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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 HMW2000 and SiO HMW5000 , and their counterparts SiO 2000 and SiO 5000 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 SiO 2000 (29.1 AE 41.0) and SiO 5000 (9.1 AE 19.5) are higher than those in SiO HMW2000 (6.0 AE 4.5) and SiO HMW5000 (5.6 AE 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.

As an alternative to conventional cell culture and animal testing, an organ-on-a-chip is applied to study the biological phenomena of organ development and disease, as well as the interactions between human tissues and external stimuli such as chemicals, forces and electricity. The pattern design of a microfluidic channel is one of the key approaches to regulate cell growth and differentiation, because these channels work as a crucial vasculature system to control the fluidic flow throughout the organ-on-a-chip device. In this study, we introduce a novel leaf-templated, microwell-integrated microfluidic chip for high-throughput cell experiments, consisting of a leaf-venation layer for fluent fluid flow, and a microwell-array layer for cell to reside. Computational fluid dynamics analysis was carried out to study the fluidic flow within leaf-venation network, which was further used to optimize the design of microwell arrays. A simple leaf-venation-mold-based microreplication method was developed to transfer the intact native leaf venation network into leaf-venation layer and 3D printing technology was used to fabricate the microwell-array layer. The layers were then assembled and used for perfusion culture, showing that leaf-templated microfluidic channels provided a sufficient culture medium for cells within each microwell. These results indicate a novel and effective strategy to generate a biomimetic microfluidic chip with an effective vascular transport system for high-throughput cell experiments.

Aims Recently, chemically modified silicone oil has been demonstrated as a reservoir for sustained release of intraocular drugs, many of which might be amphiphilic in nature. In this work, we study the effect of amphiphilic additives in silicone oil on emulsification under eye‐like movements. Methods Three silicone‐oil‐soluble surfactants, namely DC749, MQ1640 and FZ2233, were used as model amphiphilic additives. The change of viscosity was measured by a rheometer in the cone‐and‐plate geometry. The interfacial tension (IFT) between silicone oil and model aqueous phase was measured by pendant drop tensiometry. Emulsification of silicone oil was induced by simulated saccadic eye movements on a cell‐coated eye‐on‐a‐chip platform for 4 days. The number of emulsified silicone oil droplets observed in the aqueous phase was assessed daily by optical microscopy. Results Significantly more emulsified droplets were formed in silicone oil with DC749 or MQ1640 (P < 0.05). However, such increase was not directly related to the change in IFT nor viscosity. Moreover, water droplets were also found in the silicone oil, but not in the control silicone oil without additive. Conclusions The amphiphilic substances in silicone oil promoted emulsification. Besides typical oil‐in‐water drops that normally affect the eye, water‐in‐oil drops were also formed. Before silicone oil could be considered as a vehicle for drug delivery, the nature of the drug and its possible effect on emulsification and therefore on the pharmacokinetics needs to be investigated. An additional concern is that water‐in‐oil droplets in the eye would affect the optical clarity of silicone oil and might cause visual symptoms.

The interfacial tension between HA and PFO is higher than that between aqueous and PFO. This is a plausible physical explanation of how the 'soft shell' technique might work to prevent subretinal migration of PFCL.