Quantifying Thermoswitchable Carbohydrate-Mediated Interactions via Soft Colloidal Probe Adhesion Studies

Thermosensitive polymers enable externally controllable biomolecular interactions but hysteresis effects hamper the reversibility and repeated use of these materials. To quantify the temperature-dependent interactions and hysteresis effects, an optical adhesion assay based on poly(ethylene glycol) microgels (soft colloidal probes, SCPs) with mannose binding concanavalin A surfaces is used. A series of thermoresponsive glycopolymers is synthesized varying the carbohydrate type, their density, and linker type, and then grafted to the SCPs. The carbohydrate-mediated adhesion is influenced by the density of sugar ligands and increased above the lower critical solution temperature (LCST) of the glycopolymer. Importantly, a strong hysteresis is observed, i.e., cooling back below the LCST does not reduce the adhesion back to the initial value before heating. The hysteresis is stronger for hydrophobic linkers and for low carbohydrate functionalization degrees suggesting insufficient reswelling of the polymers due to hydrophobic interactions. The results are confirmed by studying the adhesion of Escherichia coli to the SCPs, where an enhanced capture of the bacteria is observed above the LCST while the detachment upon cooling is not possible. Overall, the quantitative data on the switchable adhesion of specifically binding polymers may provide potential avenues for the design of the next-generation interactive biomaterials.