Thiolated sodium alginate conjugates for mucoadhesive and controlled release behavior of metformin microspheres

The absorption of BCS III drugs can be improved by inhibiting the P-glycoprotein (P-gp) efflux and by increasing the mucoadhesion of natural polymers. In the present study, an esterification of sodium alginate (SA) with thioglycolic acid (TGA) was applied for the preparation of thiolated sodium alginate (TSA). The Ellman's test was applied to quantify the thiol group and a di-sulphide bond test was performed to confirm any SS linkages. The FTIR, DSC, XRD, ¹H NMR and charring point determinations were confirmed the thiol group of TSA. The gel like rheological properties with porcine mucous was confirmed by viscoelasticity properties and the mucoadhesion with the rabbit intestine was carried out after compression of 30 mg tablets of TSA. The content of thiol group was in the range of 320-730 μmoL/g of the polymer. The FTIR spectrum showed a characteristic peak of sulfhydryl group at 2557 cm^-1 in TSA and the reduction of the charring point from 220 °C to 178 °C was confirmed the thiolation of TSA. A direct relationship of mucoadhesion and swelling was observed with the concentration of TGA and SA, respectively. The prepared microspheres were 2-7 μm in size, excellent rheological properties and non-fickian drug release behavior was observed.