Enrichment and Identification of Neural Stem Cells in Neurospheres using Rigidity-Tunable Gels.

Stem cell fate specification is known to be regulated by mechanical cues such as cell-cell interaction and the rigidity of the extracellular matrix (ECM). At present, spheroid cultures of stem cells are conventional starting materials to generate organoids with tissue-like structures. However, the influence of ECM rigidity on stem cell mechanobiology has only been briefly explored in in vitro 3-dimensional (3D) cultures, which presents better physiological relevance than monolayer cultures. To investigate how ECM rigidity acts on neural stem cell (NSCs) to drive specific biological processes, we performed live 3D-imaging on neurospheres in medium, in 1% and 1.5% agarose gel-medium matrix. In this study, we also report a novel method of 3D spheroid expansion stress quantification. Our results revealed that neurospheres in stiffer ECM exhibited higher stem cell ratio than those in medium. Moreover, we observed a negative correlation between the signal intensity of the NSC marker, SSEA-1 (CD15), and mean stresses exerted by the cell. This observation is implicative of a sparse actomyosin network in NSCs than non-stem cells. Based on these results, we propose that enrichment of NSCs or directed differentiation may be carried out by tailoring ECM rigidity and possibly its composition.