Ultrastructural deformation of collagen.

Ultrastructure deformation studies of reconstituted and native rat tail tendon collagen revealed that deformation occurs primarily in the non-staining and presumably non-polar proline rich regions for all ages examined. At low deformation (tension and compression) the deformation occurs somewhat more between the a2 and b1 and b2 and c2 bands than within the rest of the d period. At moderate elongations (greater than 40%), the deformation becomes localized between the c2 and d bands, with subfibrils on the order of 3-15 nm being drawn across the openings between the c2 and d bands. At high elongations (100% or greater) d period splitting occur on a regular basis between the c2 and d bands, along with a retraction of the 64 nm repeat period into 60 nm segments. It is in this deformation region that the effects of molecular slip and the apparent association of the acid mucopolysaccharides can be noted. These results suggest that crosslinking, if increasing as a function of age, does not affect the deformation characteristics of the individual fibrils and that changes with age in mechanical properties should be sought in changes in the fibril size and their interaction with the surrounding matrix.