Separation of sperm and epithelial cells based on the hydrodynamic effect for forensic analysis

High efficiency sperm enrichment from forensic mock samples in bubble-based acoustic filtration devices for short tandem repeat (STR) analysis

A bubble-based acoustofluidic filtration (BAF) microfluidic device, which employs cross-flow filtration (CFF) and acoustic streaming, separates cells with high efficiency for forensic analysis. Forensic samples are typically complex and contain a substantial number of squamous epithelial cells from the female vagina, which tend to have fouling problems during filtration due to their morphological and cell adhesion differences. To overcome this issue, the BAF device utilizes bubble oscillation by bulk acoustic wave (BAW) to generate acoustic streaming, which offers additional hydrodynamic forces for side flushing cleaning and achieves effective removal within a mere 0.5 seconds. Our device is tested with imbalanced cell mixtures of sperm and epithelial cells with large disparity ratios. By concurrently employing CFF and acoustic streaming, the samples with our sperm-enrichment can achieve 91.72-97.78% for the recovery rate and 74.58-89.26% for the purity in the sperm enrichment. They are further subjected to short tandem repeat (STR) profiling, enabling the identification of perpetrators. Notably, even samples with minimal sperm cells demonstrated a significant increase in the male donor DNA ratio, while the peak heights of female alleles became virtually undetectable. The exceptional cell separation capability demonstrated by our BAF device highlights its potential applications in forensic sciences and other areas of cell biology.

Application of microfluidic technologies in forensic analysis

The application of microfluidic technology in forensic medicine has steadily expanded over the last two decades due to the favorable features of low cost, rapidity, high throughput, user-friendliness, contamination-free, and minimum sample and reagent consumption. In this context, bibliometric methods were adopted to visualize the literature information contained in the Science Citation Index Expanded from 1989 to 2022, focusing on the co-occurrence analysis of forensic and microfluidic topics. A deep interpretation of the literature was conducted based on co-occurrence results, in which microfluidic technologies and their applications in forensic medicine, particularly forensic genetics, were elaborated. The purpose of this review is to provide an impartial evaluation of the utilization of microfluidic technology in forensic medicine. Additionally, the challenges and future trends of implementing microfluidic technology in forensic genetics are also addressed.

Taking the microfluidic approach to nucleic acid analysis in forensics: Review and perspectives

Forensic laboratories are universally acknowledged as being overburdened, underfunded, and in need of improved analytical methods to expedite investigations, decrease the costs associated with nucleic acid (NA) analysis, and perform human identification (HID) at the point of need (e.g., crime scene, booking station, etc.). In response, numerous research and development (R&D) efforts have resulted in microfluidic tools that automate portions of the forensic genetic workflow, including DNA extraction, amplification, and short tandem repeat (STR) typing. By the early 2000 s, reports from the National Institute of Justice (NIJ) anticipated that microfluidic 'swab-in-profile-out' systems would be available for use at the crime scene by 2015 and the FBI's 2010 'Rapid DNA' Initiative, approved by Congress in 2017, directed this effort by guiding the development and implementation of maturing systems. At present, few fully-automated microfluidic DNA technologies are commercially available for forensic HID and their adoption by agencies interested in identification has been limited. In practice, the integration of complex laboratory processes to produce one autonomous unit, along with the highly variable nature of forensic input samples, resulted in systems that are more expensive per sample and not comparable to gold-standard identification methods in terms of sensitivity, reproducibility, and multiplex capability. This Review and Perspective provides insight into the contributing factors to this outcome; namely, we focus on the complications associated with the tremendous undertaking that is developing a sample-in-answer-out platform for HID. For context, we also describe the intricate forensic landscape that contributes to a nuanced marketplace, not easily distilled down to cases of simple supply and demand. Moving forward and considering the trade-offs associated with developing methods to compete, sometimes directly, with conventional ones, we recommend a focus shift for microfluidics developers toward the creation of innovative solutions for emerging applications in the field to increase the bandwidth of the forensic investigative toolkit. Likewise, we urge case working personnel to reframe how they conceptualize the currently available Rapid DNA tools; rather than comparing these microfluidic methods to gold-standard procedures, take advantage of their rapid and integrated modes for those situations requiring expedited identifications in an informed manner.

