Research

Collagen Fibrils

Axel Ekani-Nkodo
Physics Department, UC Santa Barbara

In collaboration with Prof. Paul Hansma (UCSB, Physics Department), we investigated mechanical properties of collagen fibrils (Type I). AFM experiments performed in Paul Hansma’s lab suggested a "tube-like" mechanical behavior of fibrils. We use micropipettes to manipulate single collagen fibrils and imaged them under a light microscope. Fibrils can buckle (B) and form "kinks" (C) under compression, suggesting that their outer shell is more rigid than their core. They also have a tendency to kink again at the same location (E).

A single collagen fibril under compression (micropipettes).

We also investigated size-exclusion in collagen fibrils and diffusion of small fluoresceinated probes by Fluorescence Recovery After Photobleaching (FRAP). Dyes were forced to travel along the fibrils, covered in oil. We observed that the larger ones (10 kD dextran, R_h=2 nm) were excluded from the fibrils whereas the small ones (fluorescein, R_h=0.4 nm) diffused inside. The diffusion coefficient obtained is slower than that in water by 5 orders of magnitude. We attribute most of the decrease to binding to the dye to collagen molecules (the dissociation constant was measured K_D=2 _M).

Left: collagen fibrils immersed in oil. Dyes are forced to diffuse along the fibrils. A) with fluorescein, B) with 10 kD dextran.

Right: times series of the fluorescence recovery in a fibril.

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RESEARCH