The synthesis of carbohydrate-functionalized thermosensitive poly(Nisopropylacrylamide) microgels and their ability to bind carbohydrate-binding pathogens upon temperature switch are reported. It is found that the microgels' binding affinity is increased above their lower critical solution temperature (LCST), enabling thermotriggerable capture of pathogens. Here, a series of microgels with comparatively low mannose functionalization degrees below 1 mol % is achieved by a single polymerization step. Upon increase in mannose density, the microgel size increases, and the LCST decreases to 26 °C. Clustering with concanavalin A indicated that binding affinity is enhanced by a higher mannose content and by raising the temperature above the LCST. Binding studies with Escherichia coli confirm stronger specific interactions above the LCST and formation of mechanically stable aggregates enabling efficient separation of E. coli by filtration. For small incubation times above the LCST, the microgels' potential to release pathogens again below the LCST is confirmed also. Compared to existing switchable scaffolds, microgels nearly entirely composed of a thermosensitive material undergo a large change in volume, which allows them to drastically vary the density of ligands to switch between capture and release. This straightforward yet novel approach is likely compatible with a broad range of bioactive ligands. Therefore, thermosensitive microgels represent a promising platform for the specific capture or release of cells or pathogens.

The temperature-dependent binding of copolymers from poly(N-isopropylacrylamide) (PNIPAM) and mannose ligands to Escherichia coli and concanavalin A (ConA) is determined. Through polymer analogous reactions using poly(N-acryloxysuccinimide) and amine-linked mannose residues with different linkers, glycopolymers are prepared with the variation of the mannose density. Quantitative adhesion inhibition assays show the inhibitory potential of the glycopolymers as a function of the mannose/NIPAM ratio and linker type above and below their lower critical solution temperature (LCST). Intriguingly, opposite temperature effects on the binding to E. coli and ConA are observed. While the E. coli inhibition is stronger above the LCST, the ConA inhibition is, in overall, weaker at elevated temperatures. When going beyond the LCST, the polymers undergo a coil-to-globule transition, forming microphases with surface-enriched hydrophilic sugar moieties exhibiting increased E. coli inhibition through steric shielding. However, the formation of such microphases above the LCST renders a fraction of carbohydrate ligands inaccessible,and the polymers remaining in the solution phase then have coil sizes below the minimum binding site spacing of the ConA receptor, explaining reduced ConA inhibition. Overall, these results suggest that the coil-to-globule transition of glycopolymers may induce lower or higher inhibitory potentials due to the adverse effects of steric shielding and carbohydrate ligand accessibility.

Adhesive processes mediated by carbohydrate‐decorated interfaces play a crucial role in many biological processes such as cell development or pathogen invasion. The involved carbohydrate scaffolds are soft and present multiple subsites forming complex and dynamic bonds to carbohydrate binding proteins. New tools and data are needed to understand how ligand presentation and mechanical properties drive these binding processes. This article highlights recent developments in the area of adhesion assays with a focus on soft biomimetic carbohydrate scaffolds as probes of adhesion forces. Key findings state that carbohydrate functionalized polymer networks largely show additive multivalency (statistical effects) and that the overall interaction forces are strongly affected by the stiffness of the network. These results indicate that phase transitions of carbohydrate bearing polymer gels may enable tunable affinity toward carbohydrate binding proteins. As an example, polymer networks undergoing large changes in mechanical rigidity, density, and spacing of carbohydrate ligands upon temperature stimulus are shown to bind or release carbohydrate binding bacteria such as Escherichia coli. The presented adhesion assays and the developed responsive systems can provide new insights into the mechanism through which carbohydrates mediate adhesion processes and establish new avenues toward scaffolds for the capture or release of cells or pathogens.

Catechol and amine residues, both abundantly present in mussel adhesion proteins, are known to act cooperatively by displacing hydration barriers before binding to mineral surfaces. In spite of synthetic efforts...

