Modeling extraction of medical device polymers for biocompatibility evaluation

Extraction testing is critical for biocompatibility evaluation of medical devices, whether to generate samples for biological testing or form the basis for toxicological risk assessment. However, it is not always clear how to compare extraction testing between different extraction conditions and sample geometries. We employ a physics-based model to elucidate the theoretical impact of extraction conditions, sample geometry and material properties on extraction efficiency (M/M⁰) and extract concentration (C/C⁰) for single-step and iterative/exhaustive extraction test methods. The model is specified by three parameters: thermodynamic contributions (Ψ), kinetic contributions (τ), and number of extraction iterations (N). We find that over the range of typical parameters for single-step extractions, M/M⁰ only approaches one (complete exhaustion) for relatively large values of Ψ (≥10) and τ(≥1). Further, the model suggests that test article geometry and solvent volume can have a dramatic and sometimes opposing effect on M/M⁰ and C/C⁰. Our results imply that iterative extractions can be approximated as a single-step extraction with scaled parameters Ψ' = ΨN and τ' = τN. The model provides a framework to reduce the biocompatibility evaluation test burden by optimizing test article and extraction condition selection and guiding development of new test protocols.