Diffusivity of 125I-calmodulin through collagen membranes: effect of source concentration and membrane swelling ratio

Diffusivity of 125I-calmodulin (MW congruent to 17,000) through collagen membranes was studied as a model for the release of macromolecules from collagen matrices. The diffusion coefficient of calmodulin through collagen membranes was determined from time-lag experiments conducted in a dialysis cell at 24 degrees C. Based on time-lag experiments, the diffusion coefficient was observed to be a function of source concentration and membrane swelling ratio after denaturation. The dependence of the diffusion coefficient on source concentration was consistent with a model involving calmodulin immobilization by the collagen membrane. At high source concentrations the diffusion coefficient of calmodulin through collagen membranes was observed to vary from about 10(-8) for uncrosslinked membranes to 10(-9) cm2/s for highly crosslinked membranes. Based on theoretical calculations, the release rate from collagen matrices may be altered by a factor of three. It was concluded that the release rate of biologically active molecules from collagen matrices can be controlled by varying the extent of crosslinking and the macromolecular concentration. Further studies are necessary to characterize the release of other macromolecules from collagen matrices.