Particle movement and fluid behavior visualization using an optically transparent 3D-printed micro-hydrocyclone

Abstract

A hydrocyclone is a macroscale separation device employed in various industries, with many advantages, including high-throughput and low operational costs. Translating these advantages to microscale has been a challenge due to the microscale fabrication limitations that can be surmounted using 3D printing technology. Additionally, it is difficult to simulate the performance of real 3D-printed micro-hydrocyclones because of turbulent eddies and the deviations from the design due to printing resolution. To address these issues, we propose a new experimental method for the direct observation of particle motion in 3D printed micro-hydrocyclones. To do so, wax 3D printing and soft lithography were used in combination to construct a transparent micro-hydrocyclone in a single block of polydimethylsiloxane. A high-speed camera and fluorescent particles were employed to obtain clear in situ images and to confirm the presence of the vortex core. To showcase the use of this method, we demonstrate that a well-designed device can achieve a 95% separation efficiency for a sample containing a mixture of (desired) stem cells and (undesired) microcarriers. Overall, we hope that the proposed method for the direct visualization of particle trajectories in micro-hydrocyclones will serve as a tool, which can be leveraged to accelerate the development of micro-hydrocyclones for biomedical applications.

FIG. 1.

Schematic illustration of the workflow for the fabrication and characterization of a transparent PDMS-made micro-hydrocyclone. The cyclone body was first printed using a wax 3D printer (critical dimensions are illustrated in the inset) and then positioned into a casting box for soft lithography. Afterward, wax materials were removed from the PDMS block, and the transparent micro-hydrocyclone was fabricated by cutting extra PDMS parts using a blade. The micro-hydrocyclone was then placed horizontally on the microscope for fluorescent, bright field, and high-speed camera imaging and microscopy.

FIG. 2.

(a) Pressure contours in the computational model of micro-hydrocyclone on the top and front planes. (b) Velocity magnitude contour on the top and front plane at the feed velocity V = 5 m/s (Q = ∼43 ml/min for each inlet). (c) Contours of Y-velocity (axial velocity) on the top and front planes. Positive velocities indicate upward fluid flow, whereas the negative velocities show the downward flow. (d) The distribution of particles with varying sizes on the front plane and the spreading of particles on different planes along with the height of the micro-hydrocyclone shown in the insets (0 is showing the position on the yellow line passing through the micro hydrocyclone center).

FIG. 3.

Microscopic picture of the inner upward vortex inside a micro-hydrocyclone at two different flow rates of 10 and 70 ml/min, which is obtained using 3 μm fluorescent particles. At the lower flow rate of 10 ml/min, the inner upward (core) vortex fluctuates along the cyclone axis, whereas at the higher flow rate of 70 ml/min, it becomes more stable. Scale bar, 1 mm.

FIG. 4.

Movement of 180 μm particle at two different flow rates of 30 and 70 ml/min. The pink dashed lines show only the unfocused particle trajectories within the micro-hydrocyclone. Based on the trajectories, in lower flow rates, particles are more likely to move back and forth through the micro-hydrocyclone chamber and fluctuate around the vertical axis, which results in the increase in the residence time.

FIG. 5.

(a) Experimental setup for fluorescent microscopy of micro-hydrocyclone. (b) Streamlines of the overflow for two different particle sizes of 10 and 100 μm. It is clear that only 10 μm particles pass through the overflow. The images were taken at Z = 2 mm and 30 mm for underflow and overflow, respectively, following the same reference as used for simulation in Fig. 2. (c) Underflow streamlines for two different particle sizes of 10 and 100 μm. Almost all 100 μm particles (efficiency >95%) went through the underflow.

FIG. 6.

(a) Schematic model of experimental setup which depicts the hemocytometer images of the feed mixture of MSCs and MCs, overflow sample showing MSCs only, and the underflow sample showing MSCs and concentrated MCs at 70 ml/min. The inset also shows the MSCs cultured on MCs via experimental and schematic illustrations. (b) Comparison of efficiency curves for MCs and MSCs over a range of feed flow rates. By increasing the flow rate from 30 to 150 ml/min, the separation efficiency of MSCs and MCs was enhanced, while the separation efficiency for MCs was up to 95%. (c) Variation on cell viability for different flow rates. Cell viability for all flow rates was more than 95%.