A mechanistically motivated constitutive model of biopolymer hydrogels with structural evolution

Understanding the deformation behavior of biopolymer hydrogels would aid in the design of artificial hydrogels and nanoparticle-based drug delivery systems, which have been extensively used in the fields of biomedicine. Here, we develop a mechanistically motivated constitutive model to elucidate the structural evolution of biopolymer hydrogels. A free energy function includingconfigurational entropy of biopolymer nanofibers, potential energy of physical cross -links, and mixing energy of water molecules is formulated. Both the micro/nanostructures and dynamic features of nanofibrous network under stretching are captured investigating the evolu-tion of physical crosslinks and water hydration. In addition, a quantitative relationship corre-lating the pore size in the nanofibrous network with mechanical stretching is proposed. Different from chemically crosslinked hydrogels, the pore size of physically crosslinked hydrogels could continuously increase under stretching, which is attributed to the straightening and bundling of biopolymer nanofibers. We further find that a low strain rate or a high swelling ratio promotes the structural evolution of biopolymer hydrogels and increases the pore size of the network. The model predictions are in good agreement with the experimental results. This work could shed light on the deformation mechanisms of physically crosslinked biopolymer hydrogels, thus providing guidelines for the design of drug delivery systems translocating within biopolymer hydrogels.