Biofunctional hydrogels based on host-guest interactions

Biological systems involve the most complex materials in the world. Mimicking biological systems is not an easy task. Materials researchers are continuing to push themselves to prepare synthetic materials that can replicate biological systems. Hydrogels have attracted great interest from materials researchers for mimicking biological systems due to their biocompatibility. One approach to preparing hydrogels is using host-guest interactions. Host-guest interactions can be achieved by using cyclodextrins (CDs) as host units and suitable guest units. Hydrogels prepared based on host-guest interactions show several functionalities, such as self-healing ability, stimuli responsiveness, the ability to function as soft actuators for use in artificial muscles, and conductive responsiveness. These functions can be attributed to reversible bond formation between the CDs and guest units. Self-healing materials, which mimic the recovery of injured skin, can be achieved if the association constant between the CDs and guests is sufficiently high. Several specific guest units can also show external stimuli responsivity (redox, pH, temperature, and light) when paired with CDs, allowing them to mimic the responsiveness of the human body to external stimuli. Light-responsive hydrogels can be used to prepare soft actuators that can be employed as artificial muscles to mimic the sliding motion of human sarcomeres. Conductive hydrogels will be required to support the function of artificial muscles in the near future. This review summarizes the advancements made in biofunctional hydrogels based on host-guest interactions.