| BackgroundSkin is the largest organ in human body and plays an important role as a barrier b etween the organism and the outside,which protects body from physical,mechanical,chemical and pathogenic microbial invasion.Meanwhile it maintains water,electrolytes and various nutrients.Skin also contains a variety of nerve endings which react to heat,cold,touch,pressure,vibration,tissue injury,and keeps people away from harmful stimuli.Further functions include excretion,absorption,storage,synthesis,aesthetics,communication and so on.In short,skin is irreplaceable to stay physical and mental healthy for human.In modern society,wound has become one of the most common clinical symptoms,and many diseases are related with skin defects.The treatment usually involved both in symptom and pathogeny,whichever therapy is inseparable from wound dressing.As the most common clinical medical supplies,dressing plays an important role on wound healing.Composition and structure of dressing determined its function.Thermoplastic polyurethanes elastomer(TPU)is a sort of organic polymer materials,which is characterized by favorable chemical stability,processability,biocompatibility and economy.TPU has already been approved by Food and Drug Administration(FDA),and used in many medical devices,but the wound dressing consisted of TPU hasn’t been reported up to now.After moist wound healing therapy,which was first presented by Professor Winter,more concerns on wound dressing turn to biomaterial,cytokines,controlled release technology,biomanufa cturing technology and so on.Producing the wound dressing by special materials and methods that imitated the nature skin has become the new trend in dressing manufacture.Thermally induced phase separation(TIPS)is the most common method to prepare porous polymer film.Based on the previous research,the bionic porous TPU membrane was fabricated combining solvent casting and particulate leaching.It had been proved that bilayer dressing could enhance the wound healing.With the productive traits of bionic TPU membrane,we predicted that it could exert a positive effect on wound healing.ObjectiveIn this research,we intended to prepare a bionic TPU membrane with bilayer porous structure by solvent casting together with particulate leaching,examine its physical characterization,biocompatibility,and pinpoint its effect on wound healing.Methods1.Preparation of TPU membrane.The bionic TPU membrane were prepared via the method combining solvent casting and particulate leaching,while the common TPU membrane were prepared via TIPS.2.Measuring structure and characterization of TPU membrane.(1)Observing its appearance and microstructure.(2)Measuring its pore size,tensile strength,elongation at break,and water vapor transmission rate(WVTR).3.Cytotoxicity of TPU membrane.Experimental Approach refers to GB/T 16886.5,and the cytotoxicity was evaluated via co-culture with primary human prepuce fibroblast.4.The effects of bionic TPU membrane on wound healing.(1)Full-thickness skin defects wound model of mouse was established to research the influence of bionic TPU membrane on wound.(2)At third day and seventh day post-wounding,the length of new epithelium and granulation thickness were measured by two independent researchers using Image J(1.50 i,National Institute of Healthy,USA),according to the H&E pathological sections sampling from wound tissue.(3)At fifth day post-wounding,the expression of the proliferating cell nuclear antigen(PCNA)and the platelet endothelial cell adhesion molecule-1(CD 31)at wound tissue were detected by western blot(WB).Results1.Two kinds of TPU membranes were prepared,and bionic TPU membrane was proved to be better than common one in appearance,tensile strength,elongation at break,and WVTR.Besides,the pore diameter in external surface of bionic TPU membrane attain micron level,so the top surface could prevent excessive water loss,providing a moist e nvironment for wound repair,as well as acting as an effective barrier to prevent the invasion of pathogenic microorganisms.Its inner structure looks like sponge with double lawyer,which reportedly beneficial for cell attachment and proliferation.2.Both TPU membranes had no adverse effects on human fibroblast viability and proliferation.3.The vivo experiment revealed that bionic TPU membrane accelerated wound healing and shortened wound closure time.The average wound closure time in the control,vaseline gauze,common TPU membrane and bionic TPU membrane groups was 9.5±0.55 days,9.3±0.52 days,8.68±0.82 days and 7.14±0.41 days,respectively.4.At third day and seventh day post-wounding,the length of newly regenerated epidermis were 1052±317μm;and 2414±703μm respectively in bionic TPU membrane group,644±176μm and 1920±654μm respectively in common TPU membrane group,481±119μm and 1570±506μm respectively in vaseline gauze group,446±143μm,1416±610μm,respectively in control group,and the granulation tissue thickness were 501±168μm,415±113μm,607±68μm and 803±118μm respectively at seventh day post-wounding,which revealed the re-epithelialization and granulation tissue formation were enhanced when wound covered with bionic TPU membrane.5.As for WB,the OD values of the PCNA band and CD31 band in the bionic TPU membrane group were both higher than the others,indicating that cell proliferation was significantly promoted in the granulation tissue,as well as newly regenerated epidermis,and revealed active angiogenesis in the wound tissue compared with the control,vaseline gauze and common TPU membrane groups.ConclusionWe prepared a new type of porous TPU membrane with favorable mechanical properties by combining immersion precipitation with particle leaching.The novel TPU me mbrane had a biomimetic structure and was designed with a gradient of pore sizes as natural skin.These membranes could promote wound healing via promoting granulation tissue formation,wound re-epithelialization and angiogenesis.The results suggested that this membrane could be used as an optimal wound dressing in the future. |
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