The formation of fibrils from collagen solutions 1. The effect of experimental conditions: kinetic and electron-microscope studies

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Abstract
The precipitation of collagen fibrils in solutions of acid-soluble collagen extracted from calf dermis was followed turbidimetrically under a range of experimental conditions and the final precipitates examined by electron microscopy. All the precipitates consisted of fibrils bearing 640 A striations and in each precipitate the distribution of fibril width was fairly narrow. Lateral aggregation of the fibrils was most pronounced in those precipitates containing the widest fibrils. When the rate of precipitation was increased by increasing the temperature or lowering the ionic strength, fibril width decreased, but when the rate was increased by reducing the pH, fibril width increased. The variation of rate of precipitation with ionic strength and pH indicates that it is controlled to a significant degree by electrostatic interaction between the soluble collagen particles. All precipitation curves showed a lag period, followed by a sigmoid growth curve. Both phases were accelerated by increase of temperature but the width of the ultimate fibrils was affected only if the temperature was increased during the lag period. It is concluded that most of the fibrils were formed during the lag period. These observations are discussed in relation to the development of collagen fibrils in vivo.

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