(420h) Beyond Ideal Networks: Understanding Poly(acrylamide)-Based Hydrogel Materials Via Atomistic Modeling

Poly(acrylamide) (PAAM)-based systems are among the most utilized hydrogel materials, with applications ranging from cell/tissue culture scaffolding to stimuli responsive drug delivery vectors. The widespread use of PAAM hydrogels is in part a result of their large water content, which can yield mechanical characteristics that match in vivo conditions, and their relatively favorable biocompatibility. Despite the ubiquitous use of hydrogel materials, the characterization of hydrogel networks at the atomistic scale has remained an elusive challenge. Polymer chains that comprise the highly solvated gels are dynamic and connected together to form network topologies that limit the applicability of standard scattering-based characterization techniques to provide a holistic description of the hydrogel network structure. As a result, to date hydrogels have primarily been described by their mesh size (ξ), which is commonly derived from Peppas-Merrill-type swelling theories. Our work seeks to further develop the understanding of hydrogel network behavior by providing insight into the local polymer network behavior through atomistic modeling and molecular dynamics (MD) simulations.

We present a new approach to generating a range of model non-ideal network topologies and compositions for PAAM hydrogels, which is based on the chemical similarity of the cross-linking unit (N,N’-Methylenebis(acrylamide)) to the acrylamide monomer. The simulated ξ is obtained directly through end-to-end distance measurements of the network polymer chains and provides validation for the gel generating methodology with experimental measurements over a range of gel compositions. Dynamic pore size distribution measurements have been performed to reveal the mobile nature of the micropore structure of the model PAAM hydrogels. Additionally, non-equilibrium MD simulations have been performed to assess the load bearing capabilities of the chains which compose the hydrogel network in response to uniaxially applied mechanical strains. Overall, this study highlights the impact that gel composition and complex network connectivity can have on dictating PAAM hydrogel properties.