The formation of fibrils from collagen solutions. 2. A mechanism for collagen-fibril formation

Abstract

Fibril formation is regarded as the result of 2 processes: (a) nucleation, i.e., the aggregation of soluble collagen particles to form nuclei, the smallest aggregates capable of existing as a separate phase; (b) growth of the nuclei into fibrils by accretion of further soluble collagen particles. It is assumed that reaction of the soluble collagen particles with the surface of the growing fibrils controls the rate of growth and that the former process is proportional to the surface area of the precipitate and to the collagen concentration. Equations are derived which qualitatively account for the occurrence of a lag period in precipitation, where the nucleation process predominates over growth, and for the observation that the final distribution of fibril width is determined during the lag period. The equation for growth gives a precise description of the shape of precipitation curves over a wide range of conditions. Predictions about fibril width are consistent with experimental observations. The activation energy for growth is calculated to be 27 kcal./mole (at pH 7.1, I 0.23, collagen concentration 0.05%).