I'm in the process of writing an article that will hopefully look into this in more detail, but from my experience working in a cultivated meat company currently, there are no alternatives that work as well as fbs. There is a company that has received around 15m usd of funding and we've tested their serum replacement, and it just doesn't work very well. So we are still using fbs. In certain applications, the concentration has to be as high as 20% in the media. Fortunately for their conscience, I don't think the scientists know the details of it's production, if they did, some would probably not come in to work anymore.