Access Type

Open Access Dissertation

Date of Award

January 2012

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Biomedical Engineering

First Advisor

Pamela J. VandeVord

Abstract

The synthesis of biomimetic hydroxyapatite-collagen composites is desirable from the perspective of graft elimination and load-bearing support when treating damaged or diseased bone. Bone is an organized network of carbonated hydroxyapatite mineralized collagen, whose strength and toughness is dependent on the organized array of mineralized collagen fibers that align with applied physiologic stresses. The apatitic calcium phosphate phase, hydroxyapatite, is promising for the biomimetic mineralization of collagen. Hydroxyapatite-collagen composites are osteoconductive and resorbable. However, the mechanical properties of these composites are one or more orders of magnitude less than bone. The aim of this study was to produce a bone-like hydroxyapatite-collagen composite with an induced collagen fiber alignment in order to improve the mechanical properties of the composite. In this study, environmental and temporal effects on the synthesis of a hydroxyapatite-collagen composite were characterized and compared to bone. Three dimensional hydroxyapatite-collagen composite scaffolds were fabricated by a combined extrusion and compaction process producing three different levels of collagen fiber alignment, which were quantified and correlated to the resultant mechanical properties. The levels of collagen fiber alignment corresponded to an expected random alignment, low longitudinal alignment, and high longitudinal alignment. The results showed that a bone-like hydroxyapatite-collagen composite is best synthesized in physiologic to alkaline pH (7.4 - 8.0) and allowed to react for 6 hours. Composite scaffolds fabricated with the low longitudinal alignment method produced the highest degree of alignment among the fabrication methods. Degree of collagen alignment produced the best strain and toughness responses. Compaction aided strength related mechanical properties. This study gives proof of concept for a collagen fiber alignment process and indicates that the mechanical properties of a three dimensional HAp/C composite scaffold fabricated by this process are dependent on the degree of collagen fiber alignment.

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