Properties of superporous hydrogels for drug delivery

The purpose of the present study was to investigate the properties of a novel hydrogel system, the superporous hydrogel. Superporous hydrogels have been developed over the last several years as a drug delivery system. Studies on superporous hydrogels made of poly(acrylic acid-co-acrylamide) were focused on the properties that will be useful in oral delivery for gastric retention and vascular implantation as a chemoembolization device. Superporous hydrogels have a porous structure that acts as a capillary network. The capillary properties of superporous hydrogels are a result of an oriented pore structure that is produced during the production. High interconnectivity is present in the majority of the superporous hydrogels, but at the surface, little interconnectivity is present. The high interconnectivity and pore structure is maintained when the superporous hydrogel is compressed radially, but the interconnection is disrupted when compression is axial. A reduction in dry volume of 80% is possible, allowing the superporous hydrogel to be small enough to be taken as an oral dosage form. The swelling of the compressed superporous hydrogels is slightly slower than the uncompressed superporous hydrogels but still much faster than a similar nonporous hydrogel. The swelling of superporous hydrogels is responsive to the environment in which the swelling takes place. In acidic conditions, superporous hydrogels swell to a much lower degree than in basic solutions because of the ionization of the acrylic acid on the polymer chains. The swollen size of the superporous hydrogel is large enough to be maintained in the stomach after ingestion. The density of the superporous hydrogel causes it to float in simulated gastric fluid, which will aid in the retention in the stomach prior to swelling. The bioadhesive properties of poly(acrylic acid) are also expected to increase retention of the superporous hydrogel at early times. Swelling of superporous hydrogels in blood is very slow due to the poor wetting of the dry hydrogel by blood and the viscous properties of blood. Plasma and serum both wet the dry hydrogel and swelled the superporous hydrogel at a much faster rate. The properties of the superporous hydrogels indicate that it will be very applicable to oral administration and vascular implantation