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H.A. Ketelson, B. Asgharian, M. Chowhan, D. Meadows; Characterization of Physical Property Attributes for Polymer Systems Used in Artificial Tear Products . Invest. Ophthalmol. Vis. Sci. 2004;45(13):70.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:To identify and compare the physical properties of various polymeric systems that are commonly used in artificial tear products and determine which properties are critical for providing superior product performance. Methodologies: Five physical property measurements were made on various ophthalmic polymeric systems and commercial artificial tear products: 1) bulk viscosity at low shear conditions; 2) lubricity between two moving surfaces; 3) dynamic interfacial tension at water/air interface; and 4) dynamic interfacial tension at water/octanol interface; 5) interfacial viscosity. Simple polymer/water solutions of various grades of HPMC, PVA, CMC, Carbomer and HP–guar were tested at ambient temperature and 35ºC. Effects of pH and ionic strength were also examined where appropriate. For bulk viscosity determinations, oscillation–stress–sweep and oscillation–frequency–sweep measurements were made at low shear stress and low frequency conditions to simulate the normal blink process. Lubricity measurements were made between two hydrophobic (polystyrene) surfaces and also between two corneal tissue samples. Dynamic interfacial tension measurements were made using the Wilhelmy plate and pendant drop methods, in air and octanol, respectively. Results:Bulk viscosity results indicated that the various samples tested had dramatic differences in performance at low shear stresses (1–100mPa) and some systems were very dependent upon pH (HP–guar) and ionic strength (Carbomer). Lubricity measurements showed that the systems based on HP–guar consistently had the best lubricity followed by HPMC and CMC. Dynamic interfacial tension measurements indicated that the polymers HPMC and HP–guar had a significant affect on surface tension at the air interface and was strongly dependent on temperature and took as long as 30 minutes to reach equilibrium. Dynamic interfacial tensions at the octanol/water interface were also strongly dependent on temperature and time. Conclusions: Bulk viscosity and lubricity experiments showed that systems based on HP–guar at ocular pH (7.5–7.8) conditions and temperature (35ºC) gave the best performance to ensure good pre–corneal retention and reduce friction between the eyelid and corneal surface. The tendency of polymers to stabilize the tear film by migrating to the tear film–air interface and the tear film–epithelium interface was evaluated with interfacial tension measurements in air and octanol. Only surface active polymers were effective and performance was strongly dependent upon temperature and time.
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