The influence of the female reproductive tract and sperm features on the design of microfluidic sperm-sorting devices

Although medical advancements have successfully helped a lot of couples with their infertility by assisted reproductive technologies (ART), sperm selection, a crucial stage in ART, has remained challenging. Therefore, we aimed to investigate novel sperm separation methods, specifically microfluidic systems, as they do sperm selection based on sperm and/or the female reproductive tract (FRT) features without inflicting any damage to the selected sperm during the process. In this review, after an exhaustive studying of FRT features, which can implement by microfluidics devices, the focus was centered on sperm selection and investigation devices. During this study, we tried not to only point to the deficiencies of these systems, but to put forth suggestions for their improvement as well.

Virus removal from semen with a pinched flow fractionation microfluidic chip

Nowadays pigs are bred with artificial insemination to reduce costs and transportation. To prevent the spread of diseases, it is important to test semen samples for viruses. Screening techniques applied are enzyme-linked immunosorbent assays and/or polymerase chain reaction, which are labor-intensive and expensive methods. In contrast to the current used screening techniques, it is possible to remove viruses physically from semen. However, existing methods for virus removal techniques have a low yield of spermatozoa. Therefore, we have developed a microfluidic chip that performs size-based separation of viruses and spermatozoa in boar semen samples, thereby having the potential to reduce the risk of disease spreading in the context of artificial insemination in the veterinary industry. As the head of a spermatozoon is at least twenty times larger than a virus particle, the particle size can be used to achieve separation, resulting in a semen sample with lower viral load and of higher quality. To achieve the size separation, our microfluidic device is based on pinched-flow fractionation. A model virus, cowpea chlorotic mottle virus, was used and spiked to porcine semen samples. With the proposed microfluidic chip and the optimized flow parameters, at least 84 ± 4% of the model viruses were removed from the semen. The remaining virus contamination is caused by the model virus adhering to spermatozoa instead of the separation technique. The spermatozoa recovery was 86 ± 6%, which is an enormous improvement in yield compared to existing virus removal techniques.

Simulating nature in sperm selection for assisted reproduction

Sperm selection in the female reproductive tract (FRT) is sophisticated. Only about 1,000 sperm out of millions in an ejaculate reach the fallopian tube and thus have a chance of fertilizing an oocyte. In assisted reproduction techniques, sperm are usually selected using their density or motility, characteristics that do not reflect their fertilization competence and, therefore, might result in failure to fertilize the oocyte. Although sperm processing in in vitro fertilization (IVF) and intrauterine insemination (IUI) bypasses many of the selection processes in the FRT, selection by the cumulus mass and the zona pellucida remain intact. By contrast, the direct injection of a sperm into an oocyte in intracytoplasmic sperm injection (ICSI) bypasses all natural selection barriers and, therefore, increases the risk of transferring paternal defects such as fragmented DNA and genomic abnormalities in sperm to the resulting child. Research into surrogate markers of fertilization potential and into simulating the natural sperm selection processes has progressed. However, methods of sperm isolation - such as hyaluronic acid-based selection and microfluidic isolation based on sperm tactic responses - use only one or two parameters and are not comparable with the multistep sperm selection processes naturally occurring within the FRT. Fertilization-competent sperm require a panel of molecules, including zona pellucida-binding proteins and ion channel proteins, that enable them to progress through the FRT to achieve fertilization. The optimal artificial sperm selection method will, therefore, probably need to use a multiparameter tool that incorporates the molecular signature of sperm with high fertilization potential, and their responses to external cues, within a microfluidic system that can replicate the physiological processes of the FRT in vitro.

Microfluidic Systems for Isolation of Spermatozoa from Testicular Specimens of Non-Obstructive Azoospermic Men: Does/Can It Improve Sperm Yield?

Intracytoplasmic sperm injection (ICSI) has allowed reproduction options through assisted reproductive technologies (ARTs) for men with no spermatozoa within the ejaculate (azoospermia). In men with non-obstructive azoospermia (NOA), the options for spermatozoa retrieval are testicular sperm extraction (TESE), testicular sperm aspiration (TESA), or micro-surgical sperm extraction (microTESE). At the initial time of spermatozoa removal from the testis, spermatozoa are immobile. Independent of the means of spermatozoa retrieval, the subsequent steps of removing spermatozoa from seminiferous tubules, determining spermatozoa viability, identifying enough spermatozoa for oocyte injections, and isolating viable spermatozoa for injection are currently performed manually by laboratory microscopic dissection and collection. These laboratory techniques are highly labor-intensive, with yield unknown, have an unpredictable efficiency and/or success rate, and are subject to inter-laboratory personnel and intra-laboratory variability. Here, we consider the potential utility, benefits, and shortcomings of developing technologies such as motility induction/stimulants, microfluidics, dielectrophoresis, and cell sorting as andrological laboratory add-ons to reduce the technical burdens and variabilities in viable spermatozoa isolation from testicular samples in men with NOA.

