Mucoadhesive properties of tamarind-seed polysaccharide/hyaluronic acid mixtures: A nuclear magnetic resonance spectroscopy investigation

Mixtures of tamarind-seed polysaccharide (TSP) and hyaluronic acid (HA), which are employed as artificial tears for ophthalmic applications in the eye dry syndrome, were investigated by NMR spectroscopy by analyzing the effect of TSP/HA ratio and total concentration on their capability to form stable aggregates with enhanced mucoadhesive properties over those of the separate polysaccharides. The effect of TSP, HA or TSP/HA mixtures on the affinity of diclofenac sodium salt (DS) to mucin (BSM) was ascertained by means of proton selective relaxation rate measurements and assumed as the basis to compare polysaccharides mucoadhesive properties. The NMR relaxation parameters of pure DS (2 mM), binary DS/BSM (5 mg/mL or 10 mg/mL) and ternary DS/BSM/polysaccharide systems (polysaccharide = TSP, HA or variable ratios TSP/HA mixtures) were compared in aqueous medium. The experimental data demonstrate that the minimum concentration of 1.5 mg/mL of each polysaccharide is needed to have formation of a stable TSP/HA aggregate endowed with NMR detectable mucoadhesive properties and inside which reciprocal synergistic interaction occurs.