| The skin is the body’s first line of defense and plays an important role in preventing bacteria or other foreign bodies from invading the body.However,skin damage is inevitable in life,and skin damage often means bacterial infection.Bacterial infections can severely hinder wound healing,and severe bacterial infections are accompanied by many complications and even lead to the death of the patient.The abuse of antibiotics has led to frequent cases of drug-resistant bacterial infections,which seriously threatens human health.Improving the efficiency of antibiotic use and reducing the amount of antibiotics is an important way to solve drug-resistant bacterial infections.In addition,wound healing is a complex process,bacterial infection and the microenvironment of the wound have an important impact on wound healing.Traditional hydrophilic dressings have limited ability to absorb exudate on the wound surface,which often results in moist wounds and easy bacterial infection,thereby delaying wound healing or further worsening wounds.Therefore,it is of great significance to develop a wound dressing that has both antibacterial,continuous moisture conduction and wound healing promotion.Based on this,in this study,a near-infrared responsive nanoworm（NW）was prepared by a nanoparticle self-assembly method,and then NW-doped silk fibroin（SNG）was prepared by electrospinning technology.The SNG fibers were then composited with chitosan and prepared by freeze-drying to obtain NW-doped silk fibroin/chitosan fiber sponge（SCSNG）.The structure and properties of nanoworms and fibrous sponges were systematically studied,their antibacterial effects in vitro and in vivo,and their roles in wound healing were studied through animal models.The specific research results are as follows:（1）Preparation and properties of near-infrared responsive nanowormsUsing displacement reaction,using nano-silver as sacrificial template and reducing agent,nano-silver was etched with chloroauric acid to prepare hollow porous nano-gold-silver cages（Au-Ag NPs）with a particle size of about 50 nm.Au-Ag-G was obtained by loading gentamicin sulfate（GM）through electrostatic adsorption.Au-Ag-G was linearly assembled using dopamine hydrochloride（DA）,and a polydopamine layer was formed on the outer layer of Au-Ag-G to obtain nanoworms（NW-G）with a particle size of about170 nm and a shell-core structure.The NW-G was coated with red blood cell membrane（RBCM）to obtain nanoworm RBCM-NW-G with a particle size of about 190 nm.The loading rate and encapsulation rate of GM in RBCM-NW-G are 11.16%and 22.3%,respectively.The near-infrared test results show that RBCM-NW-G has good near-infrared responsiveness,the temperature can reach 53℃within 1000 s under near-infrared irradiation,and the photothermal conversion efficiency is 44.9%.The release rate of GM and silver ions was significantly accelerated under near-infrared irradiation.Within 50 min,the amount of GM and silver ions released was about 14 times that of the non-irradiated group.The antibacterial test results show that RBCM-NW-G has good antibacterial properties under the combined action of GM,silver ions and photothermal effect.Under near-infrared irradiation,the antibacterial rates of RBCM-NW-G（100μg/m L）against Escherichia coli and Staphylococcus aureus were about 98.4%and 99.1%.In addition,the results of the anti-biofilm infection experiments showed that the photothermal effect of RBCM-NW-G could crack the biofilm,promote the infiltration of GM and silver ions,and then kill the bacteria at the bottom of the biofilm.（2）In vivo antibacterial properties of near-infrared responsive nanowormIn order to explore the effect of RBCM encapsulation on the circulation time of nanoparticles in vivo,the changes in the content of rice worms（NW-G）in the blood of mice after injection were studied.The results showed that after 24 h,the retention rate of RBCM-NW-G in blood could still reach 13.1%ID/g,which was 11.6%ID/g higher than that of NW-G.It shows that RBCM encapsulation can effectively improve the blood circulation time and use efficiency of NW-G.The distribution of different particles in mice was further studied by fluorescence imaging.The results showed that the concentration of RBCM-NW-G at the infection site was much higher than that of NW-G6 h after injection,and the fluorescence intensity was 4 times higher than that of the NW-G group,indicated that RBCM coating could make RBCM-NW-G aggregate efficiently at the bacterial