Reversible immobilization of drugs on a hydrogel matrix, 2. Diffusion of free chloramphenicol from poly(2‐hydroxyethyl methacrylate) hydrogels

The diffusional behaviour of chloramphenicol1 (1) from poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels is reported. The drug was trapped in the matrix cross-linked with various amounts of ethylene dimethacrylate (0,5–18 mol-%), and the diffusion was followed from disc-shaped slabs at swelling equilibrium in water (phosphate buffer, pH 7) at 37°C. The diffusion obeys the second Fick law and is rapid (D ≈ 10−8 cm2 s−1) in the case of the slightly crosslinked hydrogels used for corneal lenses. The diffusion coefficients decrease almost exponentially with increasing cross-linking ratio, and the process appears predominantly controlled by the free volume contribution of the diluent rather than by the sieving of the network.