Modular Assembly of Dynamic Polymer Networks From Heteroaffinity Cross-Links to Multivalent Proteins

Dynamic polymer networks (DPN) leverage transient cross-linking to yield macroscopic materials that exhibit self-healing and environmentally responsive behaviors. Despite the broad scope of chemical interactions available for cross-linking, imbuing those transient interactions into biologically compatible materials is difficult because many chemistries are incompatible with aqueous conditions, and it is difficult to tune preexisting biological interactions that have evolved over millions of years for specificity. To enable the assembly of chemically tunable and biologically compatible DPNs, we have developed a set of bifunctional, heteroaffinity cross-linkers (HAX) where the reactive moieties have different binding affinities to the same binding sites of an oligomeric protein. The use of cross-linking moieties with vastly different dissociation rates enables purification of protein modules with monodisperse HAX valencies. Assembly of DPNs from stoichiometrically identical pairs of protein modules then yields unique, metastable, nonequilibrium network topologies. Here, we demonstrate these concepts using the well-studied avidin-biotin interaction chemistry. We also develop a pH-sensitive HAX that yields DPNs with robust pH-responsive assembly dynamics, and demonstrate how this DPN can be made into a magnetically responsive, molecular delivery system to low-pH regions, such as tumor microenvironments.