Influence of telopeptides, fibrils and crosslinking on physicochemical properties of type I collagen films.

Type I collagen is widely used in various different forms for research and commercial applications. Different forms of collagen may be classified according to their source, extraction method, crosslinking and resultant ultrastructure. In this study, afibrillar and reconstituted fibrillar films, derived from acid soluble and pepsin digested Type I collagen, were analysed using Lateral Force Microscopy (LFM), Fourier Transform Infra-Red Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and enzymatic stability assays to asses the influence of telopeptides, fibrils and crosslinking. LFM proved to be a useful technique to confirm an afibrillar/fibrillar ultrastructure and to elucidate fibril diameters. FTIR has proved insensitive to ultrastructural differences involving telopeptides and fibrils. DSC results showed a significant increase in T(d) for crosslinked samples (+22-28 degrees C), and demonstrated that the thermal behaviour of hydrated, afibrillar films is more akin to reconstituted fibrillar films than monomeric solutions. The enzymatic stability assay has provided new evidence to show that afibrillar films of Type I collagen can be significantly more resistant to collagenase (by up to 3.5 times), than reconstituted fibrillar films, as a direct consequence of the different spatial arrangement of collagen molecules. A novel mechanism for this phenomenon is proposed and discussed. Additionally, the presence of telopeptide regions in afibrillar tropocollagen samples has been shown to increase resistance to collagenase by greater than 3.5 times compared to counterpart afibrillar atelocollagen samples. One-factor ANOVA analysis, with Fisher's LSD post-hoc test, confirms these key findings to be of statistical significance (P < 0.05). The profound physicochemical effects of collagen ultrastructure demonstrated in this study reiterates the need for comprehensive materials disclosure and classification when using these biomaterials.