High efficiency rare sperm separation from biopsy samples in an inertial focusing device

Immotile and rare sperm isolation from a complex cell background is an essential process for infertility treatment. The traditional sperm collection process from a biopsy sample requires long, tedious searches, yet still results in low sperm retrieval. In this work, a high recovery, high throughput sperm separation process is proposed for the clinical biopsy sperm retrieval process. It is found that sperm have different focusing positions compared with non-sperm cells in the inertial flow, which is explained by a sperm alignment phenomenon. Separation in the spiral channel device results in a 95.6% sperm recovery in which 87.4% of non-sperm cells get removed. Rare sperm isolation from a clinical biopsy sample is performed with the current approach. The chance of finding sperm is shown to increase 8.2 fold in the treated samples. The achieved results highly support this method being used for the development of a rapid biopsy sperm sorting process. In addition, the mechanism was proposed and can be applied for the high-efficiency separation of non-spherical particles in general.

Levitational Cell Cytometry for Forensics

Here, a method for label-free, real-time interrogation, monitoring, detection, and sorting of biological rare cells in magnetically suspended heterogeneous samples is developed. To achieve this, heterogeneous populations of cells are levitated and confined in a microcapillary channel. This strategy enables spatiotemporal differential magnetic levitation of rare fragile dead cells equilibrating at different heights based on the balance between magnetic and corrected gravitational forces. In addition, the sorting of fragile rare dead cell populations is monitored in real-time. This technique provides a broadly applicable label-free tool for high resolution, real-time research, as well as forensic evidence processing of rape kits. This method is validated with forensic mock samples dating back to 2003, isolating sperm from epithelial cells (E. cells) with >90% efficiency and >97% purity. Overall, this method reduces the processing time by over 20-fold down to 20 min, eliminating centrifugation and labels, and providing an inexpensive and high-yield alternative to the current centrifuge-based differential extraction techniques. It can potentially facilitate the forensic downstream genomic analyses, accelerating the identification of suspects, and advancing public safety.

A portable sperm cell purification instrument based on continuous flow acoustophoretic separation of sperm cells for on-site forensic sample pretreatment

Obtaining a purified male sperm specimen from the original forensic sample mixtures is a critical procedure in identifying the criminal suspect in the forensic analysis of sexual assault crimes. Differential extraction (DE) has been used as the gold standard for extracting DNA preferentially from sexual assault samples, however it is laborious, time-consuming and inefficient. In this report a continuous flow two-step acoustic cell separation scheme is proposed for the removal of cell debris and cell-free genomic contaminants, followed by separation of sperm cells from epithelial cells. Based on the above method, a portable forensic sperm cell purification instrument has been constructed for on-site pretreatment of forensic samples in sexual assault crimes, where removal of contaminants and isolation of sperm cells could be automatically performed without the use of cell lysis buffer.

The effects of dithiothreitol (DTT) on fluorescent qPCR dyes

DNA extractions of semen samples commonly utilize dithiothreitol (DTT) to reduce and disrupt disulfide bonds. Although traditional extraction techniques remove DTT before downstream analyses, the forensic DNA community has recently explored Y-screening, direct amplification, and direct cell lysis assays that omit purification but employ reducing agents to lyse spermatozoa. This study examined the impact of residual DTT on downstream processes involving fluorescent dyes. Quantification using Investigator^® Quantiplex HYres revealed a significant increase in the male DNA yield (p = 0.00056) and a >150,000,000-fold increase in the male:human DNA ratio when DTT remained in extracts versus when it was filtered out using a traditional purification method. When DTT was present with Quantifiler™ Trio, the true mean DNA yield for the large autosomal target significantly increased (p = 0.038) and the average reported DNA yields increased 1.1-fold, >9.5-fold, and 1.3-fold for the small autosomal, large autosomal, and male targets, respectively. DTT-spiked DNA standards from both kits were impacted similarly to samples with residual DTT, demonstrating that observed effects were related to DTT and not the extraction method. This study corroborates other reports that DTT adversely affects multiple dyes (e.g., Cy5, Quasar 670, SYBR Green I, TMR, and Mustang Purple^® ). Overall, DTT causes inaccurate quantities and, consequently, inaccurate calculated male:female ratios when used in conjunction with these kits. Thus, implementation of newer direct-to-PCR assays incorporating DTT should either be avoided or used only with carefully evaluated, compatible dyes.

