Reconstituted collagen fibres for tissue engineering applications

In vitro, under appropriate conditions collagen molecules spontaneously form fibrils (fibrillogenesis) with the characteristic D-periodic banding similar to native fibrils. Recently, reconstituted collagen fibres have been of interest. Due to their unique advantageous properties, such as high surface area, softness, absorbency and ease of fabrication into many product forms, biomaterial based on reformed collagen fibres have been used as a substrate for nerve regeneration, tendon and ligament replacement, wound dressing applications and suture materials. Although some work has been done, still there is little understanding of the factors affecting the physical properties of such fibres. Therefore, the aim of the work presented in this thesis was to study and better understand the influence of factors which control the structure and physical properties of extruded reconstituted collagen fibres. Acid and pepsin soluble collagen was extracted from different animal species (bovine Achilles tendon, rat tail tendon and pig tail tendon) and was extruded, using different internal diameter laboratory tubes into a series of neutral buffers, comprised of different co-agents such as sodium chloride, different molecular weight of polyethylene glycols and poly vinyl alcohols at 37°C, where fibrillogenesis occurred. After 15 minutes incubation, the fibres were washed and air-dried under the tension of their own weight. In addition, an extensive study of the effects of a wide range of cross-linking techniques (chemical, physical, biological and natural) was undertaken. The structural, mechanical (dry and wet) and thermal properties of the reconstituted collagen fibres were evaluated using optical and scanning electron microscopy, tensile mechanical tests and differential scanning calorimetry respectively. In general, it was found that the properties of the reformed collagen fibres were dependent on pre- (animal species, extraction method, collagen concentration) during- (fibre formation medium) and post- (cross-linking) fibre formation variables. A strong correlation between fibre diameter and stress at break was observed throughout this work; by increasing the diameter of the fibre either by increasing the collagen concentration, the tube internal diameter, the amount of the co-agent or via cross-linking, a decrease of the tensile strength at break was observed. The thermal properties of the matrices appeared to be dependent on the cross-linking technique utilized. Overall, it was demonstrated that reconstituted collagen fibres can be tailor made to suit a diversity of surgical needs with properties similar to or even superior to native tissues or other synthetic materials that are already in practice.