Hey, so about the scalpel tip…will it definitely not be feasible to just directly heat up the scalpel, itself? We briefly discussed this in class, but I can’t remember why we decided that this wouldn’t work. Because, if the scalpel was thing and small enough, it still might be able reach high enough temperatures….or at least moderately high so that it can be a start. Did Dennis have anything to say about this particular idea?
Hey guys, I created a Google doc with some of the info we’ll need for the poster. I started it, but it probably could benefit from some revisions.
Please also add to the Pugh Chart part–I am missing some of our previous ideas. And, if there is anything missing at all–from any of the sections (existing or not)–please add!
This is some info I got from Gary at Bovie about autoclaving the tips:
“It is not recommended to autoclave the tips. Even though Acrylonitrile Butadiene Styrene (ABS) melts at approx 450F it can become pliable or soften. I believe the deflection and service temperatures are something like 215F. However manufacturer specs can differ from one to the next. Bovie has only validated the tips through Eto sterilization.”
In a later email, he said, “The best thing to do is to autoclave the tips and see what happens. But again Bovie has only validated sterilization through Eto because this is a disposable device and is not meet to be re-sterilized. However we have non-sterile product and I believe these are only for non-invasive procedures only, not 100% sure on this if you need to know I will pass along your request to somebody that can give you a more definitive answer.”
Sounds like if we want to know if these tips can be autoclaved, we need to just throw them in an autoclave and see what happens. Maybe if we have tips after we’ve made our prototypes with the different tips, we can try this out.
“Medical devices have a wide range of materials used depending on applications. For example in disposable devices I would typical use ABS or PVC. In reusable I would use Polycarbonate or Radel. However I have used Polycarbonate in disposable as well, again depending on the application and cost.
If you are looking for reusable devices for autoclave maybe you should look into Radel. I use Radel for its ability to withstand standard and flash autoclaves (has very high temperature withstand). For example Bovie’s A901 ES pencil, its body is made of Radel and the cable is silicone.”
I went to the Radel Polyphenylsulfone site and it said: “For the most challenging applications – requiring repeated sterilization or uncompromising toughness – choose Radel polyphenylsulfone (PPSU). With a high heat deflection temperature of 405°F (207°C), it can withstand continuous exposure to heat and still absorb tremendous impact without cracking or breaking” and that it was “Steam sterilizable with better retention of impact properties”
Looking into pricing though and why the silicone is used.
After a long waiting period of getting our supplies and materials in, we finally have some good news! We built a retractable tip that extends to 5’’. This took a while to arrive at, but it is (for the most part) functioning. It functions like an antenna; there are three layers of brass rods connected by springs. The rods are of different diameters so that the tubes can fit over one another and compress down to a length of about 2’’ or so. Big thanks to Bernard!
We now need to try to modulate this tip with a scalpel. We are still waiting for our Bovie pen to come in, so testing to see if these tips can cauterize will still need to wait. This prototype is with [SG]!
yay for some good news =)
So we met with Dennis today and he helped us implement our scalpel idea. We explained to him our design idea, what we wanted the overall function to be, and how we thought our design could be carried out. He was extremely helpful in helping us drill a hole through the tip as well as providing us with an optimally sized screw + washer.
So now, we have a real Swiss army cautery tip!
We still need to do a few more things, however:
- Score the brass tubing so that it doesn’t come loose when we try to extend it.
- Use insulating material to prevent short circuiting
- Use a tab so that the user can more easily position the blade
- Implement a mechanism such that the blade is sturdy when the user is cutting through the tissue
On Monday we added an “untelescoping” feature to the tip to enable it to fit into our pen. We also tested our device in the Course 6 lab with the power source.
Our tip glowed red-hot after 2 sec at 2.8 A and 1.5 V, identical to the Bovie tip. This confirms that the electrical and heating properties are comparable to the original Bovie tip.
We were able to burn paper with the low temp cautery after fitting in out tip, indicating good interfacing. We conducted tests by passing current through a thin scalpel. It became warm after 30 sec at 3.6 A and 0.5 V. To heat it up faster we would use a smaller surface area or other materials (looking into that now).
Overall, a successful day.
Stainless steel: heat capacity - 500 J/kg-°C
Copper (not autoclavable so must be coated with Nichrome or gold which is actually not very expensive):
heat capacity 385 L/kg-C
Silicon: heat capacity 556.9 J/kg-C
Heat capacities are at approx. 200 degrees C
Other metals such as gold, silver, and platinum have lower heat capacities than stainless steel and are electrically conductive, but for cost reasons I have not included them.
Possible tip designs
Apparently 2 is not very feasible but we have accomplished 1 and 4 in its preliminary stages. 3 and 5 are still further possible design ideas.
This Pugh Chart indicates that our design is quite useful. The only design that ranks higher is the one in which the scalpel heats up (something we have been looking into and testing).
I’m also uploading the old one so we can compare and see how our ideas have changed/how we got to where we are with the project.
Final Pugh Chart (PDF)