micromachines Article
The Design, Fabrication, and Testing of an Electromagnetic Micropump with a Matrix-Patterned Magnetic Polymer Composite Actuator Membrane Muzalifah Mohd Said 1,2 , Jumril Yunas 1, *, Badariah Bais 3 , Azrul Azlan Hamzah 1 and Burhanuddin Yeop Majlis 1 1
2 3
*
Institute of Microengineering and Nanoelectronics (IMEN), Universiti Kebangsaan Malaysia (UKM), 43600 UKM Bangi, Selangor, Malaysia;
[email protected] (M.M.S.);
[email protected] (A.A.H.);
[email protected] (B.Y.M.) Faculty of Electronics and Computer Engineering (FKEKK), Universiti Teknikal Malaysia Melaka (UTeM), Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia Dept. of Electrical Electronic and Systems Engineering, Faculty of Engineering and Built Environment, 43600 UKM Bangi, Selangor, Malaysia;
[email protected] Correspondence:
[email protected]; Tel.: +60-8911-8541
Received: 28 November 2017; Accepted: 21 December 2017; Published: 31 December 2017
Abstract: A valveless electromagnetic (EM) micropump with a matrix-patterned magnetic polymer composite actuator membrane structure was successfully designed and fabricated. The composite membrane structure is made of polydemethylsiloxane (PDMS) that is mixed with magnetic particles and patterned in matrix blocks. The matrix magnetic composite membrane was fabricated using a soft lithography process and expected to have a compact structure having sufficient magnetic force for membrane deformation and maintained membrane flexibility. The magnetic membrane was integrated with the microfluidic system and functionally tested. The experimental results show that a magnetic composite actuator membrane containing of 6% NdFeB is capable of producing a maximum membrane deflection up to 12.87 µm. The functionality test of the EM actuator for fluid pumping resulted in an extremely low sample injection flow rate of approximately 6.523 nL/min. It was also concluded that there is a correlation between the matrix structure of the actuator membrane and the fluid pumping flow rate. The injection flow rate of the EM micropump can be controlled by adjusting the input power supplied to the EM coil, and this is believed to improve the injection accuracy of the drug dosage and have potential in improving the proficiency of the existing drug delivery system. Keywords: valveless electromagnetic (EM) micropump; polydemethylsiloxane (PDMS); NdFeB; polymer composite membrane; magnetic actuator; drug delivery
1. Introduction An electromagnetic (EM) actuator membrane is the most essential mechanical structure in an electromagnetically driven mechanical micropump system since a stable and reliable membrane structure against magnetic force is needed. The EM actuator membrane should be made from soft and elastic material that is able to respond to an electromagnetic field [1–3]. Having a reliable and high precision of dosage is needed when the controllable fluidic dosage and flow rate is crucial [1,2,4] such as when a fluid sample is delivered from sample storage into the human body, such as a drug delivery system [2], or into a biological analysis system, such as a lab-on-chip system [5]. Great interest in improving the quality of the mechanical component of the membrane has led to the creation of membrane material that is magnetically responsive, patternable, and highly flexible. There are many actuation mechanisms that operate the micropump system reported since several years ago, such as electrostatic, piezoelelectric, and thermal pneumatic as well [6]. Among all these Micromachines 2018, 9, 13; doi:10.3390/mi9010013
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reported mechanisms, a micropump driven by electromagnetic actuator seems to have better actuation control and an easy fabrication method. In earlier designs, an EM actuator membrane made of silicon or metal was bonded with a bulky permanent magnet glued to the top of the membrane [7–11]. Those materials are brittle, stiff, and inflexible, especially in a condition of bonding between the thin actuator membrane and a bulky magnet, which can be easily damaged or released during operation. Researchers have replaced the silicon membrane with polymeric material to generate consistent actuation, as a polymer membrane is physically soft and highly flexible [12–14]. However, changing the membrane material to a polymer cannot bear the weight of a bulk permanent magnet. In order to overcome this problem, researchers started to minimize the bulk magnet by manipulating permanent magnetic materials and structure [15,16]. An electroplated CoNiMnP array on a silicon membrane surface was extensively studied in order to find a membrane structure with a high response to the applied magnetic field [16]. Researchers have since started focusing on alternative membrane material. A stiff and brittle membranes have been replaced with a soft and flexible material. Further study on the flexible membrane has led to a new functional structure and material, achieved by creating an electroplated magnetic layer on a polymer membrane. Research done by Chang et al. [15] minimized the size of the permanent magnet by having an electroplated CoNiMnP layer on the surface of the polydemethylsiloxane (PDMS) diaphragm. Some improvements