3D Printing Of Responsive Hydrogel And Its Application

In recent years,soft actuators which convert external stimulations including temperature,pH,light,and magnetic field into mechanical deformation have fascinated great research interest due to their potential applications in the fields of healthcare,biomimetic devices and soft robots.In contrast to rigid structure,soft actuators may easily deform in response to changes in the external environment.However,so far most of the actuators are fabricated with sub-millimeter dimensions or bigger which can't be used in special fields such as cell scaffolds,micromanipulators,microrobots and so on.Therefore,the research of soft microactuator with micron level is of great significance.The fabrication of soft microactuator is a great challenge for materials selection and actuation design.In this paper,a bilayer structure poly(ethylene glycol)diacrylate(PEGda)hydrogel microactuator was fabricated by direct laser writing(DLW)based on two-photon polymerization.PEGda hydrogel can swell by adsorbing water molecules.PEGda hydrogel with high expansion rate was used as response layer and PEGda hydrogel with low expansion rate was used as passive layer.The printed PEGda bilayer hydrogel microactuator would bend due to unequal expansion when immersed in water and became a water responsive soft microactuator.The research of this paper is divided into three parts:(1)The preparation of PEGda hydrogel microstructures.The two-photon 3D printing photoresist was prepared by mixing PEGda monomers,water as solvent,and Eosin B as photosensitizer to initiate polymerization.The effects of laser power and scanning speed on the formation of PEGda hydrogel were studied.(2)Factors affecting the expansion rate of PEGda hydrogel.The effects of laser power and slicing distance on the expansion rate of PEGda hydrogel were studied.The results showed that the larger the laser power was or the smaller the slicing distance was,the lower the expansion rate was;the smaller the laser power was or larger the slicing distance was,the higher the expansion rate was.(3)The fabrication of PEGda bilayer actuator.Four factors affecting the bending radius of the actuator were studied: laser power difference,slicing distance difference,the proportion of the responsive layer and the aspect ratio of the actuator.The results showed that the larger the difference of laser power or slicing distance between the responsive layer and passive layer was,the smaller the bending radius of the actuator was.The bending radius of the actuator first decreased to the lowest value and then increased with the increasing of the ratio of the responsive layer and the aspect ratio of the actuator.The results of this study showed that the PEGda hydrogel prepared by two-photon 3D printing had a controllable expansion rate.The bending radius of the bilayer PEGda soft microactuator could be effectively controlled by four parameters.