What growth factor or factors are key to hepatocyte differentiation from iPSCs?

Answer

To begin with as endoderm, one would critically need high levels of Activin, FGF & BMP, followed by hepatocyte growth factor ( HGF) and Oncostatin in later stages of hepatic differentiation.
For detailed steps and concentration of specific growth factors used in different steps, I recommend the protocol described : Ma et al : Stem Cells Translational Medicine: 2 : 409-419, 2013