Lubricating Performance of Polymer-Coated Liposomes

Dry mouth is a troublesome condition linked to lubrication failure and leads to other diseases such as fungal infections and wounds in the oral cavity. There are many commercial salivary substitutes in the market, but none with a long-lasting lubrication effect. Polymer-coated liposomes can be an interesting formulation strategy for retrieving the symptoms of dry mouth by mimicking the micelles of saliva. In the present study, polymer coated-liposomes were prepared by the conventional thin film method and subsequently coated with three different polymers with different charge densities; alginate, chitosan and hydrophobically modified ethyl hydroxyethyl cellulose (HM-EHEC). The prepared polymer-coated liposomes were studied concerning their lubricating properties using a ball-on-disc tribometer at 2 N load at 37 °C, and their flow behaviours were also measured. Solutions of the pure polymers and dispersions of the uncoated liposomes were also studied to investigate any contributions from the individual components. A commercial dry mouth product based on HEC (hydroxyethyl cellulose) and glycerol was also included. The formulations were measured as soon as possible after preparation and some of them after >4 weeks. Results demonstrated that all the positively-charged formulations (chitosan, positive liposomes and chitosan-coated liposomes) had superior lubricating properties with friction coefficients (μ < 0.1) at orally relevant speeds (50 mm/s) as compared to the neutral or negatively-charged systems. At boundary lubrication conditions (3 mm/s), the chitosan-coated liposomes obtained an even lower friction force than the individual components, thus indicating a synergistic effect between the polymer and the liposome.