Refinement of a Hand Microtome Design -- 2
Budget: $30 – $250 USD
This project is to refine a basic sliding microtome design for non-professional users. The designed parts will be 3D printed (PETG) to assemble a working prototype. The project output should be at least one CAD file (Fusion, STEP etc.) that I can use to export STLs of different parts for 3D printing. The CAD file can also be used in the future for possible modifications.
A microtome is used for cutting ultra thin (~5um) slices of a specimen (biological material e.g. a plant stem) for evaluation under microscope. In a professional environment (e.g. an histology lab), the specimen is embedded into a paraffin block which is not simple or safe to do at home and then cut with a (professional/commercial) rotary microtome to 1-10um thick slices. The rotary microtome has its blade at a fixed position but moves the specimen block since it is solid enough barely touching the blade. Hand microtomes for non-professional users exist, and they are designed mostly on the principle that specimen is hold steady inside a hard but can be cut material (like carrot or potato) and then they are cut manually with a hand-held sharp microtome knife. A sliding microtome for non-professionals also exists, but not as common as others. See the links below for some examples.
The difference of the design in this project is (1) to use a linear rail and keeping the razor blade at an angle (similar to professional sliding microtomes) and (2) to have specimen embedded in an agar block. Agar block is not hard like paraffin but still can hold the specimen and it is simple and safe to make at home. Agar is used for making gelatin/jelly. I expect (1) to work well enough, but (2) is not tested. If (2) fails because Agar block is not good for this purpose, the design might still be useful by changing it slightly (and still use something like carrot/potato). However, this is not the scope of this project. I will create another project if such a modification is needed.
The microtome consists of a ready-to-use z-stage (micrometer controlled), an MGN9C (can be changed to different model if needed) linear rail, and to be designed 5 parts. The parts are:
- flat base: z-stage and linear rail will be mounted on this base. so a flat rectangular prism with appropriate screw holes, nothing fancy here.
- sled: which will be mounted on top of the rail block and hold a double edge razor blade at 12 degrees angle (from the base plane). A metal L part should probably be used to minimize flex on either one or both sides (it should have screw holes for that). We have to discuss which L part is suitable and if it can be sourced easily. The razor blade area should have two pins to guide/hold razor blade and two screw holes. It should also have probably 4 holes to mount sled on the rail block.
- clamp: which will clamp the double edge razor blade to minimize flex. It should have two holes for pins on the sled, and two countersunk screw holes. nothing fancy also here.
- stage: which will be mounted on top of z-stage and hold the casette (thus the agar block) and also capture the slice cut by the razor blade. It should have countersunk screw holes to be mounted on the z-stage. It should have one section close to the rail to hold the casette, another section to hold the sliced material (the material might stuck on the blade, this is OK, it will be manually moved with a brush to this section).
- casette: basically holds the Agar block, just a plastic container. I think it is the easiest way to handle the agar blocks (similar to paraffin blocks), but I am open to suggestions on this. when casette is put on the stage, the specimen is on top of the casette, so blade cuts the agar block and does not touch to the casette. The size of casette can be approx 3mm x 3mm and 1-2mm thick. The size is not critical as long as it is not very small (<2mm), it can be designed according to the stage.
An example use case:
- agar solution is prepared and poured onto a small possibly metal container
- a plant stem is put on the agar solution, and the casette is put over the plant stem
- after the solution solidified, it is turned upside down, metal container removed (like making a jelly), and casette holding the agar block is put on the stage
- z-stage is moved up as much as needed (passing the knife slightly)
- the first cut is made moving the linear rail. This cut is not important, it will not be used.
- successive cuts are made by moving the z-stage up ~50um every time. The repeatability of these cuts (i.e. each slice has to be ~50um thick) are the most important design problem. A repeatability between 20-80um is a design target.
The z-stage to be used at the moment is: https://www.tosag.ch/Z-Achse-Linearpositioniertisch-10mm
MGN9C will probably need to be 150mm or 100mm. There is no need for space optimisation to fit 100mm here if 150mm is better. Use 100mm only if it is totally ok.
The double edged (DE) razor blade design is standard, but it can be assumed that Feather 81-S will be used: https://www.feather.co.jp/en/g_Products/general01.html
A regular hand microtome is shown here: https://euromex.academy/en/uploads/producten/producten_product_taalspecifiek/MT.5500_Manual_EN_6.pdf
A sliding design hand microtome is shown here: https://euromex.academy/en/uploads/producten/producten_product_taalspecifiek/MT.5503_Manual_EN_1.pdf
Paraffin embedding procedure can be viewed in this video (3:50-4:50): https://www.youtube.com/watch?v=8Rv7Gx_4xqQ
Rotary microtome use can be viewed in this video (2:50-10:50): https://www.youtube.com/watch?v=MRIQZPCX45I
A draft design is attached (see Files). This does not show the stage or the casette but shows the base, sled and clamp.
