Hello from Hanna:
"Nothing in the capsule is properly connected, so it won't measure or transmitt anything, but one get the to see actual size of the whole system!
The process from capsule idea to being able to cast it with batteries, PCB and transducer inside was fun and educational in many ways. I started working on this straight out of university and got to practice a whole lot of what I'd learnt recently, in addition to researching more about new topics.
E.g. Both epoxy and silicone is made by mixing a part A and a part B, and that silicones curing time can be sped up by adding heat. I didn't know that before I started working at ZP. Now, we are able to encapsulate a whole little system inside both mediums!"
Our first non-functioning prototype was encapsulated in biocompatible epoxy. Inside it were two batteries, a PCB, a transducer and partly the wire sensor.
We had to make our own mould for the capsule and started with 3D-printing. As epoxy is a type of glue, we had a hard time getting the pieces out of their plastic moulds after curing, even with lubrication beforehand. Some of our test pieces are still stuck in their moulds.
The solution was to change from plastic to silicone moulds: flexible enough for the epoxy to be popped out, even without lubricants (Which we tested: We feared the epoxy would get stuck again.). Silicone has a low coefficient of friction, meaning it has a smooth and non-sticky surface. This is why we hoped the epoxy wouldn't stick at all.
Fun fact: Needles and other medical instruments meant to come in contact with skin/tissue are often coated with a thin layer of silicone. The silicone has a lower coefficient of friction than the metals used, and studies have shown patients experience less pain when poked with the coated needles.
The measurements of our firstcapsule-shaped packaging had a size of ⌀15.6mm x 38 mm and a weight of 3.2g underwater. At that size, it can be implanted in fish with a body mass above 900g, following the 2% body mass rule.
We as ZP want to be as green as possible, and we wanted to make the system re-usable. The batteries are calculated to last 3 months and after that they have to be changed. Anything covered in epoxy will stay that way, and so we decided to look for options less rigid than epoxy. We went for silicone, and will talk more about why in a later post.
Until next time,
Hanna T. Bråthen,
Engineer at ZP
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