Table 4.

Upsides and downsides of potential embedding agents for brain preservation.

Embedding agent	Upsides	Downsides
Paraffin	•Widely used, relatively inexpensive •Long-term preservation data available •Protein antigens well-preserved •Can be performed on large sample volumes	•Necessitates removal of lipids (applicable for all, to some degree) •Unclear degree of ultrastructure preservation •To our knowledge, no volumetric electron microscopy data is available for paraffin embedded brain tissue •Causes tissue shrinkage
Celloidin	•Decreased need for heating, less tissue shrinkage •Possibly better preservation of internal structures than paraffin	•Very long infiltration times, months for large tissues •Blocks must be maintained in liquid ethanol •Flammable, potentially dangerous
Epoxies	•Standard method used for high-quality ultrastructure preservation •Easy to verify preservation quality with electron microscopy •Potential for very long-term stability with storage at ambient temperature	•Highly viscous resins, require long and high temperature infiltration •Can damage protein antigenicity •No established protocols for embedding specimens the size of human brain, so would require sectioning prior to embedding
Acrylates	•Some allow for good tissue infiltration of large samples •Can polymerize at low temperature •Can have high ultrastructural preservation •Often better biomolecular preservation	•Challenging to cure large samples via UV radiation •Often reported to not yield as high of ultrastructure preservation quality as epoxy resins •Questions about long-term stability, e.g., may require storage in desiccator
Plastination agents	•Has been used to preserve whole brains and even whole bodies •Methods designed to be relatively cheap and widely accessible •• Protocols often include or can be adapted for use with epoxy or polyester resins	•Histological preservation is poorly characterized, as this is usually not the goal •Some protocols still require sectioning brains into slices •Can cause substantial shrinkage •Very long-term stability unestablished