Polymethyl Methacrylate

I'm going to trial some Polymethyl Methacrylate coatings for implant projects. This is a transparent thermoplastic making it comparable (in class) to some other more widely discussed biocoatings like PTFE and PEEK. Its biocompatibility was discovered during WWII. The earlier planes used glass while the later used Methyl Methacrylate. Shards of glass in the eye resulted in rejection and blindness whearas the Methymethacrylate shards were inert. This discovery led to the first artificial lens implants.

Brand names of this stuff include plexiglass and Acrylite, although these do contain additives to change the physical characteristics so off the shelf stuff may not be appropriate. It has some really cool useful characteristics and some possible disadvatages.

The beneficial aspects:

It's very biocompatible and appropriate for longterm implantation.

 It's inexpensive in a powder monomer form.

Many solvents can dissolve it and some ( like trichloromethane ) can be used to dissolve a bit on the surface to "weld" two pieces together.

The working temperatures for nearly all processes are totally achievable in an oven. For example it can be anneal in an oven at 90c.

It seems (haven't gotten it in yet) to be very easy to work with. Generally consisting of a powder monomer and solvent. I'm going to play around with subjecting the product with temperature to see how it affects it, but dentures for example are made at room temperature. You can even buy liquids which harden within 20 minutes.

Finally: Once set, it has very low permiability to water. This is the disadvatage of silicone that makes it a poor choice. Sure, permiability is irrellevant for say a magnet, but circuit boards are a whole other story.



It's not the strongest material around really. It can shatter under strain and stress. What little water that it does absorb decreases the overall strength too, so in the body it is going to be saturated. Overall, this isn't a huge issue as long as we aren't trying to make artificial bones or faux armor junk out of it.


How to work with it?

Well, I'm going first try spraying it onto items. Basically, I'm just going to make a solution of PMMA and a solvent. I'm thinking of using toluene although there might be other better choices. I'll use an airbrush to spray it onto a few nickel based magnets. After drying, I'll use a nickel indicator fluid I worked out for the M31s to check the integrity of the coating.

I'm also going to be trying it on a few other items to check for it's ability to bind.. for example silicone. Silicone has the advantage of being very soft and pliable.. great for larger implants. If they bond well, then PMMA could be sprayed onto a circuit board prior to being encased in silicone.

Following all of this I'm going to go through all the normal cytotox testing etc. I'm going to write up all that stuff when the time comes as I'm still missing a few key items.

The expected surface produced is similar to a glass. It's hard and inflexible.





  • what is needed to start the testing? I'm willing to pitch in time and money, This sounds perfect for what I want to be doing.
  • Sounds really interesting!
  • Well, I have a quart of dry monomer on the way. I need a solvent, a spray gun, either a compressor or a tank of nitrogen. I also need to pick up another electric hot plate.
  • If this does everything you want would this be suitable as the sole coating for magnets and other implantables?
  • how thick is the stuff when its mixed with the solvent? If its not super thick I bet you could get away with not needing a spray gun and compressor (even thought it would be cool). I know that with wood working every feels like they need a spray booth of spraying lacker on their finished thing, but a spray water bottle works perfect for small things, I wonder if it would work for this stuff to.
  • I'd be interested to hear about the results. My initial reaction is that I think that most coating methods are going to leave it too permeable, possibly to the point of being pointless for use with electronics or non-bio-compatible materials. Then again, it's a cheap enough and easy enough method that it's worth a little experimentation.
  • You mentioned trichloromethane. It really is the ideal solvent for PMMA. However, benzene is good too. What is the molecular weight of your PMMA?

    While we used a compressor those few times, and it would work, you should really go for the nitrogen if you can if you are looking for long term implantation. On the other hand, a compressor is fine for testing purposes.

    Also, I noticed you left vacuuming out of your setup. This is actually really important. Since the polymer is technically a itty bitty mesh, after curing, small amounts of solvents will be trapped in the polymer and may cause irritation issues. You'll end up getting issues not related to the polymer itself.

    This sounds pretty cool. PMMA has a long history of use in other implants. I hear that there's roughly a 5% complication rate with the bone implant method. I think that this is because of the injection technique tho, not because of the material itself.  I'm curious to see how the tests come out.
  • Unfortunately, it' doesn't look like the stuff will be delivered prior to grindfest.
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