Spiral Microchannels with Trapezoidal Cross Section Fabricated by Femtosecond Laser Ablation in Glass for the Inertial Separation of Microparticles

Abstract

The fabrication and testing of spiral microchannels with a trapezoidal cross section for the passive separation of microparticles is reported in this article. In contrast to previously reported fabrication methods, the fabrication of trapezoidal spiral channels in glass substrates using a femtosecond laser is reported for the first time in this paper. Femtosecond laser ablation has been proposed as an accurate and fast prototyping method with the ability to create 3D features such as slanted-base channels. Moreover, the fabrication in borosilicate glass substrates can provide high optical transparency, thermal resistance, dimensional stability, and chemical inertness. Post-processing steps of the laser engraved glass substrate are also detailed in this paper including hydrogen fluoride (HF) dipping, chemical cleaning, surface activation, and thermal bonding. Optical 3D images of the fabricated chips confirmed a good fabrication accuracy and acceptable surface roughness. To evaluate the particle separation function of the microfluidic chip, 5 μm, 10 μm, and 15 μm particles were focused and recovered from the two outlets of the spiral channel. In conclusion, the new chemically inert separation chip can be utilized in biological or chemical processes where different sizes of cells or particles must be separated, i.e., red blood cells, circulating tumor cells, and technical particle suspensions.

Enhanced inertial focusing of microparticles and cells by integrating trapezoidal microchambers in spiral microfluidic channels

“…Engraving glass to fabricate the microuidic channels is an iterative process in optimizing the femtosecond laser parameters to achieve the desired depth and width as well as to result in a suitable surface nish as has been investigated in earlier works. 54,55 Also, a detailed process for trapezoidal channels was introduced 25 with adjusted laser lling strategies. Once the glass wafer is engraved, it is treated in an HF-based glass etching solution (45 mL H 2 O, 100 mL H 3 PO 4 , and 30 mL HF) for 90 s to smoothen the engraved surface and get rid of any residual glass fragments.…”

“…The laser lling strategies are demonstrated in Fig. 4(b) and are further rened based on the previous work, 25 to allow for new channel features and calibration with actual laser beam performance. A set of intersecting parallel lines (0, 90, 45, and 135 ) are used to cover the channel's area and get it to the required depth.…”

“…16 Various microuidic methods were developed to achieve high-efficiency particle separation, some of them are active; which rely on external forces to manipulate microparticles such as magnetic, 17,18 dielectrophoretic (DEP), 19 optic, 20 and cell sorting with ow cytometry, 21 while others rely only on hydrodynamic forces as pinched ow fractionation (PFF), 22 Deterministic lateral displacement (DLD), 23 microvortex manipulation, 24 inertial and dean ow fractionation. [25][26][27][28][29] Passive focusing does not require complex setup and exhibits high throughput, portability, and purity. 16 In the passive technique known as inertial microuidics, microparticle focusing relies only on hydrodynamic forces inside the microchannels that affect microparticles and let them migrate towards their equilibrium positions.…”

3D Printing of Inertial Microfluidic Devices

“…Besides the aforementioned approach, other groups attempted to develop alternative strategies for the fabrication of inertial microfluidic devices. For instance, several groups reported the usage of femtosecond laser irradiation and CO 2 laser ablation techniques to produce straight and spiral shape microchannels inside a glass or PMMA [24][25][26][27][28] . Despite the simple fabrication process, the complexity of building non-rectangular cross-sections, poor surface finish, and lengthy etching steps are making them less user-friendly.…”

High-Efficiency Small Sample Microparticle Fractionation on a Femtosecond Laser-Machined Microfluidic Disc

“…Images of the spinning system setup and the fabricated glass microfluidic disc are available in the supplementary material Figures S1-S7. The microfluidic channels were drafted in AutoCAD 2018 software (Autodesk, San Rafael, CA, USA) and were fabricated in a femtosecond-laser workstation (microSTRUCT-C, 3D-Micromac, Germany) using laser strategies described in a previous work [43]. The channels and chambers were engraved using a fill strategy, which consists of 4 sets of intersecting lines that cover the area to be ablated and represents the tracks the laser will pass.…”