Tissue embedding is a tissue preparation technique used when a technician needs to be able to cut very small samples of tissue with a device known as a microtome. The tissue is supported in a medium, allowing the technician to create even, accurate cuts without crushing or otherwise damaging the tissue. The slices of tissue can be examined under a microscope to study their characteristics and collect information for use in diagnostic evaluations and other studies.
Samples of tissue can come from surgical biopsies, autopsies, and many other sources. The technician places the tissue into a cassette designed to be submerged in the embedding medium. Paraffin, plastics, epoxies, and some types of gel media can all be used. Once the medium has set, the sample can be pulled back out, inspected to confirm the embedding went smoothly, and sliced as desired. Thanks to the support of the medium, very fine tissue slices are available, allowing the technician to visualize a high level of detail.
Placement of samples in the cassette requires some training and experience, as the tissue needs to positioned appropriately for the type of study being conducted. If it is not placed right, it will be difficult to cut the desired cross sections and the sample may be ruined. Care must also be taken to process samples before embedding, following the appropriate protocol for the type of tissue and the treatment. Most labs have their own manuals for tissue embedding and other procedures and they expect technicians to follow these manuals.
Devices designed specifically for tissue embedding are available for labs in need of such equipment. These machines vary in size and design depending on the number of samples they are designed to process. Some are designed for specific embedding media, including proprietary compounds intended for specific kinds of histopathology applications. Tissue embedding equipment tends to be expensive and manufacturers have sales representatives who can provide information and advice when a lab is selecting new or replacement equipment.
Sliced sections of tissue can be mounted on slides and examined or put in storage. If part of a sample is left intact, it will also be stored after tissue embedding in case additional tests are needed in the future. Stored specimens can also be used for scientific research. The sliced samples can be stained to highlight certain features or to look for traces of specific chemicals and other compounds.