Self-Adhesive, Self-Healable, and Triple-Responsive Hydrogel Doped with Polydopamine as an Adsorbent toward Methylene Blue

As a kind of attractive biomaterial, stimuli-responsive hydrogel had been widely used in wound dressings and wearable devices. However, it remained challenging to prepare a hydrogel with both excellent self-adhesion and self-healing performances. Inspired by the adhesion mechanism of mussel, we prepared a self-adhesive, self-healing, and triple-responsive hydrogel by a hybrid system based on tunable composition of polydopamine (PDA) and polymer network composed of poly­(N,N-diethylacrylamide-co-acrylic acid). It was found that the resulting hydrogel could be directly adhered to a variety of substrates without the need of external adhesives on account of the existence of enough free catechol groups in the hydrogel. Due to the synergistic effect of PDA nanoparticles and polymer network, hydrogel also showed excellent self-healing property. Moreover, we demonstrated that the triple-responsive hydrogel as an adsorbent could efficiently remove methylene blue, and the maximum adsorption capacity was 305.4 mg/g when the optimum mass fraction of PDA was 0.4 wt % in hydrogel. The adsorption of the hydrogel toward methylene blue could be well simulated by pseudo-second-order model and Langmuir isothermal adsorption model. From the viewpoint of mechanism, methylene blue molecules could be directly adsorbed to these carboxyl, amino and catechol functional groups in the molecular structure of polymeric hydrogels by electrostatic force, π–π interaction, Van Der Waals force, hydrogen bonding, etc. Ultimately, we hoped to extend this hybrid strategy to develop multifunctional hydrogels and consequently broaden the application prospects of hydrogels in biomedical treatment and environmental protection.