High and low molecular weight hyaluronan (HA) are currently used as lubricants in several commercially available eye drops. However, the role of this polysaccharide on friction and lubrication on the eye is unknown as the current research mostly addresses joint cartilage.1 The lubrication function of HA is determined by its structure, e.g., size length of the chain, macromolecular architecture, aggregation as a function of the media, and adhesion to the ocular surface. The aim of this study was to evaluate the importance of molecular weight and lubricant composition (phosphate, borate, (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) and trehalose/phosphate buffers) on the lubricating performance of hydrophobized (sodium dodecanoyl grafted to hyaluronan) and native HA. The efficiency of HA as a boundary lubricant has been disputed in the literature. HA appears to have a stronger wear-reducing role than a friction-reducing one. Up to now, the tribological models usually included the high pressures of the joints. While typical value of the eyelid pressure on the cornea at rest being around 1 kPa. In this work, the effect of HA and amphiphilic HA will be extensively characterized in the above-mentioned buffers used in commercially available eye drops. The tribological model will be also used for evaluation of eye drops available in the European market. Furthermore, the visualization of lubricating film as a function of molecular weight of the polymer (Mw) will be discussed. The friction measurements are related to simultaneous visualization of a mucin based-contact as in vitro model, which contributes to better understanding of lubricating film on the eye ‘surface.
The tribological measurements revealed that the amphiphilic derivative decreases the friction coefficient. Moreover, medium molecular weight HA showed an enhanced mucoadhesion and lubrication properties compared to high Mw. Even though the use of trehalose enhanced the mucoadhesiveness, this ingredient is relatively high priced for commercialization. At the same time, trehalose showed an increased friction coefficient. The results here presented provide valuable information for formulation of highly performing HA-based formulations to treat eye dry disease.
- Černohlávek M, Brandejsová M, Štěpán P, Vagnerová H, Hermannová M, Kopecká K, Kulhánek J, Nečas D, Vrbka M, Velebný V, Huerta-Angeles G. Insight into the Lubrication and Adhesion Properties of Hyaluronan for Ocular Drug Delivery. Biomolecules. 2021; 11(10):1431.
The authors would like to thank the Technology Agency of the Czech Republic: Program of Industrial Research and Experimental Development 2020–2023 (TREND, Project No. FW01010060).