The softness of tissues or localized variations in hardness can directly affect sectioning, making it difficult to produce uniform, continuous sections.

To address this challenge, tissues need to be infiltrated and embedded with a suitable substance to mitigate the difficulties caused by tissue softness, enabling easier and thinner sectioning. This substance is called an embedding medium.

Once solidified, the embedding medium adjusts the hardness and toughness of the tissue to match its own properties, thereby enhancing the tissue’s rigidity and making it easier to cut. This improves both the quality and efficiency of sectioning.

So, what types of embedding media are available? And how do you choose the right one? Today, we’ll explore this topic by combining relevant research and practical experience.

Classification of Embedding media

For general optical microscope observations, paraffin, collodion, carbon wax, gelatin, etc., are used as embedding media;

For electron microscopy, epoxy resin, polystyrene resin, isobutylene resin, and water-soluble resin are used;

For hard tissue embedding (bones, teeth), plastic embedding is used, such as methyl methacrylate.

*In fact, the embedding agent is the same as the infiltrating agent. The same substance is used for infiltration and embedding, just with different names at different steps. For example, if paraffin is used for infiltration, the same paraffin is also used for embedding.

How to Choose the Right Embedding Media

Embedding media has specific requirements for tissue objects. Choosing the right embedding agent can improve embedding quality and thus improve sectioning quality.

Paraffin: The most common and classic embedding agent for histopathological section preparation, easy to use, economical, and safe.

Carbon wax: A quick-use embedding agent, with a short section preparation time, no need for dehydration and clarification, less tissue block contraction, generally a wax block can be made within 3 hours; but it is highly hygroscopic, relatively difficult to handle and preserve wax blocks. Mainly used for fatty and lipid tissue section preparation.

Collodion: Mainly used for large tissue blocks (soft tissues, organs, decalcified bone tissues, and whole femoral heads and eyeballs with diameters of 3-10 cm), can avoid the contraction of fibrous tissues and excessive hardening of muscle tissues, and maintain the original structure of the tissues. However, the operation process is time-consuming, rarely used in clinical and autopsy sections, but helpful for studying nerve, bone, and eye tissues.

Gelatin: Less used in histopathological sections, mainly for some animal experimental specimens.

Resin: Mainly used for electron microscopic section preparation, with types such as epoxy resin, polystyrene resin, isobutylene resin, and water-soluble resin, and similar usage methods. However, some harder ones may require the use of tungsten steel knives and tungsten steel knife holders, such as epoxy resin.

Plastic: Mainly used for hard tissues such as undecalcified bone tissues and teeth.

We hope this overview of embedding media enhances your sectioning workflow! If you have any questions or challenges related to tissue sectioning, please share them in the comments section. Let’s collaborate and refine our techniques together!