Rotary Microtome Disadvantages and Care

Disadvantages of Rotary Microtome

• Complex design
• Higher initial cost
• Knife is placed in the blade holder up position and can be dangerous to the operator (can be avoided with knife guard/protector)
• Not suitable for cutting large blocks

Care of the Rotary Microtome

• Brush away accumulated paraffin and tissue with a soft brush after cutting
• Wipe clean all metal parts with xylol
• Avoid continuous application of xylol to the rest of the machine (can remove the paint)
• Dry the machine carefully, especially the knife holder
• Keep the machine well oiled to prevent rust formation
• Keep the moving parts of the microtome lubricated
• Cover the microtome when not in use to prevent accumulation of dust and dirt

Types of Microtomes

• Saw microtome: for hard materials (e.g., bone, brittle material), thickness > 30 microns
• Sledge microtome: for embedded hard samples, thickness 1-60 microns, for bony samples sliced for histo-enzymes study
• Rotary microtome: for thin samples, most widely used, also called Minot microtome

Rotary Microtome

• Mechanism: hand wheel rotates through 360 degrees, moving the specimen vertically past the cutting surface (i.e., knife edge) and returning it to the starting position
• Block holder is mounted on a steel carriage which moves up and down in grooves and is advanced by a micrometer screw - cutting perfectly flat sections
• Types: manual, semi-automated, fully automated

Rotary Microtome: Types

• Manual: completely manipulated by the operator
• Semi-automated: auto cut microtome with built-in motor drive, foot and hand control, suitable accessories can cut thin sections of 0.5 to 2.0 um thickness
• Fully automated: two motors drive both the fine and the coarse advance hand-wheel, e.g., automated cryostate

Rotary Microtome Parts

• The main components of a rotary microtome are:
  • Base
  • Cassette or block holder
  • Block adjustment screw
  • Knife holder
  • Blade clamps
  • Angle of tilt adjustment
  • Thickness gauge
  • Operating handle
  • Face plate
  • Waste tray

Rotary Microtome Parts (continued)

• Microtome base plate or stage: a platform with rails that secure the knife holder base
• Knife holder base: a part that anchors the knife holder to the microtome stage
• Knife holder: comprised of the blade clamp, knife tilt, and face plate
• Cassette clamp or block holder: holds the paraffin block in place, moves up and down with each revolution while the blade is stationary
• Coarse hand wheel: moves the block holder toward or away from the knife
• Advancement hand wheel: turns in one direction and advances the block toward the knife at the specified microns
• Micron adjustment: micron settings for section thickness
• Thickness gauge: micron settings for section thickness
• Base on which the whole microtome rests

Rotary Microtome: Operation

• Fitting and adjusting the knife:
  • Install a disposable blade in the microtome
  • Set angle between the blade edge bevel and the block to 2-5 degrees (clearance angle)
  • Lock the blade in place
  • Lock the microtome hand-wheel
• Trimming:
  • Trim the edges of one block with a sharp razor blade
  • Fit the cassette paraffin block onto the cassette holder of the microtome
• Sectioning:
  • Advance the block until it is in contact with the edge of the knife
  • Set the section thickness around 15 microns
  • Coarse cut the block at 15 microns until the whole surface of the embedded tissue can be cut
  • Return the trimmed block to the cold plate for 1-2 min
  • Set the section thickness to 4-5 um
  • Remove wax debris from the knife with alcohol
  • Move to an unused area on the blade or install a new disposable blade
• Section collection:
  • Transfer the cut sections to the surface of the water bath
  • Gently separate the floating sections on the water bath with pressure from the tips of forceps to remove fine wrinkles
  • Collect sections on a clean glass slide

Advantages of Rotary Microtome

• Section thickness range: 1.0 - 60.0 µm
• Stable and less of vibration (heavier and more stable)
• Excellent for routine and research work
• Ability to cope with harder tissue
• Easy adaptation to all types of tissues (hard, fragile, or fatty)
• Ideal for cutting serial sections
• Cutting large blocks
• Cutting angle of knife is adjustable
• Large and heavier knife used - less vibration when cutting hard tissue
• Technological advances in automation improved section quality, increased productivity, and occupational safety