OPTIMIZATION OF COLLAGEN LIQUID-CRYSTALLINE ASSEMBLIES - INFLUENCE OF SONIC FRAGMENTATION

We have previously demonstrated that highly concentrated solutions of type I calf skin collagen form liquid crystalline assemblies whose three-dimensional arrangements follow geometries described in extracellular matrices. Studying these self-assemblies in vitro intimates how structures of similar appearance might self-assemble in vivo. The spontaneous long-range order of collagen triple helices is easier to obtain once the protein is fragmented by ultrasonic waves. In the present work we show by X-ray diffraction and differential scanning calorimetry that the structural stability of collagen fragments is preserved after sonication times reaching 40 min. The sonicated polypeptide chains analyzed by SDS gel electrophoresis show after 30 min of sonication a wide polydispersity in molecular weights with a population ranging from 100 kDa and higher size aggregates to small fragments of 30 kDa. The sonicated molecular population, observed in electron microscopy after unidirectional platinum shadowing, shows after 20 min of sonication a preponderant population of fragments below 90 nm in length. The present results indicate that the best time for the emergence of liquid crystalline phases corresponds, under our experimental conditions, to sonications of 20 min. The cholesteric order, monitored in optical microscopy between crossed polars, is then significantly optimized both in time and in space. (C) 1994 Academic Press, Inc.