Mailbox: how do woven blood vessels work?

Time for the mailbox: the part of the show where we read out your correspondence! This question is from listener Paola, in reference to our story in January about making replacement blood vessels out of ‘knitted’ human tissue...

Chris - Paola, the scientist in question Nicolas L'Heureux says the answer is that gases and nutrients only diffuse through the walls of blood vessels, called capillaries, that are hundreds of times smaller than the ones that he’s making for bypass operations, so that won’t be a problem. And regarding 3-D printing, it can be a powerful tool to create very small patterns like the tiny blood vessels you may be thinking of; for his larger blood vessels, it is probably simpler to create tubes using other methods. Plus, 3D printing requires something liquid that can turn solid during printing; very difficult to do with biological materials!