infection site.The photothermal properties of RBCM-NW-G in mice were investigated by near-infrared imaging.The results show that RBCM-NW-G has good photothermal properties,and the temperature of the irradiated site increases from 37℃to 48℃within 250 s of near-infrared irradiation.The in vivo infection model in mice was established to study the therapeutic effect of RBCM-NW-G on bacterial infection in vivo.The results show that RBCM-NW-G can completely recover the infection site within 15 days,and the antibacterial treatment effect in vivo is twice as high as that of GM treatment.It shows that RBCM-NW-G has a good therapeutic effect on bacterial infection in vivo,and can quickly remove bacteria from the infection site and reduce the swelling area of the infection site.The results of hemocompatibility,cytocompatibility,and major organ toxicity analysis showed that RBCM-NW-G had good biocompatibility and no obvious toxicity.（3）Preparation and properties of silk fibroin/chitosan fiber sponge loaded with nanowormNanoworm-doped silk fibroin/chitosan fiber sponge（SCSNG）was prepared by electrospinning technology,doping reconstitution method and freeze-drying method.The SCSNG sponge is composed of a hydrophilic layer and a hydrophobic layer.The hydrophilic layer sponge has a uniform porous structure with a pore diameter of about200μm,and the pores are uniformly filled with nanoworm-doped silk fibroin（SNG）;the hydrophobic layer is formed by entanglement of hydrophobic fibers,and the surface of the hydrophobic layer is evenly distributed with pores with a pore size of about 5μm.The near-infrared test results show that the SCSNG sponge has good photothermal properties and thermal insulation properties.Within 300 s under near-infrared irradiation,the surface temperature of the sponge can reach 55.2°C,while the temperature of the contact surface with the wound is only 27°C.The moisture conductivity of SCSNG sponge was studied by contact angle test and moisture evaporation test.The results show that SCSNG is able to export droplets from the hydrophobic layer to the hydrophilic layer within 6 s,and evaporate water at a rate of 3.4 Kg m-2h-1 under NIR irradiation.It shows that SCSNG has good moisture-conducting properties,which can continuously conduct moisture-conducting and effectively solve the problem of excessive wound exudate.The antibacterial test results show that SCSNG has excellent antibacterial properties,and the bacteriostatic rate against E.coli and S.aureus can reach about 100%.In addition,the research results of bacterial barrier properties show that SCSNG has a good bacterial barrier effect,which can protect the wound from being infected by foreign bacteria.（4）Healing promotion of silk fibroin/chitosan fiber sponge loaded with nanowormThe healing-promoting properties of SCSNG were explored by constructing an animal back skin wound model.The experimental results showed that on the 12th day,the wound healing rate on the back of the rabbit was close to 100%,while the wound healing rates of the blank group and the commercial dressing Aquacel?Ag group were only 32.9±1.0%and 52.1±1.2%,indicating that SCSNG has good healing properties.The results of wound histopathology showed that SCSNG（+）could effectively reduce the inflammatory response at the wound site and promote wound healing.The in vitro degradation experiments of SCSNG showed that the degradation rate at 16 days was42.66±2.1%,indicating that SCSNG had good stability.The results of blood compatibility,cytocompatibility,and metal content in major organs proved that SCSNG has good biocompatibility.Metal ions released on the wound surface do not enter the body’s circulatory system.In conclusion,in this study,a near-infrared responsive nanoworm RBCM-NW-G was prepared by the nanoparticle self-assembly method and doped to create a silk fibroin/chitosan antibacterial dressing.The dressing effectively treats biofilm bacterial infection through photothermal effect,silver ion and GM combined with synergistic antibacterial.It provides a new strategy for the treatment of biofilm infections and efficient use of antibiotics.And it can continuously export wound exudate,block foreign bacteria,and prevent wound re-infection.The sponge antibacterial dressing exhibits moisture conductivity,high antibacterial properties,and significant healing-promoting properties,which have great potential in wound healing applications. |
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