Application of hydrogels in the investigation into molecular diffusion based on refractive index measurements

A simple analytical method based on refractive index measurements was developed for in situ monitoring of the diffusion process of objective molecules in hydrogels. The diffusion process was monitored by recording the refraction of a laser beam passing through a triangular cell, which allows the determination of changes in the refractive index distribution from the deviated distance of the linear beam. Compared to conventional methods, this new method exhibits advantages such as more simplicity, lower cost, and speed. Further, the refractive index method permits the determination of the concentration distribution of solutes in the hydrogels at any time during the diffusion process under nondestructive circumstances. By applying this new method, we have investigated the diffusion process of various molecules such as sucrose, glucose, Poly(ethylene glycol) (PEG), cefazolin sodium, bovine serum albumin (BSA), and lysozyme in agarose gels. Moreover, we improved this method by introducing a precise temperature-controlled device into the monitoring system so that the effects of different temperatures on the diffusion of objective molecules can be studied. By employing Fick's second law, the diffusion behavior was investigated and the diffusion coefficients in agarose gels were therefore obtained. Amsden's physical model based on obstruction effect was applied to the simulation of the diffusion process and turned out to fit the results quite well.