Polymer Confinement via Crowding: Influence of Solvent Quality on Conformations

The structure and function of polymers in confined environments, e.g., biopolymers in the cytoplasm of a cell, are affected by macromolecular crowding. To explore the influence of solvent quality on conformations of crowded polymers, we model polymers as penetrable ellipsoids, whose shapes are governed by the statistics of self-avoiding walks. Within this coarse-grained model, we perform Monte Carlo simulations of mixtures of polymers and hard nanosphere crowders, including trial changes in polymer size and shape. Penetration of polymers by nanospheres is incorporated via a free energy cost predicted by polymer field theory. To analyze the impact of crowding on polymer conformations, we compute average polymer shape distributions, radius of gyration, and asphericity over ranges of crowder size and volume fraction. We compare simulation results with predictions of free-volume theory for polymers in good and theta solvents. Our results indicate that excluded-volume interactions significantly affect crowding, especially in the limit of small crowders. Our approach may help to motivate future experimental studies of polymers in crowded environments, with relevance for drug delivery and gene therapy.