Luận án: Tối ưu liên kết PDMS/PMMA cho vi van, bơm & tách huyết tương

國立臺灣科技大學 機械工程系 博士學位論文 學號：D10803808 開發PDMS和PMMA基板之高黏合強度，進而製 造以慣性力為基礎之微型系統，用於高效率之血 漿分離 Maximizing interfacial bonding strength between PDMS and PMMA substrates for manufacturing microvalve/micropump system for efficient blood plasma separation with inertial particle focusing technique 研 究 生：Vo Ngoc Anh Tuan 指導教授： 陳品銓 教授 中華民國一一一年六月二十九日 Abstract Polydimethylsiloxane (PDMS) and polymethylmethacrylate (PMMA) are widely used in microfluidics, due to their excellent biocompatibility, high optical transparency, and ease of fabrication. However, the existing bonding methods could not generate sufficient bonding strength and limit such applications. This thesis outlines a systematic approach to maximize the interfacial bonding strength between PDMS to PMMA. Fabrication parameters were studied by measuring bonding strength (i., burst test pressure) based on the Taguchi method.

Under optimal bonding conditions, the microchannel assembly endured air pressure exceeding 770 kPa, liquid pressure exceeding 622 kPa, and tensile test exceeding 3000 kPa. Bonding strength was sufficient to resist the entry of liquid at a rate of 6800 times greater than the microchannel volume per minute. The ability to withstand such extremely high pressure without damage to the microdevices is an indication that interfacial bonding was indeed permanent. Then, the proposed manufacturing method was also used to fabricate microfluidic devices capable of withstanding extremely high liquid pressure of 402 kPa, high flow rates exceeding 120 mL/min, and dense microchannels with gap of only 30 µm.

This proposed bonding process was used to fabricate a functional valve system of high-density configuration, which i can be potentially used in microfluidics-based assays requiring high accuracy, rapid response, and the facile management of liquid transportation. Moreover, we successfully developed a novel microfluidic device for separation blood plasma from human blood without any external valves or pumps. The concept is based on using pneumatic peristaltic micropump (PPMs) integrated with a trapezoidal cross-section for ultra-fast blood plasma separation. First, we proposed a fabrication process of PPM with high pumping rate by combining rigidly of PMMA and elasticity of PDMS.

Following the procedure to achieve excellent bonding strength of PDMS/PMMA, the PPMs could be operated under high pressure. Then, the dynamic deflection test of PDMS membrane actuator under high pulsation frequency was performed. We proved that the PPMs have excellent actuator diaphragm dynamic behavior without any mechanical fatigue or dead volume, achieving the highest pumping rate of 3,500 µL/min. Then the micropump was integrated with a spiral microchannel with trapezoidal cross-section area and used to rapidly extract plasma from human blood within 3 minutes and with a small blood volume of 200μL, with the efficient separation up to 97%.

ii List of contents Chapter 1.1 Motivation for maximizing bonding strength of PDMS/PMMA for fabrication of hybrid microfluidic devices.1 What is microfluidics.3 Bonding PDMS/PMMA for fabrication microfluidic devices .2 Microvalve and Micropump .3 Blood plasma separation .4 Objective and significance of this dissertation .5 Organization of the dissertation .1 Bonding PDMS/PMMA by surface modification .1 Surface chemical modification using one silane reagent .2 Surface chemical modification using two silane reagents .4 Separation of blood plasma using size-based particle separation with spiral microchannels. Maximizing bonding strength of PDMS/PMMA .4 Design of experiment .1 Burst test with the air .3 High-density microchannel.3 High flowrate test. Microvalve and micropump system for efficient blood plasma separation 60 4.1 Design and fabrication of microvalve .1 Design of microvalve.2 Fabrication of microvalve .2 Characterization of microvalve .1 Testing of single valve .2 High-density microvalve .3 Design and fabrication of micropump .1 Design of micropump .2 Fabrication of micropump .4 Characterization of micropump .1 Deflection of PDMS membrane .2 Pumping rate of micropump .5 Extraction of blood plasma from human blood by integrated PPM device. Conclusion, limitations, and recommendation .2 Limitation of the dissertation.

