| Burns as prevalent skin injuries,can cause skin redness,blisters,pain and other symptoms,which even injured the subcutaneous tissue,muscle and bone tissue in severe cases.For mild to moderate burns damaged deep in dermis,the choice of clinical dressing is critical for patient’s prognosis.People have developed various synthetic dressings for burn treatment to solve such problems as skin damage,pain,slow wound healing,fluid loss,and bacterial infection,in the meantime reducing treatment costs.Among bioengineering materials,hydrogels have been widely used in preparing burn wound dressings due to their low cost,excellent physical and chemical properties,and good biological properties.However,the hydrogel dressings have insufficient antibacterial properties and cannot prevent scar formation.The application of growth factors can promote tissue healing to some extent,but their low stability and short halflife usually required large doses and repeated administration over a long(short)period,which may aggravate local fibrosis and hypertrophic scar formation.Hence,using a hydrogel dressing without growth factors may reduce these side effects and achieve better therapeutic outcomes.Two-dimensional nanomaterials are high-quality raw materials for the preparation of no growth factor burn dressings,due to their excellent antibacterial and anti-inflammatory effects,good biocompatibility,and ability to regulate cell behavior.Two-dimensional nanomaterials such as graphene oxide and black phosphorus could play a certain therapeutic effect in skin injury repair,but their effects on re-epithelialization have been rarely reported.It is of great significance to relieve local inflammation and reduce the formation of scars to combine these advantages of hydrogel with two-dimensional nanomaterials for promoting epithelial healing of wounds.In Chapter 2,we firstly synthesized a composite multifunctional hydrogel(C&BPPatch)based on catechol chitosan(CA-CS),oxidized dextran(Odex),and black phosphorus nanosheets(BPNS)and characterized its physical and biological properties.The characteristic absorption peaks of Raman spectroscopy and infrared spectroscopy confirmed that BPNS was successfully doped into the hydrogel matrix.Scanning electron microscopy(SEM)results showed that BPNS could be uniformly dispersed into the hydrogel matrix with high porosity.Tissue adhesion and shear-stretching experiments showed that C&BP-Patch had excellent tissue adhesion.In the mouse liver haemorrhage model,C&BP-Patch showed excellent hemostatic properties.The results of swelling and rheological shear experiments showed that C&BP-Patch had high water content and good self-healing ability.The good cytocompatibility,rapid gelation and injectable ability of C&BP-Patch were also beneficial for the local application of burn wounds.In Chapter 3,we evaluated the photothermal antibacterial ability of C&BP-Patch both in vitro and in vivo,respectively.The photothermal experiment showed that C&BP-Patch had a high photothermal conversion efficiency and good photothermal stability,and would not cause structure collapse with cyclic illumination.Short-time irradiation(2 min)was adopted to control the wound temperature at about 42-48 ℃ to avoid secondary damage caused by excessive local temperature when exposed to infrared light.The antibacterial experiment in vitro confirmed that after near-infrared light irradiation for 2 min,C&BP-Patch could effectively inhibit the growth of Staphylococcus aureus(S.aureus),methicillin-resistant Staphylococcus aureus(MRSA),Escherichia coli(E.coli)and Pseudomonas aeruginosa(P.aeruginosa).Then,we performed Gram staining and bacterial culture of infected burn skin tissue to further verify the antibacterial effect of C&BP-Patch in vivo.The results showed that after near-infrared light irradiation for 2 min,C&BP-Patch could effectively reduce the number of bacteria in infectious burn wounds.These results indicated that C&BP-Patch had stable and excellent photothermal antibacterial properties,which could be used for infectious burn wounds.In Chapter 4,we constructed an infectious skin burn model of mice to verify the effectiveness of C&BP-Patch in vivo.Gross results showed that C&BP-Patch could accelerate the healing of mouse infectious burn wounds.H&E staining indicated that the C&BP-Patch group had new hair follicles and sebaceous glands regeneration at 21 days,with no obvious epidermis hyperplasia.Masson’s trichrome and Sirius red staining results exhibited that C&BP-Patch could promote the orderly deposition and reconstruction of subcutaneous collagen,thus reducing scar formation to some extent.Immunohistochemical staining results of vascular markers(α-SMA and CD31)and inflammatory factors(CD68,TNF-α,IL-1β,and IL-6)confirmed that C&BP-Patch could effectively promote the regeneration of subcutaneous vessels and alleviate the inflammatory response in the early stage of injury,which was beneficial to stabilize the local microenvironment.Therefore,we believed that C&BP-Patch,as a safe and effective wound dressing,can achieve rapid healing of infectious burn wounds from multiple aspects and has a good applicable prospect in the repair of burn wounds.In Chapter 5,we explored the mechanism of C&BP-Patch for promoting burn healing and its main effect components.The cell migration experiment showed that C&BPPatch played a role in promoting cell migration mainly through BPNS in it.It was found that C&BP-Patch could also promote the migration of epidermal cells in vivo by analyzing the related indexes of epidermal migration in healing tissue.Since epithelialmesenchymal transformation(EMT)is an essential part in epidermal migration process of wound healing.Therefore,we used Western Blot,immunohistochemistry stain,and real-time fluorescent quantitative PCR to analyze the expression of EMT-related proteins and genes to further reveal the effect of C&BP-Patch on EMT.These results confirmed that C&BP-Patch could inhibit the expression of epithelial-related molecules E-cadherin and cytokeratin,and promote the expression of mesenchymal-related molecules N-cadherin and vimentin to promote the migration of epidermal cells.By analyzing the expression of upstream-related molecules of EMT,we found that C&BPPatch could increase the expression of p-p38 and Snail1,while there was no obvious effect on the expression of Slug(Snail2).This indicates that C&BP-Patch may regulate the expression of EMT-related molecules by affecting the p-p38 and Snail1 signals,thus promoting the migration of epidermal cells and ultimately achieving epidermal healing of burns.In conclusion,we successfully synthesized a composite hydrogel with excellent physicochemical properties and biological functions using a chemical modification method.C&BP-Patch not only has good light-to-heat conversion efficiency and excellent antibacterial performance,but also can regulate the expression of EMTrelated molecules to promote the migration of epithelial cells by stabilizing the local microenvironment,thus achieving rapid scarless healing of mouse infectious burn wounds. |
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