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D. L. Meadows, H. A. Ketelson, J. Davis; Extensional Rheological Properties of an Artificial Tear Delivery System. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1545.
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© ARVO (1962-2015); The Authors (2016-present)
The extensional rheology of a polymer may have important influences on the tensile strength of the tear film and resistance of tear film breakage. The extensional rheology of an artificial tear delivery system (ATDS) is characterized using a capillary break-up extensional rheometer (CaBER®). The extensional viscosities and break-up times are determined and interpreted in terms of their importance in the tear film and the data is compared with marketed products.
Several marketed products and the ATDS were characterized using the CaBER®. The CaBER® experiment is performed by creating an unstable liquid bridge through a rapid stretch of a polymer fluid. The evaluation of the fluid filament mid-point diameter is measured with a laser micrometer. From this rapid stretch experiment and knowledge of the solution surface tensions the extensional viscosities were calculated.
The ATDS displayed longer break-up times (122 ms) compared to the marketed products (<10 ms) at pH 7.9. The extensional viscosity was calculated to be 5.6 Pa.s. Adjustment of the pH to 7.6 reduced the break up time to 49 ms and the extensional viscosity was 3.6 Pa.s. The ATDS was modified to simulate the effect of dilution in the eye which will increase the cross linking efficiency between polymer chains. The extensional viscosity of the modified ATDS was calculated to be 263 Pa.s and the break-up times ranged between 4100 ms to 4150 ms. In the timescale of the experiments the data suggested the ATDS was self-assembling, resulting in a strong gel-like structure which prevented deformation of the polymer under the conditions used to simulate dilution in the eye.
The ATDS displayed unique extensional rheology properties and this was magnified by modification of the formulation to mimic its dilution in the eye. Long filament break up times were observed for the modified ATDS. The extensional rheological properties associated with the ATDS appears to be an important physical property that may benefit and improve tear film stability.
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