Exploring sperm cell rheotaxis in microfluidic channel: the role of flow and viscosity.

Rheotaxis is a fundamental mechanism of sperm cells that guides them in navigating towards the oocyte. The present study investigates the phenomenon of sperm rheotaxis in Newtonian and non-Newtonian fluid media, which for the first time explores a viscosity range equivalent to that of the oviductal fluid of the female reproductive tract in rectilinear microfluidic channels. Three parameters, the progressive velocity while performing rheotaxis, the radius of rotation during rheotaxis, and the percentage of rheotactic sperm cells in the bulk and near-wall regions of the microfluidic channel were measured. Numerical simulations of the flow were conducted to estimate the shear rate, flow velocity, and the drag force acting on the sperm head at specific locations where the sperms undergo rheotaxis. Increasing the flow velocity resulted in a change in the position of rheotactic sperm from the bulk center to the near wall region, an increase and subsequent decrease in the sperm's upstream progressive velocity, and a decrease in the radius of rotation. We observed that with an increase in viscosity, rheotactic sperms migrate to the near wall regions at lower flow rates, the upstream progressive velocity of the sperm decreases for Newtonian and increases for non-Newtonian media, and the radius of rotation increases for Newtonian and decreases for non-Newtonian media. These results quantify the effects of fluid properties such as viscosity and flow rate on sperm rheotaxis and navigation, thereby paving the way for manipulating sperm behavior in microfluidic devices, potentially leading to advancements in assisted reproduction techniques.

Micropump integrated white blood cell separation platform for detection of chronic granulomatous disease.

White blood cells (WBCs) are robust defenders during antigenic challenges and prime immune cell functioning indicators. High-purity WBC separation is vital for various clinical assays and disease diagnosis. Red blood cells (RBCs) are a major hindrance in WBC separation, constituting 1000 times the WBC population. The study showcases a low-cost micropump integrated microfluidic platform to provide highly purified WBCs for point-of-care testing. An integrated user-friendly microfluidic platform was designed to separate WBCs from finger-prick blood (⁓5 µL), employing an inertial focusing technique. We achieved an efficient WBC separation with 86% WBC purity and 99.99% RBC removal rate in less than 1 min. In addition, the microdevice allows lab-on-chip colorimetric evaluation of chronic granulomatous disease (CGD), a rare genetic disorder affecting globally. The assay duration, straight from separation to disease detection, requires only 20 min. Hence, the proposed microfluidic platform can further be implemented to streamline various clinical procedures involving WBCs in healthcare industries.

Characterization of the phagocytic ability of white blood cells separated using a single curvature spiral microfluidic device.

The present work describes a microfluidic device developed for separating white blood cells (WBCs) for the Nitroblue Tetrazolium (NBT) bioassay, which quantifies the phagocytic ability of cells. The NBT test requires a small number of phagocytic cells but is highly susceptible to the presence of red blood cells (RBCs). Our inertial microfluidic device can deliver a WBC sample by removing 99.99% of RBCs and subsequently reducing the ratio of RBC to WBC from 848:1 to 2:3. The microdevice operates on a relatively higher hematocrit concentration (1% Hct) of blood. Compared to conventional WBC separation methods, the microdevice's passive, label-free nature preserves the cell properties of the original sample. A single-turn spiral microfluidic device with a rectangular cross-section is simple to fabricate, cost-effective, and easy to operate. The reported microfluidic device requires only a single drop of whole blood (⁓20 µl) obtained via the finger prick method for efficient phagocytic analysis. Also, the microdevice reported in this study achieves WBC separation in under 10 min, omitting the need for RBC lysis, density gradient centrifugation, or expensive antibodies. Supplementary Information: The online version contains supplementary material available at 10.1007/s13534-024-00414-y.

Blood plasma separation in elevated dimension T-shaped microchannel.

In recent years, microfluidic chips have proven ideal tools for biochemical analysis, which, however, demands a unique and compatible plasma separation scheme. Various research groups have established continuous flow separation methods in microfluidic devices; however, they have worked with relatively small dimension microchannels (similar to the blood cell diameter). The present work demonstrates separation of plasma by utilizing the hydrodynamic separation techniques in microchannels with size of the order of mm. The separation process exploits the phenomenon, which is very similar to that of plasma skimming explained under Zweifach-Fung bifurcation law. The present experiments demonstrates for, the first time, that applicability of the Zweifach-Fung bifurcation law can be extended to dimensions much higher than the suspended particle size. The T-microchannel device (comprising perpendicularly connected blood and plasma channels) were micro-fabricated using conventional PDMS micro-molding techniques. Three variables (feed hematocrit, main channel width, and flow rate distributions) were identified as the important parameters which define the device's efficiency for the blood plasma separation. A plasma separation efficiency of 99.7 % was achieved at a high flow ratio. Novel concepts of 2-stage or multiple plasma channel designs are also proposed to yield high separation efficiency with undiluted blood. The possible underlying principle causing plasma separation (viz. aggregation and shear thinning) are investigated in detail as part of this work. The results are significant because they show nearly 100 % separations in microchannels which are much easier to fabricate than previously designed devices.

