Research Of PEGDA/CNF Porous Tunable Poisson Ratio Tissue Engineering Scaffold's Fabrication And Property

The material design,structure design and fabrication of scaffold for tissue engineering is always the research hotspot in tissue engineering.Cellulose nano fibril(CNF),which derived from plants,is abundant,and has excellent biological properties,mechanical properties and nano-size effect,etc.But its shortcoming lies in the poor forming precision and the uncontrollable structure.The photosensitive polyethylene glycol diacrylate(PEGDA)is mixed with cellulose nanofiber,which can make full use of the their advantages and avoid the weakness.This new composite can be used in tissue engineering.Poisson's ratios are always different in various parts of biological tissues.In the design of tissue engineering scaffolds,poisson's ratio can be introduced as a design parameter to better simulate the mechanical environment of natural tissues.As one of the branches of 3D printing technology,mask projection stereolithography(MP-SLA)has the advantages of fast forming and high precision.The MP-SLA is adopted to prepare PEGDA/CNF hydrogel scaffold with variable Poisson's ratio structure,and post-treatment modification by freeze-drying method is followed to further form aerogel scaffold with better performance,which have good development potential and application prospect.This paper attempts to introduce a new material,new structures and a new fabrication method into the design and preparation of new tissue engineering scaffolds,so as to obtain an integrated solution.The main research work of this paper are listed as follows:(1)Research on the photocurable 3D printing performance and manufacturing technology of PEGDA/CNF photosensitive solutionThrough literature research,cost analysis and application prospect analysis,the visible light initiator system was determined,and then the photocuring working curve of PEGDA/CNF solution was also obtained.After analysing the single-layer curing model and multi-layer curing model,the influence of each key parameter on the working curve was found.Based on these datas,a method was proposed to improve the bonding strength at the weak joints of hydrogel supports by using the phenomenon called "over-curing".In addition,this paper also proposes a solution displacement method to improve the printing accuracy in both X and Y directions.These two physical methods can not only improve the printingaccuracy as much as possible but also avoid the possible influence of toxic additives on the cell culture.A MP-SLA 3D printing platform was also customized in this paper,in which each module was individually selected or customized based on the new material characteristics and manufacturing process.(2)Preparation and performance study of PEGDA/CNF aerogel scaffoldAfter MP-SLA process,a post-treatment method of freeze drying was introduced to construct a "two-step" method to obtain PEGDA/CNF aerogel.The new aerogel material can not only maintain the excellent properties of the original hydrogel,but also further exhibite the cellulose's function in the composite material.Cellulose can modify the microstructure of the scaffold,and provide a better microenvironment for the growth of cells.After orthogonal experiments,the effects of different material and fabrication parameters on various properties of aerogel such as porosity,mechanical properties,thermal properties and microstructure were discussed,and the optimal combination of material and fabrication parameters was finally determined.(3)Design of scaffold with tunable Poisson's ratio and study of mechanical properties of PEGDA/CNF aerogel in wet and dry stateThe stress environment that different Poisson's ratio scaffolds can provide for cell growth is analyzed,which proves the necessity of considering Poisson's ratio as a design parameter in the design of tissue engineering scaffolds.Considering the different geometry and mechanical properties between hydrogels and and the wet aerogel,mechanics parameters of the original hydrogels and wet aerogel have been tested.A swelling model has been built to accurately predict the changes of the geometry and mechanical properties between aerogel-wet and aerogel-dry.81 grid structures with various Poisson ratios were designed by changing the size parameters of the structure.The mechanical influence comes from different structural parameters and different material properties was analyzed and discussed,laying a foundation for precise control of the scaffold's Poisson ratio.(4)Study of stem cell culture experiment on PEGDA/CNF tunabel Poisson's ratio scaffoldNine groups of PEGDA/CNF scaffolds with different Poisson's ratio structures were designed and manufactured.Bone marrow mesenchymal stem cells extracted from SD ratswere implanted into the scaffolds and cultured for three weeks.The growth of stem cells on the scaffolds with different structures was measured by growth rate test and fluorescence microscope characterization.The expression level of collagen II,a cartilage marker gene,in each group of scaffolds was tested through gene detection experiment,so as to determine which group of scaffold is more conducive to the formation of chondrocytes.Which scaffold can form glycosaminoglycan secreted by cartilage could be determined by the cartilage matrix section staining.It was concluded that the zero Poisson's ratio scaffold is most conducive to the growth of stem cells and its differentiation toward cartilage.