Submitted to: Texas Society for Electron Microscopy Journal
Publication Type: Abstract Only
Publication Acceptance Date: March 15, 1996
Publication Date: N/A
Numerous papers have been published to the effect that the Anhydride/Epoxy (A/E) ratio of epoxy resins must be carefully proportioned to assure a proper mixture for infiltrating and embedding tissues used in transmission electron microscopy. The procedures for doing this are both straightforward and relatively easy. However, the problem is compounded because the various components of the resin tend to separate during tissue infiltration thus skewing the intra-tissue A/E ratio. The primary reason for this is that the rate of penetration of each component of the resin mixture is inversely proportional to the viscosity of the component and to the effective radius of its molecule. The problem is particularly apparent in some of the low viscosity resin mixtures in which the viscosity spread between its various components may be as high as 30-40 times. The result is that many tissues are actually poorly embedded and subject to a number of embedding artifacts. There are also other factors that impinge on tissue infiltration and some of these will be discussed. Specifically, we will look at 1) embedding effects related to fixation and dehydration of tissue; 2) effects of resin component viscosity; 3) reaction of epoxy resins with tissue elements; 4) uneven mixing of resin components with dehydrating fluids; 5) vaporization of resin components during vacuum infiltration; 6) embedding temperatures, high or low?; 7) temperature induced vaporization of some of the more common dehydration fluids and resin components; 8) anecdotes for eliminating A/E skewing during infiltration; 9) what all this means in relation to tissue quality, section post-staining, and image contrast--or you may be glad for a less than optimal embedding medium.