Study On Process And Application Of Digital Light Processing Based 3D Printing For Organon Chip

Organ on chip is a system containing artificial vasculature with tissue model,and their user-defined cell types and bio-mimetically geometric features have made itself very promising for several applications in the field of drug discovery and personalized medicine.So far,the demands of fabricating organ on chip with high fabrication resolution,large scale and high fidelity are increasing.The digital light processing(DLP)-based 3D printing offers great advantages in digital design,high throughput and wide usability of materials,which is a perfect method to fabricate organ on chip for both customization and mass production.However,several concerns in DLP-based 3D printing,such as fixed scale and hardware complexity are limiting its application.For printing itself,the detect of non-uniformly distributed light may cause the loss of printing resolution and effective scale at the same time.When using the DLP-based printing to fabricate artificial vasculature,fractal designs are adopted commonly.However,the fluid dynamic and tissue morphology in fractal vasculature may present huge disparity compare to their situations in natural blood vessel.When printing cartilage with gradient stiffness,the normal ways,such as pre-polymer modification and hierarchical design,will affect the mechanical integrity and geometric fidelity.In this dissertation,system development,numerical simulations and experimental studies on printing process,optimization method and application in organ on chip were carried out for DLP-based 3D printing.This work was supported by National Natural Science Foundation of China under Grant 51575485.In Chapter 1,the research background and significance of this dissertation were introduced.Then the main research contents were proposed based on the literature survey of the relevant studies.In Chapter 2,the DLP-based printing system integrated with top-down and bottom-up modules that applicable for variable printing ratio was designed and established.In Chapter 3,a"working curve" based calculation method to describe the effect of exposure time on printing thickness was developed,and the Beer-Lambert law and mass transfer equation of free radical were used to analyze the printing process.The relationship between exposure time and printing size was also studied.Optimization methods for the printing under non-uniformly distributed light were studied in Chapter 4 and 5.In Chapter 4,a numerical model was developed to investigate the effect of light power density and exposure time on printing thickness.And a multi-step exposure(MSE)method that takes advantage of a series of gradient digital masks to compensate the under-cured region with additional exposure and eventually improve the surface flatness was proposed.In Chapter 5,the relationships between the input power,grayscale of digital mask and projected light power density were studied.Then,a grayscale display method was presented to serve as a strategy for improving light uniformity,and fabricating constructs with large scale and high resolution.Based on the studies of Chapter 4 and 5,the applications of DLP-based 3D printing in the multi-scale artificial vasculars and cartilage constructs were studied in Chapter 6.In Chapter 7.the chief work and innovations of dissertation were summarized,and the further research subjects were proposed.The achievements of this research concludes three aspects.For the developed system,organ on chip related constructs,such as microfluidic chips,hexagonal hepatic models,nerve repairing conduits can be printed by PEGDA photosensitive prepolymers.The printing under ratio of 0.5～2.5 have been achieved through the top-down module and the minimal printing size was 20μm.The minimal printing size of the bottom-up system reached to 25 μm when the ratio was 1.0.In the studies of printing process and optimization,the proposed numerical model can be applied to calculated the printing thickness under certain expsosure time and power desnity.MSE method is promising to printing structures with consistent thickness,and the deviation has been reduced to 30 μm from over 350μm.After the applying of grayscale display method,the printing area has significantly increased to 90%,comparing 54%in normal printing.For the printing size in projection plane,under/over cure has also been alleviated.In the application aspect,cell patterning experiments showed that red fluorescent protein-transfected A549 human non-small lung cancer cells adhered well in the multi-scale artificial vasculars,and demonstrated further attachment and penetration during cell proliferation.60%of compression modulus has been achieved on the printed PEGDA cartilage construct.3T3 fibroblasts were seeded on the scaffold,and the biocompatibility together with physical supporting by cartilage were confirmed via CCK-8 viability test.The innovations of this dissertation arc as follows.(1)The effects of exposure time and lighe power density on printing thickness were studied and a numerical model was established.Furthermore,a multi-step exposure(MSE)method was presented,which can be used to control printing thickness under non-uni formly distributed light.(2)To improve printing resolution and range,a grayscale method was proposed and the effects of pixel value on the projected light power density were systematically studied.Experimental results demonstrated the improvements in both light distribution,printing resolution and range.(3)The bimimic masks inspired by nature capillary vessel and tree branch were designed.Then artificial vasculars with multi-scale channel were printed,which can pattern cell from the scale of 30 μm to 1000 μm.And automatic perfusion of fliud has also been achieved in the printed artificial vasculars.(4)To regulate the stiffness of printed PEGDA hydrogel without the changing of materials and geometries,an exposure time based method was proposed.Gradient cartilage constructs were designed and printed,which has demonstrated three-sectioned stiffness with considerable biocompatibility.