An automated instrument for intrauterine insemination sperm preparation

Sperm preparation is critical to achieving a successful intrauterine insemination and requires the processing of a semen sample to remove white blood cells, wash away seminal plasma, and reduce sample volume. We present an automated instrument capable of performing a sperm preparation starting with a diluted semen sample. We compare our device against a density gradient centrifugation by processing 0.5 mL portions of patient samples through each treatment. In 5 min of operating time, the instrument recovers an average of 86% of all sperm and 82% of progressively motile sperm from the original sample while removing white blood cells, replacing the seminal plasma, and reducing the volume of the sample to the clinically required level. In 25 min of operating time, density gradient centrifugation recovers an average of 33% of all sperm and 41% of progressively motile sperm. The automated instrument could improve access to IUI as a treatment option by allowing satellite doctor’s offices to offer intrauterine insemination as an option for patients without the clinical support required by existing methods.

Analytical approaches to differential extraction for sexual assault evidence

Many forensic laboratories face growing demands for the processing of DNA evidence from sexual assault investigations. In these cases, evidence collected from the crime scene or from the victim in the form of a Sexual Assault and Evidence Collection Kit (SAECK) typically contains a mixture of cells from at least two donors. Isolation of DNA contributions to link a sample to an alleged offender requires precise chemical treatment of each sample with the goal of separating epithelial cells from non-sperm cells. Currently, the vast majority of laboratories employ differential chemical lysis methods that require lengthy incubations and several manual steps, preventing complete automation. Numerous alternative methods for the differential extraction (DE) of sexual assault evidence have been developed to provide a solution to the growing backlog of samples observed in the US and other countries. Here, we will discuss the predominant methodology for the DE of DNA from sexual assault samples and review alternative approaches from literature. We illustrate three criteria that provide a measure of success in performing these types of chemical separations and examine all methods based upon these expectations. We conclude by providing some general insight into the application of DE techniques in forensic laboratories and discuss the potential future directions of alternative technologies.

Effect of microfluidic processing on the viability of boar and bull spermatozoa

The use of microfluidics in artificial reproductive technologies for manipulation or assessment of spermatozoa is unique in the sense that it is not always an end point measurement and the sample may be used afterward. During microfluidic processing, spermatozoa are exposed to shear stress, which may harm viability and functioning of spermatozoa. The shear stresses during general microfluidic processing steps were calculated and compared to estimated shear stresses during ejaculation. The viability of boar and bull spermatozoa after microfluidic processing was studied and compared to the typical handling method (centrifugation) and to a control (the sample in a tube at the same temperature). The boar spermatozoa showed a small but significant decrease in viability of 6% after microfluidic handling. Bull spermatozoa proved to be less susceptible to shear stress and were not significantly affected by microfluidic processing. These data indicate that the impact of microfluidic processing on the viability of boar and bull spermatozoa is less than the literature values reported for flow cytometry and comparable to the impact of centrifugation.

Towards a better testicular sperm extraction: novel sperm sorting technologies for non-motile sperm extracted by microdissection TESE

Non-obstructive azoospermia (NOA) is the most severe form of male factor infertility. It is characterized by a lack of spermatogenesis in the seminiferous tubules. Microdissection testicular sperm extraction (microTESE) has significantly improved testicular sperm retrieval rates compared to conventional techniques for NOA. Following testicular biopsy, the sperm is usually non-motile and contained within seminiferous tubules requiring extensive laboratory processing to find individual sperm sufficient for artificial reproductive technologies (ART). Current techniques include mechanical and enzymatic processing which is time-consuming and often damaging to sperm. We review novel techniques that may help improve sperm retrieval rates after microTESE including microfluidics (dielectrophoretic cell sorting, spiral channel sorting, and pinched flow fractionation), fluorescence-activated cell sorting (FACS), and magnetic-activated cell sorting (MACS).

