Battery-free, stretchable optoelectronic systems
I've been doing a lot of research lately on wearables and I've been finding more and more that can be applied to implants. This paper[linked at top] describes a skin-like encased heartrate monitor that is battery free and wireless. It's read through NFC and attaches to the skin like a sticker or temporary tattoo. It seems like it should be relatively trivial to encase it in biocompatible material and put it under the skin instead of over.
I'm working through some ideas right now about how to more integrate wearables and implants.