Multifunctional low temperature-cured PVA/PVP/citric acid-based hydrogel forming microarray patches: physicochemical characteristics and hydrophilic drug interaction

The characteristics of multifunctional polymeric hydrogel-forming microarray patches based on poly(vinyl alcohol)/poly(vinylpyrrolidone)/citric acid composite crosslinked at 80 °C were investigated. The swelling study showed that this composite possesses a higher swelling degree than the same polymer heated at 130 °C due to a lower crosslink density, which was then confirmed by FTIR examination. Solid-state studies revealed that lower-temperature crosslinking does not provide enough energy for the polymer to rearrange itself into a crystalline form. However, this composite polymer was shown to possess acceptable mechanical strength to insert/penetrate into the skin. The patch can function both as a means to sample model hydrophilic drugs from the skin and to deliver them when combined with a melt-type polyethylene glycol reservoir. The hydrophilic interaction between the hydrogel and drugs was investigated. A drug with a higher diffusion coefficient, modelled by theophylline (diffusion coefficient = 16.17 × 10^-6 cm²/s), can be delivered more efficiently than fluorescent sodium (diffusion coefficient = 2.32 × 10^-6 cm²/s) or cyanocobalamin (diffusion coefficient = 7.31 × 10^-6 cm²/s). This is mainly due to theophylline’s high permeability (permeability coefficient = 7.40 × 10^-5 cm/s) and weak ability to interact with the hydrogel (coefficient of partitioning = 1.3). These results indicated that the diffusion coefficient could be a useful predictive parameter to determine the delivery efficiency of the system. Furthermore, the results provide insight into how to select a suitable hydrogel for drug monitoring or delivery involving hydrophilic compounds based on the hydrophilic interaction between the polymer and the drug.