Editing Microtome (section)

==Types==

===Sledge ===
[[File:Sledge microtome.jpg|thumb|left|A sled microtome]]

A sledge microtome is a device where the sample is placed into a fixed holder (shuttle), which then moves backwards and forwards across a knife. Modern sled microtomes have the sled placed upon a linear bearing, a design that allows the microtome to readily cut many coarse sections.<ref name="Lang">{{Cite book|author=Gudrun Lang |title=''Histotechnik. Praxislehrbuch für die Biomedizinische Analytik.'' (Histology : practical textbook for analytical biomedicine)|publisher=Springer, Wien/New York|year= 2006|isbn=978-3-211-33141-5}}</ref> By adjusting the angles between the sample and the microtome knife, the pressure applied to the sample during the cut can be reduced.<ref name="Lang" /> Typical applications for this design of microtome are of the preparation of large samples, such as those embedded in paraffin for biological preparations. Typical cut thickness achievable on a sledge microtome is between 1 and 60&nbsp;μm.

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===Rotary ===
[[File:Microtome-1.jpg|thumb|A rotary microtome of older construction]]

This instrument is a common microtome design. This device operates with a staged rotary action such that the actual cutting is part of the rotary motion. In a rotary microtome, the knife is typically fixed in a vertical position.<ref name="MVM">Klaus Henkel: ''[http://www.mikroskopie-muenchen.de/cut-mikrotom.html Das Schneiden mit dem Mikrotom] {{webarchive|url=https://web.archive.org/web/20091110100611/http://www.mikroskopie-muenchen.de/cut-mikrotom.html |date=10 November 2009 }}.'' Mikrobiologische Vereinigung München e.&nbsp;V., 2006, accessed 15 February 2009</ref>

[[File:Microtome principle.svg|thumb|left|Principle of sample movement for making a cut on a rotary microtome]]
In the figure to the left, the principle of the cut is explained. Through the motion of the sample holder, the sample is cut by the knife position 1 to position 2, at which point the fresh section remains on the knife. At the highest point of the rotary motion, the sample holder is advanced by the same thickness as the section that is to be made, allowing the next section to be made.

The flywheel in many microtomes can be operated by hand. This has the advantage that a clean cut can be made, as the relatively large mass of the flywheel prevents the sample from being stopped during the sample cut. The flywheel in newer models is often integrated inside the microtome casing. The typical cut thickness for a rotary microtome is between 1 and 60&nbsp;μm. For hard materials, such as a sample embedded in a synthetic resin, this design of microtome can allow good "semi-thin" sections with a thickness of as low as 0.5&nbsp;μm.

===Cryomicrotome===
{{See also|Frozen section procedure}}
[[File:Cryostat microtome.jpg|thumb|left|A cryomicrotome]]

For the cutting of frozen samples, many rotary microtomes can be adapted to cut in a liquid-nitrogen chamber, in a so-called cryomicrotome setup. The reduced temperature allows the hardness of the sample to be increased, such as by undergoing a glass transition, which allows the preparation of semi-thin samples.<ref name="Lang" /> However the sample temperature and the knife temperature must be controlled in order to optimise the resultant sample thickness.

===Ultramicrotome===
[[File:Microtome-ultras.jpg|thumb|200px|A ribbon of ultrathin sections prepared by room-temperature ultramicrotomy, floating on water in the boat of a diamond knife used to cut the sections. The knife blade is the edge at the upper end of the trough of water.]]

An ultramicrotome is a main tool of [[ultramicrotomy]]. It allows the preparation of extremely thin sections, with the device functioning in the same manner as a rotational microtome, but with very tight tolerances on the mechanical construction. As a result of the careful mechanical construction, the linear thermal expansion of the mounting is used to provide very fine control of the thickness.<ref name="Lang" />

