Preparation And Characterization Of Cerium Oxide Nanozymes And Their Composite Hydrogels For Chronic Wound Healing

Diabetic foot ulcers are one of the most serious chronic complications in diabetic patients.Patients have disorders of metabolic pathways in the body,resulting in neuropathy and vascular disease,a complex microenvironment at the ulcer,a wound prone to infection,a long inflammatory period,a low wound healing rate,and a high chance of recurrence,resulting in a high rate of amputation in diabetic foot patients.This poses a great challenge to clinical treatment.In recent years,composite gels prepared by combining hydrogels with nanomaterials with enzymatic activity have become a hot spot for research in the field of tissue repair engineering.In this paper,a multifunctional cerium oxide nanomaterials composite hydrogel system was designed to address the current problem of poor wound healing treatment.This multifunctional cerium oxide nanomaterials composite hydrogel system is able to realize the effects of antioxidation and promotion of oxygen production as well as anti-inflammatory effects,expecting to provide a new approach for diabetic foot wound treatment in the future.The PAA-modified cerium oxide nanoparticles（CeO₂@PAA）were successfully prepared by co-precipitation method.Characterization was performed by TEM,XPS,UV-vis,DLS and zeta potential.The results showed that CeO₂@PAA has an ultra-small particle size（2.62 nm）and a nearly spherical shape.Enzyme-like activity studies showed that CeO₂@PAA has excellent superoxide dismutase-like,catalase-like and peroxidase-like activities,which can effectively scavenge reactive oxygen species（ROS）.Polyvinyl alcohol（PVA）and 1,4-benzenediboronic acid（DBPA）were cross-linked to form a macromolecular gel network（PVA/DBPA）using the cross-linking of phenylboronic ester bonds,and CeO₂@PAA was compounded into the gel network.The physicochemical properties of the composite hydrogels were evaluated using rheological tests,Fourier infrared spectroscopy,scanning electron microscopy（SEM）,swelling test analysis,ROS-sensitive degradation test analysis,redox release kinetic studies,and free radical scavenging properties,indicating that they have ROS-sensitive responsive release properties as well as ROS scavenging functions.The effect of the composite gel was evaluated at the cellular level.CCK8 with cell live-dead staining analysis showed that the material exhibited low cytotoxicity against fibroblasts（L929）and macrophages（Raw264.7）in the concentration range used in the experiments.The gel has ROS-sensitive properties and can responsively degrade and release the loaded cerium oxide nanoparticles in a high ROS microenvironment.Cerium oxide nanoparticles not only can achieve antioxidant function,but also it can decompose endogenous hydrogen peroxide to produce oxygen through its peroxidase activity,which can alleviate the hypoxic state at the wound.Cell scratching experiments and intracellular skeleton staining experiments showed that the composite gel could promote fibroblast migration by promoting the effect of cytoskeleton proliferation.Further,the surface modification of arginine-glycine-aspartate cyclic small peptide（cyclic RGD）on CeO₂@PAA material to prepare CeO₂@PAA@RGD nanoparticles was detected by flow cytometry and reverse transcription polymerase chain reaction（RT-PCR）,which showed that both CeO₂@PAA and CeO₂@PAA@RGD materials could cause macrophage pro-inflammatory factor expression levels and increased the expression of anti-inflammatory factors.Finally,the results of angiogenesis assay showed that CeO₂@PAA blocked angiogenesis,while CeO₂@PAA@RGD had no effect on angiogenesis.It is expected that CeO₂@PAA@RGD has greater potential in chronic wound treatment.