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Double-Bladed Pathology Scalpel ProjectSPRING 2018 MAE 156B SPONSORED PROJECT
UNIVERSITY OF CALIFORNIA, SAN DIEGO
Sponsored by Jonathan Lin, M.D., Ph.D.
Pathology, which is the study of the causes and effects of diseases, require pathologists to sample a lot of body tissue for analysis on a daily basis. This can be up to hundreds of tissue samples a week. The tissues are cut into 3-4 mm slices using a scalpel and are put into embedding cassettes, which can hold tissue up to 5 mm thick. In today’s market, single bladed scalpels are being widely manufactured. Unfortunately, current designs leave much to desired when cutting certain tissues.
For example, one of the tissues that pathologists have trouble cutting are eyeballs. Although these operations are rare compared to other tissues and are performed maybe once a week, it occurs often enough that the difficulties posed warrant a better redesign of the scalpel. When pathologists want to sample an eyeball, the sampled tissue should include the cornea, eye muscle, and most importantly the optic nerve at the back of the eyeball within a 4 mm cut. This however proves difficult due to the eyeball relying on “vitreous humor”, a gel like substance, to keep its shape. After the first cut, it is challenging to keep the vitreous humor from flowing out and deforming the eyeball. This disrupts the position of the optic nerve and may cause inconsistent slices. Sometimes specimens become ruined and unusable.
Project Background:
Objective:
The challenge here is to design a double bladed scalpel that can cut any desired tissue in one cut instead of two, removing the hassle of excessive maneuvering in order to keep the tissue structure from collapsing. By doing so, the pathologist can position and angle the tissues and obtain the desired part in one cut without much difficulty. The team is restricted to only use Pathco double-sided blades.
Double-sided Pathco Blades. PC: CancerDiagnostics Inc.
Link to Previous Prototype and Previously Considered Designs
Final Design:
After much deliberation, the team cut the number of possible designs down to one from an original five. This decision was aided by comparing design performances via a Pugh chart.
The design that the team is going to pursue is called the "Wedge Collet" design.
This design utilizes the idea of a collet and wedge sockets to form a double-bladed system.
The two blades would slide into the wedges, followed by two 3D printed sockets.
The blades and sockets would be constrained by a threaded collet.
The horizontal force that sockets apply on the blades would also create friction in vertical direction, which will constrain the blades.
The two blades are separated with a fixed distance of 3 mm.
Direct contact with the blades is limited to only two times.
Mounting of the blades take an estimate of 30 seconds.
Performance Result:
Annotated CAD image of
blade mounting procedure
Annotated CAD image of scalpel
Cherry tomatoes were cut using the machined scalpel in order to emulate human tissue. The width of the cherry tomatoes that were tested on were about 25 mm in diameter, which is almost the same as an eyeball sample. As can be seen in the above pictures, the tomato slices were uniformly cut. This shows that the blades were kept in parallel throughout the cutting motion. As can be seen in the first image, the samples may get stuck in between the blades. After consulting with the sponsor, this was deemed acceptable as most pathologist would have forceps to push the sample into an embedding cassette.
Below are comments on the scalpel from the sponsor:
Advantages
+ Blades are parallel and make consistent cuts
+ Mounting the blades and taking them off is much safer and faster compared to the previous 2013 prototype
+ Scalpel is light and easy to use
Could be improved
= Current cutting length available is fine, but more length would be appreciated.
Concerns
- Due to the size of the lip of the collar, the scalpel has to be used at an angle when finishing a cut.
- Sockets may get lost due to its small size
Since the demonstration to the sponsor, several adjustments have been made.
The aluminum collar has been replaced with a stainless steel lipless one. This allows the user to finish a cut without excessive maneuvering and prevents the handle from rolling on a surface.
The tip of the shaft has been shaved off to allow for more cutting length.
Currently, the team is planning to 3D print 100 sockets to mitigate the socket loss problem.
Video Demonstration of Product:
Before:
Above is a video demonstration of the blade mounting process using a previous scalpel model that was developed by UCSD Bio-engineering students in 2013. As can be observed in the video above, the blades would fall off easily while mounting and this becomes a safety hazard for the pathologist. It also takes an average of 2 minutes to mount both the blades correctly. This design is unsafe and too time consuming and thus requires a redesign.
After:
Below are video demonstrations of the blade mounting process and testing with cherry tomatoes. The scalpel was handled by the sponsor.
As can be seen from the blade mounting video above, the process is much faster and safer. The blades does not fall off and is very easy to dismantle. This was a major improvement over the 2013 prototype. The whole scalpel can be assembled within 30 seconds, much faster than the 2 minutes of the previous prototypes.
In the video above, it can be observed that the tomato slice was rather uniform. This shows that the parallelism of the blades are improved from the previous prototype. The blades also stay firmly in place after cutting. This allows the user to cut or trim the previous sample without needing to adjust the blades.
Promotional Video:
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