have been made by Su and Chen; they patterned the electroplated permanent magnet into several smaller pieces of a 7 × 7 matrix of CoNiMnP (50 × 50 × 20 µm3 ) on a square-shaped PDMS membrane. The purpose of the work was to produce a large displacement that will permit a higher volume liquid flow of the micropump [17]. In this work, we replaced the conventional magnetic membrane structure with a new functional material made of PDMS (polydimethylsiloxane) with embedded magnetic particles, which led to a more compact membrane structure with a high magnetic response and improved mechanical deformation capability. PDMS polymers were used due to their good elasticity, high flexibility, high surface strength, and their biocompatibility. Additionally, PDMS can be patterned using a soft lithography process technique [18–20]. In this paper, we present a valveless electromagnetic micropump composed with a PDMS-based magnetic-composite polymer actuator membrane with a matrix pattern. Moreover, this paper also reports the operational performance of the fabricated EM actuator and the functionality test of the EM micropump system for fluid flow control in a lab-on-chip and drug delivery system. 2. The Design and Fabrication of Electromagnetic (EM) Electromagnetic Actuator The EM micropump consists of three main components: a microfluidic component, a magnetomechanic actuator, and an electromagnetic component, as shown in Figure 1a. Studies on the microfluidic and electromagnetic components have been reported elsewhere [2,18,21–23]. Therefore, the design of the microcoil, the microfluidic channel, and the chamber will not be discussed in this paper. We focus on the improvement of the magnetomechanic actuator that consists of a permanent magnet and a deformable mechanical membrane that is responsive to the magnetic field generated by the electromagnetic coil. Theoretically, when a magnetic field generated by a microcoil interacts with the magnet particles embedded in the membrane composite, it produces force that causes the composite membrane to deform periodically (Figure 1b) [1,15].
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(a)(a) (b)(b) (a) (b) (a)of the designed valveless electromagnetic(b) (b) Figure 1. Schematic pictures (EM) micropump system (a)(a) (b) Figure 1. 1. Schematic pictures of the designed valveless electromagnetic (EM) micropump system Figure Schematic pictures of the designed valveless electromagnetic (EM) micropump system
components: (a) the pictures structure of the micropump system; (b) mechanism of electromagnetic Figure 1. Schematic ofthe the designed valveless electromagnetic (EM) micropump system Figure 1.(a) Schematic pictures ofmicropump the designed valveless electromagnetic (EM) micropump system components: (a) the micropump system; (b) thethe mechanism ofmicropump electromagnetic components: the structure structure ofof system; (b) the mechanism of(EM) electromagnetic actuation. Figure Schematic pictures of the designed valveless electromagnetic system Figure 1. 1. Schematic pictures of the the designed valveless electromagnetic (EM) micropump system actuation. components: (a) the structure of the micropump system; (b) the mechanism of electromagnetic components: (a) the structure of the micropump system; (b) the mechanism of electromagnetic actuation. components: structure micropump system; mechanism electromagnetic components: (a)(a) thethe structure of of thethe micropump system; (b)(b) thethe mechanism of of electromagnetic actuation. actuation. actuation. actuation. The push–pull action of the membrane in the pump chamber will create a pressure change in the
The push–pull action membrane pump chamber will create a pressure change The push–pull action of of thethe membrane in in thethe pump chamber will create a pressure change in in chamber and allow for the transport of the fluids from the inlet to the chamber. The direction of the The push–pull action of the membrane in the pump chamber will create a pressure change in The push–pull action of the membrane in the pump chamber will create a pressure change in chamber and allow for the transport fluids from the inlet to the chamber. The direction The push–pull action of the membrane in the pump chamber will create a pressure change The push–pull action the membrane in the pump chamber will create a pressure change inofinof thethe chamber and allow for theof transport of of thethe fluids from the inlet to the chamber. The direction fluidic flow is determined by the diffuser and nozzle design [14,24,25]. the chamber and allow for the transport of the fluids from the inlet to the chamber. The direction of the chamber chamber and allow for for the the transport transport of the the fluids from the inlet inlet to the chamber. chamber. The The direction direction of fluidic flow is determined diffuser and nozzle design [14,24,25]. the and allow fluids from the chamber and allow for the transport of of the fluids from thethe inlet to to thethe chamber. The direction of of thethe fluidic flow is determined byby thethe diffuser and nozzle design [14,24,25]. Figure 2shows shows the design specification of proposed the design proposed EM micropump consisting of a the the fluidic flow is