Diffusion in Polymer Gel Implants


Crosslinked polyacrylamide and polyvinylpyrrolidone gels have been used to subcutaneously implant 125I-labeled immunoglobulin, 125I-labeled luteinizing hormone, 125I-labeled bovine serum albumin, 125I-labeled insulin, [3H]prostaglandin F2α, and Na125I into hamsters. From the rates of absorption of the solutes, their diffusion coefficients were determined. The diffusion coefficients showed a logarithmic dependence on implant polymer concentration and solute molecular weight. Release of the solutes from gel preparations incubated 10 mM phosphate buffer (pH 7.2) at 37° revealed a similar relationship between solute diffusion coefficient, molecular weight, and the concentration of polymer. A general equation was derived that gives the expected diffusion coefficient of a substance in a polymer gel from its molecular weight, diffusion coefficient in solvent, and polymer concentration of the gel.

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