Recent advances in nanotechnology present synthetic bioinspired materials to create new controllable microenvironments for stem cell growth, which have allowed directed differentiation into specific lineages. [ 1 , 2 ] Carbon nanotubes (CNTs), one of the most extensively studied nanomaterials, can provide a favorable extracellular environment for intimate cell adhesion due to their similar dimension to collagen. It has been shown that CNTs support the attachment and growth of adult stem cells [ 3–6 ] and progenitor cells including osteoblasts and myoblasts. [ 7 , 8 ] In addition, surface-functionalized CNTs provide new opportunities in controlling cell growth. Surface functionalization improves the attachment of biomolecules, such as proteins, DNA, and aptamers, to CNTs. [ 9 ] Zanello et al. cultured osteoblasts on CNTs with various functional groups and showed reduced cell growth on positively charged CNTs. [ 10 ] Recent reports have shown that human mesenchymal stem cells (hMSCs) formed focal adhesions and grew well on single-walled CNTs (swCNTs). [ 5 , 6 ] However, the effect of naïve swCNT substrates on the differentiation of stem cells has not been reported before. Herein, we report the osteogenic differentiation of hMSCs induced by swCNT monolayer cues without any chemical treatments. Interestingly, the surface treatment of swCNTs via oxygen plasma showed synergistic effects on the differentiation as well as the adhesion of hMSCs. The stress due to the enhanced cell spreading on swCNT layers was proposed as a possible explanation for the enhanced osteogenesis of hMSCs on the swCNT monolayers. Previous reports showed that the stress to stretch stem cells on microscale molecular patterns generated the tension on actin filaments, which eventually enhanced the osteogenesis. [ 11 , 12 ] Since our method relies on monolayer coating of swCNTs, it can be applied to a wide range of substrates including conventional scaffolds without any complicated fabrication processes.
Baik, K.Y., S.Y. Park, K. Heo, K.-B. Lee, S. Hong