Tissue slices are sections of tissue cut from larger pieces or extracted organs and treated in a medium to gain insights into the working of the originating tissue or organ.
Unlike sections for histological studies, tissue slices for metabolic studies are not fixed and preserved. Rather, they are prepared immediately after the excision or after the animal has been put to sleep. Tissue slices are suspended in a medium, where they take up oxygen and nutrients, and trigger targeted biochemical processes.
In other words, tissue slices must be thin enough for oxygen to diffuse into all layers but thick enough to contain unscathed and functioning cells.
The followings are the techniques of tissue slice preparation for metabolic studies:
1. Free-hand Sectioning
Regarded as the traditional preparation, free-hand sectioning only requires a razor blade and a skilled operator to slice the prepared tissue or organ into thin sections. The blade is moistened with an isotonic solution before sectioning to prevent tissue smearing during sectioning.
In a modified version, the razor blade is attached to a small glass plate, or a double-blade cutter is used instead. The glass plate acts as a guide, supporting the slicing direction and establishing a fixed sectioning thickness.
- Least expensive and complicated technique.
- The cutting speed, frequency, angle, and distance between the blade are manually controlled, allowing users to adjust the parameters tailored to the tissue’s characteristics and the operator’s preferences.
- The quality of the tissue slices relies on the user’s skills. Too much force could shear the organization of the tissue, while too little could injure the tissue.
- The dimension of the razor blade restricts the size of the tissue slices.
- Tissue slices produced from free-hand sectioning are not uniform in size and thickness. Most tissue slices will be discarded, and only a few ones with similar size and thickness are usable for metabolic studies.[2-3]
Microtomes are a type of sectioning instrument with an operating body, a blade holder, and a knife blade. Also, users can set a predefined slice thickness and control the movement or oscillation of the blade holder, guiding when and how the blade slices through the tissue sample.
Microtome blades are exchangeable and can be made from steel, glass, or diamond.
- The sectioning angle, distance, and thickness of the slices are predefined and controlled by the microtomes, producing tissue slices that are uniform in size and thickness.
- Does not rely on users’ skills to produce quality tissue slices.
- Less wasteful, laborious, and more productive than free-hand sectioning.
- The tissue sample is placed in a block, which limits the size of the tissue sample. are limited to the dimension of the sample block.
- Users require substantial training to safely operate the microtome, including the selection of the appropriate blade type.
- Users cannot observe the progress of the sectioning—how much tissue sample has been sectioned, or which part of the samples are being sliced.
Microtomes are also used to prepare tissue slices for histological studies and microscopic examinations. To learn more about the types of microtomes and what to look out for when choosing one, check out our article on the factors to consider when buying a microtome.
3. Tissue Slicers
Tissue slicers are specifically designed to produce tissue slices for metabolic studies. Earlier versions of tissue slicers are manually operated. However, recent models have been fully automated and are often referred to as precision-cut tissue slicers.
a) Alabama Tissue Slicer
Also called Krumdieck Tissue Slicer, is a modified microtome adapted to operate when the tissue sample is partially submerged in an isotonic solution. Users can define the slice thickness by setting the position of the blade, and the tissue sample is placed in a block in a reservoir assembly filled with the isotonic medium.
Slicing occurs when the block is moved to meet the blade, which is moved back and forth to slice the tissue. Sliced tissues are removed by a strainer inside the reservoir, which traps the slices and separates them from the medium.
- Alabama Tissue Slicers can quickly produce tissue slices with uniform size and thickness.
- Tissue samples are isolated in the reservoir, allowing researchers to safely work with tissue from infectious agents.
- Sectioning is performed when the tissue is submerged, tissue slices can be acquired from highly hypoxia-sensitive tissues.
- Users do not need to be trained to produce quality tissue slices.
- The size and dimension of the tissue sample are limited to the dimension of the sample block.
- Users cannot observe the progress of the slicing as it occurs, which may be necessary when working with complex tissue.
b) Tissue Chopper
Also known as McIlwain Tissue Slicers is a type of tissue slicer inspired by the free-hand sectioning technique. The tool consists of a thin stainless steel blade, chopping arm, chopping plate, and mounting disc.