determined byspecification the diffuser and nozzle [14,24,25]. fluidic flow is determined by the diffuser and nozzle design [14,24,25]. Figure 2 the design of the EM micropump consisting a matrixthe fluidic flow is determined diffuser and nozzle design [14,24,25]. consisting of of the fluidic flow is the determined byby thethe diffuser nozzle design Figure 2 shows design specification ofand the proposed EM[14,24,25]. micropump a matrixFigure 2 shows the design specification of the proposed EM micropump consisting of a matrixFigure 2 shows the design specification of the proposed EM micropump consisting of a matrixmatrix-patterned mold structure attached to a silicon substrate and bonded with the PDMS-based patterned mold structure attached a of silicon substrate and bondedwith with thePDMS-based Figure 2structure shows design specification of proposed EM micropump consisting of a matrixFigure 2 shows thethe design specification thethe proposed EM micropump consisting ofPDMS-based a matrixpatterned mold attached tototoato substrate and bonded thethe patterned mold structure attached a silicon silicon substrate and bonded with the PDMS-based patterned mold structure attached a silicon silicon substrate and bonded with PDMS-based microfluidic component. The membrane and the microfluidic component are integrated with the microfluidic component. The membrane and the microfluidic component are integrated with the patterned mold structure attached to a substrate and bonded with the PDMS-based patterned component. mold structure attached to and a silicon substrate and bonded are withintegrated the PDMS-based microfluidic The membrane the microfluidic component with the microfluidic component. The membrane and the microfluidic component are integrated with the microfluidic component. The membrane and the microfluidic component are integrated with the electromagnetic coil to complete the micropump system. microfluidic component. The membrane and the microfluidic component integrated with electromagnetic coil to complete the micropump system. microfluidic component. The membrane and the microfluidic component areare integrated with thethe electromagnetic coil tocoil complete the system. electromagnetic coil to complete themicropump micropump system. electromagnetic to complete complete the micropump system. electromagnetic coil micropump system. electromagnetic coil to to complete thethe micropump system.
Figure 2.2. design ofof the proposed EM micropump. Figure 2. The design of the proposed EM micropump. Figure The design the proposed EM micropump. Figure 2.The The design proposed EM micropump. Figure 2. 2. The design ofofof the proposed EM micropump. Figure 2. The design ofthe the proposed EM micropump. Figure The design the proposed EM micropump.
Table shows the specific embossed matrix design of of the membrane. Two matrix structure Table shows the specific embossed matrix design ofthe the membrane. matrix structure Table 111 shows the specific embossed matrix design membrane. Two matrix structure Table 11 shows the specific embossed matrix design of the membrane. Two matrix structure Table shows the specific embossed matrix design of the membrane. Two matrix structure Table 1 1shows the specific embossed matrix design the membrane. Two matrix structure Table shows the specific embossed matrix design ofof the membrane. Two matrix structure types, types, namely, square flat and square shapes with dimensions of (1 × 1), (2 × 2), or (3 × 3), were types, namely, square flat and square shapes with dimensions of (1 × 1), (2 × 2), or (3 × 3), were types, namely, square and square shapes with dimensions of (1 ×× 1), (2 × 2), 2), or ×3), 3), were types, namely, square flat and square shapes with dimensions of (1 1), (2 ×2), or ×3), were types, namely, square flat and square shapes with dimensions of(2 1), (2 ××× 2), or (3(3(3 ×(3 3), were types, namely, square flatflat and square shapes with dimensions of (1× ×2), (2(3 orwere ×designed were namely, square flat and square shapes with dimensions of (1 × 1), or 3), to designed to observe the effects of the matrix combination on the deformation capability of the designed to observe the effects of the matrix combination on the deformation capability of the designed to observe the effects of the matrix combination on the deformation capability of the designed to observe the effects of the matrix combination on the deformation capability of the designed to observe the effects of the matrix combination on the deformation capability of the designed to observe the effects of the matrix combination on the deformation capability of the observe the effects of the matrix combination on the deformation capability of the membrane. membrane. membrane. membrane. membrane. membrane. membrane. Table 1. The The dimension thedesigned designed polymer composite membrane. Table 1. dimension ofofthe polymer composite membrane. Table 1. The dimension of the designed polymer composite membrane. Table 1. dimension of the designed polymer composite membrane. Table 1.dimension The dimension of the designed polymer composite membrane. Table 1. The dimension the designed polymer composite membrane. Table 1. The ofof the designed polymer composite membrane.
