Flotation Baths in Histology: Ensuring Perfect Tissue Preparation

Flotation tanks are essential tools in the workflow of pathology and histology laboratories, especially after paraffin sections are cut and before they are sealed. They help researchers prepare tissue samples with precision. These flotation tanks are specifically designed to float and stretch paraffin-embedded tissue sections, ensuring optimal fit of the paraffin section to the slide. By eliminating wrinkles and folds, tissue flotation baths provide excellent conditions for section preparation for seamless microscopic examination. Let's explore flotation baths, learn how they work and their importance in the laboratory environment.

What is a flotation bath

A tissue flotation bath is a specialized piece of equipment used in pathology and histology laboratories, primarily for processing paraffin-embedded tissue sections. After thin sections have been cut using a sectioning machine, the sections are transferred to a floatation bath containing water at a constant temperature (usually maintained at 40°C to 50°C). The warm water helps the tissue sections to fully unfold and flatten out any wrinkles or creases formed during sectioning, thus providing an ideal condition for subsequent patching and staining.

How does a water bath consist?

The water bath consists of a tank made of stainless steel. The lower part of the tank has a set of resistors through which heat is transferred to the water. The temperature of the water is maintained at a pre-selected temperature by means of a thermostat, thermistor or similar control device, which makes it possible to select the temperature required for different analyses or laboratory tests.

Components of Flotation Tank Components

The components of the flotation tank include: regulator, control panel, adjustment knob and basket.

1. Bath Chamber

   Water holding part, usually made of black aluminum alloy or high temperature resistant material, easy to observe the transparent slices. It is corrosion and heat resistant.

2. Regulator

   The regulator precisely controls the water temperature inside the flotation bath. It ensures stable heating, typically maintaining the temperature between 40°C and 50°C—ideal for flattening paraffin sections. Accurate regulation prevents overheating, preserving tissue integrity.

3. Control Panel

   Digital or knob interface for setting and displaying water temperature. Some models are equipped with an over-temperature alarm. It often includes digital or analog displays to show real-time temperature and may feature indicator lights for system status and safety alerts.

4. Tissue Basket (or Mesh Tray)

   The basket is used to safely retrieve tissue sections from the warm water after floating. It prevents sample damage and allows excess water to drain. Often made of stainless steel or heat-resistant plastic, it is easy to clean and reusable.

5. Power & Electronics

   Provides the electrical power needed to run the equipment and controls the heating and display systems.

6. Dry-Run Protection

   Monitors the water level and automatically stops heating when the water level is too low to avoid dry-run damage.

7. Lid

   Used to insulate and prevent dust from entering the sink.

How does Flotation Bath work?

1. Cutting tissue sections

   Ultra-thin sections, typically a few microns thick, are cut from paraffin-embedded tissue blocks using a microtome. This process requires a high degree of precision to ensure that the sections are complete and continuous.

2. Floating on the surface of warm water

   Sections are gently transferred to the surface of warm water in a tissue floatation tank. The warm water softens the paraffin and allows the tissue to spread naturally, smoothing out wrinkles. Distilled water is used for better results; also, adding 95% alcohol to the water helps to reduce surface tension and wrinkles, and sometimes adhesives are added to enhance tissue adhesion to the slide.

3. Mounting on slides

   After the tissue is fully expanded on the water surface, the operator will carefully lift the section and place it on a microscope slide, ready for subsequent staining and microscopic analysis.

Main features of the flotation bath

Precise temperature control to protect tissue samples

The digital temperature control system allows for precise regulation to prevent damage to fragile tissue sections from overheating. By maintaining a stable water temperature, it ensures that tissue integrity and clarity are maintained during the flotation and spreading process.

Ergonomic operation design

The wide open design of the floatation tank provides ample operating space for easy sliding of tissue sections. The ergonomic structure helps to improve the dexterity and efficiency of hand operation and reduce operation fatigue.

High Visibility Structure

Equipped with a dark inner groove or integrated LED lighting system that significantly enhances the contrast between tissue sections and the background, making sections easier to identify and locate, especially for processing very thin or light-colored samples.

Optimized temperature settings for different sample requirements

The temperature of the tissue floatation bath should be finely adjusted according to the type of sample and the nature of the paraffin used. A conventional setting of 40°C to 50°C, typically about 5°C to 10°C below the melting point of the paraffin used, softens the paraffin without causing structural disintegration of the sample.

Tissues with a high fat content (e.g. brain or mammary gland): lower temperatures are recommended to avoid thermal damage.

Hard paraffin: a slightly higher temperature should be used to ensure that the slices are well expanded in the water.

Maintaining the proper water temperature is essential to avoid tearing, wrinkling or dislodging of the tissue and is fundamental to obtaining high quality microtomes.

Applications of flotation bath

Flotation baths are indispensable in the following fields:

Histology: Preparing tissue samples for microscopic examination to diagnose diseases such as cancer.

Pathology: Analyzing tissues to study diseases and abnormalities.

Research laboratories: Study biological tissues for medical and scientific purposes.

Education: Teaching students proper tissue preparation techniques.

Why Temperature Matters

Maintaining the proper water temperature in the flotation tank is critical. Water that is too hot can damage or distort tissue sections. On the other hand, water that is too cold will not soften the paraffin sufficiently, making it difficult to flatten the tissue. For best results, the temperature should always be set according to the type of paraffin and tissue being used.

Conclusion

Flotation baths may seem unassuming, but they play a vital role in ensuring the accuracy of tissue preparation. The ability of these water baths to spread tissue sections simply and effectively helps provide reliable diagnostic results and supports critical medical research.