Separation efficiency of a microfluidic sperm sorter to minimize sperm DNA damage

A Simple, Centrifugation-Free, Sperm-Sorting Device Eliminates the Risks of Centrifugation in the Swim-Up Method While Maintaining Functional Competence and DNA Integrity of Selected Spermatozoa

This pilot study was conducted to explore the benefits of using a centrifugation-free device based on the migration–sedimentation (MS) technique over centrifugation-based techniques in selecting competent spermatozoa, as compared with using split human semen samples. Ejaculates from 35 men undergoing semen analysis were split into four parts where one part was retained as the neat (NE) and the other three parts were subjected to sperm selection by using migration–sedimentation (MS), density gradient (DG) separation, and swim-up (SU) techniques. Sperm functional characteristics along with mitochondrial integrity, tyrosine phosphorylation, acrosome reaction, and ultrastructure were measured. The ability of selection techniques in reducing spontaneous and radiation-induced sperm DNA lesions was assessed by the TUNEL assay. In results, MS-selected spermatozoa had higher viability (P < 0.001), longevity in terms of total motility at the end of 6 and 18 h post-extraction (P < 0.001), and mitochondrial integrity (P < 0.001) compared with those selected by DG. Furthermore, spontaneous DNA lesions were significantly reduced in MS and SU fractions compared with NE (P < 0.001). Similarly, radiation-induced sperm DNA lesions were significantly lower in MS and SU fractions (P < 0.001) compared with DG. Ultrastructural analysis using scanning electron microscopy suggested a moderate, non-significant increase in the number of spermatozoa with normal head and mid-piece in MS fraction compared with other methods. In conclusion, the MS-based device offers a centrifugation-free, efficient, and reliable sperm selection method, making it suitable for partially equipped intra-uterine insemination (IUI) laboratories or office IUI programmes. Further research should focus on the safety and clinical usefulness of the device in assisted conception programmes in general and IUI in specific.

Sperm selection in IVF: the long and winding road from bench to bedside

Spermatozoa wage battle to conquer fertilization but the traits needed to succeed remain elusive. The natural advantageous qualities that enable only a few selected sperm cells to reach the site of fertilization remain unknown. Although in vitro fertilization (IVF) facilitates the job of spermatozoa, a universally acceptable means of sperm selection is yet to be developed. No objective or reliable sperm quality indicators have been established and sperm selection is, to a great extent, based on subjective qualitative evaluation. The best method for sperm selection in IVF presents several challenges: intrinsic sperm qualities cannot be evaluated and the ideal endpoint for these studies is debatable. An ideal method for sperm selection in ART should be noninvasive and cost-effective, and allow the identification of high-quality spermatozoa and yield better outcomes in terms of pregnancy and live birth rates. This narrative review included 85 papers and focused on the new available methods and technologies that might shed some light on sperm selection in IVF. It discusses the available data on microfluidic devices, omics profiling, micronuclei studies, sperm plasma membrane markers, and other techniques, such as Magnetic Activated Cell Sorting (MACS), Raman micro-spectroscopy, and artificial intelligence systems. The new techniques herein reviewed offer fresh approaches to an old problem, for which a definite solution has yet to cross the bridge from bench to IVF clinics around the world, since clinical usefulness and application remain unproven.

Sperm selection strategies and their impact on assisted reproductive technology outcomes

The application of assisted reproductive technologies (ART) has revolutionised the treatment of human infertility, giving hope to the patients previously considered incapable of establishing pregnancy. While semen analysis is performed to access whether a sample has an adequate number of viable, motile and morphologically normal sperm cells able to achieve fertilisation, sperm selection techniques for ART aim to isolate the most competent spermatozoon which is characterised by the highest fertilising potential. Based on the semen analysis results, the correct sperm selection technique must be chosen and applied. In this review, different sperm selection strategies for retrieving spermatozoa with the highest fertilising potential and their impact on ART outcomes are discussed. In addition, advantages and disadvantages of each method and the best suited techniques for each clinical scenario are described.