Membrane TypeType Membrane Membrane Type Membrane Type Membrane Type Membrane Type Membrane Type
Dimension Dimension Dimension Dimension Dimension Dimension Dimension
Membrane TypeType Membrane Membrane Type Membrane Type Membrane Type Membrane Type Membrane Type
Dimension Dimension Dimension Dimension Dimension Dimension
Dimension
6% NdFeB 6% NdFeB NdFeB 6%6% NdFeB NdFeB 6% NdFeB Square flat. flat. Shape: Square 6%Shape: NdFeB Shape: Square flat. Shape: Square flat. Shape: Square flat. Shape: Square flat. Area/cell: 6 × flat. 66mm Area/cell: × 6 2mm22 2 Shape:Area/cell: Square 22 ×mm 66mm Area/cell: mm Area/cell: 66 ××6666× Area/cell: mm Thick: 139 µm Thick: 139 µm2 Area/cell: 6 × 6 mm Thick: 139 µm Thick:139 139µm µm Thick: Thick: 139 µm
6% NdFeB 6% NdFeB 6% NdFeB NdFeB 6%6% NdFeB 6% Shape : NdFeB Square (1 × 1) Shape : Square (1 × 1) 6%Shape NdFeB : :Square ××1) Shape Square (1 × Shape : Square (1 ×(1 1) Shape (1 1) 1) Area/cell: 5: Square × 55mm Area/cell: ×(15 2mm Shape : Square ×2 1)22 2 Area/cell: 5× mm Area/cell: 5 mm Area/cell: 5 × 555×5mm 2 Area/cell: × 5 mm Thick:~ 90 µm Thick:~ µm Area/cell: 590×µm 5µm mm2 Thick:~ 90 Thick:~90 Thick:~ 90 µm Thick:~ 90 µm
6% 6% NdFeB 6%NdFeB NdFeB NdFeB 6%6% NdFeB Shape: Square (2 ×(22). Shape: Square (2× × 2). 6% NdFeB Shape: Square 2). 6%Shape: NdFeB Shape: Square × 2). Square (2 ×(22). 22 Area/cell: 2.5 2.5 ×2.5 2.5 Area/cell: ××mm 2.5 Shape: Square (2× 2).2mm Area/cell: 2.5 mm 2 2 Area/cell: 2.5 ×2). 2.5 Shape: Square Area/cell: 2.5(2 × ×2.5 mmmm 2 Thick: ~90 µm Thick: ~90 µm Area/cell: 2.5 × 2.5 mm Thick: ~90 µm Thick: µmmm2 Area/cell: 2.5~90 × 2.5 Thick: ~90 µm
6% 6% NdFeB 6% NdFeB NdFeB NdFeB 6%6% NdFeB Shape: Square (3 × 3) Shape: Square (3(3× × 3) 3) 6% NdFeB Shape: Square 6% NdFeB Shape: Square Shape: Square (3 ×(33)× 3) 2 2 2 Area/cell: 1.66 ×1.66 1.66 mm Area/cell: 1.66 ×(31.66 mm2mm Shape: Square × 3) Area/cell: × 1.66 2 Area/cell: ××1.66 mm Shape: Square 3)mm Area/cell: 1.661.66 ×(3 1.66
Thick: 139 µm
Thick: ~90 µm Thick: ~90 µm
Thick:~ 90 µm
Area/cell: 1.66 × 1.66 mm2 Area/cell: 1.66 × 1.66 mm2
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2.1. Synthesis of Magnetic Polymer Composite Membrane
TheSynthesis polymerofwas madePolymer with aComposite SYLGARD 184 silicon elastomer kit (Dow Corning, Midland, MI, 2.1. Magnetic Membrane ®
USA) containing PDMS and curing agent, mixed at a 10:1 ratio. The PDMS mixture was then mixed The polymer was made with a SYLGARD® 184 silicon elastomer kit (Dow Corning, Midland, MI, with 6% NdFeB magnetic particles using a mechanical stirrer. USA) containing PDMS and curing agent, mixed at a 10:1 ratio. The PDMS mixture was then mixed After the mixing process, the composite magnetic polymer was spin-coated onto a prewith 6% NdFeB magnetic particles using a mechanical stirrer. developed SU8 structure. The spin coaterpolymer machine was set at 500 rpm for 10 s to spread After thematrix mixingmold process, the composite magnetic was spin-coated onto a pre-developed the composite. composite up to a was higher 800forrpm s to obtain a SU8 matrix The mold structure. was Thethen spin ramped coater machine set speed at 500 of rpm 10 sfor to 20 spread the membrane thickness of ~139 µm. A thinner membrane layer could be obtained by increasing the composite. The composite was then ramped up to a higher speed of 800 rpm for 20 s to obtain a membrane of ~139 µm. A thinner membrane could be obtained coating speed. thickness The spin-coated composite material waslayer finally hard-cured at by 60 increasing °C for 30 the min to ◦ C for 30 min to coating speed. The spin-coated composite material was finally hard-cured at 60 completely remove the remaining water content. completely remove the remaining water content.
