Measuring the Viscosity of Eye Drops

By AZoM.com Staff Writers

Topics Covered

Introduction
Significance of Measuring Eye Drop Viscosity
Measurements and Results
Conclusion
About RheoSense

Introduction

RheoSense is a key player in microviscometry, offering innovative microfluidic and MEMS based VROC (viscometer-rheometer-on-a-chip) chips. This article discusses the viscosity measurement of eye drops by means of the m-VROC.

Significance of Measuring Eye Drop Viscosity

'Dry eye' is a medical condition related to the lack of lubrication on the eye surface. It is a chronic issue for many people, causing lack of tears associated with irritation, i.e., ocular inflammation of the anterior tissues of the eye. Dry eye syndrome can be treated with over the counter drugs, which are typically water based liquid emulsions.

Shear rates are critical for eye drops. High shear rates are induced by eyelid movements, ranging from 4000 to 20000 s-1 due to closing and opening of eyelids. The viscosity measurement of eye drops at high shear rates is critical. It is difficult to perform these measurements by means of traditional rheometry instruments because of their shear rate limitations. The m-VROC is destined for high shear measurements, thereby facilitating precise measurement and analysis.

Measurements and Results

In this analysis, 1 ml of Refresh Liquigel (Allergan) was loaded into a syringe and two different tests were performed on the sample. The first test was a single point measurement where the viscosity was determined at a fixed flow rate of 100 µl/min. The viscosity was 33 cP. Since these eye drops are normally shear thinning, the magnitude of their thinning behavior was determined in the second measurement at increasing shear rates. This was measured by means of the Rate Sweep program of m-VROC.

Figure 1. Refresh Eye Drop Viscosity—Function of Shear Rate.

The shear rates measured were in the range of 1400 to 24000 s-1. As shown in Figure 1, the eye drop is a non-Newtonian liquid because it was highly shear thinning with a gradual increase in the shear rate. The practical limit of shear rate for a traditional rheometer is roughly 1000 s-1, which is very low to determine the actual shear thinning behavior of eye drop solutions. However, m-VROC is destined specially for high shear rate measurements.

Conclusion

The results clearly demonstrate the ability of m-VROC to effectively predict the behavior of a sample at very high shear rates.

About RheoSense

RheoSense Inc., is a global viscosity measurement equipment manufacturer. Its VROC (Viscometer-Rheometer-On-a-Chip) technology is the only MEMSmicrofluidic chip-based viscometry technology in the world.

This innovation provides accurate, repeatable viscosity measurement using today’s technology to reduce device footprint and sample size and is being readily adopted in BioPharmaceutical, Blood, Ink and other applications.

This information has been sourced, reviewed and adapted from materials provided by RheoSense.

For more information on this source, please visit RheoSense.

Date Added: Aug 8, 2013 | Updated: Aug 8, 2013
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