Staining, Histochemistry and Histotechnology
(Frequently Asked Questions)
Dr. John A. Kiernan
Department of Anatomy
and Cell Biology
The University of Western Ontario
How do you cut flat sections of materials embedded in poly(glycol methacrylate) (GMA) and other resins, for light microscopy?
I always use glass knives (standard or Ralph type) but using tungsten carbide should not be a problem.
Cutting speed is (in my experience) critical, and have found that very slow (almost to the point of stop!) will provide a crease free section. This is where patience is a virtue: tedious but worth the wait.
The section may tend to "roll" but this is not a problem, in fact I find this an advantage. Simply remove the section from
the blade and place onto a warm surface (the palm of your hand will suffice) and watch in amazement as the section unfolds (a bit like those fortune fish from many years ago). Then drop the section onto warm distilled water to remove any further folding. It's a bit laborious, but usually best to handle only one section at a time. I hope this is of some help. There are also a few "tricks" with the staining!
MRC Harwell, Oxfordshire, England
I have cut a lot of plastic, and here's what I do:
(1) Cut at about 6-7 microns.
(2) Soak, soak, soak! (about 2-3 hours depending on what kind of polymer).
(3) Use positively charged slides, with Elmer's glue in the waterbath.
(4) Use one of the newer, heavier microtomes (we have the Leica 2035s).
Plastic sections do not ribbon, unless you put a dab of rubber cement on the the top and bottom of the block, but usually we pick them up one section at a time.
Curling is very common. What I do is start the sectioning but do not finish; keep it attached to the block, then you can use a brush or fine forceps and unroll it, pulling at a diagonal. Leaving it attached lets you pull without completely pulling the section off the block. When you have it fairly open and flat, complete the sectioning stroke thereby releasing the section. I used to slide the MMA section onto a spatula, keeping it wet with alcohol, and then slide it off the spatula onto a slide onto a hot plate. Keep dropping alcohol onto to the section and it should flatten out.
GMA is much easier to pick off the block. Do the same thing but keep everything very dry, pick up the section with a fine forceps and drop it onto a water bath and it will flatten out. Scoop onto a slide from the water.