A couple of words of caution:

Make sure the specimen is embedded in PMMA.  If it was embedded in a mixture
containing GMA or crosslinkers you may not be able to remove the plastic, it
will gel and expand in volume and make an ugly, sticky mess.

My first job when I came to the US was the resurrection of a number of
studies (2-300 blocks) poorly embedded in PMMA, sectioned in bizzare planes,
then surface reinfiltrated in Technovit 7200.  Despite the gelling and
swelling and the loss of one or two implants, they reprocesed well enough
into Technovit 7200 to see bone and soft tissue ingrowth and ongrowth. 

Even if the specimens are embedded in pure MMA, the first step of the
dissolution of the PMMA is a softening of the plastic, it becomes jelly like
and increases in volume.  When this happens within the bone, the marrow may
be squeezed out of the medullary cavity and soft tissue structures may be
displaced. It may even squeeze the implant out of the bone.

May I ask why you want these specimens reprocessed into an epoxide based
plastic?  the only reasons I could think of are:
1. electron beam stability.    
2. preservation of bone cement.
3. producing a harder block for grinding.

If 1, stability isn't an issue, as your sections will be thick anyway.  I've
done SEM on stacks of MMA embedded orthopedic implants and stability is not
an issue on a properly gold or carbon coated specimen.  If you want to do
TEM, then I wish you lots of luck
If 2, I'm afraid the cement has been removed by the original PMMA
processing.
If 3, perhaps some modification of your cutting/grinding method will enable
you to get the section quality you require.  Many people in the US (and
europe) cut and grind PMMA embedded large orthopedic implants on a regular
basis and produce superb sections.

Just my two penneth (or should that be $0.02?  I think I might be turning
transatlantic...)

Regards

Simon

Simon Smith B.Sc. AIBMS
Supervisor, Laboratory Resources
Skeletech, Inc.
22002 26th Ave SE, Suite 104
Bothell   WA   98021
Voice: (425) 424 2663   Fax:  (425) 424 2600
E-mail: ssmith@skeletech.com  


-----Original Message-----
From: Pam Marcum [mailto:pmarcum@polysciences.com]
Sent: Thursday, May 04, 2000 7:37 AM
To: Mary Stevens; anette@biomeklab.aau.dk; histonet@pathology.swmed.edu
Subject: RE: deplasticising


Another method is to do everything stated here and briefly submerge in warm
xylene as it will dissolve the PMMA.  It is not the best but may help.  You
must then be very careful to remove the xylene before attempting to embed in
epoxy.  Soak in the first dilution mixture with several changes until no
smell of xylene is apparent in the solution.
-----Original Message-----
From: Mary Stevens [mailto:mstevens@genetics.com]
Sent: Wednesday, May 03, 2000 3:55 PM
To: anette@biomeklab.aau.dk; histonet@pathology.swmed.edu
Subject: Re: deplasticising


Remove as much plastic as possible with a saw or grinder.  Suspend the
specimen in liquid MMA, cover tightly, place it on a rotation plate.   Check
it every couple of days.  It'll depend on the size you have to
deplasticize - but it may take anywhere from 4 days to a month or two.
Change the MMA when it looks like it's getting saturated with melted plastic
(thick and gooey).   I don't know if you can get it all out enough to
re-embed in Epoxy (I've not done this - maybe some one else has.)  You can
use Acetone, instead of MMA monomer.  For the blocks we've deplasticized,
we've used both methods with good luck re-embedding in MMA again (not
epoxy).

Good luck.
BTW - the methods I've used were  reference from conversations with other
great bone people...Katie Combs, Cathy Mayton, and Susan Ryan - Thanks to
them!

Mary



>>> "Anette Milton" <anette@biomeklab.aau.dk> - 5/3/2000 7:44 AM >>>
Does anyone have experience removing PMMA from specimens of bone with
titanium-implants, because I want  to reembed the specimens in epoxy.

Anette


Anette Milton
Ortopaedic Research Laboratory
Aarhus University Hospital
Building 1A
DK-8000 Aarhus C
Denmark