Adhesion of silicone oil and emulsification: an in vitro assessment using a microfluidic device and 'Eye-on-a-Chip'

Purpose: Silicone oil (SiO) with additives of high-molecular-weight (HMW) SiO molecules, eases both the injection and removal. When used inside an eye, it remains unclear how increasing extensional viscosity of SiO might reduce emulsification. Using cell-lined models, this study aims to understand the reason why SiO with HMW is less prone to emulsification.

Methods: The adhesion of SiO was studied and recorded in a cell-coated microchannel by optical microscopy. The resistance of SiO against emulsification was tested on another cell-coated eye-on-a-chip platform, which was subject to simulated saccadic eye movements, for 4 days. Silicone oil (SiO) candidates with HMW, SiO_{HMW 2000} and SiO_{HMW 5000} , and their counterparts SiO₂₀₀₀ and SiO₅₀₀₀ without HMW, were tested. The quantity of the SiO emulsified droplets formed was assessed daily by optical microscopy.

Results: When flowing in the microchannel, SiO adheres on the cell-coated substrate. The number of droplets is generally lower in SiO with HMW than their counterparts. At the end of the experiment, the average numbers of droplets in SiO₂₀₀₀ (29.1 ± 41.0) and SiO₅₀₀₀ (9.1 ± 19.5) are higher than those in SiO_{HMW 2000} (6.0 ± 4.5) and SiO_{HMW 5000} (5.6 ± 4.1).

Conclusion: A new mechanism of emulsification of SiO is proposed: SiO adheres to ocular tissue to form emulsified droplets. The presence of HMW, which increases the extensional viscosity, may resist the break-up of SiO from the substrate to form emulsified droplets. When tested in a physiologically representative platform, the use of HMW in SiO generally reduces the number of droplets formed in vitro.