A microtome is used for cutting ultra thin (~5um) slices of a specimen (biological material e.g. a plant stem) for evaluation under microscope. In a professional environment (e.g. an histology lab), the specimen is embedded into a paraffin block which is not simple or safe to do at home and then cut with a (professional/commercial) rotary microtome to 1-10um thick slices. The rotary microtome has its blade at a fixed position but moves the specimen block since it is solid enough barely touching the blade. Hand microtomes for non-professional users exist, and they are designed mostly on the principle that specimen is hold steady inside a hard but can be cut material (like carrot or potato) and then they are cut manually with a hand-held sharp microtome knife. A sliding microtome for non-professionals also exists, but not as common as others. See the links below for some examples.
The difference of the design in this project is (1) to use a linear rail and keeping the razor blade at an angle (similar to professional sliding microtomes) and (2) to have specimen embedded in an agar block. Agar block is not hard like paraffin but still can hold the specimen and it is simple and safe to make at home. Agar is used for making gelatin/jelly. I expect (1) to work well enough, but (2) is not tested. If (2) fails because Agar block is not good for this purpose, the design might still be useful by changing it slightly (and still use something like carrot/potato). However, this is not the scope of this project. I will create another project if such a modification is needed.
The microtome consists of a ready-to-use z-stage (micrometer controlled), an MGN9C (can be changed to different model if needed) linear rail, and to be designed 5 parts. The parts are:
- flat base: z-stage and linear rail will be mounted on this base. so a flat rectangular prism with appropriate screw holes, nothing fancy here.
- sled: which will be mounted on top of the rail block and hold a double edge razor blade at 12 degrees angle (from the base plane). A metal L part should probably be used to minimize flex on either one or both sides (it should have screw holes for that). We have to discuss which L part is suitable and if it can be sourced easily. The razor blade area should have two pins to guide/hold razor blade and two screw holes. It should also have probably 4 holes to mount sled on the rail block.
- clamp: which will clamp the double edge razor blade to minimize flex. It should have two holes for pins on the sled, and two countersunk screw holes. nothing fancy also here.
- stage: which will be mounted on top of z-stage and hold the casette (thus the agar block) and also capture the slice cut by the razor blade. It should have countersunk screw holes to be mounted on the z-stage. It should have one section close to the rail to hold the casette, another section to hold the sliced material (the material might stuck on the blade, this is OK, it will be manually moved with a brush to this section).
- casette: basically holds the Agar block, just a plastic container. I think it is the easiest way to handle the agar blocks (similar to paraffin blocks), but I am open to suggestions on this. when casette is put on the stage, the specimen is on top of the casette, so blade cuts the agar block and does not touch to the casette. The size of casette can be approx 3mm x 3mm and 1-2mm thick. The size is not critical as long as it is not very small (<2mm), it can be designed according to the stage.
An example use case:
- agar solution is prepared and poured onto a small possibly metal container
- a plant stem is put on the agar solution, and the casette is put over the plant stem
- after the solution solidified, it is turned upside down, metal container removed (like making a jelly), and casette holding the agar block is put on the stage
- z-stage is moved up as much as needed (passing the knife slightly)
- the first cut is made moving the linear rail. This cut is not important, it will not be used.
- successive cuts are made by moving the z-stage up ~50um every time. The repeatability of these cuts (i.e. each slice has to be ~50um thick) are the most important design problem. A repeatability between 20-80um is a design target.
The z-stage to be used at the moment is: https://www.tosag.ch/Z-Achse-Linearpositioniertisch-10mm
MGN9C will probably need to be 150mm or 100mm. There is no need for space optimisation to fit 100mm here if 150mm is better. Use 100mm only if it is totally ok.
The double edged (DE) razor blade design is standard, but it can be assumed that Feather 81-S will be used: https://www.feather.co.jp/en/g_Products/general01.html
A regular hand microtome is shown here: https://euromex.academy/en/uploads/producten/producten_product_taalspecifiek/MT.5500_Manual_EN_6.pdf
A sliding design hand microtome is shown here: https://euromex.academy/en/uploads/producten/producten_product_taalspecifiek/MT.5503_Manual_EN_1.pdf
Paraffin embedding procedure can be viewed in this video (3:50-4:50): https://www.youtube.com/watch?v=8Rv7Gx_4xqQ
Rotary microtome use can be viewed in this video (2:50-10:50): https://www.youtube.com/watch?v=MRIQZPCX45I
A draft design is attached (see Files). This does not show the stage or the casette but shows the base, sled and clamp.
Related categories:
CAD/CAM
3D Rendering
Mechanical Engineering
3D Modelling
3D Design
3D Printing
Prototyping
3D CAD
3D Drafting