The present protocol describes a pneumatic microfluidic platform that can be used for efficient microparticle concentration.
The present article introduces a method for fabricating and operating a pneumatic valve to control particle concentration using a microfluidic platform. This platform has a three-dimensional (3D) network with curved fluid channels and three pneumatic valves, which create networks, channels, and spaces through duplex replication with polydimethylsiloxane (PDMS). The device operates based on the transient response of a fluid flow rate controlled by a pneumatic valve in the following order: (1) sample loading, (2) sample blocking, (3) sample concentration, and (4) sample release. The particles are blocked by thin diaphragm layer deformation of the sieve valve (Vs) plate and accumulate in the curved microfluidic channel. The working fluid is discharged by the actuation of two on/off valves. As a result of the operation, all particles of various magnifications were successfully intercepted and disengaged. When this technology is applied, the operating pressure, the time required for concentration, and the concentration rate may vary depending on the device dimensions and particle size magnification.
Due to the importance of biological analysis, microfluidic and biomedical microelectromechanical systems (BioMEMS) technologies1,2 are used to develop and study devices for the purification and collection of micromaterials2,3,4. Particle capture is categorized as active or passive. Active traps have been used for external dielectric5, magnetophoretic6, auditory7, visual8, or thermal9 forces acting on independent particles, enabling precise control of their movements. However, an interaction between the particle and external force is required; thus, the throughput is low. In microfluidic systems, controlling the flow rate is very important because the external forces are transmitted to the target particles.
In general, passive microfluidic devices have micropillars in microchannels10,11. Particles are filtered through interaction with a flowing fluid, and these devices are easy to design and inexpensive to manufacture. However, they cause particle clogging in micro-pillars, so more complex devices have been developed to prevent particle clogging12. Microfluidic devices with complex structures are generally suitable for managing a limited number of particles13,14,15,16,17,18.
This article describes a method to fabricate and operate a pneumatically driven microfluidic platform for large particle concentrations that overcomes the shortcomings18 as mentioned above. This platform can block and concentrate particles by deformation and actuation of the thin diaphragm layer of the sieve valve (Vs) plate that accumulates in curved microfluidic channels. Particles accumulate in curved microfluidic channels, and the concentrated particles can separate by discharging the working fluid via the actuation of two PDMS seals on/off valves18. This method makes it possible to process a limited number of particles or concentrate a large number of small particles. Operating conditions such as the magnitude of flow rate and compressed air pressure can prevent unwanted cell damage and increase cell trapping efficiency.
1. Designing the microfluidic platform for particle concentration
2. Fabrication of the microfluidic platform for particle concentration
NOTE: Figure 6 illustrates the fabrication of a microfluidic platform that concentrates particles.
3. Setting up the device
NOTE: Figure 7 shows fabricating a microfluidic platform that concentrates particles.
4. Operation of the device
Figure 8 shows the flow rate of the fluid rates for a four-stage platform operation, as mentioned in Table 2. The first stage is the loading state (a state). The platform was supplied with fluid with all valves open, and the working fluid (Qf) and particles (Qp) are almost identical as the microfluidic channel network exhibits structural symmetry. In the second stage (b state), compressed air was transported to Vs to block the particles, and as the Vs diaphragm deformed, the flow path narrowed, and the flow rate measured at the outlet port was reduced by hydraulic resistance. The flow rates of Qf and Qp were almost similar, and the difference was less than 2.67%. In the third stage (c state), compressed air was delivered to Vs and Vp for particle concentration, with Vs and Vp closed and Vf open. The measured Qp was close to zero, and the Qf was about 1.42 times that of the b state. In most cases, the flow rate doubles when both dissipation channels are in operation, but the platform has different types of hydraulic resistance in the main fluid channels and Vs, so the total flow of the working fluid is reduced. Finally (d state), compressed air was delivered only to Vf to collect the concentrated particles, and the flow rates of Qf and Qp were reversed. The flow was zero because Vf blocked Qf, and Qp was about 1.42 times the b state. The concentration ratio of the particles (Qp/(Qf+Qp) × 100) was 3.96-4.53. This shows that the sequential actuation programmed with the pneumatic valve works well due to flow changes.
Figure 9 shows the screen capturing concentrated particles. Figure 9A shows the flow state of the fluid with the three pneumatic valves not actuated, Figure 9B shows the method used to trap the particles, Figure 9C shows the sieve method, and Figure 9D shows the ejection of the concentrated beads. Particles were concentrated and accumulated in the collection area when Vs and Vp were closed, and all collected concentrated particles were released within 4 s when only Vf was closed. Therefore, the device successfully collects many particles suitable for particle collection and concentration.
Figure 1: Schematic diagram of a pneumatic microfluidic platform for microparticle concentration (P, port; Q, flowrate; f, fluid; p, particle; V, valve; s, sieve). Please click here to view a larger version of this figure.
Figure 2: Assembly of the pneumatic microfluidic platform for microparticle concentration. Please click here to view a larger version of this figure.
Figure 3: Schematic of Vs in the pneumatic microfluidic platform for microparticle concentration (P, port; Q, flowrate; f, fluid; p, particle; V, valve; s, sieve). Please click here to view a larger version of this figure.
Figure 4: CAD image of the pneumatic microfluidic platform for microparticle concentration. (A) Pneumatic channel valve. (B) Main fluid channel. (C) Interconnection fluid channel. (D) Cross image of each channel (For the dimensions of 1 to 7, see Table 1). Please click here to view a larger version of this figure.
