The blood fuel cell will soon be clotted and won’t work.
In medicine these contacts between blood and other surfaces are a big problem demanding anticoagulation therapy.
Chemical reactions using glucose will soon be exhausted. If it were so easy there would be a good way ofmeasuring blood-glucose “directly” and continuously for many years. So many diabetics -and companies- would be very very lucky.

What about the tissue-compatibility of the implanted materials? I’m not sure if it’s tested well.

What about practicability? Moving, doing sports and your cell phone is doing unwanted calls?

What about practicability? I didn’t understand how a call would work. Where is the bell, where is the speaker, where is the microphone, where is the antenna?

What about repairs?

What about changes for a newer type with better functions?

And: sorry could you lend me your cell, I need to phone…?