Date of Award

2009

Document type

Thesis

Degree Name

PhD (Doctor of Philosophy)

First Supervisor

Professor Fergal O'Brien

Keywords

Bone Transplantation, collagen-calcium phospate scaffolds, bone tissue-engineering

Abstract

Various scaffolds have been used in in vitro and in vivo studies as either cell free bone grafts or as tissue engineered constructs. However, most of these scaffolds have not made the final step into clinical applications due to several limitations. The objective of this investigation was to develop novel composite scaffolds using an established, highly porous collagen scaffold and adding a mineral calcium phosphate phase.

Two novel composite scaffolds were developed; (1) a collagen-calcium phosphate scaffold developed using a single immersion technique into simulated body fluid and, (2) a collagen-calcium phosphate (CollCP) scaffold using a biphasic immersion into calcium- and phosphate based solutions. Both novel scaffolds showed promising results with respect to their mechanical, material, structural and biological properties for bone repair and bone tissue engineering. Due to its superior results in the mechanical tests, the CollCP scaffold using the bi-phasic immersion technique was chosen for in vivo analysis.

In two in vivo experiments the CollCP scaffolds were used as (1) off-the-shelf products and as (2) tissue-engineered constructs after seeding and 28 days culturing with rnesenchymal stem cells. Collagen-glycosaminoglycan (CollGAG) scaffolds, commonly used in our laboratory, sewed as controls in both studies. In both experiments the scaffolds were implanted into a critical sized rat calvarial defect. The unseeded CollCP scaffolds showed superior results to the unseeded CollGAG scaffolds due to the presence of an osteoinductive calcium phosphate phase, leading to homogeneous cell infiltration, bone formation and partially healed defects. The tissue engineered constructs also showed in vitro osteogenesis and in vivo bone formation, with superior results seen for the CollCP scaffolds. However, the in vitro osteogenesis created a dense layer of extra cellular matrix deposition in the scaffolds leading to cell necrosis and core degradation in the scaffold centre. Additionally, an immune host response slowed down the defect healing process in the tissue engineered constructs compared to the unseeded off-the-shelf scaffolds.

In conclusion, this investigation has successfully developed a CollCP scaffold with the ability to enhance bone healing in vivo due to the presence of an osteoinductive calcium phosphate phase. The CollCP off-the-shelf scaffolds showed superior results in healing the defect compared to the tissue engineered constructs. Results indicate that this is due to core degradation and an immune response.

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Comments

Submitted for the Award of Doctor of Philosophy (PhD) to the Royal College of Surgeons in Ireland, 2009.