Microfluidic chip as a promising evaluation method in assisted reproduction: A systematic review

Abstract

The aim of assisted reproductive technology (ART) is to select the high-quality sperm, oocytes, and embryos, and finally achieve a successful pregnancy. However, functional evaluation is hindered by intra- and inter-operator variability. Microfluidic chips emerge as the one of the most powerful tools to analyze biological samples for reduced size, precise control, and flexible extension. Herein, a systematic search was conducted in PubMed, Scopus, Web of Science, ScienceDirect, and IEEE Xplore databases until March 2023. We displayed and prospected all detection strategies based on microfluidics in the ART field. After full-text screening, 71 studies were identified as eligible for inclusion. The percentages of human and mouse studies equaled with 31.5%. The prominent country in terms of publication number was the USA (n = 13). Polydimethylsiloxane (n = 49) and soft lithography (n = 28) were the most commonly used material and fabrication method, respectively. All articles were classified into three types: sperm (n = 38), oocytes (n = 20), and embryos (n = 13). The assessment contents included motility, counting, mechanics, permeability, impedance, secretion, oxygen consumption, and metabolism. Collectively, the microfluidic chip technology facilitates more efficient, accurate, and objective evaluation in ART. It can even be combined with artificial intelligence to assist the daily activities of embryologists. More well-designed clinical studies and affordable integrated microfluidic chips are needed to validate the safety, efficacy, and reproducibility. Trial registration: The protocol was registered in the Open Science Frame REGISTRIES (identification: osf.io/6rv4a).

Keywords: assisted reproductive technology; evaluation; female reproduction; microfluidic chip; microfluidics.

FIGURE 1

Overview of conventional assisted reproductive technology procedures. Gametes (sperm/oocytes) are directly obtained from males and females or extracted through in vitro manipulations. Matured oocytes are incubated with competent sperm to produce embryos in a process called in vitro fertilization. Fertilization and ongoing pregnancies can also be achieved for sperm that might not be competent using intracytoplasmic sperm injection. In vitro‐produced embryos are selected and transferred to the uterus of recipients. Alternatively, gametes, embryos, ovarian and testicular tissues can be cryopreserved and stored in biobanks.

FIGURE 2

(a) PRISMA flow diagram. (b) Histogram of eligible publications by year. (c) The 55 most used keywords to reflect diverse topics in microfluidics.

FIGURE 3

Examples of microfluidic strategies for sperm assessment. (a) The most used method to test for positive sperm rheotaxis. The immotile/dead spermatozoa (gray) are washed out with the flow, while the motile ones swim through the flow. (b) Generation of a uniform concentration gradient for chemotaxis assays. (c) A glass substrate with implemented microheaters to induce thermotaxis. (d) A chemotactic structure that simulates the entire female genital tract. (e) A microfluidic device that mimics the main reproductive tract components (bottom), including the micro‐scale grooves in the cervical surface (upper). (f) Probes with angles of 20°, 30°, and 50° were fabricated to form a uterotubal junction and trap sperm. (g) The Spermometer consists of two main channels. The spermatozoa are trapped in the interconnecting channel because of the higher fluid flow in the bottom channel. The electrode arrays are used for differential impedance analysis. (h) The microfluidic device was designed to perform single sperm whole‐genome amplification. (i) The spermatozoa are optically trapped by the beam waist of a highly focused Gaussian beam (left and middle). The spermatozoa undergo rotation and switchback oscillation when the laser beam waist is closer to the chamber wall.

FIGURE 4

Schematic representations of microfluidic platforms for oocyte examination. (a) Visualization of a deformation microcytometer with a trapped oocyte. (b) An external force is applied to push the oocytes, and the force sensor measures the reaction force. (c) The forces deform the oocytes and deflect three supporting posts. Force balance on cells under indentation and the post deflection model (inset). (d) The mechanical characteristics of oocytes in an open environment. The vibration‐induced flow serves as a cell transport mechanism. (e) Single‐cell detection with fluorometric readout. (f) Microfluidic platforms with integrated local temperature control system and capture module.

FIGURE 5

Schematic representations of microfluidic platforms for embryo analysis. (a) The concentration gradient of dissolved oxygen is formed by embryo respiration in a hemispherical area (top). The explanation for the spherical diffusion theory (bottom)., (b) Layout of electrochemical electrodes to estimate in situ oxygen consumption. (c) A droplet containing embryos and magnetic beads merges with a reagent solution under magnetic force.

FIGURE 6

Microfluidic platforms in other applications. (a) An illustration of a microfluidic gradient generator with a pressure balance zone. (b) A schematic of the thermotaxis assay chip for nematodes. The arrows represent the flow directions in the fluid and vacuum channels. (c) An illustration of the lung‐on‐a‐chip working principle., (d) 3D villus‐like structures in a gut‐on‐a‐chip. Lateral arrows indicate lateral stretching by the side chambers. (e) A schematic showing an artificial tubular hydrogel actuator structure and the motion of an object driven by an applied near‐infrared light.