The tissue sample is placed in a Petri dish or directly on a chopping plate, which moves from left to right. Simultaneously, the blade connected to a chopping arm chops the sample, typically up to 200 strokes per minute. The thickness of the slice is determined by the moving speed of the chopping plate and the frequency of the strokes.
- The resulting tissue slices have a uniform size and thickness.
- The blade attached to the chopping arm is narrow and does not disturb the soft tissue as severely as wider blades.
- Users can observe the progress of the slicing as it occurs, which is preferable when working with complex tissues.
- Tissues do not need to be submerged when slicing. However, they can be partially submerged in a Petri dish during slicing if needed.
- Large tissue must be cut to fit the chopping plate before slicing.
Related Read: Preservation Techniques: Methods for Preserving Tissue Slices
Factors to Consider When Choosing a Slicing Technique
Slicing techniques are essential in obtaining usable tissue slices. They must accommodate the features, size, and complexity of the target tissue or organ to ensure that the obtained slices can be used for metabolic studies.
Here are some points worth deliberating on when choosing a slicing technique and equipment:
1. Physical Characteristics of the Tissue
Physical features and tissue complexity play significant roles in determining the most suitable slicing techniques. The physical organization of tissue is typically the functional structure, which must not be entirely destroyed by slicing.
For instance, soft tissue and tissue with extracellular space should not be exposed to fluid for a prolonged period. Wider blades can traumatize soft tissue more than narrow blades, which are typically equipped and found in tissue choppers. In contrast, hard tissue may benefit more from microtome preparation, which possesses a wider blade, including the Alabama Tissue Slicer.[2-4]
2. Tissue Availability
If the availability of the tissue sample is limited, consider foregoing free-hand sectioning. Instead, consider using microtomes or tissue slicers which produce slices with consistent size and thickness.
Along the same line, complex tissue with little known about its cellular organization or structure may benefit more from using free-hand sectioning or tissue choppers, because users can make observations and estimations as the tissue are being sliced.
3. Equipment Maintenance
Apart from the tissue characteristics and availability, also consider the time and effort required to care for the slicing equipment when deciding to forego the free-hand slicing technique.
For example, consider choosing:
- A removable or fixed blade
After several rounds of sectioning, the edge of the blade will become dull. Fixed blades must be sharpened, while removable or disposable blades must be exchanged. Disposable blades can be more expensive. Nonetheless, removable blades allow users the option of changing the blade material, which is crucial in obtaining usable tissue slices.
- Automated or manual equipment
Modern tissue slicers can be manual, semi-automated, and fully automated. Manual models enable users to control most aspects of the slicing process. Automated tissue slicers are faster, and considered to produce more uniform tissue slices, but they are more expensive than manual and semi-automated equipment.
- Safety features
Tissue slice preparation is subjected to threats from movement and blade oscillation. Thus, slicing equipment should contain safety features such as locks and guards that contain the blade if it is damaged or discharged during the slicing.
The technique of preparing tissue slices is the heart of obtaining a snapshot of physiological and metabolic activities. Thin tissue slices with sufficient functional cells are keys to obtaining the metabolic data that represent the intact tissue and organ.
Free-hand sectioning is inexpensive and versatile but requires highly skilled users and can be wasteful. Microtomes and tissue choppers can produce tissue slices that are more consistent in size and thickness without relying on the user’s skills.
Are you looking for an affordable and versatile tissue slicer? Then check out our tissue chopper!
- Elliott, K. A. C. “ Tissue slice technique.” (1955): 3-9.
- McIlwain, H. “Techniques in tissue metabolism. 5. Chopping and slicing tissue samples.” Biochemical Journal 78.1 (1961): 213.
- Stadie, William C., and Benjamin C. Riggs. “Microtome for the preparation of tissue slices for metabolic studies of surviving tissues in vitro.” Journal of Biological Chemistry 154.3 (1944): 687-690.
- Krumdieck, Carlos L., José Ernesto dos Santos, and Kang-Jey Ho. “A new instrument for the rapid preparation of tissue slices.” Analytical biochemistry 104.1 (1980): 118-123.