[Histonet] MMA Formulation for EXAKT Grinding

[Jack Ratliff]

Nikki,

The MMA formulation you describe is one that yields a very soft block suitable for thin section (4-6 microns) microtomy. I have heard where people use this formulation for undemineralized bone and maybe even for stent work, but the softness of this formulation concerns me for the stents given the reduced stability. For me personally it is not what I use for both of these specimen types, but that is for another discussion.

It is important to note that the volume of catalyst is proportional to the total volume of solution and thus this ratio (expressed as w/w) is directly proportional to the reaction product. Now to make things a little more confusing, the reaction product is influenced by air temperature, the size/density of the specimen, the total volume of reaction product, and sometimes the embedding container and void space above the solution level and container lid. Furthermore, since this reaction or polymerization of resin is an exothermic reaction, the rate (expressed as a unit of time) at which the reaction reaches the actual point at which polymerization initiates (v-max) also then influences the amount of heat that is generated from the reaction. This then is proportional to the quality of polymerization that can be seen as either a hard clear desirable block or and over polymerized, bubbled mess!!!

It is my opinion that the bubbles in your specimen blocks are related to the build up of pressure in your container and caused by a rapid polymerization of your specimens by the use of the heated water bath (as per you concentration of catalyst to MMA/DBP solution) and lack of void space to buffer or diffuse excess heat. My feeling is that you are using too much catalyst in conjunction with the heat of the water bath to polymerize these specimens. Also, what is the volume of the solution you are polymerizing, how close are your specimen molds to each other in the water bath, and is the water level of the water bath at or above the embedding solution level in the specimen container? The heat generated from one specimen can sometimes add to the heat generated by another in close proximity. This then results sometimes in an over polymerization of one specimen (too much heat generated in the reaction) and no polymerization of another (absence of heat to drive the reaction).

Here are my suggestions:

1) If you need specimens polymerized immediately the next day, take care to space out your specimens further apart in the water bath. Also, try turning down the water bath to reduce the secondary heat used to drive the reaction. If none of this works, then look at reducing the amount of catalyst used (may want to do this first and keep everything else the same).

2) If you can spare a few days, don't change a thing with the embedding solution, try switching your molds to polypropylene containers and leave them out on the counter at room temperature (22-23C) for 2-3 days until they polymerize.

Hope this helps and it wasn't too confusing.

Jack


On Jun 25, 2010, at 3:46 PM, "Wahlberg, Nikki" <Nikki.Wahlberg <@t> bsci.com> wrote:

> Hello Everyone,
> 
> I was wondering if you could help me with my MMA formulation.  I have been using a formulation that I found in a published paper.  My current embedding formulation is 80ml MMA, 20ml Dibutyl Phthalate and 3g Benzoyl Peroxide.  The samples are embedded after three days of infiltration, one change per day, with the formulation of 80ml MMA and 20ml Dibutyl Phthalate. Lately have noticed that there is a pressure build up in the vials.  I have had a few vials burst almost immediately once placed in the heated waterbath. I am filling the glass vials full with the embedding solution, capping them and then placing them in a water bath in a 37 degree oven.  They are completely polymerized by the next morning. I am also getting bubbles in the plastic when polymerized.
> 
> I have two questions: Is there any way to get rid of the bubbles in the plastic and of more concern what do you think is causing the pressure build up?
> 
> I would really appreciate any help that you can provide.
> 
> Thank you,
> Nikki
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