Atomic force microscope images of collagen fibers

Atomic force microscopy (AFM) was used to image fibrillar and monomeric type I collagen. Protocols were developed to produce samples of air dried fibrillar and monomeric collagen suitable for AFM analysis. Pepsin-extracted, type I bovine skin collagen was polymerized on mica substrates in pH 7.4 phosphate-buffered saline at 37 °C. Monomeric collagen was adsorbed onto mica substrates in 0.012 N HCl or pH 3 buffer at 21 °C. Control samples of buffer-treated mica were also prepared. AFM images of the fibrillar collagen showed well-defined D banding of the fibrils, with a period of 70 nm. Beneath the fibrils finer fibrillar material was seen, probably oligomeric collagen. Samples prepared at acidic pH showed a meshwork of monomeric collagen with an occasional structure of oligomeric size. Control samples of mica treated with buffer only had occasional tree structures formed of crystallized buffer salts. Collagen is an important component of animal tissues and forms extracellular matrix material in combination with other proteins and glycoproteins. The studies reported here form the basis for examination of more complex collagen-containing structures of biological importance.