Investigation of Mechanical Properties in PVA Hydrogels Due to Cation Interactions Described by Reactive Forcefield Based Molecular Dynamics Simulations

Hydrogels are cross-linked networks containing water and are widely used in multiple fields due to their intrinsic softness and diffusive properties. One field of particular interest is in medical devices and tissue and organ engineering. Poly(vinyl alcohol) (PVA) is one common hydrogel where its mechanical properties can be changed by using different salt solutions, making it more appropriate for certain applications, such as artificial neuron tissue. In this study, we used the ReaxFF reactive forcefield to investigate PVA in lithium and potassium chloride. It was hypothesized that lithium might promote a proton transfer from the PVA hydroxyl groups, therefore inhibiting the PVA from forming hydrogen bonds with itself, yielding a weaker PVA hydrogel. Conversely, potassium would not promote a proton transfer, instead getting inside the PVA structure, allowing a higher density of hydrogen bonds to form, creating a stronger PVA hydrogel. We were able to show a proton transfer was favorable in the lithium case and unfavorable in the potassium case. This explains the differences in mechanical properties shown in experimental results and provides atomistic detail to motivate tunable mechanical properties in PVA hydrogels in various salt solutions.