A Review of Planar PIV Systems and Image Processing Tools for Lab-On-Chip Microfluidics

Particle Tracking and Micromixing Performance Characterization with a Mobile Device

Strategies to stir and mix reagents in microfluid devices have evolved concomitantly with advancements in manufacturing techniques and sensing. While there is a large array of reported designs to combine and homogenize liquids, most of the characterization has been focused on setups with two inlets and one outlet. While this configuration is helpful to directly evaluate the effects of features and parameters on the mixing degree, it does not portray the conditions for experiments that involve more than two substances required to be subsequently combined. In this work, we present a mixing characterization methodology based on particle tracking as an alternative to the most common approach to measure homogeneity using the standard deviation of pixel intensities from a grayscale image. The proposed algorithm is implemented on a free and open-source mobile application (MIQUOD) for Android devices, numerically tested on COMSOL Multiphysics, and experimentally tested on a bidimensional split and recombine micromixer and a three-dimensional micromixer with sinusoidal grooves for different Reynolds numbers and geometrical features for samples with fluids seeded with red, blue, and green microparticles. The application uses concentration field data and particle track data to evaluate up to eleven performance metrics. Furthermore, with the insights from the experimental and numerical data, a mixing index for particles (mp) is proposed to characterize mixing performance for scenarios with multiple input reagents.

Particle-tracking-based strategy for the optimization of agitation conditions in a suspension culture of human induced pluripotent stem cells in a shaking vessel

Suspension cultures are widely used for cell expansion in regenerative medicine and production. Shaking culture is one of the useful suspension culture methods that ensures gentle agitation. There are other shaking methods, including orbital shaking, reciprocating, and rocking; however, optimizing the shaking conditions for each method to meet cell culture requirements is time-consuming. In this study, we used a particle-tracking-based strategy for optimizing the agitation conditions. When the average accelerations of aggregates were calculated, high acceleration occurred periodically, and acceleration of the aggregates in orbital shaking was stable. Furthermore, the number of dead cells correlated with the average time of acceleration. We observed that cell growth was ideally maintained by factors such as optimal acceleration, aggregate formation, and cell death. These results indicate that the image-based analyses of aggregates help optimize the agitation conditions for the shaking suspension culture of induced pluripotent stem cells (iPSCs).

Progress towards a Miniaturised PIV System

Particle image velocimetry is an important optical flow diagnostic tool due to its capacity for investigating a whole flow field without introducing disturbances. However, a significant drawback of PIV methods is their requirement for optical access, making capturing data in closed cavities and confined spaces extremely challenging. A potential approach to overcome this difficulty is miniaturising the system and placing the optical components inside the model. Conventional cross-correlation PIV methods do not allow this due to the size of current PIV cameras. In this study, a miniaturised autocorrelation-based stereo PIV system, which is volumetrically 1.2% of the conventional PIV cameras, was developed and tested. The miniature system is compared with a conventional stereo PIV in wind tunnel experiments up to 16 m/s free stream velocity and a 1.6% velocity difference is observed in the boundary layer flow. Despite a comparatively slow measurement rate of 4.5 Hz, the miniature PIV system demonstrates the ability to measure inside confined spaces and cavities and the ability to be mounted on board models and vehicles. However, limitations remain around conducting measurements with large velocity ranges and with regions of reversed flow due to the challenge of resolving a velocity of 0 m/s.