Scanning electron microscopy of collagen fibers in intestine.

Collagen fibers of rat intestine were observed with and without mechanical stress in the scanning electron microscope. Observations were correlated with the previous results obtained by optical polarized microscopy to provide further insight into the organization and morphology of intestinal collagen. Larger fibers, approximately 4 micrometers in diameter, are densely packed in parallel undulating arrays. The initial response to stress is straightening of the original fibers. The extended fibers are biaxially oriented at +30 degrees and -30 degrees to the longitudinal direction. These large fibers appear as assemblies of subfibers. At higher magnifications, the larger fibers appear to be enmeshed in a network of small randomly oriented fibers approximately 0.2 micrometer in diameter. Study of the effect of age on fiber morphology showed that the length of the large fiber undulations increases during maturation but remains constant during aging. The diameters of large and small fibers appear not to change with age, but more of the 4 micrometers fibers are loosely associated into larger fibers which can be observed at both the optical microscope and scanning electron microscope levels. A hierarchical organization of intestinal collagen is proposed.