Comparative Study of Chemical Composition, Molecular and Rheological Properties of Silicone Oil Medical Devices

Abstract

PurposeWe evaluated chemical composition, and molecular and rheological properties in 10 commercially available silicone oils (SilOils), focusing on siloxane chains of low molecular weight (LMW components, LMWC) that are known to be “impurities” produced during the SilOil synthesis process.MethodsWe assessed the type of SilOil polymer and molecular weight distribution (MWD) by spectroscopy and conventional size exclusion chromatography, respectively. From the Cumulative MWD, we calculated the fractions of LMWC with molecular weight (M): ≤2000, ≤5000, and ≤10,000 g/mol. Due to the low MW, the content of LMWC with M ≤1000 g/mol was determined by gas chromatography-mass spectrometry. The dynamic viscosity (η) was assessed by rotational rheometry.ResultsFor all SilOils, the polymer was polydimethylsiloxane. The samples differed significantly in terms of MWD and relative LMWC fractions. Specifically, the relative fraction of all LMWC (M ≤10,000 g/mol) ranged from 2.31% to 9.40% and the content of LMWC with M ≤1000 g/mol also varied significantly (range, 51–1151 ppm). The η values were different between the SilOils, and, for many of them, from the declared viscosity.ConclusionsCommercially available SilOils differ significantly in molecular and rheologic features. These compounds contain a significant amount of LMWC, “impurities” generated during the synthesis process, acting as emulsifier, potentially inducing ocular inflammation and toxicity.Translational RelevanceThe amount of impurities in different SilOils may influence significantly their biocompatibility.

What Is the Cause of Toxicity of Silicone Oil?

“…The common standards regarding these impurities have not been established during the production and disclosure of information by manufacturers [ 26 ]. Mendichi et al and Dresp have both shown that different brands of commercially available ophthalmic SilOils contain varying amounts of LMWCs [ 27 , 28 ]. Furthermore, LMWCs have been reported to be the most abundant component by weight in all chemical impurities.…”

“…Furthermore, as the building blocks in the polymerisation of SilOil, cyclic LMWCs have a much higher content than their linear counterparts in commercially available SilOils [ 28 ]. Therefore, the presence of cyclic LMWCs in SilOil may be the key risk factor leading to cytotoxicity, which should be taken into consideration in future testing and purification regimes [ 27 ].…”

Silicone oil versus gas tamponade for primary rhegmatogenous retinal detachment treated successfully with a propensity score analysis: Japan Retinal Detachment Registry

“…3 4 9-12 In addition, it was recently reported that the quality of silicone oil medical products varied from batch to batch even under the same brand name, and that they may be toxic. [13][14][15] It has also been reported that unexplained visual impairments occurred from damages to retinal structures in eyes treated with SOT. [16][17][18] There are also reports that eyes with non-complex RD treated by SOT had poorer postoperative retinal sensitivity and visual acuity than eyes treated by GT.…”

Retinal and Corneal Changes Associated with Intraocular Silicone Oil Tamponade

“…It has to be noted that the nominal η refers to the dominant fraction of PDMS polymers of the desired length, but, despite post-synthesis purification processes, the final SO is a mixture of this fraction and a variable amount of siloxane chains of lower and higher MW [ 41 ]. Indeed, commercially available SO with the same declared η can vary significantly in terms of real η value, MW distribution and relative content of low molecular weight compounds (LMWC) [ 42 , 43 ]. In particular, LMWC, short-chain siloxane oligomers or polymers, have long been investigated due to their potentially harmful properties, being able to act as emulsifiers of SO and to diffuse from the vitreous cavity into ocular tissues [ 44 ].…”