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Brittany Coats, Jourdan Colter, Hee-Kyoung Lee, Brenda Mann, Barbara Wirostko; Coefficient of friction between carboxymethylated hyaluronic acid (CMHA-S) films and the ocular surface. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4757.
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© ARVO (1962-2015); The Authors (2016-present)
A novel hyaluronic acid polymer film, CMHA-S, is currently being developed as an ocular drug-delivery vehicle. Film retention in the inferior fornix for extended periods of time remains a challenge. Previous work by our group shows this obstacle can be overcome by careful control of the frictional interface between the CMHA-S film and the globe/eyelid. In this experimental study, we designed a custom tribometric system to quantify the coefficient of friction (COF) of CMHA-S on the eye, and evaluate the increase in friction when methylcellulose is added to the formulation.
CMHA-S films with (n=5) and without (n=15) methylcellulose were tested against ovine and human sclera. Scleral annuli and CMHA-S films were attached to a stress-controlled rheometer modified with custom fixtures. Blink Tears lubricating eye drops (Abbott Laboratories) were applied to a surrounding well to maintain lubrication throughout testing. Testing was carried out at axial loads of 0.3, 0.5, and 0.7 N. At each load, four positive and negative revolutions were applied at effective velocities of 0.3, 1.0, 10.0, and 30.0 mm/s, with a 12 second relaxation time between each set of revolutions. Loads and rates selected are replicative of physiological conditions in the eye. Two-way ANOVAs with repeated measures were used to evaluate the effect of sliding velocity and formulation (CMHA-S+/-methylcellulose) and sliding velocity and species (ovine, human) on friction.
Static and kinetic COFs of the CMHA-S film relative to ovine sclera were found to be 0.29±0.1 and 0.15±0.1, respectively. Static COF was significantly dependent on rate (p<0.0001), especially for CMHA-S with methylcellulose (p=0.0002). Kinetic COF was not affected by rate. CMHA-S with methylcellulose had 1.6 and 1.8 higher static and kinetic COFs, respectively, than CMHA-S, but damaged quicker at high loads and rates. CMHA-S tested against human sclera was not statistically different from CMHA-S tested against ovine sclera.
CMHA-S with methylcellulose had a higher frictional interaction with the globe, but it was prone to wear. This suggests that methylcellulose can be used to tailor CMHA-S frictional interaction with the globe surface and eyelid, but careful consideration of potential increased degradation must be considered.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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