Abstract
Purpose: :
Silicone oils are a proven medical device as ocular endotamponades in the treatment of retinal detachment. However, the currently available heavy tamponades are only slightly heavier than the surrounding aqueous limiting their ability to exclude the aqueous from the retina. We have developed an alternative heavy tamponade comprising a dispersion of silica nanoparticles in silicone oil.
Methods: :
Aerosil fumed silica can be dispersed into silicone oil using a straightforward mixing process. This leads to a stable, low viscosity and transparent medical device. Transparency has been achieved by employing a process known as "Refractive Index Matching". Solid-based solutions are usually turbid owing to the disruption of the light path by the particles, however, if the refractive index of the particles and the liquid are matched, light scattering is minimised and allow these silicone oil solutions to be optically clear and therefore implantable into a human eye.
Results: :
The current prototype silica-silicone oil contains 11% silica resulting in a specific gravity of 1.11 g/cm3 and a Refractive Index of 1.46. It can be manufactured using simple overhead stirring and has a peak shear viscosity of 2000 mPas which occurs around 100 s-1. We have shown good shear viscosity stability over 9 months storage at an ambient temperature of 20-25º C and also at 37º C. Preliminary studies of injection test have demonstrated that the rheological properties of this novel fluid provide a lower resistance thus making it easier to inject into the eye than current standard tamponade agents. Shear-thickened viscosity drops to 400 mPas at 400 s-1. Performance evaluation shows higher tamponade efficiency than any existing, licensed silicone oil in vitro. We have demonstrated that there is no cytotoxcity of the fluid when tested according to European Standards EN ISO 10993-5 and EN ISO 10933-12.
Conclusions: :
It is the first time that inert solids have been incorporated into silicone oil products intended for medical use. The nanoparticles have a higher specific gravity than the liquid, permitting a stepwise increase in specific gravity of the dispersion over existing tamponades. The unique advantage of this approach is the ability to tailor the specific gravity to optimise the tamponade effect in different clinical situations.
Keywords: vitreoretinal surgery • retinal detachment