Optical Fabrication And Characterization Of Responsive Hydrogel Devices

Responsive hydrogel is a kind of hydrophilic polymer with three-dimensional network,which can swell in response to environmental stimuli,such as p H,temperature,light.Due to the strong hydrophilicity,biocompatibility,and environmental friendliness,various functional devices based on responsive hydrogel have been widely used in the fields of biomedicine,tissue engineering,micro-optics,smart micromachine,etc.According to the current research progress,the properties based on hydrogel devices,including the response speed,the motion orientation and the application development have made great progress.In addition to the macrodevice,micro/nanodevices based on hydrogel,especially the ones with designable 3D structure,have potential applications in mitrotrauma intervention,osteogenic scaffold,three-dimensional cell culture,and drug release.Comparing with the existing micro/nanofabrication technology,femtosecond laser direct writing(Fs LDW)is more designable and high-precision,and can realize the preparation of complex three-dimensional structures.Moreover,Fs LDW can achieve flexible step-by-step processing and in-situ processing.Thus,Fs LDW has the advantage on fabricating complex and diverse hydrogel functional microdevices.For the purpose of improving the properties of hydrogel-based macrodevices,including fast response,controllable orientation and diverse applications,and exploring the controlled preparation,environmental response,integration of hydrogel-based micro/nanodevice,and its potential application in information transmission,optical detection,and biological simulation,in this paper,macroscale responsive hydrogel-based functional devices were fabricated by UV lithography,the characteristics and applications of the devices were studied.In addition,hydrogel-based microstructures with adjustable swelling properties were prepared by Fs LDW.Through a two-steps fabrication method,active PEG-DA hydrogel and inert methacrylate-based material could be combined.The tunable hydrogel microlens was integrated in situ into a chip with symmetrical twin microchannel,which was the first time that optofluidic and microfluidic were integrated into a single chip.More detailedly,the work in this thesis can be summarized as follows:1.Fabrication of hydrogel film actuator with fast and sensitive responsiveness.Hydrogel films were prepared by UV photopolymerization using PEG-DA as monomer,which were sensitive to the change of relative humidity.The spontaneous deformation and motion would be observed when the hydrogel films were placed under humidity gradient,and a small humidity gradient such as physiological moisture could also drive the film to deform.Due to the addition of rhodamine B,the hydrogel films displayed different degrees of pink color under different relative humidity,which can be used as the environmental humidity indicator.The ability of responsive deformation of various volatile polar solvents expanded the application scope of the film.A kind of gelatin hydrogel film with high humidity sensitivity and good mechanical properties was also prepared.When combined with PVDF film,humidity-driven deformation of the gelatin hydrogel film would lead to the deformation of PVDF film,and an alternating current signal was generated.This kind of devices can serve as humidity-driven piezoelectric generator.2.Interpenetrating network was induced into PEG-DA hydrogel film to achieve the controllable and directional deformation of hydrogel film under humidity driving.Based on the PEG-DA film,a second UV lithography process produced the rigid PEG-DA/PMMA interpenetrating network in the hydrogel film.The areas with interpenetrating network and without interpenetrating network were arranged as grating pattern.When the hydrogel absorbed water,the PEG-DA/PMMA interpenetrating network could restrict the swelling of the hydrogel to achieve directional deformation.Using the hydrogel film with interpenetrating network,a humidity-driven curtain which could automatically roll up and unfold was prepared,and a safety switch that could automatically switch off under high humidity condition was also presented,all the devices worked well.3.Fabrication of PEG-DA hydrogel micro/nanodevices based on 3D printing of femtosecond laser direct writing(Fs LDW).The PEG-DA microstructure swelled in wet environment.The influence of the fabricating parameters during Fs LDW on the swelling ability of the microstructure was investigated.Through optimizing the fabricating parameters,we presented an array of microstructures which can realize the function of nano-interconnected network and a hydrogel microstructure with pores to mimic the open and close of the stomata of plants was designed.Based on a flexible two-steps fabrication method,PEG-DA hydrogel and methacrylate-based material could be combined,the function of data storage and password transmission could be achieved by a combined binary encoding micropillar arrays.4.Dynamically tunable PEG-DA hydrogel microlens fabricated via Fs LDW.Using the responsiveness of PEG-DA to Cl-in the surrounding solution,the hydrogel microlens with tunable focal length was fabricated.Through changing the concentration of Cl-,the hydrogel microlens could swell or shrink,which adjusted the focal length and imaged microstructures at different distances.An integrated optofluidic-microfluidic twin channels chip was fabricated by one-time exposure photolithography,in which the twin microchannels on both surfaces of the substrate were exactly aligned in the vertical direction.Using this chip as substrate,the tunable PEG-DA microlens was integrated in situ into the optofluidic channel of the twin microchannels chip.The particles and cells in the microfluidic channel could be observed using the PEG-DA hydrogel microlens,and achieved the integration of optofluidic and microfluidic.