X-Message-Number: 4969
Date: Thu, 12 Oct 1995 01:58:27 -0700 (PDT)
From: Doug Skrecky <>
Subject: variations on a straight freeze

     Thanks to Joseph Strout with his analysis of my variations on a
 straight freeze. He is correct that the quick freeze technique will be
 fully effective only for a thin layer on the outside of the brain. 
 However even in the center of the brain cooling rates of over 1 C should
 I think still be possible, which should help limit ice crystal damage
 somewhat. I would like to reemphasize that the hamburger technique is not
 a usuable option since the result would be (as Mike Darwin says) a tissue
 homogenate. The food industry uses quick freezing of foods to help retain
 their palatibility. 
     As for the salami technique being impossible to impliment please
 refer to the latest issue of the Immortalist. Special tools are required
 for this to work, but it does work. 
     However with only the salami technique both avoiding tissue fixation
 (microwave & freeze substitution) and freezing without cryoprotectant
 (quick freezing) it is a shame that even though this may be the best
 technique it would still never see use due to it's very poor visual
 acceptiblity to potential patrons. On goes the thinking cap.... Uh, the
 food industry injects calcium chloride into meat to tenderize it..... I
 got it! Inject cryoprotectant into an otherwise intact brain with a
 thousand very small diameter needles. As the needles are slowly inserted
 into the brain cryoprotectant is pumped through them leaving a trail of
 this solution along the entire length of each needle. 

 Note: Permission is again here given for the following to be reprinted in
 any cryonics related publication that wishes to do so: 

                    VARIATIONS ON A STRAIGHT FREEZE
                           By Doug Skrecky

     With the circulatory system being unavailable in many cases for
 cryoprotective perfusion what are the available options? The major
 arteries can be injected with cryoprotectant, but with the capillaries
 being blocked by coagulated blood no circulation is possible. Something
 better is needed. 
     Based on my expectations of the quality of the treated tissue I group
 the following 6 techniques in order of increasing merit: 

 1. (Worst) Hamburger technique: Pretend that cryoprotectant perfusion was
 done and do the usual slow freeze. The result is hamburger. 

 2. Microwave technique: Microwaves can rapidly penetrate and fix tissue. 
 Pack the brain with ice and place in a microwave with a turntable, which
 has been top rated by Consumer's Reports for uniformity of heating. Cook
 using pulses of radiation until well done. Treat brain with
 cryoprotectants by storing it in a concentrated cryoprotectant solution
 for a week. Store in freezer until needed. (Journal of Neuroscience
 Methods 53:81-85 1994)

 3. Freeze Substitution technique: Freeze brain slowly to -10 C to limit
 ice crystal damage. Pickel brain in an anhydrous silica gel desiccant
 packed alcohol based cryoprotectant solution till ice has all melted. 
 Baste in liquid nitrogen. 

 4. Quick Freeze technique: Freeze brain slowly to -10 C to partly
 dehydrate cells and reduce subsequent intracellular ice crystal
 formation. Then dunk in liquid propane/butane cooled with dry ice. Rapid
 freezing limits extracellular ice crystal growth. Then slowly cool
 further with liquid nitrogen vapour to limit the formation of cracks due
 to increased tissue brittleness. (Biophysical Journal Vol.64 1908-1921
 1993 & Cryobiology Vol.31 506-515 1994)

 5. Salami technique: Cut the brain into slices 5 mm thick. 
 Cryoprotectants can rapidly diffuse into thin slices of tissue, thus
 preserving them well when they are frozen. The result is a Dagwood
 sandwich. (eg: see Cryobiology 24:120-134 1987)

 6. (Best) Needle technique: Inject cryoprotectant into the brain via many
 very fine needles which are slowly inserted into the brain. Then do a
 quick freeze. 


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