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Mariantonia Ferrara, Raniero Mendichi, Alberto Giacometti Schieroni, Daniele Piovani, Davide Allegrini, Mario R Romano; Comparative study of chemical composition, molecular and rheological properties of Silicone Oil medical devices.. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5795. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Silicone Oils (SilOil), considered biocompatible long-term intraocular tamponade, can cause serious complications, mainly related to emulsification. This phenomenon is influenced by their physical and chemical properties and, particularly, by the presence of “impurities” such as siloxane chains of low molecular weight (LMW components, LMWC) produced during SilOil synthesis process. Therefore, given the need of checking SilOil chemical composition, and their molecular and rheological properties, this chemical lab study aimed to evaluate the above mentioned findings in ten SilOil commercially available for ophthalmic surgery.
The type of polymer of SilOil products was checked by Fourier Transform-Infrared spectroscopy. The molecular weight distribution (MWD) of each polymer was obtained with a conventional size exclusion chromatography (SEC) system using a differential refractometer as concentration detector. From the Cumulative MWD we calculated the fractions of LMWC: M ≤ 2,000 g/mol, M ≤ 5,000 g/mol, M ≤ 10,000 g/mol. Since the quantitative analysis by SEC is not sufficiently accurate for components with the lowest MW, the total content of siloxanes with M ≤ 1,000 g/mol was determined by the more accurate mass spectrometer detector on-line to a gas chromatograph (GC-MS) method. The dynamic viscosity (η) for a broad range of shear rate was assessed by rotational rheometry.
For all SilOil the polymer was polydimethylsiloxane. The samples differed significantly in terms of both MWD and relative LMWC fractions. Specifically, the MWD was broad (with MW ranging from <1.000 to 500.000 g/mol) and the relative fraction of all LMWC (M ≤10,000 g/mol) ranged from 2.31% to 9.40%. Moreover, the content of LMWC with M ≤1,000 g/mol also varied significantly from a minimum of 51 ppm to a maximum of 1,151 ppm (fig. 1).The η values were different between the SilOil, and, for many of them, also from the declared viscosity.
Commercially available SilOil differ significantly in molecular and rheological features. These compounds contain a significant amount of LMWC with different MW, “impurities” generated during the synthesis process that act as emulsifier, potentially inducing ocular inflammation and toxicity. This may influence significantly the biocompatibility of these products.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Quantitative assessment of LMWC with M ≤1,000 g/mol of different SilOil.
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