Re: [Histonet] Microwave processing

From:Phil McArdle

   This reply is from a lab microwave vendor; since you're now officially
   forewarned, no flames, please! :-)
   That  said,  for  me, the usual suspect is the paraffin step. From the
   inception  of  microwave  processing,  this  has  always been the most
   problematic  process,  due to paraffin's non-polar nature. Pre-heating
   paraffin  to the operating temperature of the protocol has always been
   extremely  important; if the temperature of paraffin is raised by more
   than  a  degree  or  two  when  tissue  is  present, there is a strong
   potential for artifacts, inconsistency, and other problems.
   Here's  why  there's  a critical difference between merely maintaining
   paraffin   temperature,   and  raising  paraffin  temperature  in  the
   microwave.  Paraffin  does  not  absorb  significant microwave energy;
   microwaves  pass  through  wax  almost  as if it weren't there. So the
   energy  has  to  be absorbed by "something," hence EBS' recommendation
   for  a  Pyrex processing container; Pyrex does absorb small amounts of
   microwave  energy,  transferring  it  to paraffin, maintaining a given
   temperature.  Things  get  a  little  more  delicate  when  using, for
   example,  disposable  plastic  containers  instead  of  Pyrex,  making
   precise pre-heating even more critical.
   Pre-heating  produces  good,  consistent  results,  since  maintaining
   temperature  does  not  expose  patient  samples  to undue energy, but
   RAISING  the  temperature is another matter, requiring long wait times
   and,  significantly,  LOTS  of  excess  energy. Where does this excess
   energy go? All too often, patient samples, which, even after fixation,
   dehydration,  and  clearing,  are  probably  the  most polar materials
   present. In effect, tissue can take the entire "hit."
   Since  most  melted  paraffin  in today's A.P. lab is somewhere around
   60'0C,  if lab personnel skip the pre-heating step, they are using the
   microwave  to  heat  paraffin  14  - 24'0C. Besides taking a VERY long
   time,  this can expose patient samples to WAY too much energy. There's
   also  an unfortunate temptation to raise power output of the microwave
   since it's "taking too long," which may well be the worst thing to do.
   I  know  --  since  we  all use microwaves outside the lab, this whole
   concept  is  very  counter-intuitive, which is why all EBS' microwaves
   have sported door warning labels exhorting users to pre-heat paraffin.
   Preheating   paraffin   to  the  operating  temperature  does  require
   additional  time, and equipment such as an oven or additional paraffin
   pot,  assuming availability of a unit that can be set hot enough, plus
   sufficient  space  and  electrical  power.  On  the  other hand, early
   attempts  at  microwave  heating  of paraffin resulted in questionable
   solutions  like  the  addition  of  marble chips, glass marbles, glass
   discs and other more exotic (and expensive) materials.
   SHAMELESS COMMERCE WARNING: At EBS, we recognized the many benefits of
   the  ability  to   microwave  paraffin  like  any  polar reagent: time
   savings,   convenience,  and  standardization  of  procedures.  So  we
   developed  PolarHeat(TM)  (patent pending) disposable paraffin heating
   sheets.  When exposed to microwave energy, a PolarHeat sheet, properly
   placed  and  immersed in paraffin, provides safe paraffin heating at a
   speed  comparable  to  water  or  alcohol.  Although  significant tine
   savings  are  realized, more importantly, the sheets afford protection
   to  irreplaceable tissue samples, "mission critical" in the context of
   patient care. Versions are available to fit popular EBS containers and
   racks; free sample packs are available. See
   for more information, or feel free to contact me directly.
   Best regards,
   Phil McArdle
   Phil McArdle
   Microwave Product Manager
   Energy Beam Sciences, Inc.
   29-B Kripes Rd.
   East Granby, CT 06026
   Tel:  800.992.9037 x 341
   Mobile: 860.597.6796
   Fax: 860.653.0422
   I skate to where the puck is going to be, not to where it's been.
   - Wayne Gretsky
   You must be the change you want to see in the world.
   - Mahatma Gandhi
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