Abstract
Purpose :
The new generation of SiO, with long chain polydimethysiloxane (PDMS) additives of high-molecular-weight (HMW), is designed to enhance the ease of injection and removal. These oils are also claimed to be more resistant against emulsification when compared to conventional SiO. We have devised an eye-on-a-chip device to physiologically mimic conditions to induce SiO emulsification in the eye. This study aims to compare the propensity of the new oils and conventional SiO to emulsify.
Methods :
Two pairs of SiO candidates, (1) SiO 2000 cSt and its counterparts (95% SiO 1000 cSt with 5% HMW), and (2) 5000 cSt and its counterparts (90% SiO 1000 cSt with 10% HMW), were involved in this study. The HMW additive used was a liquid polydimethylsiloxane (PDMS) with molecular mass of 423 kDa. They were subjected to simulated saccadic eye movements for 4 days in an in vitro microengineered eye-on-a-chip platform. The quantity of the SiO emulsified droplets of each SiO was assessed daily by optical microscopy.
The wetting phenomenon of SiO was studied in a microfluidic parallel plate device coated with biological cells on its inner surface. A syringe pump was used to infuse and withdraw the liquids, both SiO and aqueous medium, inside the parallel plate to mimic the intraocular fluid in vivo.
Results :
In both pairs of SiO under the emulsification test, the number of SiO droplets was generally lower in SiO with HMW than their counterparts without HMW among the four days. In the wetting study, SiO adhered on the inner surface of the parallel plate device. During the induced flow, SiO with HMW was qualitatively less prone to break up from the attached surface to form floating SiO drops, when compared with their counterparts without HMW.
Conclusions :
The use of HMW in SiO significantly reduces the number of SiO droplets formed in vitro. A new mechanism of emulsification of SiO in vivo is proposed; A small portion of SiO snaps off from the bulk SiO phase and adheres on the intraocular surface. Similarly, SiO adhered can also detach and form SiO droplets due to the shear flow in the eye. The presence of HMW is expected to increase the extensional viscosity, and therefore resist the breakup of SiO from the substrate to form emulsified SiO droplets.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.