The interplay between surface micro-topography and -mechanics of type I collagen fibrils in air and aqueous media: An atomic force microscopy study

Calf skin type I collagen fibrils were regenerated from acidic solution and imaged with contact mode atomic force microscopy in air, water, and buffer solution. When imaged in air at a contact force of 20-150 nN, collagen fib rils exhibited a distinct transverse banding pattern with a period of 65 nm , consisting of high ridges and shallow grooves. The force dependence of th e images suggests that such banding pattern is attributed to the transverse contraction of the fibril upon dehydration during sample preparation, whic h reflects the tangential mass density across the fibril. Imaging in water and phosphate buffer solution at a contact force of 15 80 nN revealed hydra ted collagen fibrils with smooth surfaces. The rigidity of the collagen fib rils decreased considerably upon hydration. Scanning the cantilever tip in an aqueous medium at a contact force of 90-280 nN enabled us to probe subun it arrangement in the bulk region of the collagen fibril. The results indic ate that the molecular assembly in the hydrated fibril is akin to that in t he intact form. The image resolution was improved by stabilizing the collag en molecules through crosslinking with glutaraldehyde, which served to reso lve microfibril-like structure on the fibril surface.