Dynamic rheological studies of hydrophobic interactions in injectable collagen biomaterials

Abstract

SYNOPSISInjectable collagen is a concentrated dispersion of collagen fibers in aqueous solution that is used to correct dermal contour defects through intradermal injection. The effect of hydrophobic forces on the rheology of concentrated dispersions of collagen fibers was studied by dynamic rheological measurements over temperatures ranging from 283 to 308 K. The results are interpreted in terms of the associated relaxation time spectra and the theory of Kamphuis et al. for concentrated dispersions. Increases in fiber rigidity are seen from a progressive decrease in the slope of the linear log G' (or G") vs. log w data recorded for these dispersions as temperature is increased. A molecular interpretation 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 volume 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 temperatures above 293 K and reflects a gel transition. Thermal gelation of collagen dispersions is proposed to proceed through hydrophobically driven mechanisms of increased fiber rigidity and enhanced interfiber attractive forces. 0 1993

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