Structural Construction Of Multilayer Composite Wound Dressing And Underlying Mechanism Of Wound Healing

Skin is the largest organ in the human body and it maintains body fluids and electrolytes.Meanwhile skin functions as a first biological barrier which protects human body from the invasion of microorganisms,chemical and mechanical damage.Functions of skin will be damaged when suffered acute trauma,burns and other factors,resulting in imbalance of water and electrolyte,loss of nutrients,infection and even threatening the life of the human body.According to the characteristics of ideal wound dressing,bacterial cellulose(BC),Zein,Vaccarin(Vac),Protoporphyrin IX(PPIX)and other substrates were used and the multilayer composite wound dressing(MC)was be structurally designed and modified.The skeleton layer,the healing layer and the protective layer was prepared respectively by the substrates and drugs to form the multilayer composite wound dressing.BC membrane was prepared by using Gluconacetobacter xylinum and the bacterial cellulose membrane loaded with Vac which was performed by means of solution impregnation.We analyzed the composition and structure characteristics,mechanical properties,cytotoxicity and drug release of the material.The results showed that the BC and BC/Vac membranes had a three-dimensional network structure.BC and BC/Vac had ideal biocompatibility with the 0 grade of cytotoxicity test.BC/Vac membrane also promoted cell proliferation.Dry BC membrane showed high fracture strength,Young's modulus and low elongation at break.So it was difficult to deform but easily broken.Wet BC membrane and BC/Vac composite memberane had certain strength and good ductility.But the surface was slippery and not easy to be processed and preserved.On the other hand,there was a sudden drug release in the PBS solution of BC/Vac composite membrane analyzed by the drug release test.In order to further investigate the bacterial cellulose composite with good mechanical properties and easy to be processed and preserved,the BC/PETN composite membrane was prepared by the bio-composite method.The results showed that the BC/PETN composite membrane has nano-net structure,good flexibility and mechanical properties.It also had a good hydrophilicity with contact angle of 37.4±5.6°;high hygroscopicity with water absorption of 883% in 24 hours.It could be used as the skeleton layer in the preparation of multilayer composite wound dressing in this work.In order to fabricate active wound dressings with multiple functions,the Zein/EC composite membrane loaded with drugs(Vac and PPIX)was prepared by electrospinning.The structure,morphology and performance of the composite membrane were investigated.The results showed that the Zein/EC/Vac nanofiber membrane with a total polymer mass of 2% showed the optimal cell proliferation effect.Different concentrations of Zein/EC/Vac nanofiber membranes showed sustained release ability.It could be used as a healing layer in the preparation of multilayer composite wound dressing in this work.It was found that the Zein/EC/PPIX nanofiber membrane loaded with low concentrations photosensitizer PPIX(total polymer mass 0.5%)could effectively inhibit the growth of bacteria by the inhibition zone experiment,plate colony counting method and bacterial penetration experiment.It showed the ideal antibacterial effect and could be used as a protective layer in the preparation of multilayer composite wound dressing in this work.We further studied the structural construction of the multilayer composite wound dressing.The Zein/EC/Vac and Zein/EC/PPIX mixed solution was deposited on both sides of the BC/PETN composite membrane by electrospinning.Then the three-layer structure was reinforced with a hot press to form a multilayer composite wound dressing(MC).The model of acute skin injury in mice was established and the effect of multilayer composite wound dressing on the skin wounds of mice was evaluated.The results showed that the wound healing of mice treated with MC group reached the rate of 92.4% which was higher than the Control group and the Nano-Ag group on the 10 th day.Pathological results showed that the MC group and the Nano-Ag group had fresh epidermis and the granulation tissue to complete the tissue remodeling process on the 10 th day.The expression levels of Akt,p-Akt,eNOS and VEGF in the PI3K/Akt pathway of MC group and Control group were determined by Western blotting.The MC group was higher than the Control group and there was a significant difference between the two groups of the expression of P-Akt on the 10 th day,the expression of eNOS on the 7th day and the 10 th day,the expression level of VEGF on the 3rd day after model establishment.The above results indicated that the application of multilayer composite wound dressing(MC)may activate the PI3K/Akt signaling pathway and promote wound healing with the Vac stable released and a wet healing environment created for wound.In summary,according to the characteristics of the active dressing,a multilayer composite wound dressing(MC)is fabricated based on the bacterial cellulose membrane,electrospinning skills to prepare stable substrates,drug loaded with the functions of cell proliferation and antibacterial effects.Meanwhile,we did the research on the mechanism of wound healing when we used MC and then provided a reference and means for the treatment of skin wounds.