What approaches could you use to engineer a synthetic placenta?

From what I understand of current research, the bottleneck right now is finding a way to supply an embryo with oxygen and nutrients, and remove waste products, that doesn't rely on the the use of a 'nutrient bath'. This method relies on diffusion. Diffusion is not sufficient to supply and remove the relevant substances as it grows. The embryo literally starts dying from the inside out as it's too far from the nutrient bath.

You need to involve the circulatory system - this is the literal problem it solves. How you do that however I do not know.

I'm not sure, but I hope they make it quickly. Personally, I think this is more revolutionary than going to space.