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Paramita Bandyopadhyay, Zora Marlowe, Tammy Kleiber, Stephen R. Davio; Unique Rheologic Properties of a Lubricant Eye Drop Containing Propylene Glycol and Glycerin (Active Ingredients) and Sodium Alginate. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3838.
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© ARVO (1962-2015); The Authors (2016-present)
Rheologic measurements were performed on five OTC dry eye products to assess properties related to comfort and duration of dry eye relief. These measurements assessed shear-thinning behavior, interaction with mucin, and gel-forming behavior at low shear.
Rheology measurements were conducted on a Brookfield LVDV-III Ultra rheometer using a CP-40 spindle and on a TA Instruments AR2000 rheometer with a double-gap concentric cylinder. Product was diluted 4:1 with either Hank’s Balanced Salt Solution (HBSS) or with 10% bovine sub-maxillary mucin (BSM Type-I from Sigma) in HBSS. Viscoelastic measurements were performed with angular frequency at 10 rad/sec and oscillatory stress ranging from 0.01-100 Pa. Shear-thinning behavior [viscosity () vs. shear (γ)] was modeled using the power law equation =Kγ(n-1). Mucin interaction was assessed by rel= obs/exp where, obs= (mucin+product mix) and exp= mucin+ product. Products studied were Soothe Xtra Hydration (B+L), Systane Long Lasting (Alcon), Blink (AMO), Genteal (Ciba Vision) and Refresh Liquigel (Allergan).
Soothe Xtra Hydration (XH) demonstrated the highest mucin interaction parameter, 6.5, where the other products were within the range of 0.8 (GenTeal) to 2.15 (Refresh LiquiGel). Additionally, Soothe XH shows shear-thinning behavior with the power law exponential term, n=0.6, similar to that of human tears, n=0.71. The other products with mucin did not fit the power-law model. Viscoelastic measurements showed elastic modulus, G’, > viscous modulus, G", at low stress only for Soothe XH plus mucin, indicating a gel-like structure at rest. All other products with mucin showed G">G’ at all stress indicating no gel-like structure.
Soothe Xtra Hydration containing sodium alginate as inactive ingredient demonstrates unique rheologic properties in the presence of bovine sub-maxillary mucin. The tear-like shear-thinning behavior and strong interaction with mucin make this product uniquely suited for dry eye therapy and should afford both long duration of action and enhanced comfort to patients.
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