The disposable microtome blade is now the microtomy product of choice in the modern histopathology laboratory for the production of high-quality tissue sections to aid the diagnosis of disease. A good-quality blade is often undervalued, and this article aims to explain some of the history, skill and diversity surrounding the production and use of disposable microtome blades, and provides some useful information and guidance.
History
In the days when use of a solid microtome knife was standard practice for producing tissue sections, care of its cutting edge was of paramount importance. A sense of personal pride surrounded its upkeep. It was not acceptable to use another person’s prized knife and its upkeep took a lot of time. The longevity of its edge was dictated by the order in which tissue blocks were cut and the quality of the materials used in processing those blocks. The knife’s upkeep became a ritual of skill and the edge was sharpened and honed to perfection. Histologists were easily spotted outside the laboratory as the only people who stepped backwards quickly when any knife was dropped, rather than trying to catch it before it hit the floor.
Introduction of the disposable microtome blade to the UK was not without its problems, and, as with many new products in the histopathology laboratory, it met with a fierce resistance to change. The first widely accepted disposable blade was the Feather S35 blade, which was only accepted following persistent demonstration of the excellent results it could produce. For the first time it became possible to cut routine sections at less than 5 ?m without the need to embed and cut resin blocks using glass knives. Research, development and manufacturing skill was vital in realising this achievement, and it is not surprising that the manufacturer, The Feather Safety Razor Company, was based in Japan, a country famed for the excellence of its swords and steel production.
The Japanese city of Seki first gained renown some 800 years ago, at the end of the Kamakura period, through the work of the oriental bladesmith Magoroku of Seki. Magoroku’s weapons earned a reputation in battle for their durability and sharpness. Seki's other important reason for development as the centre of sword manufacture was its proximity to the three most important ingredients of a perfect blade – pure iron ore, a large supply of wood to produce charcoal, and clean water – which were all in abundance in the mountains surrounding Seki. Sword-forging skills and ergonomics were a legacy of the Samurai, and the skills passed down through the generations to the present day have helped to make Feather blades the consistently high-quality products that global renown.
Production
Old traditions matched with modern materials and state-of-the-art technology all play their part in producing a high-performance product. A good-quality product starts with a high-quality material, and this is austenitic stainless steel. This steel is resistant to corrosion and has good mechanical properties and special qualities of hardness and flexibility. This makes it ideal for precision blade production.
Even thickness is very important and the tolerance is 0.1 micron. This parameter is quality controlled and any material falling outside of this is rejected. Next comes grinding which passes through many ultraprecise stages to create a three-faceted blade edge. The cutting edge of a well-sharpened solid knife has a maximum tip diameter accuracy of 0.5 micron, whereas with a Feather microtome blade it is 0.1–0.2 micron, thus making it much sharper.
The next stage in production is platinum spattering, which strengthens the cutting edge. The blade is then inspected under an electron microscope before the coating processes begin. The coating of choice is sprayed on and fixed using a heating process. This results in an edge that has strength and minimal frictional resistance during sectioning.
Final quality checks are then performed. One of these involves cutting an embedded block of tissue to measure resistance. Inspections also involve measurement of blade angles and widths and a visual inspection using a microscope. Fully inspected blades are then carefully packed into cassettes and numbered internally. This audit trail guarantees product quality and ensures that all the stages are fully traceable.
Value for money
In these days of financial constraints it is important to get the best out of each microtome blade used in the laboratory. The time saved in its use compared with a solid knife is often forgotten and the cost per blade has not increased in real terms for many years.
One of the things to consider when assessing value for money is the average number of blocks that can be cut using one blade. Feather blades average 20 blocks, depending on the skill of the microtomist, and it is interesting to note that in Europe this figure is lower. Some other blades that cost less are not only shorter in their usable length but also dull quickly, resulting in fewer blocks cut per blade.
It is also useful to know that various blades are available to suit a range of requirements. These blades are finished with different coatings to give different characteristics. The S35 is the routine blade of choice in the UK, but, by sorting cases and tissue types and working to Lean systems, the choice of blade can be varied to suit individual needs. The R35 blade is more suited to cutting harder tissues such as uterus, cervix and any tough, dense tissue. Its ribboning qualities are also excellent. The N35 blade provides superior results when cutting hard or decalcified tissue.
The A22 is the sharpest Feather blade available and permits the thinnest sections to be produced – ideal when working with soft tissue such as lymphoma where section thickness can make diagnosis easier. The A35 blade is by far the best when small biopsy ribboning is required. There is also a S35L blade which is longer than normal and well suited to the production of sections from large tissue blocks.
For work in the cryostat, the C35 blade is recommended. It is made of carbon steel and not coated, which means that imperfections caused by the coating cracking at low temperatures are avoided and potential artefacts in the section are reduced. Coated blades should be ‘trimmed in’ before the best sections are produced. This results in the ‘evening out’ of the plastic top coat that is applied to the blade to protect it before use, and can be likened to stropping a solid knife to smooth the edge.
Processing is also a key factor in the production of good-quality sections and over-dehydration can lead to brittle tissue that will put undue strain on the blade edge. Good-quality paraffin wax is also vital. Wax that is inconsistent in composition or contains undissolved additives (caused by storage at too low a temperature) can cause small nicks in the blade edge.
Poor housekeeping is another cause of trouble. Embedding centre reservoirs need to be cleaned as atmospheric dust and grit can cause blade problems. Another problem can occur if the microtome is not properly cleaned and maintained. Block holders should be clean and clear of debris, and the back of a knifeholder can become pitted over time resulting in minute metal shards scoring the tissue.
Time saved by using Feather disposable microtome blades in the laboratory not only results in a cost-effective, consistent, quality result, but aids diagnosis by avoiding delays caused by the need to recut sections. This in turn frees the system, permitting faster turnaround of reports and ultimately a reduction in patient anxiety.
To improve the efficiency of the laboratory is something that is talked about incessantly, but to compromise on quality and incur extra costs seems senseless when it is in fact long-term goals that will see most benefit to the patient and the staff.