IROS2019国际学术会议论文集 2104

High speed On chip Mixing by Micro vortex Generated by Controlling Local Jet Flow Using Dual Membrane Pumps Yusuke Kasai1 Shinya Sakuma1 and Fumihito Arai1 2 Abstract Robot integrated microfl uidic chip is a key technology for microscale applications Recently the tech nology has been applied to on chip mixing which mix solutions on a microfl uidic chip because it is a promising tool to analyze not only the chemical reaction with the small sample volume but also the response of cells to en vironmental changes However these conventional mixing methods require the mixing time of millisecond order due to the diffi culty of mixing in the laminar condition of a microchannel whose Reynolds number tends to be low In this letter we propose a high speed on chip mixing by the micro vortex generated by controlling local jet fl ow using dual membrane pumps First we confi rmed that vortex was successfully generated within 20 s by the local jet fl ow The velocity and Reynolds number were analytically estimated as approximately 20 m s and 1 6 103 respectively Second we evaluated the response time of the mixing using the micro vortex We mixed 200 nm nanobead suspension and the DI water in the velocity of main fl ow of 1 m s By measuring the intensity at the certain observation area we confi rmed that our method successfully mixed solutions and the mixing time was approximately 500 s whose speed has not been achieved by conventional robot integrated on chip mixers Moreover we confi rmed that our system can control the concentration of mixed fl ow by controlling fl ow rate ratio of sample and sheath fl ow From these results we confi rmed that we achieved high speed on demand on chip mixing by the micro vortex I INTRODUCTION Microfl uidic chip is a strong tool to manipulate and or analyze microscale targets on a microscope with advantages of stable environment and small required sample volume 1 2 Recently robot integrated mi crofl uidic chip which utilizes actuation method such as magnet dielectrophoresis acoustic wave laser induced cavitation and external pumps have been developed 3 9 One interest in recent these techniques is how to achieve high speed on chip fl ow control for various applications such as high speed manipulation of cells high throughput cell sorting and investigation of high speed phenomenon such as cavitation generation 10 14 Hence high speed robotic approaches are promis ing technique to extend the microfl uidic applications This work was supported by Grant in Aid for JSPS Research Fellow 18J15242 1Y Kasai S Sakuma andF AraiarewithMicro Nano MechanicalScienceandEngineering GraduateSchoolof Engineering NagoyaUniversity Nagoya 464 8603 Japan kasai biorobotics mech nagoya u ac jp 2F Arai is with Institutes of Innovation for Future Society Nagoya University Nagoya 464 8603 Japan Previously we have developed a high speed on chip fl ow control system which utilized on chip dual mem brane pumps integrated with piezoelectric actuators 15 as shown in Fig 1 a and b By utilizing the glass membrane as a pump high speed actuation of the piezoelectric actuator can be transferred to the high speed fl ow in a microchannel One advantage of this fl ow control system is the controllability of fl ow speed since it can be controlled by the rising time and input voltage of the piezoelectric actuators This fl ow control system has utilized local fl ow in laminar condition to precisely switch fl ow path of main fl ow and showed one application of cell sorting as shown in Fig 1 c However as shown in Fig 1 d vortex will be generated even in a microchannel if the speed of the local fl ow is high enough to be turbulent condition which is no longer applicable to cell sorting Since the phenomenon is totally diff erent their application should be diff erent depending on the fl ow condition Therefore the on chip fl ow control system using membrane pumps may still have potential for another application by utilizing the micro vortex As an application of high speed fl ow control in tur bulent condition we focus on on chip mixing tech niques which mix solutions in a microfl uidic chip On chip mixing techniques are promising to analyze not only the chemical reaction with the small sample volume but also the response of cells to environmental changes for single cell analysis 16 17 Conventional on chip mixing techniques passively mix solutions with pre patterned microchannels 18 20 Recently robot integrated on chip mixing techniques