The Three-dimensional Printing And Exploration Of Applying Of The Double Network Hydrogels Based On Microfluidic Technology

In recent years,considered as the symbol of the third industrial revolution,along with rapid development,Additive three-dimensional printing technology has been widely used in daily life and industrial production.The three-dimensional bioprinting technology generally refers to the formation of biomimetic tissues and organs for biological ink by using biomimetic materials,living substances,cells,etc.The 3D bioprinting technology has been applied in the field of regenerative medicine,tissue engineering and organ microchips successfully,followed by considerable achievements.It has also been widely used in the fields of regeneration and simulation of bones,skin,artificial blood vessels,and heart tissue.With the extracellular matrix of the cell simulated by a hydrogel composed of a three-dimensional network of high water content polymer,the three-dimensional bioprinting can support cell proliferation better,which has attracted widespread attention.In recent years,a series of progress of hydrogels have been achieved in the field of three-dimensional bioprinting by controlling hydrogel shape,porosity,surface morphology,and size parameters.However,the single-network hydrogels,with low strength,are easily deformed and can’t bear weight.With the continuous deepening of hydrogel research,the mechanical properties of hydrogels forming an intertwined networks have been improved by tens times.The mechanism of this intertwined double network hydrogel with ultrastrength and toughness is so complex solidification that it can only be processed by simple techniques such as mold casting.If double-network hydrogels with excellent mechanical properties can be directly used for 3D printing to various 3D complex shapes and microstructures individually,or even be used to the fine design and manufacture of human tissues such as regenerated cartilage,joints,cervical intervertebral discs,and tendons,the development of regenerative tissues and organs,robots and other fields will be greatly improved.In this thesis,we employ a biomimetic microfluidic device as the nozzle-head in a 3D printing stage.The microfluidic nozzle consists two coaxially aligned channels,where flow the inner and outer liquid phases respectively: monomers,crosslinkers and initiators of double network hydrogel were introduced into the microfluidic device,and the curing rate of the dual network hydrogels was controlled by regulating the flow rates of the two phases and mixing the microchannels so that the double-network hydrogel passing through the microfluidic device is in a semi-cured state.In this way,the nozzle can be smoothly extruded to achieve continuous printing,and it is not easy to flow,resulting in distortion of the print molding.Based on the continuous printing of the double network hydrogel,we have constructed a two-dimensional complex pattern and a three-dimensional structure,which is difficult to be achieved with the inverse mold method.Through the stress-strain relationship measured by the built-up tensile force platform,we found that the double-network hydrogel microfibers formed by the microfluidic three-dimensional extrusion printing technology have higher toughness and their stretch rate reaches 21 times the length of their original lengths.And compared to the method of printing by additives in the literature,which has resulted in the deterioration of the hydrogel performance,the microfluidic three-dimensional extrusion printing technology we used can retain the super strength and toughness of the double network hydrogel completely.In addition,we studied the quantitative relationship between the stretch rate of the dual network hydrogel microfibers and their water content,the cross-sectional area of the microfibers,and the internal and external phase flow rates(Qin/Qout)in detail,providing technical support for the printing technology and the applications of prepared hydrogels microfiber.Finally,in order to expand the application of dual network hydrogel microfibers in flexible electronics,we printed a double-network hydrogel microfiber grid based on an electrolyte solution as a sensor.The double-network hydrogel microfibers containing electrolyte solution have excellent electrical conductivity and can be regulated by the concentration of the electrolyte solution without affecting the mechanical properties.The electrical conductivity remains unchanged when the stretching ratio reaches 11,which is based on the great differences of flexible electronic devices sintered conductive nanometer particle.After destructive testing,it was found that the prepared double-network electrolyte hydrogel grid has high toughness and it can measure and distinguish the changes of human motion signals including the amplitude and frequency of sports fully after being worn by volunteers.The research of this paper achieved the three-dimensional printing and continuous preparation of the dual network hydrogel.The obtained hydrogel microfibers have excellent mechanical properties,and with the stretching rate as high as 2100%,and the toughness as high as 1800 KJm-3,it is an ideal material for three-dimensional tissue engineering and regeneration medical accessories.Its excellent electrical conductivity and printing properties also make it possible to be used in wearable textile flexible electronic devices,such as wearable flexible supercapacitors.