Solvent compatibility for extractables analysis of silicones

A unique combination of properties, such as heat resistance, transparency, and high deformability, has led to wide adoption of silicone rubber as a material of construction in medical devices. Potential toxicity of medical devices and their components are assessed by exhaustively extracting, identifying, and semi-quantifying extractable compounds in accordance with ISO 10993-18:2020. However, solvent compatibility with silicones can present analytical challenges, as non-polar solvents may cause swelling in excess of 200% of the original volume and mass and elicit degradation. This investigation therefore explores methods to assess degradation relevant to chemical characterization, quantifies the extraction efficiency of semi-polar solvents relative to non-polar solvents, and elucidates the extraction kinetics of common extractable species. Degradation of silicone rubber was evaluated by measuring the swelling ratio, and vibrational spectroscopy was used to monitor polymer network integrity. However, the Hansen solubility parameter and dielectric constant were shown to be a more effective indicator of polymer network deformation than the Snyder polarity index when samples were exposed to 20 solvents of varying polarities. A direct comparison of extractions of silicone tubing in ethanol and cyclohexane revealed the extraction efficiency of ethanol was greater than 70% effective as compared to cyclohexane. The extraction kinetics of silicone samples suggests chemicals were almost exhaustively extracted in 10 h.