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Leica VT1200 S Materials Testing

Leica VT1200 S Fully automated vibrating blade microtome

VT1200 S

Does my bath need to be cold in order to get decent sectioning?

It is recommended to work with a cold bath to keep the physiological buffer in the buffer tray and thus the specimen cooled while sectioning. Cold puffer slows down enzyme activity and protects antigens. The second purpose of cold is to stiffen the tissue. Remember, you are not processing the tissue and embedding in paraffin nor are you freezing the tissue. The firmer tissues (e.g. muscle, heart, etc.) or fixed tissues may very well be sectioned in a room temperature bath. Unfixed neural tissue however must be chilled and oxygenated in order to get decent sectioning.

What is the best way to get my bath cold and keep it cool?

In most cases the use of crushed ice in the ice tray is quite satisfactory. Alternatively, the use of plastic encased water cubes may be used. However, there may be instances, where an exact experimental temperature is required (e.g. some of the newer immunochemical procedures). For that purpose the use of the Vibratome R900 Peltier cooler* or Minichiller with the VT1000 S/VT1200/VT1200 S is recommended. An exact temperature is selected and held +/- 1 °C. *please contact your local Leica representative to clarify whether the Peltier is available in your area.

Do I have to achieve a specific temperature when I chill my bath?

Most users select a temperature of +4 °C. 4 °C is the “natural” temperature and results when storing the buffer on ice prior to sectioning and later when using crushed ice in the ice bath to keep the buffer in the buffer tray cold.

What variables do I have to work with to obtain good sections?

1. Knife forward travel speed, 2. Amplitude, 3. Blade angle, 4. Bath temperature, 5. Section thickness The “Rule of thumb” is that softer tissues require slower forward speed, higher amplitude and frequency, steeper blade angle and cold buffer.  For fresh tissue a knife travel speed below 0.1 mm/s is recommended. The amplitude should be between 1 and 1.5 mm for the VT1200. The frequency is fixed at 85 Hz (+/- 5Hz). For fixed tissue the knife travel speed can be faster (up to 0.5mm/s) and amplitude can be lower (between 0.6 – 0.8 mm amplitude). Sectioning of fresh or fixed tissue is always easier when the specimen is cold by using cooled physiological buffer. The selection of the section thickness depends on the purpose of the study. When sectioning fresh tissue for patch-clamping, the section thickness should not be selected too thin, (must be more than 30 µm) otherwise all cells would be damaged. Most users select a section thickness between 100 and 300 µm. Fixed tissue can be sectioned thinner, the tissue is firmer due to the fixation and living cells are not needed for recording anymore.

When is the Vibrocheck needed?

The Vibrocheck can only be used with the Leica VT1200/S. The use of the Vibrocheck is recommended with each blade exchange when sectioning unfixed tissue (e.g. for patch clamping). It is used to measure the vertical deflection of the blade. With the adjustment screw on the blade holder, the blade can be tilted as long as it sits perfectly parallel to the cutting plane. A parallely positioned blade is necessary to avoid venetian blind effect on the section surface and to produce a flat, high quality section with living cells on the surface.

Are there recommendations for embedding media available?

2.5 % Agar–Agar or for heat sensitive specimens (fresh tissue) 2.5 % Agarose with a low melting point of 37 °C.

Are there daily maintenance recommendations available?

Remove all removable parts from the microtome – use a spray bottle with destilled water and wash all parts thoroughly. Afterwards use 100 % Ethanol. Dry parts on a dry cloth. Wipe control panel with a moist cloth. Please note: VT1200 does not need lubrication.

Are there preferred types of blades and why would you select a certain type?

There are 4 different types of blades available: razor blades, injector blades and sapphire blades. In most cases razor blades give a satisfactory sectioning result. They have the advantage of being reasonably priced. In the VT1200 S they can be inserted as a whole. Injector blades are about 3 times as thick as razor blades. Most customers prefer to use the thinner razor blades. Razor and injector blades are made out of metal and some customers might not like the direct contact of metal with the tissue. In case users would like to avoid metal blades in contact with the tissue, a sapphire blade is recommended. Sapphire blades are more expensive, but if handled properly can last very long, as long as no preparation tool hurts the sapphire. Sapphire blades can be re-sharpened.

I know something is wrong but I haven’t a clue as to what or why. What is my best approach?

Check the user manual and follow all instructions. In case you are still not satisfied with the results, please call Leica Microsystems Technical Service.

Are the magnets strong enough to hold specimens in place?

The cutting forces of a vibrating blade are very little. The force of the magnet is strong enough to hold the specimen disc in place.