Novel Techniques of Sperm Selection for Improving IVF and ICSI Outcomes

Almost 50% of the infertility cases are due to male factors. Assisted reproductive technologies (ARTs) allow to overcome the incapacity of these patients' spermatozoa to fertilize the oocyte and produce a viable and healthy offspring, but the efficiency of the different techniques has still the potential to improve. According to the latest reports of the European Society of Human Reproduction and Embryology (ESHRE) and the Centers for Disease Control and Prevention of the United States (CDC), the percentages of deliveries per ART cycle in 2014 and 2016 were 21 and 22%, respectively. Among the reasons for this relatively low efficiency, the quality of the spermatozoa has been pointed out as critical, and the presence of high percentages of DNA-damaged spermatozoa in patients' ejaculates is possibly one of the main factors reducing the ARTs outcomes. Thus, one of the main challenges in reproductive medicine is to ensure the highest quality of the spermatozoa used in ARTs, and specifically, in terms of genetic integrity. The latest techniques for the preparation and selection of human spermatozoa are herein discussed focusing on those proven to improve one or several of the following parameters: sperm genetic integrity, fertilization capacity, embryo production, and in vitro survival, as well as pregnancy and delivery rates following in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). In addition, we discuss the potential of techniques developed in non-human mammals that could be further transferred to the clinic.

A treatment approach for couples with disrupted sperm DNA integrity and recurrent ART failure

OBJECTIVE

To test a novel method to select spermatozoa with high chromatin integrity.

DESIGN

Specimens with high sperm chromatin fragmentation (SCF) were selected by density gradient selection (DGS) and microfluidic sperm sorting (MSS).

SETTING

Academic medical center.

PATIENT(S)

Ejaculates from consenting men were processed by DGS/MSS. Couples underwent ICSI cycles with spermatozoa processed by DGS/MSS. Clinical outcomes were evaluated after embryo transfer.

INTERVENTION(S)

SCF was measured by TUNEL. ICSI with spermatozoa selected by DGS and MSS was performed.

MAIN OUTCOME MEASURE(S)

Fertilization, embryo implantation, and pregnancy outcomes were compared between DGS and MSS.

RESULT(S)

A total of 23 men had an average SCF of 20.7 ± 10%. After DGS and MSS, the SCF was 12.5 ± 5% and 1.8 ± 1%, respectively. In couples who underwent ICSI, the average SCF was 28.8 ± 9%, which fell to 21.0 ± 9% after DGS and 1.3 ± 0.7% after MSS. Four couples underwent 11 ICSI cycles with DGS and achieved one (25%) pregnancy that resulted in pregnancy loss. In four subsequent ICSI cycles with MSS, an ongoing clinical pregnancy rate of 50% was achieved. Five additional couples underwent 12 cycles of ICSI with DGS. After preimplantation genetic testing for aneuploidy, 30.3% of the embryos were euploid. One pregnancy was achieved, resulting in pregnancy loss. With MSS, 31.5% of the embryos were euploid and 4 couples obtained a pregnancy. Finally, sixteen couples underwent 20 ICSI cycles solely with MSS at our center. Of these couples, 8 had failed 13 ICSI cycles with DGS elsewhere. These couples achieved an overall implantation of 34.5% (10/29) and a pregnancy rate of 58.8% (10/17).

CONCLUSION(S)

Microfluidic selection yielded spermatozoa with optimal genomic integrity and improved chances of obtaining a euploid conceptus.

Sperm selection methods in the 21st century

Natural sperm selection in humans is a rigorous process resulting in the highest quality sperm reaching, and having an opportunity to fertilize, the oocyte. Relative to other mammalian species, the human ejaculate consists of a heterogeneous pool of sperm, varying in characteristics such as shape, size, and motility. Semen preparation in assisted reproductive technologies (ART) has long been performed using either a simple swim-up method or density gradients. Both methodologies provide highly motile sperm populations; however neither replicates the complex selection processes seen in nature. A number of methods have now been developed to mimic some of the natural selection processes that exist in the female reproductive tract. These methods attempt to select a better individual, or population of, spermatozoa when compared to classical methods of preparation. Of the approaches already tested, platforms based upon sperm membrane markers, such as hyaluronan or annexin V, have been used to either select or deselect sperm with varied success. One technology that utilizes the size, motility, and other characteristics of sperm to improve both semen analysis and sperm selection is microfluidics. Here, we sought to review the efficacy of both available and emerging techniques that aim to improve the quality of the sperm pool available for use in ART.

Microfluidic-based sperm sorting & analysis for treatment of male infertility

Microfluidics technology has emerged as an enabling technology for different fields of medicine and life sciences. One such field is male infertility where microfluidic technologies are enabling optimization of sperm sample preparation and analysis. In this chapter we review how microfluidic technology has been used for sperm quantification, sperm quality analysis, and sperm manipulation and isolation with subsequent use of the purified sperm population for treatment of male infertility. As we discuss demonstrations of microfluidic sperm sorting/manipulation/analysis, we highlight systems that have demonstrated feasibility towards clinical adoption or have reached commercialization in the male infertility market. We then review microfluidic-based systems that facilitate non-invasive identification and sorting of viable sperm for in vitro fertilization. Finally, we explore commercialization challenges associated with microfluidic sperm sorting systems and provide suggestions and future directions to best overcome them.

