Modular assembly of transient polymer networks from heteroaffinity cross-links to multivalent proteins

Transient polymer networks (TPN) leverage dynamic 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 TPNs, 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 TPNs from stoichiometrically identical pairs of protein modules then yields unique, meta-stable, non-equilibrium network topologies. Here, we demonstrate these concepts using the well-studied avidin-biotin interaction chemistry. We also develop a pH-sensitive HAX that yields TPNs with robust pH-responsive assembly dynamics, and demonstrate how this TPN can be made into a magnetically responsive, molecular delivery system to low-pH regions, such as tumor microenvironments.