Forensic Spermatozoa Detection

Semen is crucial evidence for some sex crimes, with its sole confirmation being sperm detection. The success of sperm detection is dependent on all levels of preanalytic and analytic procedures. Specimen collection must be performed by well-trained and competent forensic physicians as well as forensic nurses, with preservation done properly before laboratory transfer. Laboratory procedures should consider archival sperm identification, by visualization, with adequate amounts separated from other cells to obtain male DNA profiles. Differential extraction is robust and accepted as the forensic standard but is time consuming and may result in male DNA loss. Thus, alternative methods and microdevices have been developed. Challenges in sperm isolation from vaginal or buccal epithelium mixes and discrimination in multiperpetrator cases have been overcome by single-cell profiling; however, problems inherent in identical twin discrimination and azoospermia have yet to be solved. Epigenetics and future molecular biomarkers may hold the key; therefore, all laboratory processes must consider DNA and RNA protection. Long-term specimen preservation should be done when possible in light of future confirmatory tests.

Improved resolution of mixed STR profiles using a fully automated differential cell lysis/DNA extraction method

Sexual assault evidence often contains sperm cells, which are typically separated from nonsperm cells using manual differential lysis procedures. The goal of this study was to evaluate the automated QIAGEN QIAcube for this purpose and to compare it to manual QIAGEN and manual organic differential methods using DNA yields and STR profile data for assessment. DNA yields were determined by qPCR, followed by multiplex STR amplification, CE analysis, and mixture interpretation. The automated method was capable of effective cell separation, producing DNA yields sufficient for STR amplification. Further, sperm fraction human:male DNA ratios from the QIAcube samples were consistently closer to the desired 1:1 and STR profiles were less likely to result in mixtures, with 6-8× fewer female alleles detected (median 1.5 alleles). Ultimately, using the QIAcube for automated differential processing of semen-containing mixtures reduces the need for downstream mixture interpretation and improves STR profile quality with substantially less hands-on time.

Separation of spermatozoa from erythrocytes using their tumbling mechanism in a pinch flow fractionation device

Men suffering from azoospermia can father a child, by extracting spermatozoa from a testicular biopsy sample. The main complication in this procedure is the presence of an abundance of erythrocytes. Currently, the isolation of the few spermatozoa from the sample is manually performed due to ineffectiveness of filtering methods, making it time consuming and labor intensive. The spermatozoa are smaller in both width and height than any other cell type found in the sample, with a very small difference compared with the erythrocyte for the smallest, making this not the feature to base the extraction on. However, the length of the spermatozoon is 5× larger than the diameter of an erythrocyte and can be utilized. Here we propose a microfluidic chip, in which the tumbling behavior of spermatozoa in pinched flow fractionation is utilized to separate them from the erythrocytes. We show that we can extract 95% of the spermatozoa from a sample containing 2.5% spermatozoa, while removing around 90% of the erythrocytes. By adjusting the flow rates, we are able to increase the collection efficiency while slightly sacrificing the purity, tuning the solution for the available sample in the clinic.

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.

Separation of sperm and epithelial cells based on the hydrodynamic effect for forensic analysis

In sexual assault cases, forensic samples are a mixture of sperm from the perpetrator and epithelial cells from the victim. To obtain an independent short tandem repeat (STR) profile of the perpetrator, sperm cells must be separated from the mixture of cells. However, the current method used in crime laboratories, namely, differential extraction, is a time-consuming and labor-intensive process. To achieve a rapid and automated sample pretreatment process, we fabricated a microdevice for hydrodynamic and size-based separation of sperm and epithelial cells. When cells in suspension were introduced into the device's microfluidic channels, they were forced to flow along different streamlines and into different outlets due to their different diameters. With the proposed microdevice, sperm can be separated within a short period of time (0.5 h for a 50-μl mock sample). The STR profiles of the products in the sperm outlet reservoir demonstrated that a highly purified male DNA fraction could be obtained (94.0% male fraction). This microdevice is of low-cost and can be easily integrated with other subsequent analysis units, providing great potential in the process of analyzing sexual assault evidence as well as in other areas requiring cell sorting.