Microwave Induced Ethanol Bath Bonding for PMMA Microfluidic Device

Journal of Harbin Institute of Technology( New Series), Vol 23, No 2, 2016doi:10.11916/j.issn.10059113.20l6.02.006Microwave Induced Ethanol Bath Bonding for PMMA Microfluidic DeviceXiaowei Han", Xiaowei Liu, Li Tian, He Zhang and Cuicui ZhuangKey Laboratory of Micro-systems and Micro-structures Manufacttof educationHarbin Institute of Technology, Harbin 150001, ChinaAbstract: High bonding strength, low deformation and convenient procedure are all very important aspects inthe microfluidic device fabrication process. In this paper, an improved microwave induced bonding technology isproposed to fabricate microfluidic device based on methyl methacrylate( PMMA). This method employsethanol as the bonding assisted solvent. The ethanol not only acts as the microwave absorbing material, but alsoworks as the organic solvent in bath. The presented research work has shown that the bonding process can becompleted in less than 45 s. Furthermore, the convenient bonding only applies microwave oven, beakers andtionmicrostructures on PMMA microfluidic device. Finally, a 4 layers micro-mixer has been fabricated using theproposed bonding technique which includes 15 trapezoid micro-channels, 9 T-type mix units and an X-type mixunit. Experimental results show that the proposed bonding method have some advantages compared with severaltraditional bonding technologies, such as hot pressing bonding, ultrasonic bonding and solvent assisted bondingmethods in respect of bonding strength, deformation and bonding process. The presented work would be helpfulfor low coat mass production of multilayer polymer microfluidic devices in labKeywords: PMMA; microwave bonding; multilayer microfluidic device; micro-mixerCLC number. TP391.Document code. AArticle id:1005-9113(2016)02-0040-06device[8-10. However the deformation of microstructures1 Introductioncan not be ignored due to the pressure involved in thebondingFurthermore, aMicro total analysis systems (u-TAS)have been temperature approximately equal to glass transitionwidely used in trace detection in different fields such as temperature(Tg) is applied and kept under pressurebiology and medicine. In recent years, many micro until the bonding process is completedfabrication techniques have been developed for microstructures are easily deformed. Liu 4 proposed aapplication on polymer. So, more and more microfluidic plasma assisted method to achieve surface modificationmethod which decreases the bonding temperatureThe development of W-TAS tends to integrate much Hence, the thermal bonding temperature is decreasedore functions in limited size of microchip. Thus, from 100 C to 85 C. However, it is not possible toof three-dimensional structures fabrication and interface due to the low then pressure to the bondingmultifunctional integration should be achieved by means directly transfer heat andmultilayer bonding. Today, many hard polymers deformation rate of the polymer at temperature Tsuch as methyl methacrylate( PMMAResearchers have proposed ultrasonic bonding anonate(PC) have replaced silicon and glass microwave bonding techniques to achieve effectivedue to their better properties such as optics, bondingThese two methods are capable ofincompatibility and low cost. Therefore, we have providing direct interface bonding at low bondingdeveloped a microwave bonding technique whichpressure. Furthermore, both of these two methods havesuitable for multilayer bonding based on hard polymer achieved short bonding time. Therefore, they can gainsuch as PMMA. This method will be helpful for high bonding strength with low deformationintegration and three dimensionalUltrasonic bonding generally involvfabrication of H-TASdirectors to conduct ultrasonic energy. The ultrasonicMany commonly known bonding methods are energ中国煤化工 s in several seconds toavailable based on the polymer Thermal bonding is a seal-fabrication of the eneywidely used method for bonding a PMMA microfluidic direeCNMHGequenceReceived 2015-04-10coRrespondingauthorE-mail:hanxiaowei2017@163.comJournal of Harbin Institute of Technology( New Series), Vol 23, No 2, 2016bonding. Microwave bonding utilizes the microwaves to Electronic balance FAl604, Shanghai Liangpinheat the microwave absorbing materials at the interface Instrument Co. Ltd. Shanghai, China) has been usedof the PMMA substrates directly. Then, PMMa to weigh the reagentssubstrates are melted to seal the microfluidic device. 