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Dr. Jamal Baroud
11-15-2000, 06:21 AM
Many thanks all those have answered to my inquiry:

>I look for a practical way to keep
>bone cement at a low viscosity after
>the mixing procedure.

I received the following thorough suggestions:

(1) Reducing the benzoyl peroxide initiator in the powder through heat
degradation. Perhaps degrade one pack of powder at 80 degrees C for 24
hours (ref. Rijke & Rieger, J Biomed Mater Res, 1977) and them mix it
50/50 with a fresh pack of powder. -suggested by Paul D. Postak-

(2) Reducing the accelerator by diluting the monomer with monomer without
N,N-dimethyl-p-toluidine (DMT). -suggested by Paul D. Postak-

(3) Chill the *monomer only* before mixing.
-suggested by Robert Day, Todd Baldini-

(4) Cooling down the component prior the mixing,
You will probably have 2 - 3 more minutes as
compared to room temp PMMA.
-suggested by James J. Stone, Alan S. Litsky, Francesco Fabbri,
Peter A. Cripton-

(5) Increasing the monomer : powder ration
-susggested by Alan S. Litsky, Peter A. Cripton -

(6) Using different cement. PMMA cements vary quite
significantly in their viscosity-time profiles between mixing
and completion. For example, Palacos cement remains workable for a
significantly longer time than CMW1.
-suggested by Andrew New, Francesco Fabbri, Peter A. Cripton-

(7) Delay the setting by spreading the cement out and not
keeping it in a large mass, which inhibits the exothermal temperature
rise and hence the curing reaction.

(8) Try vibrating the PMMA; it's shear thinning! - suggested by James
Shippen-
(9) Chilling the cement before mixing. suggested by Andrew New-

Thanks a lot for these thorough answers.

Jamal Baroud


-----------------------------------------------------------------------
Dear Jamal,
In our research we have successful extended the polymerization
time of PMMA by cooling the components individually prior to mixing and by
increasing the monomer:powder ratio. Neither is as convenient as mixing
the cement right out of the packages but either might address your concerns.

Sincerely,

Alan S. Litsky, M.D., Sc.D.
------------------------------------------------------------------------
Jamal,

There are a couple of options. First you could use a cement designed to have
longer handling time. You will find that PMMA cements vary quite
significantly in their viscosity-time profiles between mixing and completion
of polymerisation. For example, Palacos cement remains workable for a
significantly longer time than CMW1. If you want to stick with one cement,
another option is to chill the cement before mixing. This will also extend
the working time. There is some literature on this, if you're interested,
e.g. Hansen D, Jensen JS. Prechilling and vacuum mixing not suitable for all
bone cements. Handling characteristics and exotherms of bone cements. J
Arthroplasty 5(4), 287-90, 1990

Hope this is useful

Andy

Andrew New
------------------------------------------------------------------------
I apologize in advance for the low-quality of my suggestion:
1) to use low-viscosity bone cement,
2) which should be kept at lower-than-usual temperature before mixing
(so to lengthen the polymerisation time).
Best regards.

Francesco Fabbri

------------------------------------------------------------------------
Store PMMA packages in the refrigerator before mixing would be one way ..
You will probably have 2 - 3 more minutes as compared to room temp PMMA
packages

For your information, please see a paper:

Stone, J.J., Rand, J.A., Chiu, E.K., Grabowski, J.J. and An, K.N.,
"Cement Viscosity Affects the Bone-Cement Interface in Total Hip
Arthroplasty,"
J. of Orthopaedic Research 14:834-837, 1996


Sincerely,

James J. Stone, Ph.D.

------------------------------------------------------------------------
Dr. Baroud,
Simplest is reduce the monomer and polymer temperature before
mixing. Several physicians use 4 degrees C or ice baths. Additionally
you can reduce the benzoyl peroxide initiator in the powder through heat
degradation. Perhaps degrade one pack of powder at 80 degrees C for 24
hours (ref. Rijke & Rieger, J Biomed Mater Res, 1977) and them mix it
50/50 with a fresh pack of powder. Secondarily, you can reduce the
accelerator my diluting the monomer with monomer without
N,N-dimethyl-p-toluidine (DMT). I have never tried either dilution
method.

pdp

Paul D. Postak, B.Sc.
------------------------------------------------------------------------
Hi Dr Baroud:

One way you may be able to slow the polymerization of the PMMA is to keep it
cooled. Less polymerized PMMA is also less viscous. Another option is to
increase the proportion of the liquid monomer when you mix the components. I
also believe that some PMMA manufacturers offer a "low viscosity" PMMA for
injection.

Good luck
Peter A. Cripton, PhD
------------------------------------------------------------------------
I don't like the PMMA vertebroplasty, for several reasons, but the best
way to extend the working time for PMMA is to either :
1. use Low Viscosity cement (Zimmer LVC is one of the slowest).
2. Chill the *monomer only* before mixing.
Do not freeze, just a standard household refrigerator is fine.
Lower the theatre temperature too, if you can.

Rob. Day
------------------------------------------------------------------------
Hi

Try vibrating the PMMA; it's shear thinning!

James Shippen

------------------------------------------------------------------------
Dr. Baroud,

We've chilled the liquid monomer in an ice water bath to slow the
polymerization process to give us more time to work with the PMMA before it
sets. I've only used it in making specimens for mechanical testing. It
seems to work but I don't have any data on how much is slows the
polymerization process.

Regards,
Todd Baldini

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