Live births from artificial insemination of microfluidic-sorted bovine spermatozoa characterized by trajectories correlated with fertility

Selection of functional spermatozoa plays a crucial role in assisted reproduction. Passage of spermatozoa through the female reproductive tract requires progressive motility to locate the oocyte. This preferential ability to reach the fertilization site confers fertility advantage to spermatozoa. Current routine sperm selection techniques are inadequate and fail to provide conclusive evidence on the sperm characteristics that may affect fertilization. We therefore developed a selection strategy for functional and progressively motile bovine spermatozoa with high DNA integrity based on the ability to cross laminar flow streamlines in a diffuser-type microfluidic sperm sorter (DMSS). The fluid dynamics, with respect to microchannel geometry and design, are relevant in the propulsion of spermatozoa and, consequently, ultrahigh-throughput sorting. Sorted spermatozoa were assessed for kinematic parameters, acrosome reaction, mitochondrial membrane potential, and DNA integrity. Kinematic and trajectory patterns were used to identify fertility-related subpopulations: the rapid, straighter, progressive, nonsinuous pattern (PN) and the transitional, sinuous pattern (TS). In contrast to the conventional notion that the fertilizing spermatozoon is always vigorously motile and more linear, our results demonstrate that sinuous patterns are associated with fertility and correspond to truly functional spermatozoa as supported by more live births produced from predominant TS than PN subpopulation in the inseminate. Our findings ascertain the true practical application significance of microfluidic sorting of functional sperm characterized by sinuous trajectories that can serve as a behavioral sperm phenotype marker for fertility potential. More broadly, we foresee the clinical application of this sorting technology to assisted reproduction in humans.

Guidance and Self-Sorting of Active Swimmers: 3D Periodic Arrays Increase Persistence Length of Human Sperm Selecting for the Fittest

Male infertility is a reproductive disease, and existing clinical solutions for this condition often involve long and cumbersome sperm sorting methods, including preprocessing and centrifugation-based steps. These methods also fall short when sorting for sperm free of reactive oxygen species, DNA damage, and epigenetic aberrations. Although several microfluidic platforms exist, they suffer from structural complexities, i.e., pumps or chemoattractants, setting insurmountable barriers to clinical adoption. Inspired by the natural filter-like capabilities of the female reproductive tract for sperm selection, a model-driven design, featuring pillar arrays that efficiently and noninvasively isolate highly motile and morphologically normal sperm, with lower epigenetic global methylation, from raw semen, is presented. The Simple Periodic ARray for Trapping And isolatioN (SPARTAN) created here modulates the directional persistence of sperm, increasing the spatial separation between progressive and nonprogressive motile sperm populations within an unprecedentedly short 10 min assay time. With over 99% motility of sorted sperm, a 5-fold improvement in morphology, 3-fold increase in nuclear maturity, and 2-4-fold enhancement in DNA integrity, SPARTAN offers to standardize sperm selection while eliminating operator-to-operator variations, centrifugation, and flow. SPARTAN can also be applied in other areas, including conservation ecology, breeding of farm animals, and design of flagellar microrobots for diagnostics.

Application of microfluidic technologies to human assisted reproduction

Microfluidics can be considered both a science and a technology. It is defined as the study of fluid behavior at a sub-microliter level and the investigation into its application to cell biology, chemistry, genetics, molecular biology and medicine. There are at least two characteristics of microfluidics, mechanical and biochemical, which can be influential in the field of mammalian gamete and preimplantation embryo biology. These microfluidic characteristics can assist in basic biological studies on sperm, oocyte and preimplantation embryo structure, function and environment. The mechanical and biochemical characteristics of microfluidics may also have practical and/or technical application(s) to assisted reproductive technologies (ART) in rodents, domestic species, endangered species and humans. This review will consider data in mammals, and when available humans, addressing the potential application(s) of microfluidics to assisted reproduction. There are numerous sequential steps in the clinical assisted reproductive laboratory process that work, yet could be improved. Cause and effect relations of procedural inefficiencies can be difficult to identify and/or remedy. Data will be presented that consider microfluidic applications to sperm isolation, oocyte cumulus complex isolation, oocyte denuding, oocyte mechanical manipulation, conventional insemination, intracytoplasmic sperm injection, embryo culture, embryo analysis and oocyte and embryo cryopreservation. While these studies have progressed in animal models, data with human gametes and embryos are significantly lacking. These data from clinical trials are requisite for making future evidence-based decisions regarding the application of microfluidics in human ART.