using electroki netic pump microvalve oscillator and acoustic wave generator have been developed because the techniques have great advantages of timing control and short required mixing length Phan2015 21 24 However these conventional mixing methods require the mix ing time of millisecond order due to the diffi culty of mixing in the laminar condition of a microchan nel whose Reynolds number tends to be low High speed mixing in the order of sub milliseconds will contribute to analysis of fast phenomenon for exam ple mono dialkylation of aromatic compounds and response of Synechocystis cell to osmotic stimulation 25 26 Thus it is challenging but promising to achieve the high speed on chip mixing with on demand timing IEEE Robotics and Automation Letters RAL paper presented at the 2019 IEEE RSJ International Conference on Intelligent Robots and Systems IROS Macau China November 4 8 2019 Copyright 2019 IEEE Sample inlet Sheath inlet vertical Outlets Priming port Glass membrane Microfluidic chip glass Si glass layers a Sheath inlet horizontal Pump B b 2 Top view e 2 Before mixing e 3 Mixing by micro vortex e 4 After certain time b 1 Side view Pump BPump A Pump B Pump A Local flow Main flow c 1 Low input voltage c 2 Flow path switching d 1 High input voltage d 2 Vortex generation Voltage Time Voltage Time e 1 Continuous high input voltage Voltage Time Pump A Pump B On chip membrane pump Piezoelectric actuator Attachment Glass membrane Pump A Main flow Push Pull Pull Push Fig 1 Concept of on chip high speed fl ow control system using on chip membrane pumps a Confi guration of the on chip high speed fl ow control system b Conceptual image of the fl ow path switching by the local fl ow with low input voltage c Conceptual image of the vortex generation by the local jet fl ow with high input voltage d Conceptual image of the on chip mixing using the micro vortex with continuous high input voltage control In this letter we propose a high speed on chip mix ing by the micro vortex generated by controlling local jet fl ow using dual membrane pumps As shown in Fig 1 e we utilized the vortex to mix solution in a microchannel by continuously applying push pull local jet fl ow First we confi rmed that vortex was successfully generated within 20 s by the local jet fl ow The velocity and Reynolds number were analytically estimated as approximately 20 m s and 1 6 103 re spectively Second we evaluated the response time of the mixing using the micro vortex We mixed 200 nm nanobead suspension and the DI water in the velocity of main fl ow of 1 m s By measuring the intensity at the certain observation area we confi rmed that our method successfully mixed solutions and the mixing time was approximately 500 s Moreover we confi rmed that our system can control the concentration of mixed fl ow by controlling fl ow rate ratio of sample and sheath fl ow From these results we showed an example of application of high speed fl ow control in turbulent condition and confi rmed that we achieved high speed on demand on chip mixing using the micro vortex II DESIGN FOR HIGH SPEED ON CHIP MIXING The key of active high speed on chip mixing is how to generate the high speed local fl ow for mixing While the laminar condition in the microfl uidic chip con tributes to the stable environment for cell manipula tions and analyses the turbulent fl ow contributes to facilitates mixing of solutions Therefore it is important to locally generate mixing fl ow while the fl ow condi tion except the mixing area is maintained as the laminar fl ow The fl ow condition is determined by Reynolds number which is given as follows Re Du 2wsidehSiu wside hSi 1 where u is a mean velocity of fl ow is a kinematic viscosity of fl owing liquid wsideand hSiare the width and height of the side microchannel and D is a hy draulic diameter of a microchannel which is givens as D 2wsidehSi wside hSi in case of a rectangular cross sectional microchannel Schematic of the membrane pump and microchannel is shown in Fig 2 Since the wside hSi and are fi xed parameter for a certain experi ment only u is a controllable parameter to obtain high Reynolds number Furthermore since wsideis in the order of micro meter in a microchannel extremely high u value is required to obtain the turbulent condition As for our on chip mixing system using the mem brane pumps the volume and actuation speed of the membrane pump determine the velocity of the local jet fl ow By assuming that the circumference of glass membrane is fi