2.2. Magnetic Properties of Magnetic Polymer Composite 2.2. Magnetic Properties of Magnetic Polymer Composite
The The magnetic property of the polymer composite was studied by analyzing the hysteresis curve magnetic property of the polymer composite was studied by analyzing the hysteresis curve usingusing a vibration sample magnetometer showsthe the hysteresis loop of synthesized a vibration sample magnetometer(VSM). (VSM). Figure Figure 33shows hysteresis loop of synthesized PDMS:NdFeB at room temperature 1.2T T and a 6% mixture composition, PDMS:NdFeB at room temperatureand andwith with aa magnetization magnetization ofof1.2 and a 6% mixture composition, found to be the optimum composition [26]. It can be seen that the magnetic property still exists found to be the optimum composition [26]. It can seen that the magnetic property still exists in thein the magnetic composite material differentthicknesses. thicknesses. magnetic composite material atatdifferent 0.06
0.04
0.02 Magnetic Field (G) 0 -15000
-10000
-5000
0
5000
-0.02
10000
15000
139µm 64µm
-0.04
39µm
-0.06
Figure 3. The hysteresis 6%NdFeB NdFeBpolymer polymer composite. Figure 3. The hysteresisloop loop of of the the 6% composite.
It can be seen that thethe layer significanteffect effectonon magnetic properties of the It can be seen that layerthickness thickness has has a a significant thethe magnetic properties of the composite material. This is probably due to the amount of magnetic particles contained in composite material. This is probably due to the amount of magnetic particles contained in the polymer the matrix. The thicker the layer, greater magnetization can be. A 139 µm membrane thickness polymer matrix. The thicker thethe layer, thethe greater the magnetization can be. A 139 µm membrane shows a saturated remanence magnet of 37.637 mT. The coercivity value of the polymer composite is thickness shows a saturated remanence magnet of 37.637 mT. The coercivity value of the polymer about 2720 G, which thewhich force required to produce a zero magnetism in a magnetism material. composite is about 2720isG, is the force required to produce a zero in a material. 2.3. Electro-Mechanical Properties of Magnetic Composite Membrane
2.3. Electro-Mechanical Properties of Magnetic Composite Membrane To evaluate the electromechanical properties of the magnetic composite membrane, a membrane
To evaluate electromechanical properties ofconducted the magnetic composite membrane, a membrane deflection testthe using a laser displacement meter was in open air (without the attachment of deflection test usingcomponent). a laser displacement meter was conducted inaopen air stage, (without the attachment the microfluidic The measurement system consists of probing a power supply, of the microfluidic The measurement system4 shows consists a probing stage,ofathe power a Gaussian meter,component). and a laser displacement meter. Figure theofschematic diagram membrane deflection measurement (a) and the fabricated under the laserdiagram probe of supply, a Gaussian meter, and a laser setup displacement meter. Figuremembrane 4 shows the schematic during the measurement (b). the membrane deflection measurement setup (a) and the fabricated membrane under the laser probe during the measurement (b).
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(a) (a)
(b) (b)
Figure 4. Schematic setup for the measurement of actuator membrane displacement (a) and the Figure 4. Schematic setup forfor the of actuatormembrane membrane displacement (a) and Figure 4. of Schematic setup themeasurement measurement of actuator displacement (a) and the the photograph the fabricated actuator under test (b). photograph of the fabricated actuatorunder under test (b). photograph of the fabricated actuator (b).
For the test, an alternating current (AC) voltage was applied to the electromagnetic for about 60 Forthe the test,test, an an alternating current (AC) voltageThe was applied to the electromagnetic forembossed about Formembrane the alternating current (AC) voltage was applied to the electromagnetic about 60 s 60 s until gave a steady state response. composite membrane with afor varied smatrix until the membrane gave a steady state response. The composite membrane with a varied embossed until the membrane gave a steady state response. The composite membrane with a varied embossed structure was then measured. The maximum deflection for all membrane types is plotted in matrix then measured.The Themaximum maximum deflection membrane types is plotted in in matrix structure waswas then measured. deflectionfor forallall membrane types is plotted Figure 5. structure Figure 5. Figure 5.