94 v List of tables Table 1-1 Summary of material properties for common and trending microfluidic thermoplastics such as: PMMA, COC, PS, PC [8]. 6 Table 1-2 Comparison of various reported bonding between PDMS-PMMA. Five primary variables and their corresponding values influencing bonding strength. Results of eighteen experiments based on factors and levels listed in, s is standard deviation and S/N is signal to noise ratio.

44 Table 3-3 Factor analysis based on average S/N ratios. 47 vii List of figures Figure 1-1 Characteristic length scales (approximate) of microfluidic and nanofluidic systems in relation to that of various biological entities [2]. 1 Figure 1-2 Silicon nanowire system for cardiac biomarker detection. (a) Image of silicon nanowire (SiNW) device array chip, integrated with microfluidic system for fluid exchange.

Fluids are deposited into the acrylic well through the inflow tube on the left (red arrow) and removed from the outflow tube on the right (blue arrow). (b) Schematic showing the layout of the SiNW device array on the chip. A total of 36 clusters of 5 nanowires each were available for use. (c) SEM image of a cluster of nanowires.

Each nanowire is individually addressable by oxide- passivated metal contact lines running out to the edge of the chip [4]. 4 Figure 1-3 a) Micrograph and schematic of a PDMS pneumatic microvalve, (b) 3D diagram of an elastomeric peristaltic Quake’s pump [26]. 14 Figure 1-4 Component of human whole blood. Schematic of the process flow for bonding between a PMMA and a PDMS substrate [17].

The surface modification process for bonding PMMA and PDMS [18]. Schematics illustrating procedures for (a–f) surface modification with 2% MPTMS at room temperature on a non-silicon substrate, and (g–i) bonding of an oxidized non-silicon substrate with oxidized PDMS realized at room temperature for 10 min [20]. (a) Surface hydroxylation of PDMS and plastic substrates by O2 plasma treatment for 1 min. (b) Aminosilane and epoxysilane anchoring on the O2 plasma-treated PDMS and plastic substrates, respectively.

28 Figure 2-5 Schematic illustrating bonding mechanism. (a) Coating of low- molecular-weight PDMS on thermoplastic surface. Bonding of (b) PDMS with thermoplastic or (c) two thermoplastics. A thin layer of low-molecular-weight PDMS was formed on the surface of an aminosilane-functionalized thermoplastic via an amine–epoxy bond, and two substrates were finally bonded by forming a siloxane (Si–O–Si) bond [23].

Cross-sectional views of a three-layer monolithic PMMA/PDMS membrane valve (A) and exploded and assembled illustrations of a single PMMA/PDMS membrane valve (B). a: PMMA pneumatic wafer; b: displacement chamber; c: PDMS membrane; d: PMMA fluidic wafer; e: pneumatic channel; f: fluidic channel [10]. (a) Schematic illustrations of the micro membrane valve composed of PMMA–PDMS–PMMA substrates and its actuation by applying positive or negative pressure. (b) Micrographs showing the valve opening/closing with the applied pressures as indicated.

(c) Relation between the valve-controlling pressure (Pvalve) and the critical pressure of Pfluid to open/close the valve. Dashed line indicates Pvalve = Pfluid [24]. Design and characterization of the normally closed microvalve. Schematics of the operation of the valve, (a) open, (b) closed, and (c) exploded view of the valve architecture.

(d) Image showing a fabricated chip under a microscope. A 3D scale diagram of an elastomeric peristaltic pump. The channels are 100 μm wide and 10 μm high. Peristalsis was typically actuated by the pattern 101, 100, 110, 010, 011, 001, where 0 and 1 indicate “valve open” and “valve closed,” respectively.

This pattern is named the “120°” pattern, referring to the phase angle of actuation between the three valves. Other patterns are possible, including 90° and 60° patterns. The differences in pumping rate at a given frequency of pattern cycling were minimal. (B) Pumping rate of a peristaltic micropump versus various driving frequencies.

