastic moduli of mineralized fibrils.

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