Cool to see them featured! Those where developed in our lab (disclosure: I am the lab lead, below the Prof, but only tangentially involved in this research) mostly by one of my colleagues, who is just finishing his PhD. I can tell you that it was quite a journey to get this thing out.
See the website which links the research paper for more info: https://open-earable.teco.edu/
Cool thing is e.g. the sensing of the in ear canal pressure, what you can use for cool interactions:
https://publikationen.bibliothek.kit.edu/1000133751