Conditioned serum-free medium from umbilical cord mesenchymal stem cells has anti-photoaging properties - Qiuying Liu; Zhenyu Luo; Shaoqing He; Xinlei Peng; Sheng Xiong; Yifei Wang; Xueyun Zhong; Xiangrong Zhou; Carol A. Eisenberg; Bruce Z. Gao (Biotechnology Letters, 2013)