Wound dressing has been an important branch of biomedical materials research.Skin damage caused by abrasion after falling and clinical incision after surgery are the most common wounds in real life.Compared with the wounds at flat areas of human body, it is still challenging to treat the wounds at special areas such as joints, popliteal fossae, axillae, and muscle folds. Poor adhesive performance, difficult fixation, and incomplete coverage are the main reasons. Moreover, in clinic, most wounds are sterilized with 75% alcohol or iodine, by covering with cotton gauzes. Therefore, regular disinfection and dressing replacement are necessary due to lack of antibacterial property of cotton gauze. In addition, fixed cotton gauze dressing needs to be taped, and sometimes, the skin is allergic to tape material. To this end, designing a stretchable, adhesive, antibacterial, and biocompatible dressing is of great clinical significance.

Hydrogels are a class of 3D network gels formed by chemical and/or physical crosslinking.Because of their superior biocompatibility, controllable physical properties, natural drug-loading structure, and abundant functional groups, hydrogels have gradually become a hotspot of medical wound dressing. To date, hydrogels have been successfully applied to treat skin defects,infected wounds,burn wounds,diabetic feet,and wet wounds inside the body.Based on the healing requirements of different wounds, one or more functions such as good tissue adhesion, excellent mechanical property, antibacterial capability, cell crawling promotion, physical contraction, local immune regulation, and antitumor property have been implanted in the hydrogel dressings, such as Cur-QCS/PF, QCSP/PEGS-FA, OSA-DA-PAM,PDA@AgNPs/CPHs, NPs-P-PAA,and STP hydrogels. However, the existing hydrogel dressings were difficult to achieve a satisfactory balance among the multiple functions. For example, due to the presence of quaternary ammonium salt, both Cur-QCS/PF and QCSP/PEGS-FA hydrogels showed excellent antibacterial property, but their tensile strain (below 100%) and adhesion strength (less than 8 kPa) were not satisfactory. OSA-DA-PAM and STP hydrogel dressings had good adhesion and stretching performances, but no antibacterial property. With the catechol structure and nanosilver, PDA@AgNPs/CPHs  and NPs-P-PAA  hydrogels exhibited excellent tissue adhesion and antibacterial properties, but use of silver-functionalized biomedical materials could give rise to cumulative toxic effect of heavy metal in organisms.Therefore, it is still highly challenging in preparing a hydrogel dressing with ideal tissue adhesion, good stretchability, broad-band antibacterial capability, cell crawling promotion, and bio-compatibility by a facile and efficient material design.

Herein, a new class of highly stretchable, adhesive, biocompatible, and antibacterial hydrogel dressings is designed and prepared by introducing poly(diallyl dimethyl ammonium chloride) (pDADMAC) brushes grafted from bacterial cellulose (BC) nanofibers (BC-g-pDADMAC, BCD) into polydopamine/polyacrylamide (PDA/PAM) hydrogels. For the as-prepared multifunctional BCD/PDA/PAM hydrogels, the PAM component has good biocompatibility and stable crosslinking structure, and is thus used as the hydrogel scaffold.Inspired by the biological adhesion of dopamine from mussel, the PDA component has abundant catechol groups and thus can adhere to various surfaces, especially special areas needing large movements. More importantly, the BCD component not only has rigid BC backbones to enhance the mechanical property of hydrogels, but also has pDADMAC brushes with broad spectrum and low toxic positively charged quaternary ammonium groups for providing high-efficiency and long-lasting antibacterial performance. Moreover, the positively charged pDADMAC brushes could help attract negatively charged epidermis cells and thus promote cell crawling and proliferation.Therefore, our BCD/PDA/PAM hydrogels have superior mechanical behaviors with high tensile strength (21–51 kPa), large tensile strain (899–1047%) and ideal compressive performance, and demonstrate stable covering, little displacement, long-lasting antibacteria and fast wound healing.