Mucoadhesion, hydration and rheological properties of non-aqueous delivery systems (NADS) for the oral cavity

Objectives Effective delivery of oral care actives from conventional hydrogel formulations is often compromised by poor retention associated with shear forces present in the mouth, salivary washout and over-hydration of the gel which can lead to structural breakdown and adhesive failure. Non-aqueous gels offer the opportunity to formulate rheologically acceptable vehicles with higher concentrations of bioadhesive polymer than is possible using water as the primary solvent. Accordingly, this study describes the formulation and characterisation of the rheology, hydration and bioadhesive properties of a range of non-aqueous delivery systems (NADS). Methods The formulations were composed principally of glycerol, with varying amounts of polyethylene glycol (PEG) 400 and Carbopol® 974P being incorporated in the ranges 0–31.34% and 0–4% (w/w). Work of adhesion (WOA) and maximum force of detachment (Fmax) were determined using a Dartec tensile tester after application of a normal force. Rheology was assessed using a Bohlin CS CVO rheometer. Results WOA and Fmax increased with increasing compression time and Carbopol concentration. Addition of 30% (w/w) PEG 400 to the formulation containing 2% Carbopol in glycerol improved bioadhesive function. Formulation rheology was largely controlled by the Carbopol concentration, and to a lesser extent by the concentration of PEG 400 and these, in turn, largely determined the bioadhesion parameters and rates of hydration. Conclusion The results of this in vitro study suggest that bioadhesion, and consequently potential drug bioavailability, would be enhanced by use of a water miscible non-aqueous delivery vehicle such as glycerol containing a bioadhesive polymer such as Carbopol with the addition of controlled amounts of PEG as plasticiser.