Design,Fabrication And Cell Manipulating Experiments Of An Electrothermally-actuated Microgripper

With the development of science and technology,the research and application in biological and medical engineering demand more and more manipuations in micrometer scale and with high accuracy.Biological cell manipulation is the primary impetus and the key technology behind in vitro fertilization,cloning,drug discovery,and gene engineering.The traditional micropipette-based micromanipulation,a major current technology employed in biological cell manipulation,is far from enough to meet the demanding reqirements in success rate,consistency,efficiency,precision,flexibility etc.An alternative technology,the electrothermally-actuated microgripping becomes a new option because it is featured with compact and reliable structure design,capability in producing high force and large displacement at a lower actuation voltage,high flexibility for micromanipulations.However,current reseach efforts are still on the static design which limits the function and performance of electrothemally-actuatated grippers,and hence its applications to biological cell manipulations.The objective of this thesis is to significantly improve the performance of electrothermally-actuated microgippers,and make electrothermally-actuated microgripping a promising techonogy for biological cell manipulations in biological and medical engineering.Therefore,this thesis presents the deep and systematic studies on static modelling and parameter analysis,dynamic modelling and analysis,structure design,fabrication,experimental testing,feedback control,and cell manipulation experiments of the electrothermally-actuated microgrippers.The main research work of this thesis is summariezed as follows.(1)The coupled-field multi-physics(electro-thermal and thermo-mechanical)submodels are established for the V-and Z-shaped electrothermal actuators operating both “in vacuum” and “in air” conditions.Combining the two sub-models,the complete static model of the V-and Z-shaped electrothermal actuators are developed.Systematic parameter studies and performance comparisons are also peformed to provide insights and guidance to the design of electrotheral actuators.(2)The partial-differential dynamic equations are established for V-and Z-shaped electrothermal actuators.The natural frequencies and the associated mode shapes of the V-and Z-shaped beams are derived and analyzed based on the modal dynamics considering both axial and longitudinal vibrations.Comprehensive parameter studies are conducted and shows that that the electrothermal part dominates the overall dynamics of the electrothermal actuators.Then ordinary-differential dynamic equations are developed,and the dynamic responses are analyzed for the design and control of electrotermally-actuated microgrippers.(3)The preliminary structures of V-and Z-shaped electrothermal microactuators are designed and fabricated based on the MEMS micromachining technologies and the fabrication process.Then,a series of experimental tests are performed on the fabricated electrothermal microactuators including static response,dynamic response,oxidation,and buckling.The preliminary designs are further improved based on parameter analysis and testing results,and the output displacement of the modified V-shaped electrothermal actuators has been greatly improved.A compliant micro-gripping mechanism has been developed using the method of topology optimization.Experimental testing of the electrothermally-actuated micro-gripper is conducted,and results show that the output displacement can completely fulfill the requirements of biological cell manipulations.(4)The transfer functions of both the electrothermal actuators and the electrothermally-actuated microgrippers are formulated based on the developed dynamic equation,and the general material properties are calculated via experimental tests to further improve the model.The simulations and experiments of the P-and PDcontrol of the electrothermal actuator and electrothermally-actuated microgripper are conducted,and results show that the response speed can be greatly increased.(5)A robotic micromanipulation system is established for handling biological cells using the proposed electrothermally-actuated microgrippers.The system consists of the micromanipulators,the precision stage,the electrothermally-actuated microgripper,camera,and microscope etc.The software system is developed for the robotic micromanipulation system.The software systems have image display,device connect,manual manipulation,automatic manipulation,and feedback control modules.The developed robotic micromanipulation system is tesed based on the experiments of zebrafish egg handling using the in-house developed microgrippers and electrothermal actuators.