Stimuli-responsive Poly(Acrylic Acid)-based Hydrophobic Association Hydrogels

Hydrogels have attracted a large amount of interest.Hydrogels are endowed with high flexible property and play important roles in various applications due to their excellent abilities to absorb and retain water,such as tissue engineering,biomedical,sensors and so on.However,many applications need hydrogels with good mechanical properties or stimuli-responsive properties.Thus,many researchers have prepared tough hydrogels as well as proposed some toughening theories and prepared different stimuli-responsive hydrogels in response in various stimuli.There are many good results.There are a lot of reports about tough hydrogels based on energy dissipation mechanism.These hydrogels are strong and tough without any broken or fracture under deformation.Many toughening theories are generated,including hydrophobic association,hydrogen bonding,dipole–dipole interactions,metal ion coordination,double network and macromolecular microspheres.Among them,hydrophobic association has been generally accepted.In this paper,the tough hydrogels are successfully prepared by hydrophobic association.The hydrophobic segments are introduced into the hydrogel system and self-assembled to micelles acting as dynamic crosslinking points in the presence of surfactant.The hydrogels meet good mechanical properties,because the molecular chains in micelles dissociate and slide to dissipate amount of energy under deformation.However,the stimuli-responsive hydrogels are needed in some applications in response in environmental stimuli.Some papers about gel-sol transition of stimuli-responsive hydrogels are reported.These hydrogels are potential using in many applications,such as drug release and drug delivery.But the applications are limited due to the poor mechanical properties of the hydrogels.Some special applications need both good mechanical properties and stimuli-responsive properties of hydrogels.So the hydrogels with good mechanical properties and stimuli-responsive properties are necessary to design.In this paper,the mechanically tunable hydrogels with good mechanical properties and stimuli-responsive properties based on hydrophobic association are successfully prepared using environmental material,acrylic acid.It is envisioned that the mechanically stimuli-tunable strategy would provide new insights for designing the novel stimuli-responsive hydrogels and,in a way,broaden the applications of the hydrogels.