Application of femtosecond laser microsurgery in assisted reproductive technologies for preimplantation embryo tagging

Assessment of the zona pellucida microdissection on its thickness in mammalian embryos

The zona pellucida (ZP) is a dynamically changing object that plays an important role during the preimplantation stage of embryogenesis. The ZP thickness may affect the implantation success and pregnancy rate, it is considered as a prognostic factor in a number of studies. The study was aimed to assess the dynamic changes in the mouse embryonic ZP thickness after laser assisted hatching (LAH) that involved breaching the ZP integrity at the blastocyst stage. Femtosecond laser pulses were used to perform the zona microsurgery. The zona thickness was measured both at the stage of blastocyst microsurgery (~Е3.5, i.e. 3.5 days of embryogenesis) and at the hatching stage (~Е5). Significant differences in the ZP thickness were revealed in the control group of embryos: from 6.21 µm (Е3.5) to 5.4 µm (Е5). The changes in thickness from 6.6 µm (Е3.5) to 6.2 µm (Е5) observed in the group subjected to LAH were non-significant. Tracing the ZP thickness of a particular embryo from the blastocyst stage to the hatching stage made it possible to estimate the thinning coefficients in the experimental and control groups. The findings that indicate lower tensile strength of the zona in case of LAH can provide the basis for further research on the ZP properties in case of using the embryo cryopreservation protocols.

From Zygote to Blastocyst: Application of Ultrashort Lasers in the Field of Assisted Reproduction and Developmental Biology

Although the use of lasers in medical diagnosis and therapies, as well as in fundamental biomedical research is now almost routine, advanced laser sources and new laser-based methods continue to emerge. Due to the unique ability of ultrashort laser pulses to deposit energy into a microscopic volume in the bulk of a transparent material without disrupting the surrounding tissues, the ultrashort laser-based microsurgery of cells and subcellular components within structurally complex and fragile specimens such as embryos is becoming an important tool in developmental biology and reproductive medicine. In this review, we discuss the mechanisms of ultrashort laser pulse interaction with the matter, advantages of their application for oocyte and preimplantation embryo microsurgery (e.g., for oocyte/blastomere enucleation and embryonic cell fusion), as well as for nonlinear optical microscopy for studying the dynamics of embryonic development and embryo quality assessment. Moreover, we focus on ultrashort laser-based approaches and techniques that are increasingly being applied in the fundamental research and have the potential for successful translation into the IVF (in vitro fertilization) clinics, such as laser-mediated individual embryo labelling and controlled laser-assisted hatching.

Controlled hatching at the prescribed site using femtosecond laser for zona pellucida drilling at the early blastocyst stage

PURPOSE

To study whether the application of femtosecond laser pulses for zona pellucida (ZP) drilling of blastocysts at the embryonic or abembryonic poles can promote hatching to start immediately through the hole formed and ensure high hatching rates and embryo viability.

METHODS

Mouse blastocyst (E3.5) ZP were microdissected with femtosecond laser pulses (514-nm wavelength, 280-fs pulse duration, 2.5-kHz repetition rate) close to the trophoblast or inner cell mass (ICM). The sizes of the holes formed were in the range of 4.5-8.5 μm. Additional longitudinal incisions (5-7-μm long) on either side of the hole were created to determine whether hatching had started at the correct position. Embryos post-laser-assisted ZP drilling and intact embryos were cultured under standard conditions for 2 days; embryo quality was assessed twice daily. The hatching rates and in vitro and in vivo implantation rates (only for embryos with ZP dissected close to the ICM) were estimated.

RESULTS

Femtosecond laser-assisted ZP drilling at the early blastocyst stage facilitated embryo hatching to start at the artificial opening with probability approaching 100%. Despite the artificial opening's small size, no embryo trapping during hatching was observed. Both experimental groups had higher hatching rates than the control groups (93.3-94.7% vs. 83.3-85.7%, respectively). The in vitro implantation rate was comparable with that of the control group (92.3% vs. 95.4%). No statistically significant differences were obtained in the in vivo implantation rates between the experimental and control groups.

CONCLUSIONS

Blastocyst-stage femtosecond laser microsurgery of ZP is fast and delicate and enables the hatching process to be initiated in a controlled manner through a relatively small opening, with no embryo trapping.

Preimplantation genetic testing as a component of root cause analysis of errors and reassignment of embryos in IVF

The risks of embryo/gamete mix-up are a threat to the integrity of the IVF process, with significant implications for affected families. The use of preimplantation genetic testing through single-nucleotide polymorphism array or next-generation sequencing technology can help to identify, characterize and ultimately help, in some cases, to find the root cause, and to mitigate the extent of these errors for a given patient or laboratory.

Recent progress in optical probing and manipulation of tissue: introduction

This feature issue of Biomedical Optics Express represents a cross-section of the most recent work in tissue optics, including exciting developments in tissue optical clearing, deep tissue imaging, optical elastography, nanophotonics in tissue, and therapeutic applications of light, amongst others. A collection of 33 papers provides a comprehensive overview of current research in tissue optics, much of it inspired and informed by the pioneering work of Prof. Valery Tuchin. The issue contains three invited manuscripts and several mini-reviews that we hope will benefit researchers in this exciting area.