Interpenetrating Polymer Networks of Poly(Acrylic Acid) and Polyacrylamide for Sustained Verapamil Hydrochloride Release

Interpenetrating polymer networks (IPNs) of poly(acrylic acid) (PAA) and polyacrylamide (PAAm) were synthesized and applied as drug delivery systems for verapamil hydrochloride (VPM). The IPN network density was controlled by changing IPN composition. Thus, when increasing the PAAm to PAA weight ratio, the network density increases as revealed by the equilibrium swelling ratio and microhardness measurements. The SEM study of the IPNs' morphology showed phase separation at nano level where PAAm domains with size below 100 nm are finely dispersed into the PAA matrix. The thermal study on the IPNs confirmed that both components are finely mixed as one T-g was detected for all IPNs' compositions. T-g vs. composition dependence obeyed the Gordon-Taylor equation and deviated negatively from the Fox equation thus confirming weak interactions between PAA and PAAm. The VPM loading into PAA/PAAm IPNs resulted into amorphization of the drug as well as in a IPNs' T-g increase as revealed by differential scanning calorimetry (DSC). The in vitro release of VPM shows that the IPNs of PAA/PAAm are suitable systems for sustained drug delivery. It was established that by changing IPNs' composition it is possible to obtain different drug release kinetic profiles.