Research On The Establishment Of Ordered Structures Of Nanocomposite Hydrogels And The Regulation Of Their Mechanical And Electrical Properties

Hydrogel is a series of materials with high water retention capacity and threedimensional network structure.PHEMA hydrogel has good biocompatibility and inherent advantages in the fields of biomedicine and tissue engineering.However,PHEMA hydrogel has poor ductility and poor mechanical strength,which limits its application in various scenarios.To cope with this,modifying PHEMA hydrogels into composite hydrogels with other materials is an important direction of current related research.Nanofibers(such as carbon nanotubes)have the characteristics of high aspect ratio,and some of them have good mechanical properties and electrical conductivity.Using nanofibers to reinforce hydrogels can effectively improve the mechanical and electrical properties of composite hydrogels.Most of the reported nanofiber composite hydrogels obtained isotropic reinforced composites by doping with disordered nanofibers.The high aspect ratio of nanofibers is not effectively utilized.PHEMA hydrogel composites with ordered nanofibrous structure were successfully fabricated by the direct ink writing(DIW)3D printing method using fluid shear force to induce the ordered arrangement of nanofibers.The printing process of fluid-induced ordered nanofiber hydrogel composites,and the mechanical and electrical properties of the hydrogel composites fabricated by this method were explored.The main works are as follows:(1)Based on the DIW method,a 3D printing system for the fabrication of hydrogels composite with ordered nanofibrous structure was built using a bifurcated pipeline feeding device and a photocatalytic curing device.The effects of technical parameters in the printing system,such as ambient temperature and viscosity of hydrogel precursors during the process,were explored,and the hydrogel 3D printing process was improved according to the different needs of materials.(2)The CNT-PHEMA composite hydrogel samples containing ordered carbon nanotubes(CNTs)were prepared.The microstructure was observed by SEM,and it was found that the CNTs were uniformly dispersed.In mechanical property tests,the modulus of CNT-PHEMA samples are 169% higher than that of pure PHEMA samples.The mechanical properties of CNT-PHEMA samples are anisotropic,and the difference in modulus in the orthogonal direction is 1:1.81.The electrical property test shows that the resistivity of CNT-PHEMA samples is 45.8% of that from pure PHEMA samples.The resistivity of the sample shows anisotropy,and the resistivity difference in the orthogonal direction is 1:0.82.The electromechanical coupling properties of samples were determined,and their resistivity increased with increasing stretching speed.(3)Ag NW-PHEMA composite hydrogel samples containing ordered silver nanowires(Ag NW)were prepared,and their mechanical and electrical properties were tested.The modulus and resistivity of the samples show anisotropy.(4)SCF-PHEMA composite hydrogel samples containing ordered short carbon fibers(SCF)were prepared,and the microscopic morphology was observed by SEM.The SCF in the sample is uniformly dispersed and arranged in an orderly manner(the fiber accounts for 84.2% within the inclination angle ±20°).The mechanical properties and electrical properties of the samples were tested.The anisotropy of the mechanical properties and electrical properties of the SCF-PHEMA samples was the same as that of the CNT-PHEMA samples and the Ag NW-PHEMA samples.(5)Using the 3D printing system and the CNT-PHEMA composite hydrogel scheme mentioned above,the CNT-PHEMA hydrogel block samples were fabricated in an orthogonal stacking manner to demonstrate the application potential of the method in printing 3D structures.The mechanical properties,electrical properties and piezoresistive properties of CNT-PHEMA hydrogel blocks were measured,and the resistivity of the hydrogel bulk sample in the interlayer direction reaches 700% of that along the layer direction.