Enhancing the Mechanical Properties of a Hydroxyapatite-Collagen Bone Surrogate

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 bonelike 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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Year

Entry

1974

Reilly DT, Burstein AH, Frankel VH. The elastic modulus for bone. J Biomech. May 1974;7(3):271-275.

1974

Evans FG, Vincentelli R. Relations of the compressive properties of human cortical bone to histological structure and calcification. J Biomech. January 1974;7(1):1-10.

1987

Schaffler MB, Burr DB, Frederickson RG. Morphology of the osteonal cement line in human bone. Anat Rec. March 1987;217(3):223-228.

1978

Moyle DD, Welborn JW III, Cooke FW. Work to fracture of canine femoral bone. J Biomech. 1978;11(10-12):435-440.

1996

Martin RB, Lau ST, Mathews PV, Gibson VA, Stover SM. Collagen fiber organization is related to mechanical properties and remodeling in equine bone: a comparsion of two methods. J Biomech. December 1996;29(12):1515-1521.