This is addressed in the video. Cells growing in a flat plane don't form complex connection as we would see in a real organ. One way address that is to grow th

This is addressed in the video. Cells growing in a flat plane don't form complex connection as we would see in a real organ. One way address that is to grow the as organoids. You can think of organoids like 'cells growing in a non-flat surface'. This mean the cells would have all 3 dimensions to grow and form connections. The problem with that is that you need a LOT o cells, and they are expensive. The way around it is to create neurons from skin cells. But that has its own set of challenges.