Silica-coated calcium pectinate beads for colonic drug delivery

The aim of this work is to develop novel organic-inorganic hybrid beads for colonic drug delivery. For this purpose, calcium pectinate beads with theophylline are prepared by a cross-linking reaction between amidated low-methoxyl pectin and calcium ions. The beads are then covered with silica, starting from tetraethyoxysilane (TEOS), by a sol-gel process. The influence of TEOS concentration (0.25, 0.50, 0.75 and 1.00 M) during the process is studied in order to modulate the thickness of the silica layer around the pectinate beads and thus to control the drug release. The interactions between the silica coating and the organic beads are weak according to the physicochemical characterizations. A good correlation between physicochemical and in-vitro dissolution tests is observed. At concentrations of TEOS beyond 0.25 M, the silica layer is thick enough to act as a barrier to water uptake and to reduce the swelling ratio of the beads. The drug release is also delayed. Silica-coated pectinate beads are promising candidates for sustained drug delivery systems.