Improvement Measures For Tissue Engineering Cartilage

Objective: Cartilage is a type of elastic and smooth tissue with rubber-like liner,covering and protecting the end of the long bone of the joint,providing low friction and lubrication surface for the joint,and acting as cushion for pressure transmission.However,the ability of self-healing of cartilage is very limited because of its aneural and avascular nature.Once the loss exceeds the deposition,the net decrease of extracellular matrix is inevitable.This usually marks the early stage of osteoarthritis,a common disease that affects 10% of the world's population over 60.In recent years,as a concept of "implantable cell,stimulator,biomaterial delivery and support system",tissue engineering has shown good performance in physical structure,chemical composition and mechanical behavior,and in the realization of alternative products with natural tissue characteristics.As a new method of tissue engineering,3Dbioprinting can be used to design implants according to the original anatomical imaging data of specific lesions and create a three-dimensional structure of tissue through layer-by-layer assembly,so as to realize the reconstruction of cartilage structure at all levels and depth components in vitro.Biomaterials for cartilage tissue engineering and bioprinting are usually soft natural hydrogels,such as agarose and gelatin.However,the mechanical properties of hydrogels are usually much lower than those of the loaded tissues.In this case,due to its excellent mechanical strength and adjustability,but poor biological properties,the synthetic polymer becomes the choice to compensate for the defects of natural materials.In order to better understand the structural design of tissue-engineered cartilage scaffold,and to verify the better mechanical properties of synthetic polymer fiber and explore its related properties,I have two specific experimental purposes: 1.Optimize the printer to be used in our laboratory,explore the impact of different printing settings on the printing structure,and determine the printing parameters of the actual printed three-dimensional structural samples;2.In order to modify and improve the original structural design,through the comparison of compression test and compressive modulus,test and verify the better performance of new designs.Methods: The G-code programs were designed by ourselves and the designed graphic samples were printed out by Inkredible+ bio-printer.The statistical parameters of each aspect were measured to explore the "melt-extrusion" printing method and determine the optimal printing settings.After that,more complex PCL scaffolds were printed out by the same printing method,and the measuring software and equipment provided by our laboratory were used to test the mechanical properties of those PCL scaffolds.In order to select the most ideal sample pattern,we measured the porosity and mechanical property of each sample,and made a statistical comparison between the same group and different groups.Results: The mechanical properties of the experimental samples were similar to those of human articular cartilage,and the compressive modulus of the samples with different patterns/ sizes were different.Conclusion: The results of the experiment proved the applicability of the printed sample clinically.In addition,different compressive moduluses of samples with different patterns /sizes provided a new perspective for adjusting the mechanical properties of the scaffold by setting different line spacing / pattern design in the bio-printer system.However,the resolution of bioprinting can still be improved to a higher level through more complex approaches.Furthermore,various types of natural / synthetic materials have a lot more potential combinations,which can be further explored in future experiments.