LIF and teratoma: Intriguingly, when the mESCs maintained on the gels without LIF for 5 days were transplanted for 7 weeks, they were able to grow into a well-developed teratoma (Fig. S3B, dashed-circle on the left) consisting of cell types of three germ layers, much larger than the teratoma generated from the mESCs on the rigid substrate without LIF (Fig. S3B, dashed-circle on the right).