Separation of progressive motile sperm from mouse semen using on-chip chemotaxis.

Abstract: Microfluidic devices can better control cellular microenvironments compared to conventional cell migration assays. Over the past few years, microfluidics-based chemotaxis studies showed a rapid growth. New strategies were developed to explore cell migration in manipulated chemical gradients. In addition to expanding the use of microfluidic devices for a broader range of cell types, microfluidic devices were used to study cell migration and chemotaxis in complex environments. Furthermore, high-throughput microfluidic chemotaxis devices and integrated microfluidic chemotaxis systems were developed for medical and commercial applications. In this article, we review recent developments in microfluidics-based chemotaxis studies and discuss the new trends in this field observed over the past few years.

Abstract: Sperm selection is essential to assisted reproductive technology (ART), influencing treatment outcomes and the health of offspring. The fundamental challenge of sperm selection is dictated by biology: a heterogeneous population of ~108 sperm per milliliter with a short lifetime in vitro. However, conventional sperm selection approaches result in less than 50% improvement in DNA integrity. Here, a clinically applicable microfluidic device is presented that selects sperm based on the progressive motility in 500 parallel microchannels. The result is a one-step procedure for semen purification and high DNA integrity sperm selection from 1 mL of raw semen in under 20 minutes. Experiments with bull sperm indicate more than 89% improvement in selected sperm vitality. Clinical tests with human sperm show more than 80% improvement in human DNA integrity, significantly outperforming the best current practices. These results demonstrate the presence of a sub-population of sperm with nearly intact chromatin and DNA integrity, and a simple clinically-applicable lab-on-a-chip method to select this population.

Abstract: One in six couples of reproductive age worldwide are affected at least once by some form of infertility. In vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) are widely-available assisted reproductive technologies (ART). The identification and isolation of the most-motile sperm with DNA integrity are essential to IVF and ICSI, ultimately affecting treatment consequences and the health of offspring. Recently, microfluidic technologies been developed to sort sperm according to sperm morphology, motility, DNA integrity, and functionality for IVF techniques. There have also been emerging applications in wildlife conservation, high-throughput single-sperm genomics, sperm-driven robotics, and in-home fertility testing. We review a broad range of studies applying the principles of microfluidics to sperm research.

Abstract: Fertilization and reproduction are central to the survival and propagation of a species. Couples who cannot reproduce naturally have to undergo in vitro clinical procedures. An integral part of these clinical procedures includes isolation of healthy sperm from raw semen. Existing sperm sorting methods are not efficient and isolate sperm having high DNA fragmentation and reactive oxygen species (ROS), and suffer from multiple manual steps and variations between operators. Inspired by in vivo natural sperm sorting mechanisms where vaginal mucus becomes less viscous to form microchannels to guide sperm towards egg, a chip is presented that efficiently sorts healthy, motile and morphologically normal sperm without centrifugation. Higher percentage of sorted sperm show significantly lesser ROS and DNA fragmentation than the conventional swim-up method. The presented chip is an easy-to-use high-throughput sperm sorter that provides standardized sperm sorting assay with less reliance on operators's skills, facilitating reliable operational steps.

Abstract: Spermatozoa are highly specialized cells that can be easily obtained and purified. Mature spermatozoa are transcriptionally and translationally inactive and incapable of protein synthesis. In addition, spermatozoa contain relatively higher amounts of membrane proteins compared to other cells; therefore, they are very suitable for proteomic studies. Recently, the application of proteomic approaches such as the two-dimensional polyacrylamide gel electrophoresis, mass spectrometry, and differential in-gel electrophoresis has identified several sperm-specific proteins. These findings have provided a further understanding of protein functions involved in different sperm processes as well as of the differentiation of normal state from an abnormal one. In addition, studies on the sperm proteome have demonstrated the importance of spermatozoal posttranslational modifications and their ability to induce physiological changes responsible for fertilization. Large-scale proteomic studies to identify hundreds to thousands of sperm proteins will ultimately result in the development of novel biomarkers that may help to detect fertility, the state of complete contraception, and beyond. Eventually, these protein biomarkers will allow for a better diagnosis of sperm dysfunctions and aid in drug development. This paper reviews the recent scientific publications available from the PubMed database to address sperm proteomics and its potential application to characterize male fertility and contraception.

Abstract: Microsystems create new opportunities for the spatial and temporal control of cell growth and stimuli by combining surfaces that mimic complex biochemistries and geometries of the extracellular matrix with microfluidic channels that regulate transport of fluids and soluble factors. Further integration with bioanalytic microsystems results in multifunctional platforms for basic biological insights into cells and tissues, as well as for cell-based sensors with biochemical, biomedical and environmental functions. Highly integrated microdevices show great promise for basic biomedical and pharmaceutical research, and robust and portable point-of-care devices could be used in clinical settings, in both the developed and the developing world.

Abstract: The shrinking of liquid handling systems to the micron and submicron size range entails moving into the area of small Reynolds numbers. The fluid dynamics in this regime are very different from the macroscale. We present an intuitive explanation of how the different physics of small Reynolds numbers flow, along with microscopic sizes, can influence device design, and give examples from our own work using fluid flow in microfabricated devices designed for biological processing.

Abstract: Contrary to the prevalent view, there seems to be no competition in the mammalian female genital tract among large numbers of sperm cells that are racing towards the egg. Instead, small numbers of the ejaculated sperm cells enter the Fallopian tube, and these few must be guided to make the remaining long, obstructed way to the egg. Here, we review the mechanisms by which mammalian sperm cells are guided to the egg.

Abstract: Mammalian cells cultured on 2D surfaces in microfluidic channels are increasingly used in drug development and biological research applications. These systems would have more biological or clinical relevance if the cells exhibit 3D phenotypes similar to the cells in vivo. We have developed a microfluidic channel based system that allows cells to be perfusion-cultured in 3D by supporting them with adequate 3D cell–cell and cell–matrix interactions. The maximal cell–cell interaction was achieved by perfusion-seeding cells through an array of micropillars; and 3D cell–matrix interactions were achieved by a polyelectrolyte complex coacervation process to form a thin layer of matrix conforming to the 3D cell shapes. Carcinoma cell lines (HepG2, MCF7), primary differentiated (hepatocytes) and primary progenitor cells (bone marrow mesenchymal stem cells) were perfusion-cultured for 72 hours to 1 week in the microfluidic channel, which preserved their 3D cyto-architecture and cell-specific functions or differentiation competence. This transparent 3D microfluidic channel-based cell culture system also allows direct optical monitoring of cellular events for a wide range of applications.