Kinetics of swelling and drug release from PNIPAAm/alginate stimuli responsive hydrogels

Stimuli responsive hydrogels are very attractive for applications in sustained and/or targeted drug delivery systerns. As the release of drugs is related to the swelling behavior of hydrogels, the swelling kinetic studies become of great importance to appreciate the release kinetics from hydrogel matrices. Hydrogels with high performance properties have been prepared from N-isopropylacryl amide (NIPAAm) and sodium alginate, crosslinked with N,N'-methylene-bis(acrylamide) (MBAAm). This study is focused on the investigation of swelling and drug release kinetics, coupled by morphological studies. The kinetic parameters of the swelling at different temperatures for hydrogels samples have been evaluated and confirmed their temperature-responsive behavior. The swelling rate constant (k(sw)) decreases of with increasing temperature and slight increases with the alginate content in the samples. The drug release kinetic study from the prepared hydrogel matrices was performed in twice-distilled water and ethanol for bioactive agents as vanillin and ketoprofen, respectively. An increase of alginate content results in a slower rate and smaller percentage of vanillin and ketoprofen released. It has been established that the ketoprofen occurs according with case 11 of transport and vanillin release behavior occurs by an anomalous transport mechanism. The values of the release rate constant (k(r)) decreased by increasing swelling degree in case of 75/25 NIPAAm/alginate hydrogels and decreased also by increasing content of alginate in hydrogels with various compositions. Morphological studies performed by environmental scanning electron microscopy (ESEM) evidenced a relaxed network at high relative humidity, which explain both swelling and release profiles.