Blastocyst Vitrification

S.SASIKUMAR ,M.SS.,(PhD)Senior Embryologist

NOVA IVI FERTILITY,Chennai

Vitrification• Process that produces a glasslike

solidification of living cells that completely avoids ice crystal formation during cooling. It completely avoids ice crystal formation in cryopreserved cells during warming to recover the cells for biological applications

Vitrification TechniquesVitrification Techniques

• Traditional Vitrification

(1998- early 2000s)

• Ultrarapid vitrification

(2000-...today)

Problems Associated with Traditional Vitrification Procedures

• High levels of cryoprotectants are toxic to embryos • (4-10 M compared to 0.5-1.0M)

• Procedure must be performed at 4oC• Technically demanding

Advantages of Ultra-Rapid Vitrification

• Increases in cooling rates alleviates toxicity of high levels of cryoprotectants

• Can be performed at room temperature or 37oC

Vitrification solutions

DMSO+Acetamide+ propylene glycol

Ethylene glycol+ Ficoll+Sucrose

Ethylene glycol+ DMSO

Ethylene glycol+ glycerol

Slow Freezing solutions

DMSO /1-2 PROH + Sucrose

Glycerol+

Sucrose

From Kasai et al. RBM Online 2004

Base medium+

Cryoprotectant

Differences of slow freezing and vitrification

Slow-freezing• low levels of

cryoprotectants• slow controlled rates

of cooling (0.3oC/min)• slow dehydration to

minimize ice-crystal formation

• takes hours

Vitrification• high levels of

cryoprotectants• very fast cooling rates• (~20,000oC/min)• fast cooling rates result in

solidification of solution into glass-like structure (no crystallization)

• takes seconds

Vitrification Slow cooling

Control of solute penetration Yes No

Control of dehydration rate Yes No

Duration out of the incubator 10min. 3 hrs.

Prolonged temperature shock No Yes

Fracture of ZP No Possible

Capture by growing ice crystals

No Possible

Equipment and running costs Inexpensive Expensive

Vitrification & Slow-cooling

Kuleshova et al. F&S 2002

Variables in Vitrification

• Cooling &warming rates:Ideal vitrification protocol must pass rapidly through the critical temperature zone of 15 to – 5ºC to decrease chilling injuries. High warming rates by directly plunging cells into the warming solution is suggested (-196 to 37ºC)

Variables in Vitrification• Concentration of the cryoprotectant:

To achieve high cooling rates requires the use of high concentrations of the cryoprotectant solution which depresses ice crystal formation, so a critical concentration is required but in some cryoprotectants, this minimal concentration (Cv) can lead to either osmotic or chemical toxicity

Variables in Vitrification• Sample size and carrier systems

• Sample size should be minimized to reduce the duration of vapour coat and to increase the cooling rate, minimizing the volume of the vitrification solution as much as possible is necessary to facilitate vitrification by higher cooling rates

• To minimize the volume of the vitrification solution special carriers are used for vitrification process

** Open pulled straws ** Flexipet- denuding pipette ** Microdrops ** Electron-microscopic copper grids ** Hemistraw system ** small nylon coils or nylon mash ** Cryotop,cryotip ** Cryoloop

Carriers for vitrification

Cryotop

Cryotip

Cryotip

Kuwayama et al.,RBM Online 2005

Cryoloop

Hampton Research, Laguna Niguel, CA, USA

Nylon loop

(20µm wide; 0.5-0.7 mm in diameter)

Thin film of cryoprotectant solution by surface tension

Embryos are placed by pipette

Advantages of Cryoloop Vitrification

• Lack of thermoinsulating layer maximizes

heat transfer (>20,000oC/min)

• Easy manipulations

• Constant visualization of embryo

• Cryoloop stored within cryovial

• Procedure is performed at 37oC

Necessity of blastocyst vitrification ?

• Increasing application of BT especially for some selected cases results with supernumerary blastocysts for freezing to increase cumulative pregnancy rates per oocyte retrieval

• A reliable procedure for the cryopreservation of blastocysts is needed, because after fresh ET, only small number of supernumerary blastocysts are likely to be available for cryopreservation

• Based on the published cochrane data (2008), vitrification appears to result in significantly higher survival and pregnancy rates

Blastocyst vitrification

• First pregnancy after human blastocyst vitrification was achieved by Yokota et al., HR 2000

• EG- based vitrification solutions are widely used as it has a low toxicity with rapid diffusion into the cell through ZP and cellular membrane

• 1st. Vit.sol. EG+DMSO• 2nd. EG+DMSO+Ficoll+ Sucrose, • Warming: Decreasing concentrations of Sucrose sol.

are preferred• Concentration of cryoprotectants are decreased to

7.5% from 25% over the years of experience

Blastocyst vitrification

• Is it the most effective and successful method to cryopreserve embryos at blastocyst stage???

Faster re-expansion after thawing with vitrification method

Slow Freezing Vitrification

No of. blastocysts

72 81

Survival Rate(%) 56.9 (41/72) 84 (68/81)*

Higher survival rates with blastocyst vitrification

Artifical shrinkage by microneedle

Artifical shrinkage by laser

Large blatocoele of more developed blastocysts may disturb the efficacy of vitrification due to

inappropriate Dehydration and permeation of cryoprotectant, which may cause ice crystal formation in the rapid cooling and warming steps of vitrification. Ice crystal formation can be avoided by reducing fluid content of the blastocoele of more

developed blastocysts

RESULTS• Vitrification as a cryopreservation method

has many primary advantages and benefits based on the published data

• Vitrification protocols are now starting to enter the mainstream of human ART

• The reports of successfully completed pregnancies following vitrification are encouraging for further research

• More studies on vitrification and thawing procedures are needed to develop more efficient and optimal vitrification methods

Concerns regarding Vitrification• LN2 still remains to be a potential source of contamination since the

technique is based on direct contact between the vitrification solution containing cryoprotectant agents and LN2. So from a clinical point of view:

• Is there a need to sterilize LN2? How is it possible to maintain its sterility

• Cross contamination with viruses?? ( No publication since 1985, about 450 publications)

• Closed systems should be used in clinical human IVF in the future to avoid this concern.(Like CBS HS vitrification straws, Cryotip……) New clinical trials with safer closed systems should be applied

• Low toxicity vitrification solutions must be designed in the future

• Genetical structure of the vitrified cell?? Chromosal abnormalities, gene expressions ...... More studies are needed to prove the safety of the technique

Successful Vitrification