Dielectrophoresis of spermatozoa in viscoelastic medium

Electrically-driven handling of gametes and embryos: taking a step towards the future of ARTs

Electrical stimulation of gametes and embryos and on-chip manipulation of microdroplets of culture medium serve as promising tools for assisted reproductive technologies (ARTs). Thus far, dielectrophoresis (DEP), electrorotation (ER) and electrowetting on dielectric (EWOD) proved compatible with most laboratory procedures offered by ARTs. Positioning, entrapment and selection of reproductive cells can be achieved with DEP and ER, while EWOD provides the dynamic microenvironment of a developing embryo to better mimic the functions of the oviduct. Furthermore, these techniques are applicable for the assessment of the developmental competence of a mammalian embryo in vitro. Such research paves the way towards the amelioration and full automation of the assisted reproduction methods. This article aims to provide a summary on the recent developments regarding electrically stimulated lab-on-chip devices and their application for the manipulation of gametes and embryos in vitro.

Enrichment of bovine X-sperm using microfluidic dielectrophoretic chip: A proof-of- concept study

The microfluidic dielectrophoretic (MF-DEP) chip is a new, economical and readily-available technology that might be used to enrich X-sperm for increasing female offspring in dairy farms. In this study, we sought to develop an MF-DEP chip to enrich X bovine sperm. The MF-DEP chip was composed of an electrode attached to a glass slide and a microchannel made from polydimethylsiloxane. Sex-sorted sperm from flow cytometry were used to identify optimal electric field conditions while unsorted sperm were later tested for sorting efficiency. The results show that during dielectrophoresis some sperm attached to the electrode (called positive DEP; pDEP) whereas other moved away from the electrode (called negative DEP; nDEP). X and Y-sperm responded to dielectrophoresis differently depending on various factors such as buffers, voltages, and frequencies. We found that the condition 4 V 1 MHz significantly reduced (P < 0.05) the percentage of Y-sperm to nearly 30 and therefore enriched X-sperm. The sorting efficiency was dependent on buffer, bull, sorting cycle, flow rate, electrical voltage, and frequency. Notably, the best sorting buffer found in this experiment was the conducting buffer, but this buffer significantly reduced sperm viability and motility. Other sperm-friendly buffers, TRIS and mHTF, were also used, but could not enrich X-sperm. In conclusion, this is a proof of concept that the MF-DEP chip can be effectively used to enrich bovine X-sperm. However, more research must be performed particularly to find the best sorting buffer to effectively sex-sort sperm while providing high motility and sperm viability.

Manipulation of micro- and nanoparticles in viscoelastic fluid flows within microfluid systems

Manipulation of micro- and nanoparticles in complex biofluids is highly demanded in most biological and biomedical applications. A significant number of microfluidic platforms have been developed for inexpensive, rapid, accurate, and efficient particle manipulation. Due to the enormous potential of viscoelastic fluids (VEFs) for particle manipulation, various emerging microfluidic-based VEFs techniques have been presented over the last decade. This review provides an intuitive understanding of VEF physics for particle separation in different microchannel geometries. Besides, active and passive VEF methods are critically reviewed, highlighting the potential and practical challenges of each technique for particle/cell focusing, sorting, and separation. The outcome of this study could enable recognizing deliverable VEF technology with the promising prospect in the manipulation of submicron biological samples (e.g., exosomes, DNA, and proteins).