[Histonet] Semi-thin Epon Sectioning with wrinkles

[Fred Ross-Cisneros]

Dear All,
 
I'm cutting cross-sectional profiles of human optic nerve processed for
and embedded in epon (plastic) on a DuPont-Sorvall MT-2B ultramicrotome.
The tissue is 4 mm wide (2mm thick). I am using a diamond knife for
semi-thin sectioning (Histoknife by DDK) and cutting these sections
usually at 0.5 microns (but I've tried cutting thinner). I'm getting
lots of wrinkles in the sections and would like to know if anyone has a
technique of flattening such large sections on a glass slide. I've tried
chloroform vapor with no success. I have also kept the sections on the
water bubble longer (glass slide on a hot plate, of course). I am aware
several factors (which I have tried to control for) can contribute to
wrinkling in plastic sectioning (i.e.-soft block, dirty or dull knife,
cutting speed, etc., etc.). One factor I cannot get around is the large
block face. I personally feel the block is quite hard (brittle).
 
I look forward to your recommendation(s).
 
Thank you.
 
Fred N. Ross-Cisneros
Neuro-Ophthalmology Lab
USC Keck School of Medicine and
Doheny Eye Institute