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.

affinity of linked biomolecules, e.g., by varying their accessibility to control their specific binding. Thermoresponsive polymers with a lower critical solution temperature (LCST) between 30 and 40 °C are most frequently used for such applications, where poly(N-isopropyl acrylamide) (PNIPAM), poly(N-vinyl caprolactam) or poly(oligoethylene glycols) are well-known examples. [10] As bioligands conjugated to such LCST polymers, carbohydrates have recently gained attention since they dominate biomolecular interactions on the cellular level and drive numerous physiological processes in the healthy or diseased state. [11] For example, lectins, a class of carbohydrate binding proteins, mediate cell adhesion, communication, fertilization, or pathogen invasion. [12,13] To target carbohydrate binding pathogens or lectins directly, responsive carbohydrate ligand presenting polymers are being employed in microgels, [14-16] on nano particle surfaces, [17-19] 2D-surface coatings, [4] and linear or branched polymers. [20-23] Although many studies could show a temperature controllable affinity shift of thermoresponsive glycopolymers, the cause for this behavior and the molecular details are not well understood. For example, when increasing the temperature above the LCST, some studies found that the affinity increased, [16,17,24] whereas other studies obtained decreasing carbohydrate binding affinities. [4,20,21] The factors that may increase the binding affinities upon temperature increase are: 1) an increase of carbohydrate subunit density due to an increase of statistical rebinding or subsite binding. [25-27] 2) An increase of carbohydrate surface density due to the formation of a compact polymer globule where the hydrophilic carbohydrates enrich at the surface. [28] 3) A smoother surface upon polymer collapse leading to a reduced steric repulsion. [29,30] On the other hand, the collapse of the thermoresponsive polymer above the LCST can lead to a reduced accessibility of the carbohydrate units, e.g., due to the more compact polymer globules or aggregate formation. [21] These potentially negating mechanisms make it hard to predict the change in glycopolymer affinity upon the temperature induced coil-to-globule transition. In addition, the use of these materials is often motivated by being able to remotely "switch" the ligand-receptor interaction on and off, implying reversible ligand-receptor complex formation and dissociation. However, such reversible binding of LCST polymers was rarely shown and typically limited to 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...

The preparation of thermoresponsive mannose functionalized monolayers of poly(N‐isopropylacrylamide) microgels and the analysis of the specific binding of concanavalin A (ConA) and E. coli above and below the lower critical solution temperature (LCST) are shown. Via inhibition and direct binding assays it is found that ConA binding is time‐dependent, where at short incubation times binding is stronger above the LCST. Given larger incubation times, the interaction of ConA to the microgel network is increased below the LCST when compared to temperatures above the LCST, possibly due to increased ConA diffusion and multivalent binding in the more open microgel network below the LCST. For E. coli, which presents only monovalent lectins and is too large to diffuse into the network, binding is always enhanced above the LCST. This is due to the larger mannose density of the microgel layer above the LCST increasing the interaction to E. coli. Once bound to the microgel layer above the LCST, E. coli cannot be released by cooling down below the LCST. Overall, this suggests that the carbohydrate presenting microgel layers enable specific binding where the temperature‐induced transition between swollen and collapsed microgels may increase or decrease binding depending on the receptor size.

The synthesis of carbohydrate-functionalized biocompatible poly(oligo(ethylene glycol) methacrylate microgels and the analysis of the specific binding to concanavalin A (ConA) and Escherichia coli (E. coli) is shown. By using different crosslinkers, the microgels’ size, density and elastic modulus were varied. Given similar mannose (Man) functionalization degrees, the softer microgels show increased ConA uptake, possibly due to increased ConA diffusion in the less dense microgel network. Furthermore, although the microgels did not form clusters with E. coli in solution, surfaces coated with mannose-functionalized microgels are shown to bind the bacteria whereas galactose (Gal) and unfunctionalized microgels show no binding. While ConA binding depends on the overall microgels’ density and Man functionalization degree, E. coli binding to microgels’ surfaces appears to be largely unresponsive to changes of these parameters, indicating a rather promiscuous surface recognition and sufficiently strong anchoring to few surface-exposed Man units. Overall, these results indicate that carbohydrate-functionalized biocompatible oligo(ethylene glycol)-based microgels are able to immobilize carbohydrate binding pathogens specifically and that the binding of free lectins can be controlled by the network density.