Figure 5. The deflection theEM EMactuator actuator membrane anan alternating current (AC)(AC) inputinput voltage Figure 5. The deflection ofofthe membranewhen when alternating current voltage signal is applied. Figure deflection of the EM actuator membrane when an alternating current (AC) input voltage signal 5. is The applied. signal is applied. Figure 5 clearlyshows showsthat that the the membrane embossed design contributes to Figure 5 clearly membranewith witha 3a × 3 ×3 matrix 3 matrix embossed design contributes to the highest deflection of approximately 12.87 µm. The membrane with an embossed 1 × 1 matrix had Figure 5 clearly shows that the membrane with a 3 × 3 matrix embossed design contributes to the highest deflection of approximately 12.87 µm. The membrane with an embossed 1 x 1 matrix had the lowest deflection value. Thisisis because because membranes with larger embossed matrices more the deflection of approximately 12.87the µm. The membrane with anembossed embossed 1 x are 1 matrix had thehighest lowest deflection value. This the membranes with larger matrices are more rigid, which makes them hard to bend. Smaller cubes make the membrane more flexible, and spaces the lowest deflection value. Thistoisbend. because the membranes larger embossed matricesand are spaces more rigid, which makes them hard Smaller cubes makewith the membrane more flexible, between matrix cubes are utilized during deformation. rigid, which makes them to bend. Smaller cubes make the membrane more flexible, and spaces between matrix cubes arehard utilized during deformation. These results confirm an early simulation study done where a membrane with a smaller magnet between matrix cubes are utilized during deformation. These results confirm an early simulation study done where a membrane with a smaller magnet will produce a higher deflection [27].
results confirm an early simulation study done where a membrane with a smaller magnet will These produce a higher deflection [27]. will produce a higher deflection [27]. 3. Pump System Integration 3. PumpThe System Integration EM pump was fabricated using a standard MEMS process. The process can be divided into 3. Pump System Integration three parts: the electromagnetic component, the magneto-mechanic component, and the The EM pump was fabricated using a standard MEMS process. The process canmicrofluidic be divided into component. Each component of the system was fabricated separately. The step-by-step fabrication The EM pump was fabricated using a standard MEMS process. The process can be into three parts: the electromagnetic component, the magneto-mechanic component, and thedivided microfluidic process is shown in Figure 6. three parts: the electromagnetic component, magneto-mechanic component, and the microfluidic component. Each component of the systemthe was fabricated separately. The step-by-step fabrication component. Each component of the system was fabricated separately. The step-by-step fabrication process is shown in Figure 6. process is shown in Figure 6.
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Figure 6. The fabrication process of the EM pump. Figure 6. The fabrication process of the EM pump.
The process started with the fabrication of an electromagnetic field generator at the bottom of The process thespiral fabrication of an electromagnetic field generator at thetobottom of the actuator (Stepstarted 1). A with planar coil wire was manually wounded and attached the glass the actuator (Step A planar spiral coil wire awas manually and attached the glass substrate. The coil1). wire was used to generate magnetic fieldwounded that interacts with thetopermanent substrate. The coil wire was used to generate a magnetic field that interacts with the permanent magnet. The diameter of the wire core was 160 µm, and the cladding around the core was about 16 magnet. diameter of thethe wire core was membrane 160 µm, andand the coil cladding around coreAwas aboutcoil 16 was µm. µm. TheThe spacing between composite was about 0.3the mm. copper The the composite was about 0.3 mm. A copper coil was then thenspacing looped between in the planar and glued membrane to the top ofand thecoil glass substrate. looped in the planar and glued to the top of the glass substrate. The fabrication of the actuator membrane started with spin coating the synthesized magnetic The fabrication membrane started withstructure spin coating synthesized magnetic polymer composite of onthe to actuator a predefined SU8 mold matrix on athe glass wafer. The coated polymer composite on to a predefined SU8 mold matrix structure on a glass wafer. The coated polymer polymer composite material was then hard-cured in an oven for 30 min at 60 °C. Finally, the cured ◦ C. Finally, the cured polymer composite material was then hard-cured antransferred oven for 30tomin 60silicon polymer composite layers were peeled offin and theat top wafer, which was hollow composite layers were peeled off and transferred to the top silicon wafer, which was hollow with 2 and with dimensions of 6 × 6 mm , to form the actuator membrane (Step 2). To complete theand actuator 2 , to form the actuator membrane (Step 2). To complete the actuator system, dimensions of 6 × 6 mm system, the glass wafer with an electromagnetic coil was bonded with the PDMS-based actuator the glass wafer an electromagnetic membrane and with chamber (Steps 1 and 2).coil was bonded with the PDMS-based actuator membrane and chamber (Steps 1 and 2). The microfluidic component was fabricated in a similar way. The process started with pouring The microfluidic component wasSU8 fabricated a similar The way.mold The process started pouring and the the pure PDMS onto a predefined mold in structure. structure waswith hard-cured pure PDMS onto a predefined SU8 mold structure. The mold structure was hard-cured and transferred transferred to the actuator membrane surface to form a complete pump system (Step 3). to theFigure actuator to form complete pumpmicropump system (Stepcomponents 3). 7amembrane shows thesurface prototype of athe developed before system Figure 7a shows the prototype of the developed micropump components before system integration. In Figure 7b, we can see that the magnetic membrane can be properly transferred to a integration. In Figure 7b, we can see that the magnetic membrane can be properly transferred to a silicon substrate and is ready for the actuation test. Figure 7c shows the complete pump structure after the actuator was bonded with the microfluidic component. The leaking test was conducted in order to ensure that there were no leaks in the chamber or the channel.