Dimension of microvalves = 100 μm by 100 μm by 10 μm; applied air pressure = 50 kPa [26]. A schematic illustration of the S-shape pneumatic microchannel with the integrated microvalve and microflow sensor. Note that the pneumatic microvalve controls the injection of the fluid flow and the microflow sensor measures the pumping rate. The phased deflection of the membranes located at the intersections of the S-shape microchannel and the fluidic microchannel generates a peristaltic effect which drives the fluid along the microchannel.

Parameters X and Y denote the length and separation, respectively, of the coils of the S-shape microchannel [51]. a Simplified fabrication process of the micropump based on SU- 8 lithography and PDMS replication. The SEM images of the b SU-8 template and c PDMS inverse structure after replication [52]. Fabrication, performance and characterization of the micropumps.

36 Figure 2-13 (a) Image of design. (b) Bright field image of the outlet system.8 ml/min flow rate (F1), two focused streams are observed, the narrow stream in the middle of the channel is formed by 7.32 μm particles and the broad stream near the inner channel wall is the composite of three streams of 10, 15, and 20 μm particles. (d) Fluorescent image of the focused streams of all three particles, 10 μm, 15 μm, and 20 μm in diameter, at the flow rate of 2. (e) x Normalized focusing position of particles (x is the distance of the focused stream from the inner channel wall, and w is the width of the channel) as function of De.

37 Figure 2-14 Schematic illustration of the blood plasma separation using a spiral channel with a trapezoidal cross-section. Under the influence of inertial lift and Dean drag forces, blood cells are focused and concentrated near the inner wall around the vortex cores, and blood plasma is collected from the cell-free region (outer wall). The bifurcation point is positioned closer to the inner wall to facilitate a large volume of plasma collection [63]. Brightfield images of the channel while filtering blood.

(a) Solidworks model of the spiral channel indicating areas of imaging. (b) Image of the first bifurcation with blood cells not completely filtered; the shadow boxed in red shows the cells passing the bifurcation to be filtered again by the second spiral. 38 Figure 3-1 Schematic illustration showing the process used to bond PDMS to PMMA. The system used to measure the burst pressure of the bonded microfluidic chips.

Results of burst tests on devices fabricated using the various parameter combinations; (a) No.6 shows failure at the PDMS–PMMA interface under pressure of 55 kPa; (b) No.11 in which chip remained intact under pressure of 622 kPa; (c) No.15 showing local failure under pressure of 101 kPa; (d) enlarged photo of No. 46 Figure 3-4 S/N ratios and bonding strengths corresponding to five main factors and three levels: (a) GPTMS concentration; (b) APTES concentration, (c) radio frequency power, (d) plasma treatment duration, (e) pressure within barrel reactor. The system is used to measure the burst pressure with the air of the bonded microfluidic chips. (a) PDMS/PMMA chip with are bonding by 22 mm × 22 mm for the tensile test; (b) The microchip was set on a tensile test machine; (c) The tensile test of the PDMS/PMMA bonding at a force 1.

(a) Layout of microfluidic device used to determine the effectiveness of high-density microdevices. The chip included main microchannel (No. 1) (width of 200 µm and depth of 100 µm), four secondary microchannels (width and depth of 100 µm) with various spacing between adjacent microchannels (No. 2) 30 µm; (b) the chip after xii injecting red dye ink and compared to a ten dollar coin; (c) Microscopic image of sub-microchannels (No.

SEM cross-sections showing excellent bonding between PDMS- PMMA with gaps of (a) 30 µm, and (b) 50 µm after experiments. 55 Figure 3-9 (a) System used to conduct experiments of high flow rates, including a peristaltic pump, two reservoirs, a connector, a pressure sensor, a pressure meter, and the microchip; (b) Experiment setup. Experiment setup for measuring pressure versus flowrate in microchannels with various cross sections: (a) 100µm × 100µm, (b) 200µm × 500µm, (c) 300µm × 500µm, and (d) 500µm × 500µm.