1 Biosystems and Biomaterials Division, Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, USA. Electronic address: [email protected].
2 Biosystems and Biomaterials Division, Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, USA.
3 Stem Cell Engineering Research Group (SCERG), Biotechnology Research Institute for Drug Discovery, AIST, Tsukuba, Ibaraki, Japan.