Molecularly imprinted polymers as drug delivery systems for the sustained release of glycyrrhizic acid

The aim was to synthesize molecularly imprinted polymers (MIPs) with high recognition properties towards glycyrrhizic acid and to evaluate the performance of these materials to act as base excipients in glycyrrhizic acid sustained release in gastrointestinal simulating fluids.

MIPs were synthesized using methacrylic acid (MAA) as acidic, 2-(dimethylamino)ethyl methacrylate (DMAEMA) as basic, and 2-hydroxyethylmethacrylate (HEMA) as neutral functional monomers, while ethylene glycol dimethacrylate (EGDMA) was chosen as a crosslinking agent. The imprinting effect was evaluated by binding experiments using glycyrrhizic acid and glycyrrhetic acid (analogue molecule) solutions and in-vitro release studies were performed in gastrointestinal simulating fluids.

Good recognition and selectivity properties were found in all the synthesized materials in both ethanol and ethanol-water mixture. The release from non-imprinted polymers was indeed higher at acidic pH, while a slower release was observed in MIPs' case, because of the presence of imprinted cavities in the polymeric structure. The stronger capacity of MAA to interact by hydrogen bonds with the template makes MAA-containing MIPs the most effective materials in both rebinding and release experiments.

The release tests confirm the applicability of imprinted polymer for glycyrrhizic acid sustained release in gastrointestinal simulating fluids.