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silicon substrate and Micromachines 2017, 9, 13 is ready for the actuation test. Figure 7c shows the complete pump structure7after of 11 the actuator was bonded with the microfluidic component. The leaking test was conducted in order Micromachines 2017, 9, 13 7 of to 11 ensure that there were no leaks in the chamber or the channel.
(b) (b)
(a) (a)
(c) (c)
Figure 7. (a) The components of the fabricated EM micropump before integration; (b) integration of the microfluidic and magnetomechanic components only; and (c) the micropump system after Figure 7. (a) (a) The The components components thefabricated fabricated EMmicropump micropump before integration; integration of Figure 7. ofofthe EM before integration; (b) (b) integration of the integration. the microfluidic and magnetomechanic components only; and (c) the micropump system after microfluidic and magnetomechanic components only; and (c) the micropump system after integration. integration.
Figure 8 shows a picture of the tested micropump filled with deionized (DI) water colored red. Figure 8 shows a picture of the tested micropump filled with deionized visible (DI) water colored red. Red Figure DI water was aused to make liquid flow inside micropump for colored monitoring 8 shows picture of the the tested micropump filledthe with deionized (DI) water red. Red DI water wasbeused to make the liquid flow inside the micropump forwas monitoring purposes. purposes. It can themake picture everything works well. Novisible leaking Red DI water wasseen usedinto thethat liquid flow inside the micropump visiblespotted. for monitoring It can be seen in the picture that everything works well. No leaking was spotted. purposes. It can be seen in the picture that everything works well. No leaking was spotted.
Figure 8. The photographs of the EM micropump under the leaking test. Figure 8. The photographs of the EM micropump under the leaking test. Figure 8. The photographs of the EM micropump under the leaking test.
4. Fluid Flow Test of EM Micropump 4. Fluid Flow Test of EM Micropump 4. Fluid Flow Test of EM Micropump The functionality of the micropump was verified using a fluid flow test through the microfluidic The functionality of the micropump was verified using a fluid flow test through the microfluidic channel. The coil wasoffed with a continuous AC voltage supply bytest a function generator with The functionality the micropump was verified using a fluid flow through the microfluidic channel. The coil was fed with a continuous AC voltage supply by a function generator with controllable frequency. For the measurement of the micropump flow rate, the liquid flow at the outlet channel. The coil was fed with a continuous AC voltage supply by a function generator with controllable frequency. For the measurement of the micropump flow rate, the liquid flow at the outlet tube was monitored using the measurement Aigo digital microscope (Aigo Digital Technology controllable frequency. For the of the micropump flow rate, the liquidCo., flowLtd., at theBeijing, outlet tube was monitored using the Aigo digital microscope (Aigo Digital Technology Co., Ltd., Beijing, China). experimental shown in microscope Figure 9 consists of fluidTechnology sample storage, fluidBeijing, tubing tube wasThe monitored using set the up Aigo digital (Aigo Digital Co., Ltd., China). The experimental set up shown in Figure 9 consists of fluid sample storage, fluid tubing connecting sample storage and the pump, the power supply and control, Aigo fluid microscope, China). Thethe experimental set up shown in Figure 9 consists of fluid sample the storage, tubing connecting the sample storage and the pump, the power supply and control, the Aigo microscope, an observerthe screen, andstorage the fluid storage at thethe open end of the fluid theAigo othermicroscope, side of the connecting sample and the pump, power supply and tubing control,onthe pump system. an observer screen, and the fluid storage at the open end of the fluid tubing on the other side of the pump system.
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an observer screen, and the fluid storage at the open end of the fluid tubing on the other side of the pump system. Micromachines 2017, 9, 13 8 of 11 Micromachines 2017, 9, 13
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Figure 9. 9. The of the the measurement measurement system system for for the the EM EM micropump micropump test. test. Figure The photograph photograph of Figure 9. The photograph of the measurement system for the EM micropump test.
