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.

Hydrogel Microparticles as Sensors for Specific Adhesion: Case Studies on Antibody Detection and Soil Release Polymers.

Adhesive processes in aqueous media play a crucial role in nature and are important for many technological processes. However, direct quantification of adhesion still requires expensive instrumentation while their sample throughput is rather small. Here we present a fast, and easily applicable method on quantifying adhesion energy in water based on interferometric measurement of polymer microgel contact areas with functionalized glass slides and evaluation via the Johnson⁻Kendall⁻Roberts (JKR) model. The advantage of the method is that the microgel matrix can be easily adapted to reconstruct various biological or technological adhesion processes. Here we study the suitability of the new adhesion method with two relevant examples: (1) antibody detection and (2) soil release polymers. The measurement of adhesion energy provides direct insights on the presence of antibodies showing that the method can be generally used for biomolecule detection. As a relevant example of adhesion in technology, the antiadhesive properties of soil release polymers used in today's laundry products are investigated. Here the measurement of adhesion energy provides direct insights into the relation between polymer composition and soil release activity. Overall, the work shows that polymer hydrogel particles can be used as versatile adhesion sensors to investigate a broad range of adhesion processes in aqueous media.