1) Grow the endometrium using stem cells (It has already been done (Cambridge, 2017))
2) Attach the embryo to it and allow the placenta to grow.
In 2003, there was a researcher at Columbia who did something like this, but there was no technology to create endometrium tissue. She used some donated infertile tissues, but the rat embryos did attach to it and grow, although the growth itself was retarded. That's understandable since the endometrium has some special secretory functions. So what could be the issues with the method I have suggested?
A lot of the new approaches seem to involve artificial placentas , which are probably not very easy to create. The don't seem to be the most obvious approach either. I think a large part of the issue is that you won't get funding if you say you want to create an artificial womb, because of the ethical issues involved. So you have to show some connection to neonatal stuff and hence the easiest approach is neglected. Am I right in this assessment?