2.2 Bonding ProcedureThe microstructure deformation is relatively small due toThe PMMa plates are cut into square substratesthe short heating time and rapid temperature rise. Some 2 cmX 2 cm size. Then, the films are tore on theresearchers apply solvent to assist the microwave substrates. The PMMa substrates are cleaned in thebonding based on the PMMA microfluidic devices 2. ultrasonic cleaning equipment for 5 min andHowever, bubbles are produced if solvent is applied vacuum oven. To decrease bonding area errors andonly at the interface of the two substrates. This causes avoid bubbles at the interface, the alignment andreduction in the bonding strength due to the effective fixation of two PMMA substrates should be performedcontraction of the bonding areaunder the metallurgical microscope in alcohol solutionIn this paper, our work aims to provide a fast, before bonding. Alcohol is applied as poor organicreliable, flexible and low cost microwave bonding solvent and PMMA substrates are fixed by using bindermethod which involves poor solvent to fabricate clips. Then, we put the fixed the PMMA substrates aremultilayer microfluidic chip The proposed method has fixed in a 80 mL cubage beaker with 45 mL alcoholproduced better results comparable to the bonding poured in. This ensures that the surface of the liquidstrength and minimum deformation of the microfluidic alcohol is higher than the fixed pmma substrates. Thechips which are bonded by other heating bonding alcohol is heated in the microwave oven with differentmethods. Furthermore, the achieved bonding rate of the power and time. Thus, different results of microwavemicrofluidic chips is close to other microwave bondingbonding are obtained. Bubbles cause leakage andtechniques. In our study, the developed microwave reduction in the bonding strength due to the contractionbonding technique is used successfully to bond of the bonding interface effective area. To ensuremultilayer micro-mixer comprising of four layers. The repeatability of each experiment, the heated alcohol isdeformation of the micro-channels can be significantly replaced after each experiment. To guarantee no bubblereduced through the microwave power and radiation appearance after bonding at the interface of thetime adjustment by detecting the results of the sampleshe binder clips should press PMMAafter each bonding. Moreover, we have achieved both substrates evenly. Furthermore, the difference ingood bonding strength and minimum deformation by PMMA substrate thickness should not be greater thananalyzing the experimental results without any bubbles. 3 um at 1.5 cmx 1.5 cm square in size. Fig. 1(a)he whole bonding process can be completed in a shows the fixed PMMA substrates in the beaker andhousehold microwave ovenFig. 1( b)is the substrates after bonding. Thesubstrates are bonded under 350 W microwave power2 Experimental Section100%0. The PMMA substrates are employed without2.1 Equipment and materialschannels to avoid errors in detection of thThe pmma substrates used in this work are bonding strength due to the size error of bonding area3.0 mm in thickness( Stone into Gold Trading Co, LtdDongguan, China ) The micro-channels fabrication is 3 Results and Discussioncarried out using micro-precision engraving machineVIP3530, Thai Power Electronic Equipment 3.1 Bonding StrengthBeijing )Co, Ltd. Beijing, China ). The PMMaFig. 