Types of magnets that have been used

edited February 2015 in Magnets
Hi, first of all I'd like to say that I'm new here. :P

I've been lurking around a bit, and it seems to me that so far most discussions revolve around magnet implantation. However, most people seem to be using neodymium magnets which are pretty strong. My question is: has anyone used any other types of magnets and how effective they are (in terms of sensing electromagnetic waves)?

I'm thinking whether there is a more biocompatible option out there and I am wondering what is the minimum amount of magnetism needed for the neurons to start picking up electromagnetic waves.


  • Welcome.
    Interesting question. For a long time I have wondered about maghemite which is biocompatible and non-toxic to humans. I don't know if it would be strong enough or break up after being inside a person. 
  • Well, given that it's biocompatible (meaning that the immune system is either going to not respond to it or going to isolate it, which is the case for other implants) and it's not going to be mechanically loaded I'm somewhat doubtful that it will break up. I'm more concerned with the amount of strength the magnet will have and if it is enough to pick up electromagnetic waves.
  • Keep in mind that "biocompatible"/"non-toxic" isn't a bifurcation light switch type of answer. Configuration matters. I think your thinking of nanoparticles which is a whole different beast from claiming a macroscopic object is compatible.
  • It depends.

    The reason why older hip implants are not as biocompatible as newer ones where the contacts are ceramics on plastics instead of metal on metal because metal on metal wears off to release small particles which causes the immune system to go nuts. 

    Also, when considering hip implants we're talking about loading, which means that their mechanical properties matters a lot as bones respond to loading (it's a phenomenon known as stress shielding where bone start to get absorbed and the implant loosens because the bone doesn't get loaded as much). Which is why configuration matters because that changes the mechanical properties (there's research in my final year of studying biomedical engineering where they are looking into making titanium foams which has mechanical properties similar to bone).

    I would believe that in the case of magnetic implants the chemistry/straight out cyto-toxicity of the material would matter more because only those two would determine whether or not the implant straight gets dissolved and releases something toxic or the implant kills cells which trigger an immune response. So if something is not toxic when it is in nanoparticle form where it is small enough for the macrophages to eat them (if it is cytotoxic, the macrophages die and the inflammation triggers and more white cells come and try to eat the things and die and the cycle escalates), I would think that it is very unlikely that it would be problematic when it is in macroscale.
  • Well, the two things that make me leery are surface and effects like curing. These aren't biocompatibility issues per se, but if the macro object doesn't have a either a mirror like smooth finish or alternatively some kind of coat that prevents adhesion then you can get some serious fouling issues which more or less over ride the properties of the material itself. Also, Glims recently ripped me a new arse when I was coating a workstation in the lab with resin. Basically, I was using a resin without care as to the proportions of hardener resulting in places where it hardened at the surface... but left inferior regions within. This doesn't apply to maghemite sure, but it got me thinking about care in the use of resin for implants. There are a lot of nifty resins that are biosafe, but I image that if improperly cured/applied etc. that it could make that rating void. I agree with your reasoning though that if it's ok at a micro level, then the macro is likely ok as well. Good reasoning.
  • Well, you're very likely to get fouling with most implants anyway because that's what the immune system does: the white cells cannot eat it, it recognizes it as foreign, and therefore it encapsulates the implant and pretend that it is not there (well, not quite as anthropomorphic but you get the idea).That happens even with hip implants and back then (my last year in biomedical engineering) it is considered to be "the best situation you can expect" because that means that implant is not leaching out stuff and cause problems.

    There's only one scenario I can think of where the surface itself becomes cytotoxic though: that is if it has mico-needles like asbestos fibres which can "harpoon" and kill cells. But I'm not sure how that applies to something like maghemite.
  • With new coatings, you don't necessarily have that biofouling. I know about some coatings that have less than 5% fouling. I'm sure you know how awesome that is. While that requires a lab as opposed to sending it out, I feel like we should aim high, instead of just being comfortable with "the best you can expect".
    Encapsulation is not the only option. Truly biocompatible coatings can chill inside without causing issues. Best example i can think of are zwitterioninc hydrogel coatings on silk mesh internal dressings...

    As for cyto , you can also have adhesion, chemical, leaching, and rxn issues among others. 
  • True. Not to mention the diamond coating in artificial hearts which stops blood from clotting on the surface. I'm just more thinking in the direction that for magnet implantation encapsulation doesn't matter too much for the purpose (unless it gets to the point where the sensitivity decreases).
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