4.10.
ARALDITE EMBEDDING
109
DMP-30. Rohm and Haas Co., Philadelphia, distributes DMP-30. The
hardener, DDSA, is a commonly available chemical.
Luft's other introduction, the use of propylene oxide as an intermediate solvent between alcohol and the epoxy mixture, has already been
partly considered (Chapter 4.3). He found that even traces of non-reactive
solvents (which include alcohols) left in the resin mixture seriously affect
the sectioning qualities of the resultant block. Thus, he chose propylene
oxide deliberately as a substance which was a "reactive" dilutant that
could partake in the polymerization of the epoxy should traces of it remain. There is no doubt that the use of this intermediate solvent facilitates the uniform impregnation of tissue by the plastic mixture in Araldite embedding, as well as when using any other epoxy. Its use allows a
relatively rapid infiltration of the mixture and removes uncertainty about
the final results. It obviates the numerous gradual steps of infiltration
detailed by the Glauerts, with relatively prolonged soaking in each.
Luft originally proposed polymerizing with a graded series of temperatures, from 35°-60°C, over a 36 hour period. This proves not to be necessary for no deleterious effect of a direct exposure to 60°C can be detected. In any case, the temperature and length of exposure should be
standardized to assure uniformity. Although it may be possible to section
some blocks after just an overnight polymerization, such a short period
of time even at 60°C will not produce a standardized product, and Luft's
recommendation of two nights and a day seems best.
During the last year we have discovered that we can store frozen
mixtures of Araldite with its hardener and its accelerator.
This follows
the lead of Minick (1963) who demonstrated this possibility in the case
of Epon. We use a freezer operating at —35°C, and, for convenience,
package prepared Araldite mixtures in 10 ml disposable syringes. These
need only be warmed to room temperature to be used, and the syringes
serve as excellent dispensers for filling embedding capsules.
Since we started using Araldite in our own laboratory in the manner
recommended by Luft (1961), we have not had any serious difficulties
with its use. For over 2 years it has been our standard embedment with
which all others have been compared. It is my personal opinion that it
shows less "grain" at very high resolution than any other established embedment. Its only important disadvantage is that it finally comes to have
the greatest electron density of any embedment, but this is partly because
of its great thermal stability when compared with the other plastics. Its
reliability makes it a very valuable embedment.
ARALDITE EMBEDDING
109
DMP-30. Rohm and Haas Co., Philadelphia, distributes DMP-30. The
hardener, DDSA, is a commonly available chemical.
Luft's other introduction, the use of propylene oxide as an intermediate solvent between alcohol and the epoxy mixture, has already been
partly considered (Chapter 4.3). He found that even traces of non-reactive
solvents (which include alcohols) left in the resin mixture seriously affect
the sectioning qualities of the resultant block. Thus, he chose propylene
oxide deliberately as a substance which was a "reactive" dilutant that
could partake in the polymerization of the epoxy should traces of it remain. There is no doubt that the use of this intermediate solvent facilitates the uniform impregnation of tissue by the plastic mixture in Araldite embedding, as well as when using any other epoxy. Its use allows a
relatively rapid infiltration of the mixture and removes uncertainty about
the final results. It obviates the numerous gradual steps of infiltration
detailed by the Glauerts, with relatively prolonged soaking in each.
Luft originally proposed polymerizing with a graded series of temperatures, from 35°-60°C, over a 36 hour period. This proves not to be necessary for no deleterious effect of a direct exposure to 60°C can be detected. In any case, the temperature and length of exposure should be
standardized to assure uniformity. Although it may be possible to section
some blocks after just an overnight polymerization, such a short period
of time even at 60°C will not produce a standardized product, and Luft's
recommendation of two nights and a day seems best.
During the last year we have discovered that we can store frozen
mixtures of Araldite with its hardener and its accelerator.
This follows
the lead of Minick (1963) who demonstrated this possibility in the case
of Epon. We use a freezer operating at —35°C, and, for convenience,
package prepared Araldite mixtures in 10 ml disposable syringes. These
need only be warmed to room temperature to be used, and the syringes
serve as excellent dispensers for filling embedding capsules.
Since we started using Araldite in our own laboratory in the manner
recommended by Luft (1961), we have not had any serious difficulties
with its use. For over 2 years it has been our standard embedment with
which all others have been compared. It is my personal opinion that it
shows less "grain" at very high resolution than any other established embedment. Its only important disadvantage is that it finally comes to have
the greatest electron density of any embedment, but this is partly because
of its great thermal stability when compared with the other plastics. Its
reliability makes it a very valuable embedment.