There have been some rudimentary prototypes built, but that's about it. Some are capable of very simple tasks.

A bit of googling can get you a publication history of the researcher mentioned as pioneering the field: https://scholar.google.com/citations?hl=en&user=q0n-slAAAAAJ... . From a glance, there aren't any actual biological engineering papers here. And he's a physicist, not a biologist.

So, I suspect that there aren't papers on it because no one is actually doing it.