Photo-controlled spatiotemporal sequential release of MXenes/NO gas from bilayer (clean-cure) hydrogel promotes healing of MRSA biofilm-infected diabetic ulcer wounds.

Despite the success in designing intelligent materials for diabetic ulcer wound (DUW) healing, it is often challenging to consider the entire healing process, from early antibacterial and anti-inflammatory effects to late matrix remodeling and angiogenesis characteristics, by on-demand releasing of multiple therapeutics. Herein, we designed a versatile bilayer (GCM/Clean-GDA/Cure) hydrogel dressing with light-controlled, spatiotemporal sequential release of MXene nanosheets (MX NSs)/nitric oxide (NO) gas for the healing of methicillin-resistant Staphylococcus aureus (MRSA) biofilm-infected DUWs. The lower GCM layer comprised carboxymethyl chitosan-gelatin and cerium oxide (CeO2)-decorated MX NSs (CO-MX). The upper GDA layer consisted of dopamine-modified methacrylated gelatin (GelMA-DA) with L-arginine (L-Arg) as a precursor. Under NIR irradiation, the GCM hydrogel released photothermal-induced CO-MX NSs as self-regenerating antioxidants, exhibiting 98.25 % inhibition against MRSA and 96.37 % inhibition against Pneumonia aeruginosa. The abundant oxygen vacancies and reversible Ce(III)/Ce(IV) redox pairs of the released Ce species from CO-MX NSs could attenuate inflammation and promote early macrophage polarization. The light-assisted gel-sol thermal transition of the lower GCM layer further exposed the upper GDA layer, providing a conducive microenvironment for angiogenesis and tissue remodeling. L-Arg in the GDA layer could enable light-controlled in situ release of NO gas activated by elevated reactive oxygen species (ROS), reaching 7.71 μM within 10 min of exposure to NIR light. Thus, the NIR-assisted bilayer treatment group achieved a 97.74 % wound closure rate. Finally, the transcriptomic analysis validated the activation of regenerative pathways and suppression of excessive inflammatory and metabolic stress signals. Together, the photo-controlled sequential release of MX NSs and NO gas from the bilayer could expand the application of light-responsive nanomaterials, providing an innovative therapeutic modality for in situ treatment of diabetic wounds infected by highly drug-resistant MRSA biofilms.