I feel one of the biggest challenges in organoid culture is in delivering nutrients and gas exchange especially as the organoids grow. Thoughts or recommendations?

Answer

Organoids need a continuous feed of fresh nutrients and waste removal as the culture expands in size and since they are not vascularized, as suggested in your question. There are 3 recommendations that have been used for this purpose:

1. Researchers have been successfully culturing and maintaining organoids embedded in Corning Matrigel matrix droplets which are then suspended in media in Corning Spinner Flasks. Lancaster and Knoblich maintained cerebral organoids of 4 mm in size for up to 15 months. Please refer to the protocol in this paper.
2. We have successfully cultured intestinal organoids by frequently (2 to 3 times a week) changing the media for 2 mm organoids and maintained them for up to 6 weeks. McCracken et. al., passaged these organoids for up to 140 days using this protocol.
3. Perfusion is an option that can continuously replenish the nutrients and remove wastes and is more increasingly utilized in organ-on-chip cultures to maintain all the nutrients, growth factors, metabolites in a constant equilibrium once optimized so cultures can be maintained much longer than static cultures.