These extremely thin cuts are important for use with [[transmission electron microscope]] (TEM) and [[serial block-face scanning electron microscopy]] (SBFSEM), and are sometimes also important for light-optical microscopy.<ref name="MVM" /> The typical thickness of these cuts is between 40 and 100&nbsp;nm for transmission electron microscopy and often between 30 and 50&nbsp;nm for SBFSEM. Thicker sections up to 500&nbsp;nm thick are also taken for specialized TEM applications or for light-microscopy survey sections to select an area for the final thin sections. [[Diamond knives]] (preferably) and glass knives are used with ultramicrotomes. To collect the sections, they are floated on top of a liquid as they are cut and are carefully picked up onto grids suitable for TEM specimen viewing. The thickness of the section can be estimated by the [[thin-film interference]] colors of reflected light that are seen as a result of the extremely low sample thickness.<ref>{{cite journal | author = Peachey Lee D. | title = Thin Sections: A study of section thickness and physical distortion produced during microtomy | journal = J Biophys Biochem Cytol | volume = 4 | issue = 3 | pages = 233–242 | year = 1958 | pmid =  13549493| doi = 10.1083/jcb.4.3.233| url = http://jcb.rupress.org/cgi/reprint/4/3/233.pdf | pmc = 2224471}}</ref>

===Vibrating ===
The vibrating microtome operates by cutting using a vibrating blade, allowing the resultant cut to be made with less pressure than would be required for a stationary blade. The vibrating microtome is usually used for difficult biological samples.<ref name="Lang" /> The cut thickness is usually around 30–500&nbsp;μm for live tissue and 10–500&nbsp;μm for fixed tissue.<ref>{{Cite journal|last=Krumdieck|first=Carlos L.|date=January 2013|title=Development of a live tissue microtome: reflections of an amateur machinist|url=http://www.tandfonline.com/doi/full/10.3109/00498254.2012.724727|journal=Xenobiotica|language=en|volume=43|issue=1|pages=2–7|doi=10.3109/00498254.2012.724727|pmid=23009272|s2cid=6108637|issn=0049-8254|url-access=subscription}}</ref>

===Saw ===
The saw microtome is especially for hard materials such as teeth or bones. The microtome of this type has a recessed rotating saw, which slices through the sample. The minimal cut thickness is approximately 30&nbsp;μm and can be made for comparatively large samples.<ref name="Lang" />

===Laser ===
{{See also|Laser microtome}}
[[File:Laser-microtome-schematic.png|thumb|A conceptual diagram of laser microtome operation]]

The [[laser]] microtome is an instrument for contact-free slicing.<ref name="Lasermicrotome">Holger Lubatschowski 2007: ''Laser Microtomy'', WILEY-VCH Verlag GmbH, Biophotonics, S. 49–51 ([http://www.photonicnet.de/Aktuelles/partner/2007/06/laser_microtomy_optik-photonik_juni_2007.pdf PDF] {{webarchive|url=https://web.archive.org/web/20110719072556/http://www.photonicnet.de/Aktuelles/partner/2007/06/laser_microtomy_optik-photonik_juni_2007.pdf |date=19 July 2011 }}). {{doi|10.1002/opph.201190252}} {{free access}}</ref> Prior preparation of the sample through embedding, freezing or chemical [[fixation (histology)|fixation]] is not required, thereby minimizing the artifacts from preparation methods. Alternately this design of microtome can also be used for very hard materials, such as bones or teeth, as well as some ceramics. Dependent upon the properties of the sample material, the thickness achievable is between 10 and 100&nbsp;μm.

The device operates using a cutting action of an infrared laser. As the laser emits a radiation in the near infrared, in this wavelength regime the laser can interact with biological materials. Through sharp focusing of the probe within the sample, a focal point of very high intensity, up to [[Terawatt|TW]]/cm<sup>2</sup>, can be achieved.  Through the non-linear interaction of the optical penetration in the focal region a material separation in a process known as photo-disruption is introduced. By limiting the laser pulse durations to the femtoseconds range, the energy expended at the target region is precisely controlled, thereby limiting the interaction zone of the cut to under a micrometre. External to this zone the ultra-short beam application time introduces minimal to no thermal damage to the remainder of the sample.

The laser radiation is directed onto a fast scanning mirror-based optical system, which allows three-dimensional positioning of the beam crossover, whilst allowing beam traversal to the desired region of interest. The combination of high power with a high raster rate allows the scanner to cut large areas of sample in a short time. In the laser microtome the laser-microdissection of internal areas in tissues, cellular structures, and other types of small features is also possible.