The tissue it sits in isn’t that fragile as to let round soft plastic to damage it. If you feel your own arm you’ll probably notice that your fingers aren’t enough to crush what’s in there, even if you push really hard. Now imagine a little plastic pill that weighs a couple grams siting in the same spot.
Your body has two ways of dealing with foreign invaders: killing and disabling. It will send out white t-cells first to deal with the implant and an inflammation will indicate their losing battle. After this has failed the body will build cells around the object and encase it in an inert goo like structure. This will scarrify and attach itself to surrounding tissues stopping it from moving.
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