PDMS Coating, the right way and the wrong way
As many of you know, I tend to talk a lot of ish about PDMS (silicone) coatings. Part of this comes from the fact that in a lot of implant situations there are other options. But another reason is the methodology used to coat the device in silicone.
Sometimes, silicone is your best option. There will be no TiN coatings on circuit boards, for instance. So what do you do?
Well, I'm kind of bringing this up now because of a project we have been working on, that trandermal. Some part of this device is going to have to be coated in silicon, it's just an unfortunate effect of design. I want to show the differences between the silicone that we and body mod artists have normal access to, and how a non production method coating looks, super up close and personal.
This here is a comparison of a magnet coated in silicon from another source, and one that I did in the lab just the other day.
The top two images are the standard mold type coating. The bottom two are using a spray coating technique I worked up back at university. Both shots were taken at 400x
A couple of things to note. The top coating has no dark line. Why? This is because the coating is so thick that you can't see the edge of the coating and the magnet inside at the same time. Added bulk can be an issue. The roughness of the edges is caused by the removal from the mold, tho it is possible that these were in a sheet and just punched out. Regardless, what you are seeing is a raggedy little edge, prime for bacterial and platelet adhesion and other types of fouling. Not happy. Luckily, silicone is pretty inert, so it is fairly resistant to these issues. My question is, why make it worse?
Now to the bottom images. These are the two roughest spots I could find. You'll notice the characteristic pockmarking that you will find in silicone. It is technically a polymer mesh. The coating is significantly more thin. Some of the blur that we are getting in these images is due to the thin, smooth coating. It's hard to focus on the entirety a thin smooth area that goes around a curve with a microscope. I actually took a bunch of pictures, working my way through the layers, and may turn them into a gif... The point being is that with this method, you significantly reduce the "edges" another thing I like to complain about when talking about implant design.