Simple physical model of collagen fibrillogenesis based on diffusion limited aggregation.

Type I collagen is a rod-like protein which self-assembles in a regular array to form elongated fibrils. The process of fibril formation, termed fibrillogenesis, is driven by the increase in entropy associated with loss of water from the bound monomers. A model based on diffusion limited aggregation (DLA) was used to investigate some of the mechanisms involved in this process. The aggregates created in the model displayed several features in common with collagen fibrils including an elongated morphology and a preference for tip growth. Analysis of these aggregates revealed a linear relationship between mass and distance from the tip, consistent with experimental observations. Intrafibrillar fluidity was introduced into the model by using a surface diffusion term. This led to the formation of aggregates with more compact morphologies. These results strongly implicate the role of diffusion limited growth in collagen fibril formation.