Positive rheotaxis extended drop: a one-step procedure to select and recover sperm with mature chromatin for intracytoplasmic sperm injection

PURPOSE

The purpose of this study was to develop a novel one-step ICSI approach to select sperm with better chromatin maturity than the conventional method.

METHODS

This was a pilot diagnostic study, which prospectively recruited men during a 6-month period in a University-affiliated infertility centre. Forty consecutive semen samples were provided for analysis. The positive rheotaxis extended drop (PRED) was set up creating a pressure and viscosity gradient. Each semen sample was divided into four aliquots: one aliquot for density gradient centrifugation (DGC), two aliquots for PRED (fresh semen (PRED-FS) and processed semen (PRED-DGC)), and one aliquot as the control (FS). In PRED, a mean of 200 spermatozoa were collected consecutively without selection from the outlet reservoir. The aniline blue assay was used to assess chromatin immaturity.

RESULTS

The mean channel length, measured from inlet to outlet, was 32.55 ± 0.86 mm, with a mean width of 1.04 ± 0.21 mm. In 82.5% of cases (33/40), at least 50 spermatozoa were captured between 15 and 30 min. Improved chromatin maturity after the DGC preparation and the PRED approach was observed in all samples. This was reflected by a mean reduction from 28.65 ± 8.97% uncondensed chromatin in the native ejaculates to 17.29 ± 7.72% in DGC and 0.89 ± 1.31% in the PRED approach (P < 0.01).

CONCLUSIONS

The PRED method may improve the current ICSI technique by providing it with its own sperm selection process. ICSI would probably become an even more complete technique comprising selection, capture and injection of the male gamete.

Non-Invasive Approaches to Epigenetic-Based Sperm Selection

Since sperm size and form do not necessarily provide information on internal sperm structures, novel sperm markers need to be found in order to conduct assisted reproductive therapies (ART) successfully. Currently, the priority of andrologists is not only to select those sperm able to fertilize the oocyte, but also a high quality of sperm that will guarantee a healthy embryo. Evidence of this shows us the importance of studying sperm intensively on genetic and epigenetic levels, because these could probably be the cause of a percentage of infertility diagnosed as idiopathic. Thus, more attention is being paid to posttranslational modifications as the key for better understanding of the fertilization process and its impact on embryo and offspring. Advances in the discovery of new sperm markers should go hand in hand with finding appropriate techniques for selecting the healthiest sperm, guaranteeing its non-invasiveness. To date, most sperm selection techniques can be harmful to sperm due to centrifugation or staining procedures. Some methods, such as microfluidic techniques, sperm nanopurifications, and Raman spectroscopy, have the potential to make selection gentle to sperm, tracking small abnormalities undetected by methods currently used. The fact that live cells could be analyzed without harmful effects creates the expectation of using them routinely in ART. In this review, we focus on the combination of sperm epigenetic status (modifications) as quality markers, with non-invasive sperm selection methods as novel approaches to improve ART outcomes.

Novel agents for sperm purification, sorting, and imaging

The stringent selection of viable spermatozoa ensures the transmission of high-quality genetic material to the egg during fertilization. Sperm heterogeneity within or between ejaculates and between males obliges varied post-collection handling of semen to assure satisfactory fertility rates. The current techniques used to assess sperm generally detect non-viable and non-fertilizing gametes in the ejaculate, but do not permit the investigation of semen for improved fertility outcomes. Advances in technology, however, have spurred the search for new approaches to enrich semen with high-quality spermatozoa and to track intra-uterine sperm migration. This review highlights the current and future methodologies used for sperm labeling, selection, tracking, and imaging, with specific emphasis on the recent influence of nanotechnology.

Microfluidic partition with in situ biofabricated semipermeable biopolymer membranes for static gradient generation

We report an in situ biofabrication strategy that conveniently partitions microfluidic networks into physically separated while chemically communicating microchannels with semipermeable biopolymer membranes, which enable the facile generation of static gradients for biomedical applications. The biofabrication of parallel biopolymer membranes was initiated with the dissipation of trapped air bubbles in parallel apertures in polydimethylsiloxane (PDMS) microfluidic devices, followed by tunable membrane growth with precise temporal and spatial control to the desired thickness. Static gradients were generated within minutes and well maintained over time by pure diffusion of molecules through the biofabricated semipermeable membranes. As an example application, the static gradient of alpha factor was generated to study the development of the "shmoo" morphology of yeast over time. The in situ biofabrication provides a simple approach to generate static gradients and an ideal platform for biological applications where flow-free static gradients are indispensable.