We are doing the slow freezing using planar.we have been using cook freezing media and its protocol. the freezing program starts at + 22 degree celsius and the seeding is done manually at -6.5 degrees and then held for 10 minutes. the process continues till -35.0 degrees at a rate of -00.30 C/min. then it plunges rapidly to -150.0 degrees at a rate of -50.0 C/min.
We have always control deviation at 93-97%( some where in between) and it has always been so. at 97% it is only at -38 degrees. so I think the problem lies there. mostly we have less than 50% survival.
I was curious as to why it happens. our post thaw survival rates and FET results have always been dismal. the explanation given to me by the service personnel was that this control deviation will happen most of the time as at this time the chamber drops its temp rapidly. he says it is not a problem with the machine or anything. does anyone have a clue as to what could be the reasonand if so how can it be corrected. thanks in advance
The Planer freezer provides a control deviation message if the actual chamber temperature deviates from the required programmed temperature. This may occur at ramp changes from slow to fast cooling (e.g. your ramp of - 0.30 C/min to -50.0 C/min) if the nitrogen supply is not capable of supplying an adequate flow of liquid. Under optimum conditions, when the nitrogen supply is good, the ramp change will be handled correctly and no control deviation alarm activated. However, an alarm may occur if the liquid nitrogen supply is not at the correct pressure (either 22 psi or 5 psi depending on configuration) or, if using a Planer pump, the filter requires replacing or finally if the dewar (MVLAB 20 / 30) requires thawing and cleaning.
Perhaps the more crucial point to note is that the control deviation you describe will not be causing an effect on the post thaw survival rates and FET results as it occurs in the plunge section of your program where it is getting to the lowest temperature as fast as it can. If you experience lower than expected results you may need to investigate further than this problem.
(Planer are assuming the ramp is completed with no further issues and the deviation has no noticeable effect on the graph)
Kind regards Nick Pattenden - 02 September 2008
Just complete the program at -35 degree or -40 degree, then direcly place the straw to liquid nitrogen dewer. Weihua Wang - 25 August 2008