2 illustrates the heating rate during thesubstrates are cleaned by using ultrasonic cleaning bonding process at different microwave powers. It canequipment KQ-5200DB, Kun Shan Ultrasonic be seen that the maximum temperature is stayingInstruments Co, Ltd, Kun Shan, China ) Vacuum oven 81C compare to 78 4C which is the theoretical( DZF-6020, Shanghai Jing Hong Laboratory Instrument boiling point of ethanol. Therefore, the maximumCo, Ltd Shanghai, China )dried PMMA substrates afterrature is still much lower than Tk ofcleaning. Household microwave oven MS-1968TW, PMMA. Low temperature can decrease the deformationTianjin Le Jin Electronic Appliance Co, Ltd. Tianjin, of thhctr∴… ng the bonding processChina) can provide the microwave bonding power. The FurtI中国煤化工oied14.7N/cm2metallurgical microscope( C3203A, Shanghai Precision bondCNMH Glow as compared toInstrument Co, Ltd. Shanghai, China is used for 1 215 N/cm" maximum bonding strength. Low bondingevaluating bonding result and testing micro-mixer. All pressure can also decrease the deformation rate of thethe reagents used are the analytical reagents( Tianjin PMMA substratesKermel Chemical Reagent Co, Ltd. Tianjin, China)Journal of Harbin Institute of Technology( New Series), Vol 23, No 2, 2016(a) Fixed PMMA substrates in the beaker(b) PMMA substrates after bondingFig1 PMMA substrates before and after microwave bondingin Fig 4. The maximum bonding strength is1 215 N/cm" at 700 W microwave power. The bondingstrength increases with the increase of the microwavepower. Furthermore, the bonding strength alsoIncreases wmicrowave power. However, the bonding strengthIncreases very slowly at 350 WTime(s)ConnectorFig2 Heating rate at different microwave powerForcePMMADifferent microwave power and bonding time resultin different bonding strengths and deformation of themicro-channels. The household microwave oven hasFig 3 The bonding strength measurethree power levels: 350 W, 490 W and 700 W. Thebonding time was set from several seconds to tens oThe VDWF ( Vander Waals force)of moleculesand the covalent bonds between the atoms determineseconds. The bonding strength is measured using the bond strength of polymer. The dissolution of thedrawing force meter( Wuxi Dajishan InstrumentEngineering Equipment Co, Ltd. Wuxi, China)atolymer is small due to the fact that alcohol is a poordifferent bonding conditions. The bonding strengthsolvent for PMMA. because the curly molecular chairmeasurements are shown in Fig. 3. It illustrates theare difficult to loosen. the Pmma substrates volumedrawing force meabarely expand in the beginning stages of theand the sketch of the drawing force measurements. The process. Hence, the bonding strength is mainlybonded substrate is glued to the connectors by usingdetermined by the covalent bonds. When the bondingtwo components modified acrylate adhesives temperature reaches a maximum value, the bonding(GLH-302, Fushun GELIAHAO Chemical Co, Ltdstrength begins to decrease due to the expansion ofFushun, China). The bonded substrate is then fixed to curly molecular chains. The increased VDWF may leadthe connectors and dried at room temperature for 24 hto covalent bonds breakage at temperature near T'After that the bonding strength of the bonded substrate3.2 Structural Deformationis measured by imposing drawing force. Then theTo assure the fabricating quality of the microbonding strength can be calculated by averaging the device, the deformation of the microstructure should bedrawing forces to an area of 2. 25 cm. each中国煤化工 micro- channel s can bemeasurement is repeated five times and the bondinCNMHGulastrength is calculated as an average valueThe relationship between bonding time anebonding strength at different microwave powers has where, So and S, are the cross-section areas of thebeen investigated. The experimental results are shown micro-channel before and after bonding, respectively42Journal of Harbin Institute of Technology( New Series), Vol 23, No 2, 2016same time. It should be indicated that the fabricatedmicrochannel passed through the entire PMMAsubstrate before bondingConsequentlyerror which is caused by the sample preparation durinthe deformation measurement▲350W1015202530354045Bonding time(s)(a)700W1000Fig 5 Results of deformation measurement of microchannel中宁at different microwave power051015202530354045ne(s)Fig. 6 A cross-section of a trapezoid microchannel beforeand after bonding4 Applicationa 4 layers 3D micro-mixer is designed andfabricated to evaluate the performance of the microwavebonding. Then this microfluidic device is tested byemploying theories of incompressible Newtonian flowand mass transport in our