Miscibility study of carrageenan blends and evaluation of their effectiveness as sustained release carriers

Polymeric matrices of ι-, κ- and λ-carrageenans and ι-, κ- and λ-carrageenans blends, prepared by simple mixing and by solvent evaporation technique, have been tested for controlled release delivery of Tolterodine l-Tartrate. X-ray diffraction (XRD), infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and viscometry measurements showed that although all weight ratios of carrageenans blends were immiscible, carrageenans formed complexes with the drug through hydrogen bonding. In solid dispersions formulations although the drug was almost immediately dissolved (due to its amorphous character), an amount remained absorbed into polymer matrix and was not released, probably due to hydrogen bonding. When physical mixtures of pure carrageenans and Tolterodine l-Tartrate were prepared, release rate was slower and when λ-carrageenan was used, an almost controlled release formulation was achieved. However, real controlled release formulations were achieved only when physical mixtures of ι-/λ-carrageenans and Tolterodine were used. Thus, the combination of different types of carrageenans could change the carrier’s behaviour.