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Title: Collagen-hydroxyapatite scaffolds for bone tissue engineering
Author: Wahl, Denys Adrien
ISNI:       0000 0001 3550 4725
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2007
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Biodegradable scaffolds are an important aspect of bone tissue engineering as they provide an alternative approach to bone grafts and biomaterials substitutes. The work achieved in this thesis describes the manufacturing process of collagen and collagen-hydroxyapatite scaffolds. Bovine type I collagen has been mixed to commercially obtained and manufactured hydroxyapatite (HA) particles to mimic the main natural extracellular components ofbone. Collagen sheets possessing different levels of dehydration - air drying (AD), dehydrothermal treatment (DHT) and CPD - have been characterised using infrared (FTIR), thermal (DSC), topographical (AFM), mechanical (DMA) and biodegradation (collagenase assay) analyses. Severe dehydration by CPD does not appear to denature nor crosslink collagen, but results in the reduction of the fibrils d-banding periodicity from 67nm to 63.7nm. Collagen exposed to DHT showed increased Young's modulus (E) and resistance to biodegradation, suggesting the formation of intermolecular crosslinks. However, thermal and infrared analyses indicated denaturation of the tropocollagen molecule, especially at high temperature oftreatment (l20°C). HA particles have been manufactured using a wet chemical synthesis to resemble bone apatite. The calcium phosphate phase of HA was confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). These particles contained 6.2% carbonate substitution (type A and type B) and were constituted from smaller rod-like crystals of the order of 15-20nm in diameter and 79-120nm in length. The ability to manufacture collagen-HA scaffolds is shown to rely on the stability ofthe swollen collagen fibres in the initial dispersion, which is pH dependent. Changing the collagen and HA content of the dispersion as well as the freezing rate during processing had an effect on the porosity, pore size distribution, mechanical properties and biodegradation rate ofthe composite scaffolds. Hybrid scaffolds have been manufactured containing different regions displaying varying properties. Finally, a solid freeform fabrication process has been developed to produce 3D moulds of stearic acid. This process allows for the external shape of the scaffold to be tailored and for internal architectures, such as microchannel pathways, to be incorporated within. These are essential developments in the field oftissue engineering.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available