(26b) Modeling Surfactant and Drug Transport from P-Hema Hydrogels

Surfactants are commonly incorporated into hydrogels to increase solute loading and attenuate the drug release rates. Drug transport in these systems is strongly coupled to the surfactant transport. We have investigated the microstructure, and transport of drug and surfactant in poly-hydroxy ethyl methacrylate (p-HEMA) gels loaded with Brij surfactants and an immunosuppressant drug, Cyclosporine A (CyA). This talk will focus on measurements and modeling of the drug and the surfactant transport, along with measurements of swelling, mechanical and optical properties. The SEM imaging clearly shows presence of about 50 nm aggregates inside the gel. The aggregates are distributed heterogeneously as patches that are a few microns in size and the patches are separated by a few microns. Results also show that the transport of CyA through the surfactant-laden gels is controlled by diffusion through the gel but the transport rates are reduced due to partitioning of the drug in the surfactant aggregates that form inside the gel. The transport rates for drug are coupled to the transport rates of surfactant, which are also diffusion controlled. The models developed are validated by experiments conducted with gels of different thicknesses and surfactant loadings. The models for the surfactant and drug release are fitted to the experimental data to obtain partition coefficient between drug concentration inside the micelle and that in the gel. These models can be very helpful in tuning the drug release rates from hydrogels by controlling the surfactant concentration. The results also show that surfactant laden p-HEMA gels exhibit an extended release of CyA and so contact lenses made with this material can be used for extended ocular delivery of CyA which is currently used to treat dry eye disease.