Design,fabrication And Performance Of Flexible Digital Microfluidic Chips Based On Inkjet Printing

Digital microfluidics(DMF)based on electrowetting-on-dielectric(EWOD)driving mechanism is a new microfluidic technology,which can handle liquid with picoliter to microliter level.It has attracted the attention of many researchers with its unique advantages.This technology can control the droplets by applying voltage to implement a variety of basic operations such as droplet dispensing,transportation,merging,mixing and splitting.It has the advantages of small sample or reagent consumption,less sample reaction and analysis time,easy to realize automatic and precise quantitative control of the droplet.However,the traditional chip micromachining technology has high cost,complex and time-consuming manufacturing process,which discourages many ordinary users;moreover,the conventional square electrode will result in low performance of droplet operations due to various reasons.For example,in the repeated droplet dispensing and splitting operation,the volume precision and accuracy of micro-droplets are low,which will affect the correctness and reliability of biochemical analysis results.Therefore,the study on DMF chip based on EWOD is carried out from four aspects in this paper to solve the above problems,including basic theoretical analysis,modeling and simulation,flexible chip fabrication technology development and droplet operation,optimization of electrode geometry and layout,and closed-open hybrid configuration design.Firstly,the basic concepts and principles of electrocapillary technology,electrowetting technology and EWOD technology were introduced.The dynamics model was established through the force analysis of droplet motion,and the droplet motion in a variety of planar and curved configurations was dynamically simulated by Simulink.The mechanism of four basic droplet operation based on EWOD was analyzed and simulated with Comsol Multiphysics,which provided basic theoretical support for the subsequent chip fabricating process optimization,electrode geometry and layout optimization and structure design and optimization.Secondly,the fabrication technology of flexible DMF chips was developed and optimized by using flexible printed electronics technology.The electrode layer was fabricated on three kinds of flexible substrate by multi-layer inkjet-printing nano silver conductive ink.A layer of Teflon? AF-1600 was coated on PVDC and PMP insulating film by showering with a disposable dropper to form dielectric-hydrophobic layer,so as to fabricate low-cost flexible chips suitable for common users.Scanning electron microscopy(SEM),atomic force microscope(AFM)and digital multimeter were used to analyze the effects of different flexible substrates,different printing modes,and different dielectric materials and other factors on surface continuity,uniformity,conductivity and the output spatial resolution of electrodes and dynamic performance of the droplets.The number of printing layers,electrode spacing and the line width of conductive silver wire on different substrates were determined.In the different configurations of three flexible substrate chips,all the basic droplet operations were implemented through EWOD,including closed configuration,open configuration and curved configuration.The droplet operating performance on different substrate chips was compared and analyzed.The results show that the fabrication process of flexible chip reduces the requirements of the chip on the surface quality of the substrate,and the droplet driving voltage is mainly determined by the electrode layer conductivity and electrode spacing.Then,based on the three basic principles of droplet dispensing and splitting,the geometry and layout of the dispensing and splitting electrodes were optimized to improve the volume precision and accuracy of a single working droplet dispensed and split.The optimized dispensing electrode scheme greatly reduced inconsistency and inaccuracy of droplet volume,and the splitting electrode optimization scheme not only greatly improved the performance of equal volume splitting,but also effectively applied to unequal volume splitting of droplets,which greatly improved the volume precision and accuracy of child droplets.The regular hexagon electrode was used instead of the square electrode for droplet transport and mixing,which increased droplet motion directions at any position on the chip,improved mixing performance of two heterogeneous droplets in 2×N array mixer,and shortened the uniform mixing time.Finally,the closed and open configurations were integrated on a single flexible chip and optimized.The dynamic characteristics of the droplet at the boundary between the two configurations were studied by using force balance analysis method,and the conditions for the droplet to cross the boundary were derived,so as to obtain the optimization measures for realizing the free back-and-forth movement between the two regions.The influences of different spatial transverse,longitudinal positions and the thickness of the top plate in closed region on droplet motion were analyzed.The spatial transverse position mode of the top plate,the spacing range of the top and bottom plates and the appropriate thickness of the top plate were determined to facilitate the free back-and-forth movement between the two regions.This topic involves interdisciplinary study and application.The fabrication process of flexible chips points out the direction for low-cost and mass production of digital microfluidic chips,which has certain inspiration and guiding significance.The improvement of droplet operation performance and the integration technology of closedopen configurations have important practical significance and practical value for the application of digital microfluidic chip in many fields.