(663h) Rapid Predictions of Solute Diffusivity in Polymers Using Molecular Simulations

Solute diffusion in medical devices comprising polymeric materials may raise public health issues, where toxicological risks may arise via unintended leaching from implanted devices. However, accurately measuring solute diffusion coefficients (D) at physiological temperature is a challenge, both experimentally and with simulations. Although molecular dynamics (MD) simulations can be used to predict D for gases in polymers with great accuracy, it remains challenging to quantify D for larger molecules (molecular weight > 100 g/mol), like plasticizers, dyes, or drugs. Heavier molecules diffuse more slowly, so both experiments and simulations can take months of real time to arrive at an estimate of D [1, 2]. Here, we discuss a method to bypass these time-consuming approaches. We show a link between D and the Debye-Waller factor (u²), a measure of solute ‘caging’ between diffusive hops. Using MD, we simulate a variety of polymer/solute combinations across the glass transition. Above the so-called mode-coupling temperature T_C, there is an apparently universal linear relation between ln D and 1/u². Below T_C, this relation still provides an upper bound on D, which may be a useful limit when assessing medical device safety in practice. Because u² can be quantified in very short MD simulations, this suggests a means to rapidly estimate D [2].

1. C. Forrey, D. M. Saylor, J. S. Silverstein, J. F. Douglas, E. M. Davis, Y. A. Elabd, Prediction and validation of diffusion coefficients in a model drug delivery system using microsecond atomistic molecular dynamics simulation and vapour sorption analysis. Soft Matter 10, 7480-7494 (2014).
2. D. M. Saylor, S. Jawahery, J. S. Silverstein, C. Forrey, Communication: Relationship between solute localization and diffusion in a dynamically constrained polymer system. The Journal of Chemical Physics 145, 031106 (2016).