SUBFIBRILLAR STRUCTURE OF TYPE-I COLLAGEN OBSERVED BY ATOMIC-FORCE MICROSCOPY

We have imaged native rat tail and reconstituted bovine dermal type I collagen by atomic force microscopy, obtaining a level of detail comparable to that obtained on the same samples by transmission electron microscopy. The characteristic 60-70-nm D periodicity consists of ridges exhibiting high tip-sample adhesion alternating with 5-15-nm-deep grooves having low adhesion. We also observe an intraperiod or ''minor'' band consisting of 1-nm-deep grooves, and ''microfibrils'' arranged parallel to or inclined approximately 5-degrees to the fibril axis. In air collagen fibrils exhibit negligible compression under the forces exerted by the tip. When immersed in water the subfibrillar features disappear and the fibrils become softer, compressing by 5% of their height under an 11-nN force. Material on the surface of the sample sometimes accumulates on the atomic force microscope tip; contrary to expectation such tip contamination can improve as well as reduce resolution.