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남궁현,KABA ABDI MIRGISSA,오현규,전현진,윤정환,Haseul Lee,김도현 한국바이오칩학회 2022 BioChip Journal Vol.16 No.1
We report a quantitative and systematic method for determining 3D-printing and surface-treatment conditions that can help improve the optical quality of direct-printed microfluidic devices. Digital light processing (DLP)-stereolithography (SLA) printing was extensively studied in microfluidics owing to the rapid, one-step, cleanroom-free, maskless, and high-definition microfabrication of 3D-microfluidic devices. However, optical imaging or detection for bioassays in DLP-SLA-printed microfluidic devices are limited by the translucence of photopolymerized resins. Various approaches, including mechanical abrasions, chemical etching, polymer coatings, and printing on transparent glass/plastic slides, were proposed to address this limitation. However, the effects of these methods have not been analyzed quantitatively or systematically. For the first time, we propose quantitative and methodological determination of 3D-printing and surface-treatment conditions, based on optical-resolution analysis using USAF 1951 resolution test targets and a fluorescence microbead slide through 3D-printed coverslip chips. The key printing parameters (resin type, build orientation, layer thickness, and layer offset) and surfacetreatment parameters (grit number for sanding, polishing time with alumina slurry, and type of refractive-index-matching coatings) were determined in a step-wise manner. As a result, we achieved marked improvements in resolution (from 80.6 to 645.1 lp/mm) and contrast (from 3.30 to 27.63% for 645.1 lp/mm resolution). Furthermore, images of the fluorescence microbeads were qualitatively analyzed to evaluate the proposed 3D-printing and surface-treatment approach for fluorescence imaging applications. Finally, the proposed method was validated by fabricating an acoustic micromixer chip and fluorescently visualizing cavitation microstreaming that emanated from an oscillating bubble captured inside the chip. We expect that our approach for enhancing optical quality will be widely used in the rapid manufacturing of 3D-microfluidic chips for optical assays.
A Laser-Micromachined PCB Electrolytic Micropump Using an Oil-Based Electrolyte Separation Barrier
백선혁,김학현,황희원,KABA ABDI MIRGISSA,김현식,정민섭,김진태,김도현 한국바이오칩학회 2023 BioChip Journal Vol.17 No.2
We report a laser-micromachined electrolytic PCB micropump with an oil separation barrier. As advances in terms of miniaturization and performance from our previous mesoscale PCB electrolytic pump (Kim et al. in Sens Actuators A Phys 277:73–84, 2018), we employed a simple yet rapid tape-based laser-machining technique called tape-liner-supported plastic laser micromachining and pattern transfer to fabricate a microfluidic coverslip for a PCB electrode chip. Using our microfabrication technique, the coverslip is bonded to a PCB chip to form an enclosed microscale pump with a high machining precision and no need for alignment of intermediate adhesive tapes with structural layers as commonly done in previous tape-bonding work. The completed micropump demonstrated excellent pumping performance: flow rate up to 24.49 ml/min and backpressure up to 394 kPa. Electrochemical activation of electrodes consisting of a train of voltage pulses and sweeps improves the pumping performance. In order to prevent unwanted interspersion between the electrolyte and working fluid, various separation diaphragms were previously employed, but at the cost of limited working volume and flow rate as the diaphragms were permanently anchored to the pump body. Here we propose to use an oil plug as an untethered (mobile) separation barrier. After a systematic study of properties of common oils, we tested fluorinated oil (HFE-7500), hexadecane, and tetradecane as the candidate barrier materials. HFE-7500 was chosen because its interface was stable and did not degrade pumping performance for the flow-rate range of 8.47 μl/min–2.48 ml/min. We expect our micropump with the oil plug to be used as an excellent pressure source for integrated lab-on-a-chip devices, especially lab-on-a-PCBs.