xed end and the displacement of the Fig 2 schematic of the membrane pump and microchannel a Side view b Top view piezoelectric actuator is applied at the center of the membrane the volume of the local jet fl ow C is described as follows 15 C r2 0 4 2 where r0is the radius of the membrane Since can be controlled by input voltage of the piezoelectric actuator can be described as a function of the input voltage by assuming the displacement is linear against voltage max Vmax Vin 3 where max Vmaxand Vinare maximum displacement maximum input voltage to obtain the maximum dis placement and input voltage respectively By assuming that the actuation time of piezoelectric actuator is linear the velocity of the local jet fl ow u can be described as follows u C A t r2 0 max 4wsidehSiVmax Vin t 4 where A and t are the cross sectional area of the side microchannel for the local jet fl ow and rising time of the piezoelectric actuator respectively Here t is determined by the rising time of the input voltage which can be controlled by the function generator as shown in Fig 1 d 1 As we can see from Eq 4 we can control the velocity by changing Vinand t From Eqs 1 and 4 Reynolds number of the side microchannels is given as follows Re r2 0 max 2 wside hg Vmax Vin t 5 From Eq 5 we can see that large displacement by high input voltage Vinand fast response time t of a actuator contribute to obtaining high Reynolds number As for the dimensions of the microfl uidic chip large radius of the membrane r0 small width wsideand height hSiof the side microchannel also contribute to obtaining high Reynolds number To achieve the response time of mixing in the order of sub milliseconds the vortex for mixing should be generated in tens microseconds which is equivalent to tens kHz in terms of a frequency of the actuation Hence we use a piezoelectric actuator AE0505D08DF NEC TOKIN Co Ltd Japan whose maximum displacement and resonant frequency are 9 1 m and 138 kHz respectively High natural frequency of the glass membrane is also required for the high speed actuation to avoid undesirable resonant oscilla tion The natural frequency of the glass membrane can be described as follows 15 f 10 21 2 r2 0 s Eh2 g 12 1 2 6 where E hg and are the Young s modulus the thickness the density and the Poisson s ratio of the membrane material respectively In this letter the ra dius and the thickness of the glass membrane were designed as 1 mm and 0 3 mm respectively In this case the natural frequency was calculated as 769 kHz which is much higher than the resonant frequency of the piezoelectric actuator Considering the fabrication process of Si substrate in the section III A the height hSi and width wmainof the main microchannel are designed as 200 m and 200 m respectively The width wside and length lsideof the side microchannel are designed as 50 m and 25 m respectively Assuming the rising time and kinematic viscosity as 10 s and 10 6m2 s the maximum velocity and Reynolds numer of local jet fl ow can be calculate as 71 m s and 5 7 103 respectively III MATERIALS AND METHODS A Fabrication of microfl udic chip Figure 3 shows the fabrication process of the mi crofl uidic chip The microfl uidic chip was fabricated through the same fabrication manner of Ref 15 The microfl uidic chip consists of high rigidity three layers borosilicate glass layer top layer silicon layer mid dle layer and borosilicate glass layer bottom layer Main and side microchannels were fabricated in the Si layer using deep reactive ion etching DRIE The microchannel for vertical sheath fl ow was fabricated in the glass layer using HF etching A part of the top glass layer works as the glass membrane The brief explana tion of the fabrication process is as follows First the microchannel for vertical sheath was fabricated in the glass layer using HF etching as shown in Figs 3 i and 3 ii Second the main and side microchannels were iii Patterning etching mask after anodic bonding v Patterning etching mask for sandblast i Pattering etching mask ii HF etching and cleaning Cover Base layers Channel layercover layer iv DRIE vi Sandblast Packaging vii Anodic bonding channel layer and base layer Glass SU 8Si OFPRCr Au SCM250 Fig 3 Fabrication process of the microfl uidic chip fabricated in the Si layer using DRIE after bonding the Si layer and the bottom glass layer as shown in Figs 3 iii and 3 iv Third holes as inlets and outlets were fabricated using the sandblast as shown in Figs 3 v and 3 vi Finally the fabrication of the