STRUCTURAL STUDIES ON THERMALLY SHRUNKEN COLLAGEN FIBERS FROM RAT TAIL TENDON

Structural changes during thermal shrinkage of the collagen fibers from the rat tail tendon were investigated mainly by small-angle X-ray diffractions, and a series of plausible models were presented to demonstrate the structure changes of the tropocollagen levels in the collagen fibers, shrunken thermally or drawn mechanically. Using the Patterson functions for the cylindrically symmetric system on the collagen fibers, the structural changes in the microfibrils repeating units, consisting of alternating gap and overlap regions, were investigated and compared with the macroscopical dimensional changes. When thermally shrunken above 200°C, the lengths of the gap regions were shrunken at a higher rate than the total lengths of the repeating units to result in the drastic shortening of the macroscopically dimensional changes, and the collagen molecules tended to distort their orientations from the roughly parallel to the fiber axis.The density of the cross-linkage was quantitatively estimated from the measurements of the equilibrium stress-elongation relationship of the swollen specimen in the unique solvent (the equivolume mixture of 8.0 M LiBr/HO(CH2CH2O)2CH3). The important roles of the cross-linkage on the mechanisms of thermal shrinkage and mechanical elongation of the collagen fibers should be emphasized from the viewpoints of the relation between the macroscopic dimensional changes and the microscopically structural changes.