Separation of motile human sperms in a T-shaped sealed microchannel.

Microfluidic methods act as an effective motile sperm separation technique used in infertility treatments. This work presents a standalone microfluidic device to separate motile sperm cells from non-motile sperm cells and debris. The separation mechanism is based on the centrifugal force acting on sperms and the ability of progressive motile sperms to swim upstream. The separation of motile sperm is carried out using a simple T-shaped microchannel which constitutes three reservoirs: one inlet and two outlets. Herein, one of the outlets is kept sealed. The sealed channel leads to a high-velocity gradient and a rheotaxis zone at the T junction resulting in the separation of motile sperms. Separated sperms are isolated in a sealed channel with a low Reynolds number flow so that sperms cannot have a net displacement, which ensures that the sperms do not re-enter the fluid flow. CFD simulation is conducted to study the flow fields inside the channel and experimental investigation is carried to observe the separation behaviour of sperms. The reported device provides 100% sperm separation efficiency and ensures the entrapment of sperm cells for a longer period. A modified colorimetric nitroblue tetrazolium test conducted on separated sperm cells shows that there is only a marginal increase in superoxide (O2 -) production, proving normal sperm integrity. This device offers an effective and safe alternative to conventional sperm sorting methods. Supplementary Information: The online version contains supplementary material available at 10.1007/s13534-022-00229-9.

Disease diagnostics using hydrodynamic flow focusing in microfluidic devices: Beyond flow cytometry.

The multi-disciplinary field of microfluidics has the potential to provide solutions to a diverse set of problems. It offers the advantages of high-throughput, continuous, rapid and expeditious analysis requiring minute quantities of sample. However, even as this field has yielded many mass-manufacturable and cost-efficient point-of-care devices, its direct and practical applications into the field of disease diagnostics still remain limited and largely overlooked by the industry. This review focuses on the phenomenon of hydrodynamic focusing and its potential to materialize solutions for appropriate diagnosis and prognosis. The study aims to look beyond its intended cytometric applications and focus on unambiguous disease detection, monitoring, drug delivery, studies conducted on DNA and highlight the instances in the scientific literature that have proposed such approach.

Blood Plasma Microfluidic Device: Aiming for the Detection of COVID-19 Antibodies Using an On-Chip ELISA Platform.

COVID-19 is a public health emergency of international concern. Detection of SARS-CoV-2 virus is an important step towards containing the virus spread. Although viral detection using molecular diagnostic methods is quite common and efficient, these methods are prone to errors, laborious and time consuming. There is an urgent need for blood-based tests which are simple to use, accurate, less time consuming, portable and cost-effective. Human blood plasma contains water, proteins, organic and in-organic substances including bacteria and viruses. Blood plasma can be effectively used to detect COVID-19 antibodies. The immune system generates antibodies (IgM/IgG proteins) in response to the virus and identification of these antibodies is related to the presence of the infection in the patient in the past. Therefore, detecting and testing the presence of these antibodies will be extremely useful for monitoring and surveillance of the population (Petherick, Lancet 395:1101-1102, 2020). Herein, we describe and propose a microfluidic ELISA (enzyme-linked immunosorbent assay) system to detect COVID-19 antibodies on a lab-on-chip platform. We propose to first separate plasma from whole human blood using a microfluidic device and subsequently perform the detection of antibodies in the separated plasma using a semi-automated on-chip ELISA.

Microdevice for plasma separation from whole human blood using bio-physical and geometrical effects.

In this research work, we present a simple and efficient passive microfluidic device for plasma separation from pure blood. The microdevice has been fabricated using conventional photolithography technique on a single layer of polydimethylsiloxane, and has been extensively tested on whole blood and enhanced (upto 62%) hematocrit levels of human blood. The microdevice employs elevated dimensions of about 100 µm; such elevated dimensions ensure clog-free operation of the microdevice and is relatively easy to fabricate. We show that our microdevice achieves almost 100% separation efficiency on undiluted blood in the flow rate range of 0.3 to 0.5 ml/min. Detailed biological characterization of the plasma obtained from the microdevice is carried out by testing: proteins by ultra-violet spectrophotometric method, hCG (human chorionic gonadotropin) hormone, and conducting random blood glucose test. Additionally, flow cytometry study has also been carried on the separated plasma. These tests attest to the high quality of plasma recovered. The microdevice developed in this work is an outcome of extensive experimental research on understanding the flow behavior and separation phenomenon of blood in microchannels. The microdevice is compact, economical and effective, and is particularly suited in continuous flow operations.