Probing Thermoresponsive Behavior and Protein Adsorption Difference of Linear and Looped Poly(N-Isopropylacrylamide) Brushes

Looped or cyclic polymers without chain ends exhibit unusual physicochemical properties and have been explored for emerging applications in surface coatings, nanolithography and electronic patterning, and drug or gene delivery. However, there is little information reported on the topological effect of the thermoresponsive looped brush on corresponding properties. Herein, two types of poly(N-isopropylacrylamide) (PNIPAM) terminated with one and two thiol groups are selected to bond with gold chips to form linear and looped PNIPAM brushes. The difference in conformational transition and protein adsorption behaviors for the two types of brushes at different temperatures has been evaluated using quartz crystal microbalance with dissipation measurements. The looped brushes exhibit anomalous hydration retention and negligible thermal hysteresis. Crucially, looped topology overcomes dehydration by enforcing extended conformations that can sustain the hydration barriers during collapse and further reduces protein adsorption. This work provides new insights into understanding the impact of different topological structures on conformational transitions and the corresponding protein adsorption, enriching the scope of research on temperature-responsive polymers.