Tuning commensurability in twisted van der Waals bilayers.

Moiré superlattices based on van der Waals bilayers1-4 created at small twist angles lead to a long wavelength pattern with approximate translational symmetry. At large twist angles (θt), moiré patterns are, in general, incommensurate except for a few discrete angles. Here we show that large-angle twisted bilayers offer distinctly different platforms. More specifically, by using twisted tungsten diselenide bilayers, we create the incommensurate dodecagon quasicrystals at θt = 30° and the commensurate moiré crystals at θt = 21.8° and 38.2°. Valley-resolved scanning tunnelling spectroscopy shows disparate behaviours between moiré crystals (with translational symmetry) and quasicrystals (with broken translational symmetry). In particular, the K valley shows rich electronic structures exemplified by the formation of mini-gaps near the valence band maximum. These discoveries demonstrate that bilayers with large twist angles offer a design platform to explore moiré physics beyond those formed with small twist angles.

Altered gene expression in human adipose stem cells cultured with fetal bovine serum compared to human supplements.

Mesenchymal stromal cells (MSCs) are promising candidates for innovative cell therapeutic applications. For clinical scale manufacturing regulatory agencies recommend to replace fetal bovine serum (FBS) commonly used in MSC expansion media as soon as equivalent alternative supplements are available. We already demonstrated that pooled blood group AB human serum (HS) and thrombin-activated platelet releasate plasma (tPRP) support the expansion of multipotent adipose tissue-derived MSCs (ASCs). Slight differences in size, growth pattern and adhesion prompted us to investigate the level of equivalence by compiling the transcriptional profiles of ASCs cultivated in these supplements. A whole genome gene expression analysis was performed and data verified by polymerase chain reaction and protein analyses. Microarray-based screening of 34,039 genes revealed 102 genes differentially expressed in ASCs cultured with FBS compared to HS or tPRP supplements. A significantly higher expression in FBS cultures was found for 90 genes (fold change ≥2). Only 12 of the 102 genes showed a lower expression in FBS compared to HS or tPRP cultures (fold change ≤0.5). Differences between cells cultivated in HS and tPRP were hardly evident. Supporting previous observations of reduced adhesion of cells cultivated in the human alternatives we detected a number of adhesion and extracellular matrix-associated molecules expressed at lower levels in ASCs cultivated with human supplements. Confirmative assays analyzing transcript or protein expression with selected genes supported these results. Likewise a number of mesodermal differentiation-associated genes were higher expressed in cells grown in FBS. Quantifying adipogenic and osteogenic differentiation lacked to demonstrate a clear correlation to the supplement due to donor-specific variances. Our results emphasize the necessity of comparability studies as they indicate that FBS induces a culture adaptation exceeding that of ex vivo culture in human supplements and thus may contribute to the therapeutic potential.