design. The micro-mixer051015202530354045contains 9 3D T-type mix units and a 2D X-type mixunit. The exploded view of the multilayer micro-mixerBonding time(s)is shown in Fig. 7( a). The microstructures of themicro-mixer are provided in Fig. 7(b). Fig 8(a)isFig 4 The bonding strength at different microwave power the cad drawing and Fig. 8( b) is the 4 layers ofThe changes of the microchannel cross section micro-mixer before bondingarea are calculated by using open source softwareFig 9(a) shows a multilayer 3D micro-mixer afterImage J. The values are the averages of three bonding. The bonding of 4 layers is achievable in unitmeasurements in Fig.5. It is found that the deformation time. Moreover, there are no bubbles between adjacentrate increases with the increase of microwave power and layers due to the uniform heating on the bodies of PMMAbonding time. Low deformation has been achieved duesurfaces. The wholtoheating and中国煤化工 leakage.Fg:9(b)isaFig 6 shows a cross-section deformation of a trapezoid scanCNMH GO SEMmicro-channel before and after the bonding, The micro- surface of the micro-mixer before and after bonding. Itchannel is bonded under 700 W for 40 s. The found that swelling of the polymer is not involved in thisdeformation of the micro-channel is 5.1%. and the microwave induced ethanol bath bondibonding strength is as high as 1 156 N/cm at theJournal of Harbin Institute of Technology( New Series), Vol 23, No 2, 2016Top layersecond layerThird layerInlet 2outlet(a) The exploded view of multilayer micro-mixerThe microstructures of micro-mixerFig. 7 The diagram of micro-mixela) The CAd drawing of micromixer(units: mm)(b) The 4 layers of micro-mixer before bondingFig 8 The design and fabrication of multilayer micro-mixer20 umBefore(a)Amultilayer 3D micro-mixer after bonding(b)A SEM picture of surface of PMMA substrateFig9 A multilayer 3D micro-mixer after bondingThe proposed design achieves effective mixShenzhen, China. is used to inject rhodamineemploying two approaches. The 2D and 3D structures B(6.26 mmol/L)as sample A and methyl greendecrease concentration by folding micro flow of the (1.23 mmol/L)as sample B. After that, the mix effectsamples. Then, the long microchannel raises mix effect by observed through the metallurgical microscope. Fig 10increasing diffusion distance. The reason for this is thatshows the contrast of the mix effects in flow rate ofwhen the fluid velocity is extremely slow, mixing0.1 mL/h. Fig. 10( a) shows the flow of rhodamine Bprimarily determined by the molecules diffusion, the without mixing, and Fig. 10(b) shows the flow ofrelated time and the fluid contact area. Syringe pump rhodamine B mixed with methyl green. Uniformly mixing(SN-50F6, Sino Medical-Device Technology Co, Ltd. is observed in Fig. 10(b)YH中国煤化工CNMHG(a) Flow of rhodamine B(c)Flow of rhodamine B mixed with methyl greenFig 10 Contrast of mixing effect in flow rate of 0. 1 mlhJournal of Harbin Institute of Technology( New Series), Vol 23, No 2, 2016[5 Currie C A, Shim J S, Lee S H, et al. Comparin5 Conclusionsand glass microchips for electrophoretic separationsphoresis,2009,30(24):4245-4250In this paper, an improved microwave bonding [6 Land K J, Mbanjwa M B, Govindasamy K, et al. Low costtechnology has been demonstrated which can overcomefabrication and assembly process for re-usable 3Dthe conflict between bonding strength and micro structuredimethylsiloxane( PDMs) microfluidic networks.holding. In our study we have achieved both highBiomicrofluidics,2011,5(3):036502-036502-6.bonding strength and low microstructure deformation in [7 Farshchian B, Park S, Choi J, et al. 3D nanomolding for lab-on-less than a minute by employing microwave inducedhip applications. Lab on a Chip, 2012, 12(22): 4764-4771ethanol bath bonding. Furthermore, we have presented [8 Zhu X, Liu G, Guo Y, et al. Study of PMMa thermal bondinour bonding method with general instrument, such as13(3/4)microwave oven, beakers and binder clips. Ethanol bath[9 Nayak N C, Yue C Y, Lam Y C, et al. Thermal bonding ofMMA: effect ofr molecular weight. Microsystemprovides powerful microwave heating. We can achieveTechnologies,2010,16(3):487-491high bonding strength