Polydopamine Nanoparticles Incorporated Smart NIR Stimuli-responsive Hydrogel

Hydrogels are widely applied in tissue regeneration because of its internal three-dimensional structure, water retention and biocompatibility. Stimuli-responsive hydrogels can response to stimuli by phase transformation or volume change and realize specific functions. Near-infrared (NIR) responsive hydrogels, as one type of stimuli-responsive hydrogel, can be precisely controlled by the radiation intensity, exposure time of the light source, and irradiation sites. Traditional NIR responsive materials include graphene oxide, gold nanoparticles, carbon nanotubes and polypyrrole. However, the cytotoxicity or potential toxicity of these materials limits their application in biomedical field. In this study, we report a NIR stimuli-responsive hydrogel incorporated with polydopamine nanoparticles (PDA-NPs), a kind of mussel-inspired material. The hydrogel can not only respond to NIR stimuli, but also have good biocompatibility, tissue affinity and adhesiveness.Firstly, PDA-NPs were prepared by oxidative self-polymerization, which possessed photothermal effect as proven by temperature rise of PDA-NPs dispersion with near-infrared (NIR) radiation. Then, PDA-NPs were dispersed in N-isopropylacrylamide (NIAPM) monomer solution to form PDA/PNIPAM hydrogels by free radical polymerization. The hydrogel can response to NIR stimuli by phase transition and volume change due to the temperature sensitive PNIPAM.PDA/PNIPAM smart hydrogel can achieve triple response effects, as demonstrated by NIR triggered dexamethasone release experiment, NIR driven actuation and NIR assisted fracture healing experiment. In drug release experiment under NIR radiation, the drug released from hydrogel incorporated with PDA-NPs release is 16% higher than that from control group without PDA-NPs. In NIR driven actuation, PDA/PNIPAM smart hydrogel bent significantly within 30 seconds in response to NIR radiation. In NIR assisted fracture healing experiment, fractured PDA/PNIPAM hydrogel can effectively heal with NIR assistance, and the healing degree of fractured hydrogel increase with PDA-NPs contents.Furthermore, PDA-NPs was coated on hydrogel surfaces (PDA/PNIPAM-C) to improve its tissue adhesiveness and growth factor/protein immobilization ability. The tissue adhesion strength of PDA-NPs modified hydrogel increase 145%, compared with control group without PDA-NP coatings. Secondly, PDA/PNIPAM-C hydrogel realize sustained release for alkaline phosphatase and epidermal growth factor (EGF) owing to PDA functional groups immobilizing biomolecules. Finally, PDA/PNIPAM-C hydrogel show good cell affinity because of the cell affinity of PDA. The hydrogel with PDA coating as skin dressing was evaluated by dorsal skin defect repair experiments. PDA/PNIPAM-C loaded with EGF epidermal growth resulted in 68.5% wound closure in the postoperative 9 days. These results indicated that PDA coating on the hydrogel and EFG have a synergistie effect on wound repair and improve skin repair ability of the hydrogel.In summary, this study combined thermo-sensitive PNIPAM and mussel-inspired PDA-NPs to form NIR-responsive hydrogel with good biocompatibility. Furthermore, PDA-NPs was coated the surface of hydrogel to improve its adhesiveness with skin tissue and biomolecules immobilization ability.These new type of hydrogel can be used to skin repair and shorten the skin healing time.