Microtome: Types. Advantages and Disadvantages. Working Principle, Care and Maintenance.

Dr Pramila Singh

Microtomy

Microtomy is a technique to prepare a thin section of tissue specimen for its microscopic examination.

4.1 Microtome: Microtome is an instrument to cut thin, and uniform sections of tissues for microscopic examination. It is an essential instrument to prepare tissue sections to be mounted on the microscope glass slide. Microtome consists of a sturdy base(stage), a specimen holder or chuck, a knife holder or blade holder, and a mechanism to move tissue specimens against the knife.

Parts of Microtome: The microtome consists of the following parts

• 1. Stage: It is a platform to hold the knife holder base securely,

• 2. Clamp or holder's arm: It securely holds the microtome blade or knife

• 3. Specimen holder: It holds tissue specimens securely. It can adjust the position of the tissue specimen for cutting.

• 4. Knife or blade: It is a cutting tool for section cutting of tissue specimens.

• 5. Hand wheel or adjustment knobs: It is used to fix the thinness of the tissue section cutting.

• 6. Microtome locking mechanism: It locks the microtome once the setting is achieved. It ensures stability during the section-cutting process.

4.1.1 Types of microtome

There are different types of microtome. These are Manual, semiautomatic, or fully automatic. Examples of microtomes Manual microtomes, Rotary microtomes, Sledge microtomes, cryostats, Ultra microtomeS, and laser microtomeS.

• 1. Manual microtome: It is operated manually. Pathologists move tissue blocks against the knife using a hand wheel or crank.

  • Advantages

  • ·1.  Compact and portable

  • ·2.  It is easy to obtain a thin section of the tissue specimen,

  • · 3. Greater control over the cutting process

  • ·4.  Minimal maintenance

  • ·5.  Suitable for a wide range of tissue specimens

  • ·6.  The individual develops skills for precise cutting

  • ·7.  Cost-effective

  • Disadvantages

  • ·1.  Inefficient for large samples,

  • ·2.  It requires a Skilled Operator,

  • ·3.  Require physical effort from the operator

  • ·4.  Not suitable for hard and brittle samples,

  • ·5.  More sample damage

  • ·6.  Change in thickness of tissue sections.

• 2. Sledge microtome: The pathologist moves the microtome blade against the tissue specimen to cut a thin section of the tissue specimen.

  • Advantages:

  • ·1.  Accurate and constant tissue section thickness

  • ·2. Tissue section thickness is adjustable

  • ·3. Minimal tissue damage

  • ·4. Produce high-quality tissue section

  • ·5. Suitable for a large number of tissue specimens

  • ·6. Enhance safety

  • ·7. Reduced operator efforts

  • ·8. No effect on change of operator

  • Disadvantages:

  • ·1. Noisy machine

  • ·2. Larger and bulky in size

  • ·3. Complex machinery,

  • ·4. High maintenance and repair cost

  • ·5. Require operator training

  • ·6. Not compatible with all tissue specimens,

• 3. Rotary microtome: The tissue block is fixed on a rotary mechanism. The knife moves in a circular motion to cut tissue sections continuously from the tissue block.

  • Advantages

  • ·1.  High accuracy in thin tissue section cutting

  • ·2.  High-quality tissue section with minimal effort

  • ·3.  Programmable to decide the thickness of the tissue section

  • ·4.  The less physical effort of the operator

  • ·5. Less skilled operators can operate it

  • ·6. Efficient for a large number of samples

  • ·7. Minimal sample damage

  • ·8.  Increased safety

  • ·9. No change in thickness of tissue section on change of operator

  • Disadvantages

  • ·1. Expensive

  • ·2. Require skilled operator

  • ·3.  Time-consuming

  • ·4.  Limited thickness of tissue section

  • ·5. Mechanical vibration

  • ·6. Sample distortion

• 4. Cryostat: It is also called freezing microtome. It has a knife made of glass. It is used to prepare thin sections of frozen tissues.

• 5. Ultra-microtome: Ultra-thin section of tissue specimen is prepared by using an ultra-microtome. An ultra-thin section of tissues is required for electron microscopy.

• 6. Laser microtome: The laser technique is used to cut thin sections of tissue specimens. There will be no physical touch of tissue and microtome part during section cutting of tissue specimens.

4.1.2 Advantages of microtome

• · 1. Uniform and consistent tissue section

• · 2. High-quality tissue section

• · 3. Versatility to cut soft to hard tissue into thin tissue section

• ·4.  Time efficiency

• · 5. Staining compatibility

• Disadvantages of microtome

• · 1. The requirement of a technically skilled technician

• · 2. Distortion or tearing of tissues during section cutting

• · 3. The time-consuming operation of cutting the tissue section

• · 4. The thickness of the tissue section varies from 2 to 5 micrometers only. Limited thickness range,

• · 5. High cost of microtome machine.

Working principle:

• Principal: Microtome moves knife moves across tissue black to cut the thin section of tissue. This section of tissue has a uniform thickness. Some microtomes have moving tissue blocks. Tissue block moves across microtome knife to form uniform thickness of tissue section

• Care and Maintenance: Care and maintenance are a must to ensure optimum performance of the longevity of the microtome. A microtome is a delicate instrument to cut a thin section of tissue block. The following guidelines should be followed to care for and maintain microtome.

  • 1. Regular cleaning

  • 2. Regular blade care

  • 3. Timely blade changing

  • 4. Timely oiling and lubrication

  • 5. Regular servicing

  • 6. Proper alignment and calibration

  • 7. Avoid forceful handling

  • 8. Proper storage

  • 9. Proper training for laboratory technician

  • 10. Appropriate use of personal protective equipment (PPE).

Dr Pramila Singh