due to the covalent bonds resulted 10) Kelly R T, Woolley A T Thermal bonding of polymericby the ethanol bath in the microwave bonding process. Wecapillary electrophoresis microdevices in water. Analyticalhave gain 1 215 N/cm as the maximum bonding strengthChemistry,2003,75(8):1941-1945at microwave power of 700 W with 35 s microwave heating [I1]LiJ M, Liu C, Qiao H C, et al. Hot embossing/ bonding of atime. Furthermore low deformation of microstructurepoly ethylene terephthalate)( PET) microfluidic chippossible due to the short bonding time, weak bondingJournal of Micromechanics and Microengineering, 2008, 18pressure and low bonding temperature below T, of PMMa(1):015008.doi:10.10880960-1317/18/1/01500812] Sun Y, Kwok Y C, Nguyen N T. Low-pressure, highThus. we can achieve 0. 1%o as minimum deformation attemperature thermal bonding of polymeric microfluidicmicrowave power of 700 W for 10 s. Moreover, we havedevices and their applications for electrophoretic separationalso gain good results with 709 N/cm bonding strengthJournal of Micromechanics and Microengineering, 2006, 16and 1. 1% deformation under microwave power of 350 Wfor 35 s. Finally, we have fabricated a 4 layers micro- 13 Wang X, Zhang L, Chen G. Hot embossing and thermalmixer which includes 15 rectangle micro-channels.9T-of poly ( methylthacrylate) microfluidic chipstype mixing units and an X-type mixing unit as ausing positive temperature coefficient ceramic heatervalidation of the microwave bondiAnalytical and Bioanalytical Chemistry, 2011, 401(8): 2657research has achieved the goal of providing a low cost, [14 Liu J, Qiao H, Liu C, et al. Plasma assisted thermal bondingfast convenient and reliable bonding technology for massfor PMMA microfluidic chipsfabrication of multilayered microfluidic devices basethe polymer in the lab. The experimental resulf d onmicroelectrodes, Sensors and Actuators B. Chemical. 2009141(2):646-651indicated that this technology can performs well, and[15]Sun Y, Luo Y, Wang X. Micro energy director array infuture investigation of it wide applications for othertrasonic precise bonding for thermoplastic micro assemblpolymers such as polyethylene (PE) and polycarbonateJournal of Materials Processing Technology, 2012, 212(6)1331-1337(PC) will need to be continued. Our research is capable [16]Ng S H, Wang Z F, De Rooij N F Microfluidic connectors byof simplifying the fabrication process of H-TAS based onultrasonic welding. Microelectronic Engineering, 2009. 86polymer. Thus, it may provide reference to other(4):1354-135researchers and accelerate application of multifunctional [17 ] Zhang Z, Wang X, Luo Y, et al. Thermal assisted ultrasonicbonding method for poly( methyl methacrylate)( PMMAmicrofluidic devices. Talanta, 2010, 81(4): 1331-1338References18 Mani K B, Hossan M R, Dutta P. Thermal analysis ofmicrowave assisted bonding of poly methyl methacrylate[1] Yang Y A, Lineiy c. thread -based microfluidicsubstrates in microfluidic devices. International Journal ofsystem for detection of rapid blood urea nitrogen in wholeHeat and Mass Transfer, 2013, 58(1): 229-239blood. Microfluidics and Nanofluidics, 2014, 16(5): 887-894. [19 Yussuf AA, Sbarski 1, Hayes J P, et al. Microwave welding[2 Huft J, Da Costa DJ, Walker D, et al. Three-dimensionalof polymeric-microfluidic devices. Journal of Micromechanicslarge-scale microfluidic integration by laser ablation ofand Microengineering, 2005, 15(9): 1692-1699interlayer connections. Lab on a Chip, 2010, 10( 18): 235820 Yussuf AA, Sbarski I, Hayes J P, et al. Single-modeicrowave sealing of polymer-based microfluidic devices[3 Li JKe X, et al. Fabrication of a thermoplast中国煤化工 tonics Europe. Internationalmultilayer microfluidic chip. Journal of Materials Processing hermally assisted solvent bonding for low-cost PMMA,2004.74-81Technology,2012,212(11):2315-2320CNMH GD et al. microwave-induced[4 Chen L, Wang G, Lim C, et al. Evaluation of passive mixingbehaviors in a pillar obstruction poly dimethylsiloxaneicrofluidic devices. Journal of Micromechanics andmicrofluidic mixer using fluorescence microscopy. MicrofluidicsMicroengineering, 2010, 20( 1):015026and Nanofluidics, 2009, 7(2): 267-273