Rheological properties of binary and ternary protein-polysaccharide co-hydrogels and comparative release kinetics of salbutamol sulphate from their matrices.

Rheological properties of binary (AgarGelA and AgarGelB) and ternary (AgarGelAB and GelABAgar) co-hydrogels of agar (polysaccharide) with gelatin A and gelatin B (proteins) were studied to investigate their differential viscoelastic behavior. Two sets of rheological experiments, isochronal temperature and isothermal frequency sweep, were performed and the storage modulii, G' was measured which could be correlated to the gel strengths. Two separate peaks at 70°C and 35°C, corresponding to melting temperatures of agar and gelatin gels respectively, were obtained when derivative of G' with respect to temperature, dG'/dT was plotted against temperature which clearly showed the presence of two separate networks of gelatin and agar interconnected to each other. The results revealed that AgarGelAB was the strongest and AgarGelA was the weakest gel among all the gels studied. In order to see the effect of gel microstructure on drug encapsulation and release behavior, a model drug salbutamol was encapsulated in various gel matrices and the release of the same was seen in phosphate buffer pH 7.4, in simulated gastric fluid pH 1.2 (SGF) and in simulated intestinal fluid pH 6.8 (SIF) media. The drug release behavior universally followed sigmoidal kinetics invariant of gel composition. It is concluded that the hydrogel microstructure influenced the release behavior and best release, in all the three media, could be found with binary gel, AgarGelB, and ternary gel, AgarGelAB. Finally, microstructure of these gels is proposed.