Laser-assisted fabrication of deterministic lateral displacement structures on P20 die steel masters for microfluidic particle separation

Micro features play a vital role in microfluidic devices as they induce laminar or patterned flow. Laser micromachining is an evolving technique in the fabrication of such micro features with various complicated shapes and sizes on metallic and polymeric surfaces. A variety of shapes and sizes are utilized in biomedical applications, such as bio-implants, bioreactors and particle separation modules. In this research work, the authors have attempted to fabricate a passive device for particle separation that works on the principle of Deterministic Lateral Displacement (DLD). Displacement of the particles in the microfluidic regime separates the particles in a size range of 5-17 mu m. This separation is accomplished using appropriately placed microposts which act as diversions for the flow lines, bifurcating them into primary and secondary branches. The authors have fabricated these features using a two-step process: fabrication of P20 die steel masters using 1030 nm Ultrashort Pulsed Laser (Yb) and transferring the features to poly dimethyl siloxane (PDMS)-based polymeric devices using soft fabrication. The circular posts of diameter 40 +/- 2 mu m and triangular features inscribed in a circle of diameter 40 +/- 2 mu m are arranged in three configurations with varying row shift fractions (epsilon), namely 0.45, 0.57 and 0.70, resulting in a tilt angle (alpha) of 25 +/- 1 degrees, 30 +/- 1 degrees and 35 +/- 1 degrees. The effect of the tilt angles on the pressure and velocity gradients on the fluid flow and the particle deformation is studied. The microscopy of the fabricated steel masters and PDMS devices is carried out to characterize the micro-features for their shape, size and the heat-affected zones. 3D profilometry is carried out to determine the quality of the micro-holes. Polymeric devices are further fabricated using die steel masters by soft fabrication.

Automated summary

In this research, the authors have utilized laser micromachining to fabricate micro features in microfluidic devices for particle separation. By appropriately placing microposts, the authors achieved separation of particles in the size range of 5-17 micrometers. The effect of tilt angles on fluid flow and particle deformation was also studied.