Chun SY, Mack DL, Moorefield E, Oh SH, Kwon TG, Pettenati MJ, Yoo JJ, Coppi PD, Atala A, Soker S. Pdx1 and controlled culture conditions induced differentiation of human amniotic fluid-derived stem cells to insulin-producing clusters. J Tissue Eng Regen Med. 2015 May; 9(5):540-9.