Preparation Of Small Intestinal Submucosa Skin Tissue Engineering Scaffold Based On Cryogenic Extrusion Bioprinting

Bone exposed wounds have always been a very intractable challenge in the field of traumatic orthopedics.In recent years,based on the tissue engineering,the combination of tissue engineering skin substitute and vacuum sealing drainage technique has been expected as a promising treatment for rapid closure of bone exposed wounds in clinical practice.To achieve this goal,an ideal skin tissue engineering scaffold is needed.There are three specific requirements for the skin tissue engineering scaffold due to the particularity of exposed bone wounds,including a macroscopic porous structure,suitable mechanical strength and certain antibacterial property.This thesis aims at the above three requests,and gradually dissects from three aspects divided into four chapters.Firstly,based on the decellularized small intestine submucosal(dSIS)bio-ink,the dSIS skin tissue engineering scaffolds with macroscopic porous structure were successfully fabricated through the integrated strategy of cryogenic extrusion bioprinting(CEB),freezedrying and cross-linking technique.The effects of the substrate temperature,printing speed,printing pressure and layer height on the printing process were detailedly discussed.Secondly,the prepared dSIS skin tissue enginerring scaffolds were characterized by physicochemical property tests,in vitro cell experiments and in vivo animal experiments.The influences of the material and structure on the properties of scaffolds were emphatically studied.In terms of physicochemical properties,the pore size of the scaffolds will affect their shrinkage deformation,swelling behavior and mechanical property.The results of the cell experiments verify that the macroporous structure of the scaffolds can promote the proliferation and migration of fibroblasts as well as the expression of collagen I,collagen III and fibronectin.The animal experiment proves that the dSIS skin tissue engineering scaffold has the ability to accelerate the healing of bone exposed wounds.Thirdly,mechanical properties of the dSIS scaffolds were improved.The dSIS bio-ink was modified with sodium alginate(SA)through the physical blending cross-linking strategy.Then,by means of the stepwise crosslinking method,the dSIS-SA composite scaffolds were successfully prepared and characterized.The results show that SA can improve the mechanical properties of the scaffolds and modify the microporous structure of the filaments.However,it also increased the shrinkage deformation and decreased the water absorption rate during swelling.More importantly,it inhibited the proliferation of skin fibroblasts.The influence of SA on the properties of the scaffolds can provide assistances for the design of dSIS/SA ratio.Finally,the antibacterial property of the dSIS-SA composite scaffolds was ameliorated.Copper-doped mesoporous bioactive glass(Cu-MBG)was prepared by a template selfassembly method and then Cu-MBG with different mass fractions were mixed into dSIS-SA bio-ink.After that,Cu-MBG-dSIS-SA antibacterial scaffolds were printed by CEB and were characterized.The results indicated that,with the increase of mass fraction of Cu-MBG,the antibacterial and mechanical properties of the composite scaffolds were significantly enhanced,and the shrinkage deformation was also reduced.Nevertheless,the scaffolds containing high content(more than 1.5 wt%)of Cu-MBG were cytotoxic.The effects of the Cu-MBG on the physicochemical and biological properties of the scaffolds will be of benefit to the customization of Cu-MBG content.In summary,the skin tissue engineering scaffolds,which can promote the healing of bone exposed wounds,with excellent physicochemical and biological properties were successfully prepared,laying the foundation of the fabrication of an ideal tissue engineered skin substitute for bone exposed wounds.