Abstract
Purpose: :
The extensional rheology (ER) of polymers used in artificial tear solutions (ATS) has not been well documented. By following the diameter change of a polymer filament subjected to an extensional response, the contribution of the tensile strength and resistance to breakage can provide important information towards improving ATS. The ER of Systane ULTRA® is characterized using a capillary break-up technique (CaBER 1®). The extensional viscosities (EV) and polymer filament diameter change (PFDC) are determined and interpreted in terms of their contribution to tear film structure. The data is compared with marketed products.
Methods: :
The marketed products and Systane ULTRA® were characterized using the CaBER 1®. The CaBER 1® creates an unstable liquid bridge via a rapid stretch of a polymer fluid. The evaluation of the PFDC mid-point diameter is measured with a laser micrometer. From this rapid stretch experiment and knowledge of the solution surface tensions the EV’s were calculated.
Results: :
Systane ULTRA® displayed longer PFDC, 122ms, and higher calculated EV, 5.6Pa.s, compared to the marketed products. Adjustment to pH 7.6 reduced FDC to 49ms and EV to 3.6Pa.s. Systane ULTRA® was modified to probe the removal of sorbitol to more closely mimic the dilution effect in the eye. The EV of Systane ULTRA® without sorbitol at pH 7.9 was 263kPa.s with the FDC near 4125ms. Systane ULTRA® was modified with no sorbitol at pH of 7.6 to study the influence of calcium. In this case the PFDC increased from 612ms, no calcium, to 3,678ms, with calcium. The EV of Systane ULTRA® increased to 443Pa.s with calcium. In the timescale of the experiments, the data suggested Systane ULTRA® was self-assembling to generate a strong gel-like structure which prevented deformation of the polymer.
Conclusions: :
Systane ULTRA® displayed unique extensional rheology properties and this was magnified by modification of the formulation to mimic its dilution and interaction in the eye. Long FDC’s were observed for the modified Systane ULTRA® formulations. The extensional rheological properties associated with Systane ULTRA® appear to be an important physical property that may benefit and improve the tear film structure.
Keywords: cornea: tears/tear film/dry eye