ABSTRACT We explore the possible reversible formation of hydrogels through electrostatic interactions between four‐arm star‐shaped block copolymers, consisting of a polyethylene glycol (PEG) inner block and either an anionic polystyrene sulfonate PEG 27 ‐ b ‐PSS 108 4 or a zwitterionic polybetaine PEG 27 ‐ b ‐PCBMAAm 110 4 as outer block. The combination of both can induce attractive or repulsive electrostatic interactions depending on the solution pH value and ionic strength. The polymers were synthesized using controlled atom transfer radical polymerization (ATRP). The charge of PEG 27 ‐ b ‐PCBMAAm 110 4 was further investigated by potentiometric titration and zeta potential measurements. Using oscillatory shear rheology, we demonstrated the required conditions for hydrogel formation. Stable hydrogel formation is observed within a wide pH range (6.8 –9.5), corresponding to the protonation states of the carboxylic acid groups that facilitate electrostatic interactions. We also showed how the hydrogel stability is influenced by parameters like block copolymer concentration and ionic strength. Coarse‐grained simulations provided molecular‐scale insights, revealing charge regulation effects and the energetic favorability of electrostatic complexation up to high pH values. Overall, our results demonstrated the key design principles, as the polyelectrolyte length, ionic strength, and charge regulation effects, for the formation of partially reversible hydrogels, triggered by changes in the solution pH. Furthermore, we showed that understanding the desired conditions for hydrogel formation requires a combination of experimental characterization with modeling approaches.
Grün et al. (Sun,) studied this question.