microfl uidic chip was complited by bonding the Si layer and the top glass layer as shown in Fig 3 vii B System confi guration Figure 4 shows the experimental setup and the confi guration of the on chip mixing system The mi crofl uidic chip was set on the inverted microscope IX71 Olympus Co Ltd Japan as shown in Fig 4 a The piezoelectric actuators are attached on the glass membrane in the microfl uidic chip using Z stage TSD253 L TSD253 RL Sigma Koki Co Ltd Japan All tubes for inlets and outlets are connected in the jig which fi xes the microfl uidic chip on the inverted mi croscope Sample solution of 200 nm nanobead 5020A Thermo Fisher Scientifi c Co Ltd USA suspension and the sheath solution of DI water are introduced from a sample inlet and two sheath inlets respectively The introduced sample solution is three dimensionally focused by horizontal and vertical sheath fl ow By controlling fl ow rate ratio we can control the con centration of mixed solution Figure 4 b shows the schematic of experimental system The process of mix ing in the microfl uidic chip is observed using high speed camera Phantom v1611 Nobby Tech Co Ltd Japan with the frame rate of 200000 fps The starts of mixing and recording are simultaneously triggered by an external manual trigger After receiving the trigger the input voltages from a function generator WF1967 NF Co Ltd Japan are amplifi ed through amplifi ers Fig 4 Experimental System a Photograph of the experimental setup b Schematic of the experimental system HSA4014 NF Co Ltd Japan and sent to the piezo electric actuators We synchronized the actuations of two piezoelectric actuators by supplying two input voltages with same frequency and opposite phase from one function generator The sample and sheath fl ow are introduced using a pressure pump MFCS EX Fluigent Co Ltd France During the experiments the fl ow rates of sample and sheath fl ow are measured using fl ow meters SLI 0430 SLI 1000 SLI 2000 Sensirion Co Ltd Japan C Sample Preparation In this paper we used 200 nm nanobead suspnesion as a mixing sample The concentration of nanobead suspnesion was adjusted to be 1wt The nanobeads suspension was introduced from the sample inlet On the other hand DI water was introduced from the horizontal and vertical sheath inlets The diff usion co Fig 5 On chip vortex generation by the local jet fl ow a Experimental images of on chip vortex generation with passing time b FEM analytical images of on chip vortex generation with passing time effi cient of nanobead D can be calculated from Stokes Einstein equation as follows 27 D kT 6 R 7 where k T and R are Boltzmann constant temper ature viscosity of solvent and radios of the particle which diff uses into the solvent respectively In the case of temperature of 25 C the diff usion coeffi cient of 200 nm nanobead can be calculated as 2 5 10 12m2 s Comparing with fl uorescent dye such as Rhodanime B whose diff usion coeffi cients are in the order of 10 10 m2 s 28 the 200 nm nanobead can be considered as a diffi cult example of on chip mixing IV EXPERIMENTS AND RESULTS A On chip vortex generation Figure 5 a shows an experimental result of high speed on chip vortex generation by local jet fl ow see also supplementary movie of vortex generation In this experiment the DI water was fi lled in the main micorchannel and alcoholic solution Eta Cohol 7 Sankyo Chemical Co Ltd Japan was fi lled in the membrane pumps for visualization of the local jet fl ow Since the density of these solutions is diff erent the developing procedure of the vortex can be visualized as the shadowgraph image The velocity of the main fl ow was set to be almost 0 m s in this experiment The input voltages to the piezoelectric actuators and its rising time were set as 120 V and 10 s respectively One time push and pull actuation was applied in this experiment As shown in Fig 5 a the local jet fl ow was generated and fl owed into the static fl ow in the main microchannel after receiving the trigger From Fig 5 a we can see that the vortex were successfully generated in the microchannel in 20 s after the trigger Then the generated vortex reached the wall of the main microchannel in 40 s Since it is diffi cult to observe the velocity of the local jet fl ow even if using the high speed camra with the frame rate of 200000 fps we analyzed the vortex generation by Finite Element Method FEM analysis using COMSOL Multiphysics COMSOL Multiphysics v5 3a COMSOL AB Stockholm Sweden to estimate the velocity of the lo