Glucose recovery with bare and hydrogel-coated microdialysis probes: experiment and simulation of temporal effects.

In vitro microdialysis glucose sampling was used to test the transient and steady-state suitability of antifouling hydrogel coatings, composed of 2-hydroxyethyl methacrylate, vinylpyrrolidinone, and poly(ethylene glycol). The in vitro glucose diffusion coefficients of bare microdialysis membranes and hydrogel coatings were determined experimentally to be 1.1 x 10-6 and 3.2 x 10-6 cm2/s, respectively. These values were used to numerically simulate the effect of the hydrogel on glucose transport across the microdialysis membrane using a convection-diffusion transport model. The times for dialysate at the exit of the bare and hydrogel-coated microdialysis probes to reach 95% of steady state were calculated to be 20 and 66 s, respectively. However, the experimental data showed that 95% of steady-state glucose recoveries were reached after 4-5 min. Numerical simulations incorporating the Taylor dispersion in the outlet tubing showed the time difference was caused almost completely by convective transport in the outlet tubing with negligible contribution from analyte profile broadening. These data indicated that the hydrogel coatings imposed 44% reduction in glucose permeability and consequently 26% reduction in the percent recovery. The effect of hydrogel coatings on the time to reach the steady-state recovery was insignificant compared with the time required for convection of glucose in the outlet tubing.