Collagen Fibril Intermolecular Spacing Changes with 2-Propanol: A Mechanism for Tissue Stiffness

Materials composed primarily of collagen are important as surgical scaffolds and other medical devices and require flexibility. However, the factors that control the suppleness and flexibility of these materials are not well understood. Acellular dermal matrix materials in aqueous mixtures of 2-propanol were studied. Synchrotron-based small-angle X-ray scattering was used to characterize the collagen structure and structural arrangement. Stiffness was measured by bend tests. Bend modulus increased logarithmically with 2-propanol concentration from 0.5 kPa in water to 103 kPa in pure 2-propanol. The intermolecular spacing between tropocollagen molecules decreased from 15.3 to 11.4 Å with increasing 2-propanol concentration while fibril diameter decreased from 57.2 to 37.2 nm. D-spacing initially increased from 63.6 to 64.2 nm at 50% 2-propanol then decreased to 60.3 nm in pure 2-propanol. The decrease in intermolecular spacing and fibril diameter are due to removal of water and the collapse of the hydrogen bond structure between tropocollagen molecules causing closer packing of the molecules within a fibril. We speculate this tighter molecular packing may restrict the sliding of collagen within fibrils, and similar disruption of the extended hydration layer between fibrils may lead to restriction of sliding between fibrils. This mechanism for tissue stiffness may be more general.