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Investigating silicone oil emulsification in eye chamber models


Type

Thesis

Change log

Authors

Wang, Ru 

Abstract

The emulsification of silicone oil in intraocular liquid is an unwanted complication occurring after retinal detachment repair. The repair surgery consists of removing most of the intraocular liquid and replacing it by a tamponade fluid. Silicone oils with dynamic viscosities in the range 1-5 Pa s are often used as tamponades due to their high biocompatibility and chemical stability. Emulsification of the oil can occur during the tamponade stay in the eye chamber and the droplets can potentially lead to loss of or impairment of vision. The aim of the project is to establish the mechanisms by which the silicone oil emulsifies and understand the different factors involved in this phenomenon. Two potential emulsification mechanisms have been studied using experimental investigations. A 3D model of the eye chamber, driven by a stepper-motor reproducing the eye geometry and saccadic motion, was developed to study the first hypothesis of bulk emulsification at the interface between oil-aqueous phases. The stability of the interface was investigated over an extensive range of experimental scenarios, supported by analytical and numerical calculations. The addition of surfactant to the aqueous phase modelled the effect of surface-active molecules on the interfacial properties. Low viscosity ratio, low interfacial tension and strong inertial motion resulted in large deformation of the oil-aqueous interface but did not result in interface breakup and droplet formation. Bulk emulsification was therefore excluded as the mechanism causing the oil droplets formation. The second hypothesis concerned the stability of the three-phase contact line (TPCL) between the two liquid phases and the retinal surface. Hydrophobic silane coatings on flat solid substrates were used as a first approximation of the retina. The TPCL motion and stability was studied on uncoated and coated substrates. Above a critical substrate speed, the drag of the TPCL by the substrate led to a transition from partial to complete wetting of the liquid, leaving an oil film on the surface. The presence of printed silane features affected the dewetting of the TPCL and led to the destabilization of the oil film into shorter oil strands pinned to the feature. The shape of the oil strands depended on the surface energies and contact angles, and the oil strand length and width increased with increasing substrate velocity and feature width. However, none of the pinned droplets detached from the features under the motions accessible by the set-up and by the stepper motor device. The bulk emulsification hypothesis was reported to be the mechanism responsible in much of the literature on this topic. The experimental findings reported here indicate that surface-driven emulsification is more likely to be responsible of oil droplet formation. Confirmation of the hypothesis requires further investigation to establish which physiological and flow conditions will promote detachment of SiOil droplets from surface features.

Description

Date

2021-11

Advisors

Wilson, D Ian
Snead, Martin
Alexander, Philip

Keywords

Emulsification, Silicone oil, Retinal detachment, Interface engineering, Fluid dynamics

Qualification

Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge