Instructions on Cryo-Cup Grinder
The Cryo-Cup Grinder is a mortar and pestle specifically designed to pulverize and powder soft plant and animal tissue samples at dry-ice or, preferably, liquid nitrogen temperatures. It consists of a double-wall insulating cup into which is embedded a stainless steel, semi-circular bowl or mortar. Up to 5 grams of the tissue is placed in the pre-cooled mortar and ground to a fine powder with a special pestle made of non-heat conductive plastic. Two different-sized pestles are provided for a variety of applications.
Selecting the correct size pestle: For samples over 1 gram start with the smaller polypropylene ball (1 3/8 inch diameter). Use the larger ball (1 7/8 inch diameter) with smaller samples. The larger ball gives a finer grind.
Cooling the Cryo-Cup Grinder
Using a Dewer ("Thermos") flask as the container, draw about a cup of liquid from a liq N2 tank. Slowly pour liq N2 into the stainless steel mortar. At first, liq N2 will quickly evaporate off the cup’s surface. Continue to slowly add liq N2 until a small amount of liq N2 remains in the stainless steel cup. The Cryo-Cup Grinder (CCG) is now cold enough to proceed with grinding. There is no need to have a puddle of liq N2 in the CCG. The cup should retain its cold temperature long enough to complete the grinding. Further addition of liq N2 may be needed if you are working up multiple samples.
The pestle (the black ball plus black handle), made of chemically inert plastic, is a poor heat conductor. That is the intent of the design. The pestle will not transfer heat to the sample during grinding. Do not try to thoroughly pre-cool the pestle. At most, cool its surface briefly with liq N2 - this is good enough. Deep cooling the pestle will cause stress cracks and eventual failure of the pestle ball.
There is an exception to this advice. If you have purchased the accessory solid stainless steel ball, it should be thoroughly cooled before use. A stainless steel ball on the pestle is only needed if you are processing many samples and the grinding process goes on for an extended time.
The tissue sample MUST BE HARD FROZEN in liq N2 before attempting to grind. Otherwise, the wet tissue will stick to the cold motar and make grinding difficult.
Begin with a downward, circular motion of the pestle inside the cup. Sometimes it will be necessary to gently hammer the sample with the pestle to break it up into smaller sized pieces so that the circular motion of the pestle can finish the grinding. Work quickly in transferring the ground sample for further processing. Once removed from the stainless steel cup surface it can quickly thaw.
Cleaning the Cryo-Cup Grinder
Remove the stainless steel insert of the mortar by turning the cup upside down and rapping the cup against a table top. Prompt washing and drying of all parts is recommended. Despite the name "stainless steel", it can corrode when in contact with biomaterial. If desired washed parts can be autoclaved. Another way to decontaminate and sterilize the Crypcup is to soak it in a 1 to 10 dilution of household bleach for 5 minutes. Rinse well afterward with distilled water.