Ok here we gooooooo....
Are the various flex implants in any way visible under the skin?
For the most part, no.. but it really depends on location and tissue tension. More on that below...
I'm mostly referring to the hand/fingers. I would imagine this depends on how skinny your fingers are and where the implant is located, but I was hoping I could get a rough answer.
You're correct, it really depends on if there is tension or not. If the tag can lay flat under your skin and not cause any tension, it will be invisible, and in some cases undetectable even if you poke at yourself.
I measured my middle finger to have a diameter of about 18-20 mm at the widest between the knuckle and the first joint, would it be possible to implant a flex tag there?
You could fit a flexNT but not likely a flexDF or VivoKey. Back of the hand or arm above the wrist is recommended in those cases. In fact, the finger is not recommended at all... it is a very difficult place to work for an artist, with very tight work area and close proximity to tendons.. it's just a difficult place to work. I happened to put the first flexNT there because i thought it was a convenient placement.. and I could fist-bump readers.
Would it be visible under the skin?
Mine is not visible. Other people who have them in fingers don't seem to have issue with them showing either.
Is it uncomfortable to touch where a flex implant is implanted (after healing)? What about light hits or rubbing the skin above?
I've had no issues what-so-ever after it's fully healed. I've not heard of anyone else having issues either. However if the install is not a good one, and the tag is off-center or rotated - basically causing tension under the skin - then there will be problems and it will likely have to come out. One person has had this situation crop up and after months of sharp pains when moving certain ways or bumping it, the flexNT was removed and the finger healed nicely.
Can the flex implants be felt under the skin when you move your hand or fingers?
The tendon does move under the finger, but it's in a sheath that keeps its movement isolated. The flexNT rests above this sheath and cannot be felt when I move or flex my finger.
Have there been made any tests on the flex implants (MRI safe, airport scanners, etc.) like there has been on the x-series?
No MRI testing has been done on flex devices, primarily because the x-series are so much more risky than the flex when it comes to MRI exposure. An x-series has copper wire instead of traces, but that wire is wound around a ferrite rod. The amount of magnetically saturatable material in an x-series transponder that could be heated or pulled on by an MRI's magnetic field is extremely high when compared to the materials inside a flex tag.
As far as the airport goes, I've been through several airport security checkpoints with 3 x-series, 2 flex, and an m31 magnet in my body.. no issues. I once did get a hit on a high-strung metal detector though.. it was the m31 that tripped it up, but the guy couldn't find it with the handheld wand, so he let me pass.
Any news regarding the chip for the Vivokey? I know NXP has been delaying the chip for the Vivokey multiple times, but last I heard they promised september.
Still on track for September. Just talked to my NXP contact about it yesterday.
What are the expected dimensions of the Vivokey?
At this point, the same as the flexDF. That's not likely to change, but it's not finalized yet either.