Particle focusing is an important functionality useful in a wide set of biological applications. Nevertheless, it is still challenging to realize it in microfluidics, especially in a low pressure system, because of the intrinsic 2D nature of standard microfluidic devices; long channels or complicated device geometries with several lateral channels are usually needed to avoid this limitation. In this work we present the fabrication and optimization of a compact microfluidic chip, which is capable to perform 3D particle focusing at high flow rates, thanks to the superposition of inertial focusing and intense Dean flow in tightly curving 3D channels. The device layout comprises alternating helices and straight channel sections permitting particle focusing with driving pressures < 1 bar due to the compactness of this chip. Beads characterization is performed, demonstrating the possibility of the chip to effectively focus 15 μm size sample using a single inlet and with no need of additional lateral channels that could complicate the sample processing procedure. Femtosecond laser micromachining followed by chemical etching is used to fabricate the device. This technique is a two-step process that permits fabrication of 3D structures in fused silica substrates and it is a fundamental tool to obtain 3D helices in the substrate. A surface fabrication approach has been used to avoid tapered channels. We envisage the use of this chip for high speed flow cytometer applications.
Petra Paié, Francesca Bragheri, Dino Di Carlo, and Roberto Osellame, "A 3D particle focusing device based on tightly curving 3D microchannels," Proc. SPIE 10061, Microfluidics, BioMEMS, and Medical Microsystems XV, 1006109 (Presented at SPIE BiOS: January 29, 2017; Published: 20 April 2017); https://doi.org/10.1117/12.2251941.
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