Printing Three Dimensional Antibacterial Functional Artificial Dermal Substitute Promotes Wound Repair

Research background and objectiveClinically,skin defects which caused by a variety of factors are very common.Large areas of skin defects are difficult to completely heal by autologous-tissue repair.Various scars and deformities remain on the wound after healing,which brings a huge burden on the patient's family and socio-economics.Currently,skin grafting is the most commonly method for repairing skin defects in clinical practice.Two main issues need to be solved in Skin grafts transplantation: source of skin grafts and survival of transplanted skin.Autologous skin grafts are the most commonly used skin grafts,but a large number of burn patients have the problem of insufficient autologous skin sources.Tissue engineered skin(TES)have great application prospects in supplying of transplanted skin.The number of TES is gradually increasing,but infection remains a key issue for the survival of TES transplants.Nano-silver(Ag NPs)is an antibacterial material with a small particle size,large surface area,high-activity,and low-melting point.It has been widely used in the medical field because of its excellent performance of non-resistance,anti-bacterial,safety and promoting wound healing.As an artificial antibacterial material,its antibacterial activity is far greater than that of ordinary silver ion bacteriostatic agents.Currently Ag NPs have been widely used in clinical and animal experiments,and have achieved ideal antibacterial effects,which can promote wound healing and reduce risk of wound infection.If Ag NPs is added to biological materials,it can inhibit the growth of bacteria and help solve the survival problem of TES transplantation to a certain extent.In tissue engineering,3D bioprinting has been comprehensively carried out,providing stronger technical support for skin tissue engineering.It uses biological "ink" to locate loaded drugs,growth factors,and cells,etc.,and prints layer by layer to precisely build the required tissue or organ.In recent years,the rapid development of biological three-dimensional printing technology has provided fast and accurate methods for the development of tissue scaffold materials.Various biological "inks",such as collagen,gelatin,hyaluronic acid,have been successfully applied and 3D printed.Collagen and gelatin are the most commonly used natural hydrogels due to their good biocompatibility.However,these hydrogels have insufficient mechanical properties and fast degradation rates,and their use as skin scaffolds is limited.Construction of tissue engineered skin using 3D bioprinting technology--Ag NPs-GelMA composite hydrogel.The in vitro bacteriostatic activity and cytotoxicity of Ag NPs were measured.The GelMA hydrogel was compared with the Ag NPs-GelMA composite hydrogel to evaluate and determine the antibacterial activity,physical properties,microstructure,and cell proliferation activity.MethodsFirstly,the antibacterial activity and cytotoxicity of nanosilver were measured in vitro to determine its effect on cell viability.GelMA was provided by the Laboratory of Polymer Department of Zhejiang University with a degree of substitution of 70%.An extruded 3D printer was used to print the hydrogel.In this study,Ag NPs-GelMA composite hydrogel were compared with GelMA hydrogel.The fibroblast suspension was tiled on the hydrogel and mixed and the proliferation activity of cells was measured with CCK-8.We measured the physical properties of the scaffold and observed the internal microstructure.The antibacterial effect of nano-silver and Ag NPs-GelMA composite hydrogel was measured in vitro.Statistical analysis was performed using Student-t test.Results(1)Nano-silver has excellent antibacterial properties;Nano-silver have obvious cytotoxic effect above the concerntration of 10 ppm.(2)Three-dimensional printing results show that both GelMA hydrogel and Ag NPs-GelMA composite hydrogel can achieve rapid cross-linking,and have good structural fidelity.(3)Scanning electron microscope observe the results that the three hydrogels have a pore structure that communicates with each other.(4)CCK-8 measurement showed that the cells on the GelMA hydrogel scaffold had good cell viability.Ag NPs-GelMA composite hydrogel did not show cytotoxicity until the Ag NPs concentration was as high as 100 ppm.(5)The antibacterial experimental study of the scaffold showed the antibacterial effect of Ag NPs-GelMA composite hydrogel.Conclusion1.Nano-silver has a good antibacterial effect at low concentrations.When the concentration of nano-silver was more than 10 ppm,the cytotoxicity increased with the increase of the concentration.2.In this experiment,Ag NPs-GelMA composite hydrogel was designed for 3D printing to construct skin dermal substitutes.The research results show that the Ag NPs-GelMA composite hydrogel has good biocompatibility,strong mechanical properties and obvious antibacterial properties,and has a short gelation time and high fidelity of the printed construct.In the future,it is expected to solve key problems in the survival of TES as an antibacterial functional artificial dermal substitute.