Well, when people say "organ on a chip" it sounds completely synthetic, but some organ-on-a-chip designs (and many organoid platforms) actually require the killing of untold numbers of mice to generate the matrix compounds. So that would just be an industrial obfuscation of who is doing the killing: now it is not the scientist doing all the killing but the Matrigel manufacturer. But to be fair, this will likely change over time as more synthetic approaches are developed. And the lung-on-a-chip described in this article does not use Matrigel. So I think it is actually a pretty good example of moving away from animal use in biomedical research.