As far as why Dr Tsuji had this delay, I suspect it is for other reasons. One reason could be problems with poor hair quality - the wiry consistency we talked about and which we saw with his pictures of human hairs growing from a mouse’s back. That could be a problem for two reasons. One is the fact that it’s growing in a mouse. The other is that the technique at it is now, is just producing wiry looking hairs, period.
Also note that Dr Christiano is working on a similar project growing follicles outside the body (just one off several projects she’s working on, another one is JAK inhibitors). The report on her work that I posted and other reports said the hairs she’s growing are “colorless”.
Those issues could be big problems in leveraging this thing to the point where it’s commercially viable. I think maybe the problem is not that they can’t grow human hair follicles outside the body. The problem may be the aesthetic quality of the hairs… Maybe the delays are associated with trying to improve this.
I think some of these issues could be solved by adding a mix of cellular growth factors to the developing follicle germs as they are being grown, if possible.