RESUMEN
The aim of this work was to study the performance of chitosan (CB) grafted with acrylamide (CB-g-A) as prolonged drug release matrix as compared with unmodified chitosan. A non-pH dependent swelling behaviour for the matrix tablets based on grafted chitosan was observed. The overlaping between degree of swelling measured by weighing (DSw) and measured by increase of diameter (DSd) up to 240 minutes showed that the swelling process could be isotropic. The non-pH dependent swelling behaviour of these matrices could be explained by the partial substitution of amine groups of the chitosan chain by acrylamide. The grafting reaction provides an ionizable amine group by a neutral amide group which make the matrix non pH-dependent. On the contrary, the matrix tablet based on chitosan showed a pH dependent swelling behaviour where the swelling process could be anisotropic. The higher degree of erosion and swelling of the formulation based on CB-g-A600 (%G = 600) compared with the formulation based on chitosan and CB-g-A418 (%G = 418) could explain the higher fraction of theopylline released. For all formulations studied in this work, the amount of theopylline released from the matrix tablets was found to be controlled by a combination of the diffusion process and relaxation of the polymeric structure. These results match with the controlled swelling behaviour and low degree of erosion observed for these systems.