Abstract
Purpose: :
To characterize the rheological and tribological properties of a novel artificial tear delivery system (ATDS). The mechanism by which the ATDS responds to mechanical and chemistry changes is discussed.
Methods: :
For bulk viscosity determination, steady state flow and oscillation measurements were made using a controlled stress rheometer. Interfacial rheology measurements were made using an oscillation drop technique. The rheological changes as a function of pH, lysozyme, mucin and ATDS modification changes were studied. Friction measurements were made using a pin-on-disc tribometer and pericardium tissue as the substrate. Marketed artificial tear products were used as controls in the experiments for comparison purposes.
Results: :
The steady state flow and oscillation experiments indicated the ATDS displayed significant sensitivity towards shear stress, pH and ATDS composition changes to simulate dilution in the eye. The viscosity of the ATDS decreased from 22cps to 17cps at 1.0s-1 when the pH was decreased from 7.9 to 7.6. In the frequency sweep, the elastic moduli decreased from 3.4x10-4Pa to 1.1x10-4Pa, at a frequency of 1.0 Hz and a stress of 1.0µN.m, when the pH was decreased from 7.9 to 7.6. The ATDS is a viscous dominant system in the pH range of 7.9 to 7.6. The steady state flow experiments showed a continuous increase in viscosity measured at 1.0s-1 when ATDS was modified to simulate dilution in the eye. The interfacial rheology experiments showed lysozyme and mucin were effective at increasing the elastic moduli of the ATDS. The tissue-on-tissue friction measurements showed that a significant reduction in friction occurred when the ATDS was modified to simulate dilution in the eye.
Conclusions: :
This study showed that the ATDS contributed towards reducing friction and increasing the bulk and interfacial viscoelasticity when the ATDS was modified to simulate dilution in the eye. These changes coupled to the synergistic effects when the ATDS is combined with lysozyme and mucin indicate the ATDS should provide long lasting lubrication and surface protection in the eye.
Keywords: cornea: tears/tear film/dry eye