Parallel Assembly of Collagen Fibrils on Mica Surface and Steps
Collagen is the most abundant protein in human body and the major component of the extracellular matrix. It self-assembles into fibrillar structures that exhibit characteristic 67-nm bands called the D-period. Despite decades of research, the molecular mechanism by which collagens assemble into ordered fibrillar structures is not well-understood. In this work, self-assembly of type-I collagen molecules in vitro was monitored using atomic force microscopy at different time points under various conditions. Control parameters include: monomer concentrations, pH, types of electrolytes, ionic strength, and incubation temperature. Presence of potassium and phosphate ions, and prolonged incubation were found to be essential for the formation of D-periods on the fibril. When assembled on a mica surface, the growth was fast and almost unlimited in the longitudinal direction but relatively slow in the direction transverse to the fibril axis. This resulted in fibrils aligning in parallel on mica surface. The spacing between collagen fibrils decreased over time. We also observed collagen assembly near regions containing steps on mica. At narrow steps (approximately 700 nm wide), collagen fibrils grew along the direction of the crack. However, for a shallow step (about 15 nm height), we observed collagens covering the crack, presumably because the thermal fluctuation of collagen was sufficient enough to overcome the height of the step. Further studies are necessary to elucidate the possible assembly patterns and underlying mechanisms of collagen assembly at surface boundaries, which will be useful for developing defined matrices for biomaterial applications.
Leow, Wee W (2010). Parallel Assembly of Collagen Fibrils on Mica Surface and Steps. Honors and Undergraduate Research. Available electronically from