Mucoadhesive polymers: Synthesis and in vitro characterization of thiolated poly(vinyl alcohol)

The aim of this study was to synthesize thiolated poly(vinyl alcohol) (PVA) and to evaluate its mucoadhesive properties. Thiourea and 3-mercaptopropionic acid were utilized in order to obtain thiolated PVAs, namely, TPVA(1) and TPVA(2), respectively. TPVA(1) and TPVA(2) displayed 130.44 +/- 14.99 and 958.35 +/- 155.27 mu mol immobilized thiol groups per gram polymer, respectively, which were then evaluated regarding reactivity of thiol groups, swelling behavior and mucoadhesive properties. Both thiolated PVAs exhibited the highest reactivity at pH 8.0 whereas more than 95% of free thiol groups were preserved at pH 5.0. Thiolation of PVA decelerated water uptake and prolonged disintegration time of test discs compared to unmodified PVA. Contact time of TPVA(1)- and TPVA(2)-based test discs on porcine intestinal mucosa was 3.2- and 15.8-fold prolonged, respectively, in comparison to non-thiolated PVA as measured by rotating cylinder method. According to tensile studies on mucosa, the total work of adhesion (TWA) and the maximum detachment force (MDF) were increased when compared to PVA. Furthermore, thiolated PVAs preserved higher percentage of viable cells compared to unmodified PVA within 24 h as evaluated by MTT assay. Accordingly, thiolated PVA represents a novel excipient that can likely improve the mucoadhesive properties of various pharmaceutical formulations. (C) 2016 Elsevier B.V. All rights reserved.