Dr. Masashige

Innovator in Assisted
Reproductive Technology

Dr. Kuwayama's

Dr. Masashige Kuwayama–a renowned cryobiologist, the visionary behind the Cryotec Method and Chairman of Reprolife–has revolutionized cryopreservation in Assisted Reproductive Technology (ART). With breakthrough advancements in solution composition, device design, and simplified protocols for vitrification, he has significantly improved success rates, not only for embryos but also for oocytes, which are particularly sensitive to cryopreservation.

In 1991, he made history by successfully vitrifying mammalian blastocysts, marking a new era in reproductive technology. Driven by excellence, he achieved human oocyte vitrification in 1999, expanding reproductive options.

Dr. Kuwayama's early recognition of the need for a safer oocyte cryopreservation method stems from his desire to provide more opportunities for women in their late 30s facing age-related infertility. By offering flexibility in lifestyle and family planning, his method addresses their specific needs.

Additionally, his approach has proven invaluable for women undergoing cancer treatment, particularly those with blood cancer, who often experience loss of ovarian function and subsequent infertility as a side effect. Through pre-emptive oocyte freezing, these women now have the possibility of future conception. His vitrification methods, initially pioneered in Japan, have become global standards, improving success rates worldwide.

Dr. Kuwayama's latest accomplishments include a next-generation vitrification method and the introduction of Cryotec Ready to Use (RtU) products, simplifying the process with improved solutions and record-high viscosity.

With unwavering dedication, Dr. Kuwayama continues to drive technological advancements, striving for the highest rates of oocyte and embryo survival while ensuring a stress-free vitrification process for embryologists.


Achieved successful cryopreservation of bovine in vitro fertilized blastocysts using vitrification method


Successfully implemented vitrification for bovine oocytes


Successfully applied the minimum volume cooling (MVC) technique to practically implement human oocyte cryopreservation using the vitrification method


Developed a vitrification kit for human oocytes


Introduced the Cryotop method


Established the world’s first human egg bank in Japan, focusing on cancer patients


Pioneered the establishment of the first human egg bank in the USA


Achieved successful pregnancies and deliveries using vitrified oocytes in the United States, South America, and Europe


Developed the Cryotip method


Successfully vitrified human ovarian tissue


Created HPC based vitrification solution along with The Cryotec Method


Developed the Cryotec Ready to Use series

Dr. Kuwayama’s

Vitrification revolutionized cell freezing–offering a faster and more accessible method than previous ones. However, it demands meticulous skills and adherence to strict protocols.

In recognizing the skill-intensive
nature of vitrification,
Dr. Kuwayama has dedicated over
30 years of his life to the
continuous improvement of
his vitrification method,
The Cryotec Method.

His aim was to provide a technique that ensures consistent results for everyone, addressing concerns about variations and stresses faced by embryologists.

The Cryotec Method's 
Solution Modifications

In the Cryotec Method, Dr. Kuwayama aimed to alleviate the stress of working under strict time restrictions for embryologists. He achieved this by modifying the solutions, which reduces cytotoxicity from cryoprotective agents enhancing the chances of successful preservation and allows for more time flexibility in each step.

in Device Design

Dr. Kuwayama's work in the Cryotec Method not only brought advancements in solution composition but also revolutionized device design. Dedicated plates for vitrification and warming improved simplicity and enhanced cell protection through slower osmotic changes. Additionally, Dr. Kuwayama's emphasis on ease of handling and safety led to the creation of the Cryotec (freezing device), featuring a square-shaped handle for convenient labeling and a comfortable grip for embryologists.

Streamlining Vitrification

In traditional methods, the step involving Vitrification Solution (VS) often showed inconsistencies among operators' skills. It was crucial to ensure the substitution of Equilibrium Solution (ES) with VS around cells before the cooling step with liquid nitrogen. However, judging this substitution was ambiguous and subjected to strict time restrictions. Thanks to Dr. Kuwayama's innovative development, the Cryotec Method's design enables even junior embryologists to easily identify the substitution from ES to VS with the specific gravity of each solution.

Droplet Minimization

In the Cryotec Method, Dr. Kuwayama eliminated the need for minimizing the volume of Vitrification Solution (VS) at loading step to reduce surface tension. Through improved solutions and devices, Dr. Kuwayama achieved safer vitrification without the need for this measure.


Is there any time restriction for the ES step?

Only the maximum time is fixed; for Cryotec products, it is 15 minutes for oocytes and blastocysts and 12 minutes for cleavage-stage embryos. For Cryotec Ready to Use products, it is 13 minutes for oocytes and blastocysts and 10 minutes for cleavage-stage embryos.

As there is no minimum time, you can proceed to the VS step when the volume of oocyte/embryo recovers to the original volume, the volume before the start of freezing, even if the time is less than the maximum time. On the other hand, even if the volume has not completely recovered, be sure to proceed to the VS step when the maximum time is reached.

Are there any time restrictions on the VS1/VS2 steps?

No. In the VS1 step, proceed to VS2 when oocytes/embryos stop floating. In the VS2 step, confirm re-shrinking of oocytes/embryos and proceed to loading. You do not need to worry about time in any step, so please focus on observing oocytes/embryos.

What is the appropriate inner diameter of the glass pipette used for freezing and thawing?

Use the one with a size suitable for the oocyte/embryo to be frozen. We recommend 140 to 150 μm for oocytes/cleavage-stage embryos and 200 to 250 μm for blastocysts.

What should I do if no shrinkage occurs in VS?

If shrinkage is seen in ES, shrinkage should also occur in VS. However, it may be difficult to see depending on the angle of oocytes/embryos. So, stir the surroundings with a pasteur pipette and check them from multiple directions.

What is the appropriate size of the droplet when loading?

A droplet diameter should be 300 to 700 μm. As the width of Cryotec sheet is 1400 μm, it should be approximately 1/3 of it at minimum and half of it at maximum.


Blastocoele expansion status at time of transfer affects clinical pregnancy
outcome following single frozen euploid blastocyst transfer
Lee C.S.S.
Alpha Fertility Centre (Malaysia)
Paternal Age Does Not Influence Euploidy in Blastocysts
Low S.Y.
Alpha Fertility Centre (Malaysia)
100% Post-warmed Survival Rate for 1491 Blastocysts
in Alpha Fertility Centre
Low S.Y.
Alpha Fertility Centre (Malaysia)
The Cryotec Method yields 100% post-thaw survival rate,
high clinical pregnancy and implantation rates in euploid blastocysts
Low S.Y.
Alpha Fertility Centre (Malaysia)