Figure 5: Fabrication image of the pneumatic microfluidic platform for microparticle concentration. Please click here to view a larger version of this figure.
Figure 6: Schematic of the cross-section of the 3D fluidic channel network during fabrication. (A) Molds are created for the curved fluid chamber and fluid channel for replica molding. (B) Plasma bonding of the PDMS layer after curing to a glass wafer. (C) Liquid PDMS is poured into the SU-8 mold to create the interconnection channel. (D) The fluid chamber and fluid channel structure are arranged in liquid PDMS on the SU-8 mold. (E) The system is inflated by the thermal pressure of the air layer. (F) The inflated structure and SU-8 mold are removed. Please click here to view a larger version of this figure.
Figure 7: Schematic of the pneumatic microfluidic platform set up for micro-particle concentration. Please click here to view a larger version of this figure.
Figure 8: The flow rate of the fluid rates for a four-stage platform operation. The Qf and Qp working fluid flow rates following set Vf and Vp operating times (particle concentration times) in a pneumatic microfluidic platform with a Vs of 15 kPa. a-d show the pneumatic microfluidic platform operation state according to Table 2. (1) Sample loading, (2) Sample blocking, (3) Sample concentration, (4) Sample release. Please click here to view a larger version of this figure.
Figure 9: Operation of the microparticle concentrator. (A) Before the operation. (B) Microparticle sieving. (C) Microparticle sieve completion. (D) Release of concentrated particles. Please click here to view a larger version of this figure.
Number | Structure | Width (W) or diameter (D), (μm) | |||
1 | Pneumatic chamber | 1200 (D) | |||
2 | Pneumatic channel | 50 (W) | |||
3 | Fluid channel | 200 (W) | |||
4 | Fluid chamber for Vs | 800 (D) | |||
5 | Fluid chamber for Vp (Vf) | 400 (D) | |||
6 | Interconnection chamber | 400 (D) | |||
7 | Interconnection channel | 200 (W) |
Table 1: Dimensions of the pneumatic microfluidic platform (1 to 7 in Figure 4).
State | Pneumatic Microfluidic Platform Operation |
Pneumatic Valve Operation | |||
Signal | Vs | Vf | Vp | ||
a | Loading | 4 | OFF | OFF | OFF |
b | Blocking | 1 | ON | OFF | OFF |
c | Concentration | 2 | ON | OFF | ON |
d | Release | 3 | OFF | ON | OFF |
Table 2: Pneumatic microfluidic platform operation by pneumatic valve operation, shown in Figure 8.
This platform provides a simple way to purify and concentrate particles of various sizes. Particles are accumulated and released through pneumatic valve control, and no clogging is observed because there is no passive structure. Using this device, the concentration of particles of three sizes is presented. However, the operating pressure, the time required for concentration, and the rate may vary depending on the device dimensions, particle size magnification, and the pressure at Vs18,20,21.
When performing step 3.1, air bubbles may remain on the curved surface of the channel. When the air bubble remains, the environment in the channel changes, so it is necessary to check the channel very carefully through a microscope before operation.
Compared with previous studies, this platform has some advantages and disadvantages. In the dielectrophoretic method, fewer target particles are used22. An additional process was required to prepare particles to enhance the physical interaction between particles and external forces22,23. Complex design issues must be considered to increase the separation efficiency in magnetophoretic separation systems5,22. This platform showed higher separation efficiency than the ultrasonic method, which can separate samples at high flow rates24. However, because this platform does not have a passive structure, no clogging effect25,26,27 was observed when beads were trapped and accumulated, unlike the passive method.7,10 This platform can be used for water pretreatment when concentrating and extracting suspended bio-particles, as the operation is not affected by the properties of the physical particles18,21.
The authors have nothing to disclose.
This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(Ministry of Science and ICT). (No. NRF-2021R1A2C1011380).
1.5 mm puncture | Self procduction | Self procduction | This puncture was made by requesting a mold maker based on the Miltex® Biopsy Punch with Plunger (15110-15) product. |
4 inch Silicon Wafer/SU-8 mold | 4science | 29-03573-01 | 4 inch (100) Ptype silicon wafer/SU-8 mold |
Carboxyl Polystyrene Crosslinked Particle(24.9 μm) | Spherotech | CPX-200-10 | Concentrated bead sample1 |
Flow meter | Sensirion | SLI-1000 | Flow measurement |
High-speed camera | Photron | FASTCAM Mini | Observation of concentration |
Hot plate | As one | HI-1000 | heating plate for curing of liquid PDMS |
KOVAX-SYRINGE 10 mL/Syringe | Koreavaccine | 22G-10ML | Fill the microfluidic channel with bubble-free demineralized water. |
Laboratory Conona treater/Atmospheric plasma | Electro-Technic | BD-20AC | Chip bonding/atmospheric plasma |
Liquid polydimethylsiloxane, PDMS | Dow Corning Inc. | Sylgard 184 | Components of chip |
Microscope | Olympus | IX-81 | Observation of concentration |
PEEK Tubes | SAINT-GOBAIN PPL CORP. | AAD04103 | Inject or collect particles |
Polystyrene Particle(4.16 μm) | Spherotech | PP-40-10 | Concentrated bead sample3 |
Polystyrene Particle(8.49 μm) | Spherotech | PP-100-10 | Concentrated bead sample2 |
Pressure controller/μflucon | AMED | μflucon | Control of air pressure |
Spin coater | iNexus | ACE-200 | spread the liquid PDMS on SU-8 mold |