Sodium alginate-magnesium aluminum silicate composite gels: characterization of flow behavior, microviscosity, and drug diffusivity.

The aims of the present study were to characterize the flow behavior and thixotropic properties of sodium alginate-magnesium aluminum silicate (SA-MAS) composite gels with various ratios of SA and MAS, and to investigate the drug diffusivity and microviscosity of the composite gels. Moreover, interaction of SA and MAS in the form of dry composite was examined by using Fourier Transform Infrared (FTIR), and a possible structure model of SA-MAS composite gel was illustrated. Incorporating MAS into the SA gels provided higher viscosity and changed the flow behavior from Newtonian to pseudoplastic with thixotropy. This was due to the formation of electrostatic force and intermolecular hydrogen bonding between SA and MAS, leading to a denser matrix structure of the composite gels. Increasing the content of MAS decreased the drug diffusivity but increased the microviscosity of the composite gels. The denser matrix structure of the composite gels had a higher tortuosity, resulting in slower drug diffusion through water-filled channels in the gels. This finding suggested that incorporating MAS into the SA gels could improve the flow behavior and sustain drug release from the gels because of the formation of a matrix structure between SA and MAS in the gels.