The functionality test of the fabricated EM micropump was performed by analyzing the flow The Thefunctionality functionalitytest testofofthe thefabricated fabricatedEM EMmicropump micropumpwas wasperformed performedby byanalyzing analyzingthe theflow flowrate rate through observation of the liquid flow inside the fluidic tubing for 30 min. The fluid flow was rate through observation the liquid inside the fluidic tubing 30 min. fluid flow was through observation of theofliquid flowflow inside the fluidic tubing for for 30 min. TheThe fluid flow was then then calculated as the distance of fluid traveling through the fluid tubing with a diameter of 0.37 mm then calculated the distance of fluid traveling through fluid tubing with a diameter 0.37mm mmin a calculated as the as distance of fluid traveling through the the fluid tubing with a diameter ofof0.37 in a certain observation time. in a certain observation certain observation time.time. The measurement of the flow rate was taken with the presence of three types of micro-coil, The measurement of the the flow flow rate three types of of micro-coil, The measurement of rate was was taken takenwith withthe thepresence presenceofof three types micro-coil, namely, a single planar coil, a larger copper planar coil, and a double planar coil that generates a namely,a asingle singleplanar planarcoil, coil, aa larger larger copper copper planar coil that generates a a namely, planarcoil, coil,and anda adouble doubleplanar planar coil that generates different magnetic field. micropump with with a flatcomposite composite membrane and an embossed differentmagnetic magneticfield. field. The The EM EM micropump and anan embossed different The EM micropump withaaflat flat compositemembrane membrane and embossed matrix composite membrane of 3 × 3 and 2 × 2 were tested. An AC supply current from the function matrixcomposite compositemembrane membraneof of33× × 33 and AC supply current from thethe function matrix and 22 ××2 2were weretested. tested.An An AC supply current from function generator micro-coil. The The function functiongenerator generatorwas wasset setwith with a 10 Vpp square wave, 0.235 generatorwas wasfed fedto tothe 10 Vpp square 0.235 generator was fed to the themicro-coil. micro-coil. The function generator was setawith a 10 Vppwave, square wave, mA, The flow flowrate rateofofeach eachmicropump micropump plotted graph mA,and anda a11Hz Hzoperating operating frequency. frequency. The is is plotted in in thethe barbar graph 0.235 mA, and a 1 Hz operating frequency. The flow rate of each micropump is plotted in the bar graph shown shownininFigure Figure10. 10. shown in Figure 10.
Figure Fluidflow flowrate rateversus versuscoil coiltypes. types. Figure 10. 10. Fluid Figure 10. Fluid flow rate versus coil types.
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It is clearly seen from Figure 10 that the micropump with a membrane matrix of 3 × 3 (the blue bar) had the highest flow rate, 6.523 nL/min. The flat composite membrane (the green bar) had the lowest liquid flow rate for all coils. Moreover, the micropump with the double planar coil, compared to the micropumps with a single planar and a larger planar coil, had a higher flow rate. This is because the magnetic field produced by the double coil (0.63 mT) is the highest among all others. As stated in a previous report [26], the magnetic field generated by the planar electromagnetic coil will directly interact with the permanent magnet and hence produce a magnetic force that pushes and pulls the membrane, allowing for an improved pumping route. These results reflect that a lower membrane deflection will produce a low liquid flow rate. It can be seen then that the fabricated device was able to deliver fluid at an extremely slow flow rate, below the range reported previously [6]. It was also shown that the fluid flow characteristic was proportionally related to membrane deformation. Therefore, the injection flow rate could be controlled by adjusting the frequency, the signal type, and the height of the input power supplied to the electromagnetic coil. We showed here that magnetic fields generated by microcoils and a smaller matrix membrane design can be used to significantly control the fluid flow rate of the micropump. Such a controlled flow rate is believed to have very high potential in enhancing fluid injection system capability for continuous drug delivery. 5. Conclusions In this work, an EM micropump with a matrix composite membrane was successfully designed, fabricated, and tested. The composite is a mixture of PDMS and 6% NdFeB particles and designed to be an embossed matrix membrane for the micropump. The design eradicates the need for bulk magnets, allowing for a more compact and simple design. Embossed matrix membranes of 1 × 1, 2 × 2, and 3 × 3 were built, and the 3 × 3 matrix membrane produced the highest membrane deflection value, 12.87 µm. As a micropump, the 3 × 3 matrix membrane attained the highest flow rate of 6.523 nL/min when the micropump was driven by a double planar coil. The designed EM micropump has been successfully used with nano-dose sample injection and thus is highly desirable for applications that require very high injection resolutions for high accuracy dosages, especially in lab-on-chip and drug delivery systems. Acknowledgments: This work was supported by the Ministry of Higher Education under Long-term Research Grant Scheme (LRGS Project) Grant No. LRGS/2015/UKM-UKM/NANOMITE/04/01 and Fundamental Research Grant Scheme (FRGS Project) Grant No. FRGS/1/2016/TK05/UKM/02/2. Author Contributions: J.Y., A.A.H. and B.Y.M. conceived and designed the experiments; J.Y., M.M.S. and B.B. performed the experiments; M.M.S. analyzed the data; M.M.S. contributed reagents/materials/analysis tools; J.Y. and M.M.S. wrote the paper. Conflicts of Interest: The authors declare no conflict of interest.
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