The swollen polymer network hypothesis: Quantitative models of hydrogel swelling, stiffness, and solute transport

The introduction of the work Makromolekule by Herman Staudinger in 1919 brings back an understanding of the very early days of polymer science when characterizing the molecular structure of exact networks was a main goal of research. Here, we present updates to a swollen polymer network hypothesis with a focus on hydrogel physical properties. We discuss the connections between hydrogel structure, swelling behavior, mechanical properties, and transport properties, including the most substantial developments since the original Flory-Rehner model (1944) of swollen polymer networks. In addition to analyzing well-established and recent contributions to the swollen polymer network hypothesis, we introduce novel amendments that combine the insights of existing models. We suggest that coordinating rubberlike elasticity theory, equilibrium swelling theory, and mesh size theory will help to develop a universal predictive model for swelling, stiffness, and solute diffusivities in a diverse array of hydrogel formulations. (C) 2020 Elsevier B.V. All rights reserved.