A thermodynamic study of relative extractability of ethanol to blood simulating solvent in extractables and leachables analysis of medical devices by Abraham’s Solvation Parameter Model

A thermodynamic study of over-extraction of blood contacting medical devices by ethanol to ethanol/water binary cosolvent mixture (50/50, v/v), as a blood simulating solvent, in chemical analysis of medical devices is evaluated by Abraham’s solvation parameter model using five representative materials (low density polyethylene or LDPE, silicone, polyurethane or PU, polyoxymethylene or POM, and polyacrylate or PA). The Abraham’s model is initially used to calculate the material-solvent partition system coefficients by the corresponding partition system constants and representative extractables compounds between five materials and ethanol/water (and methanol/water) cosolvent mixtures at different volume fractions. The partition system constants are indirectly derived by a “thermodynamic circle conversion” method, based on material-water partition systems and solvent-water water partition systems. The material-solvent (mixture) partition coefficient, $P_{M/Solvent}$=$C_M/C_{Solvent}$, defined as the concentration in the material phase divided by the concentration in the solvent phase, is used as an indicator of the solvent extraction strength. $\log \left(P_{M/Solvent}\right)$ values are computed for all material-solvent pairs using the representative extractables compounds, mostly from Wayne State University experimental descriptor database (WSUEDD). The predictive ${\log }_{10}\left(P_{M/Solvent}\right)$ values between LDPE and silicone materials and ethanol/water (and methanol/water) cosolvent mixtures are compared with the available experimental values to assess the model’s predictive accuracy. Afterward, the predictive ${\log }_{10}\left(P_{M/Solvent}\right)$ values of ethanol to ethanol/water binary cosolvent mixture (50/50, v/v) are used to calculate relative extractability (RE), as an indicator of over-extraction. Several conclusions can be drawn from this study. First, the predicted partition coefficients are confirmed by available experimental values (LDPE and silicone). Second, the over-extraction of medical devices by ethanol to the blood simulating solvent is less important for more polar extractables, but pronounced for more nonpolar compounds, for example up to a thousand-fold at ${\log }_{10}\left(P_{o/w}\right)$=10. Third, this over-extraction is also affected by the phase volume ratio between material and solvent phases. Over-extraction is significantly minimized using small phase ratio (or large solvent volume). Finally, Abraham’s solvation parameter model is once again demonstrated as an invaluable and capable tool in solvent selection and extraction of medical devices.