Human Airway Mucus: Cactus-like Conformations of Associative Polymers

The unique fractal structure of macromolecules in human bronchial epithelial mucus is determined by small-angle neutron scattering. Hybrid Monte Carlo/molecular dynamics simulations of a minimal coarse-grained model of polymers with associative groups distributed evenly along the chain contour is found to reproduce the experimental form factor. A unique "cactus" model resulting from loops of different orders is proposed. Predictions with number and spacing between associative groups are given for the scaling of the polymer radius of gyration, contact probability, and pairwise interchain interactions.