DYNAMIC RHEOLOGICAL STUDIES OF HYDROPHOBIC INTERACTIONS IN INJECTABLECOLLAGEN BIOMATERIALS

Injectable collagen is a concentrated dispersion of collagen fibers in aqueous solution that is used to correct dermal contour defects throu gh intradermal injection. The effect of hydrophobic forces on the rheo logy of concentrated dispersions of collagen fibers was studied by dyn amic rheological measurements over temperatures ranging from 283 to 30 8 K. The results are interpreted in terms of the associated relaxation time spectra and the theory of Kamphuis et al. for concentrated dispe rsions. Increases in fiber rigidity are seen from a progressive decrea se in the slope of the linear log G' (or G'') vs. log omega data recor ded for these dispersions as temperature is increased. A molecular int erpretation of this result was obtained by treating collagen fibers as a liquid crystalline phase of rigid-rod collagen molecules that have phase-separated from aqueous solution. Hydrophobic forces affect the v olume fraction of water that is present in the phase-separated fibers, which, in turn, affects the rigidity of the fibers. Distinct yielding behavior (in the nonlinear viscoelastic region) occurs at temperature s above 293 K and reflects a gel transition. Thermal gelation of colla gen dispersions is proposed to proceed through hydrophobically driven mechanisms of increased fiber rigidity and enhanced interfiber attract ive forces. (C) 1993 John Wiley & Sons, Inc.