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H. A. Ketelson, J. Davis, D. Meadows; Characterization of an Anionic Lipid Stabilized Ocular Emulsion Containing HP-Guar. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6264.
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To study the physico-chemical properties of a novel artificial tear emulsion product technology based on an anionic phospholipid, mineral oil, HP-Guar and the demulcent propylene glycol. Adhesion, spreading pressures, steady state flow rheology and friction measurements were used to evaluate the emulsions for use as a restorative tear replacement eye drop displaying ocular surface protectant benefits.
The emulsions were formed using mineral oil and a novel blend of interfacial substances with processing via in-line homogenization. Emulsions were adjusted to pH’s between 7-8. Adhesion and spreading experiments were evaluated by Langmuir Trough, elipsometry and light microscopy. Steady state flow and dynamic rheology profiles were obtained using a controlled state rheometer. Friction coefficients were measured using a pin-on-disc tribometer with pericardium tissue as the substrate.
Contact angle measurements indicated that the liquid/vapor surface tensions of the emulsions varied between approximately 70 mNm-1 at pH 7 to 56 mNm-1 at pH 8. The maximum estimated spreading pressures for the o/w emulsion were between 6-8 mNm-1. The emulsions at elevated pH (>7.4) displayed thixotropic behavior. For example, steady state flow experiments on emulsions at pH’s > 7.4 showed that that the viscosity decreased from 146 cps to 4.6 cps as the shear rate increased from 0.01s-1 to 1s-1, respectively. The emulsions also showed significant reductions in their coefficients of friction. For example, the friction coefficients for the emulsions were less than 0.1 for pH’s greater than 7.4.
The data showed that a stable oil-water emulsion containing HP-Guar, an anionic phospholipid and a demulcent can be generated as a novel artificial tear product. The artificial tear product has a novel composition blend to provide ocular surface protectant properties.
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