STABILIZATION OF FLUID CHOLESTERIC PHASES OF COLLAGEN TO ORDERED GELATED MATRICES

Liquid crystalline assemblies occur spontaneously in highly concentrat ed solutions of type I acid-soluble calf skin collagen. The degree of order, identified by optical microscopy in polarized light, varies fro m a random distribution of molecules at low concentrations to highly o rganized structures as the concentration increases up to 80 mg/ml. Ult rastructural studies using classical techniques of chemical fixation a re inappropriate for liquid crystalline phases due to the absence of s table links maintaining their three-dimensional order. In order to ana lyse the collagen liquid crystalline phases by electron microscopy the viscous preparations were stabilized under ammonia vapour. Observatio ns of the gels in polarized Light indicated that the liquid crystallin e order, established at acidic pH in a sol state, persists at neutral pH in a gel state. Transmission electron microscopic observations allo w us to validate the geometrical model interpreted from observations i n polarizing microscopy, that is continuously twisting orientations in cholesteric phases characterized by typical series of arced patterns when viewed in oblique sections. A significant result is that the ultr astructure of the stabilized liquid crystalline collagen faithfully mi mics fibrillar patterns described in vivo in extracellular matrices. T his strongly supports the hypothesis that liquid crystalline propertie s are involved in the morphogenesis of collagen matrices. (C) 1995 Aca demic Press Limited