3D Printing Of Multi-functional,Multi-material Hydrogels And Their Mechanical Models

Hydrogel which is composed of hydrophilic three-dimensional polymer network and a large amount of water is widely used in many fields,including flexible electronics,soft robotics and bio-engineering.Recently,three-dimensional(3D)printing which has been deeply explored to fabricate customized structures of smart materials enables hydrogels to be applied in more fields.In general,the initial hydrogel precursors need to be modified to meet requirements of 3D printing.Without degrading the printing performance,it is significant that higher water content of hydrogel should be developed.On the other hand,the 3D printing of pure hydrogel cannot meet various applications requiring complicated structure,so it is important to develop the multi-material 3D printing based on hydrogel.Furthermore,four-dimensional(4D)printing hydrogels is an emerging method to mimick dynamic architectures due to reversible large deformation and smart response to various chemical or physical stimuli.Besides studying the above topics,this thesis also develops the constitutive model suitable for the anisotropic swelling of printed hydrogels,which provides a theoretical foundation for the interpretation and prediction of the mechanical properties of 4D printing hydrogels.The main contents of this thesis are described as follows.(1)To develop 3D printing of multhifunctional hydrogels.As well known,internal supporting materials determine the printing performance while not change the proper functions of hydrogels.Herein,Carbomer is shown to be a highly efficient internal supporting material capable of assisting printing multi-functional inks,including double network(DN)hydrogel,magnetic hydrogel,temperature-sensitive hydrogel and bio-gel,with a low dosage(at least 0.5% w/v).Super high water content(99.5%)of hydrogel colloid can be printed.The printing performance,mechanical effects,and biocompatibility of multi-functional hydrogels are investigated.Novel devices enabled by 3D printing of multi-functional hydrogel are further demonstrated,such as loadable web,soft robot,four-dimensional(4D)printing leaves,and hydrogel Petri dish.Especially,the results of biocompatibility test indicate this internal supporting material has huge potential in biomedical engineering.(2)To develop multimaterial 3D printing of hydrogel-polymer hybrids.Hydrogel-polymer hybrids have been widely used for various applications.Here,we develop a simple yet versatile multimaterial 3D printing approach to fabricate complex hydrogel-polymer 3D structures.The hybrid structures are printed on a self-built Digital Light Processing(DLP)based multimaterial 3D printer.Hydrogels can be printed with diverse other UV curable polymers including elastomer,rigid polymer,ABS-like polymer,shape memory polymer and other(meth)acrylate based UV curable polymers.The interface bonding problem between hydrogels and these materials is solved and the mechanism is explained.We demonstrate a number of applications based on this multimaterial 3D printing approach.This method paves a new way for the application of hydrogel-polymer composite structure.(3)To develop an anisotropic swelling model for Direct Ink Writing(DIW)printed hydrogel-fiber composite.Based on homogenous swelling,we add a new decouple free-energy function which describes the anisotropic mechanical properties of embedded fibers.A dispersion parameter that characterizes the degree of anisotropy is introduced into this function and it is also related to the shear-induced distribution of fibers in DIW printed filaments.We implement this theory as a user-defined material(UMAT)in the commercial finite-element software,ABAQUS,and compare the numerical solutions with analytical results and experimental data to verify the proposed model.Finally,diverse numerical cases are analyzed and can predict the subsequent deformation of 4D printing hydrogel.Meanwhile,the predicted results are verified by experiments.