Stress relaxation in tunable hybrid (chemical+physical) hydrogels

Hydrogels are great for biomedical applications because they are easily made biocompatible and, like the tissues they need to interact with, consist largely of water. Tight control over their mechanical properties promises great improvement for their usability in these applications, but a detailed understanding of how properties follow from molecular architecture is lacking. Here, we present a computational study of a highly designable class of gels: 4-arm star polymers that are held together by a combination of chemical (permanent) and physical (reversible) crosslinks. In these materials, the permanent bonds provide long-term integrity while the reversible bonds provide switchability of mechanical properties. Using coarse-grained molecular dynamics simulations, we determine at which ratio of permanent to reversible crosslinks we can achieve a gel that is tunable between fluid and solid behavior, and analyze the effect of the reversible crosslinks on the long-term stress relaxation properties of the resulting materials.