Unfortunately, EGF and FGF are large molecules that have difficulty crossing the blood-brain barrier, the meshlike network of tightly woven cells that lines the blood vessels of the brain.

• 遗憾的是，EGF与FGF是大分子，很难穿过血脑屏障（这是由许多细胞紧密交织而成的网状构造，形成脑血管的内衬）。