(n 3).bc:ns(P> 0.05), *, # (P< 0.05); Studentst-test.(sobre)Brightfield micrographs and related traction force roadmaps of micropatterned solitary hMSCs subjected to OM(d)or AM(electronic)for seven days, and stained for ALP(d)or Lip(electronic).White-colored rectangles in micrographs highlight cell boundaries. gels NVP-BAW2881 effects not only mechanised rigidity, but also the quantity of ligand, leaving doubt regarding the relevant contribution of the two matrix properties for the noticed cellular response. Artificial ECM analogs such as for example polyacrylamide or polyethylene glycol gels, which differ rigidity by modulating the quantity of cross-linker, has exposed that substrate rigidity only Rabbit polyclonal to ZAK can modulate many mobile functions, which includes NVP-BAW2881 stem cellular differentiation46. However, modified cross-linker amount effects not only mass technicians, but also molecular-scale materials properties which includes porosity, surface area chemistry, backbone versatility, and binding properties of immobilized adhesive ligands7,8. As a result, whether cellular material transduce substrate rigidity in the microscopic size (eg sensing the rigidity between adhesion sites) or the nanoscopic size (eg sensing local alterations in receptor-ligand binding characteristics) remains an open question7,8. While hydrogels will continue to play a major role in characterizing and controlling cell-material interactions, alternative approaches are necessary to further elucidate the basis by which cells sense changes in substrate rigidity. Here we report that micromolded elastomeric micropost arrays9,10can decouple substrate rigidity from adhesive and surface properties (Fig. 1). Our strategy involved a library of replica-molded arrays of hexagonally spaced poly-(dimethylsiloxane) (PDMS) microposts from microfabricated silicon masters, which presented the same surface geometry but different post heights to control substrate rigidity (Supplementary Fig. 1and Online Method). Post height determines the degree to which a post bends in response to a NVP-BAW2881 horizontal traction force. We characterized micropost rigidity by computing the nominal spring constant,K, using the finite element method (Fig. 1ac). The library of micropost arrays spanned a more than 1,000-fold range of rigidity from 1.31 nN/m up to 1 1,556 nN/m. This micropost array library is available to laboratories without the need for reproducing the original silicon templates (www.seas.upenn.edu/~chenlab/micropostform.html). == Figure 1. == Micromolded elastomeric micropost arrays to engineer substrate rigidity. (a) Graphical depiction of finite-element method (FEM) analysis of microposts of different heightsLeach bending in response to applied horizontal traction force (F)of 20 nN (seeOnline Methods). (b) Micropost deflectionis plotted as a function ofFfor microposts of heights used in (a), as calculated by FEM analysis. (c) Nominal spring constantKas a function ofL,as computed from FEM (bars), and from the Euler-Bernoulli beam theory (dark yellow curve).Kmeasures micropost rigidity. (df) Scanning electron micrographs of hMSCs plated on PDMS micropost arrays of the indicated heights. White rectangles show where the bottom images were taken. Scale bars: 100 m (top), 50 m (bottom left), 30 m (bottom middle), and 10 m (bottom right). Human mesenchymal stem cells (hMSCs) have previously been shown to respond to microenvironmental cues6,11. We examined how hMSCs cultured on micropost arrays would respond to changes in micropost rigidity. On rigid microposts, hMSCs were well-spread (Fig. 1d) with prominent, highly organized actin stress fibers and large focal adhesions (FAs) (Supplementary Fig. 2). In contrast, cells on soft microposts displayed a rounded morphology with prominent microvilli (Fig. 1f), disorganized actin filaments, and small adhesion complexes (Supplementary Fig. 2). Morphometric analysis of cell populations revealed strong correlation between FAs and cell spreading, regardless of micropost rigidity (Fig.2ac). We further observed strong correlation between traction force and cell spreading, with a substantially smaller independent effect of micropost rigidity on traction force (SupplementaryFig.3). Overall, these observations suggested that cell shape, FA structures, and cytoskeletal (CSK) tension were tightly coupled systems involved in rigidity sensing. The responses were similar to those reported on hydrogels of varying rigidities, but they further suggest that rigidity sensing occurred at a micrometer scale, likely between FAs, since the nanoscale mechanics at the top of individual microposts (which could directly impact adhesion receptor binding) remain unchanged. == Figure 2. == Quantitative analysis of cell morphology, FA, and traction force during rigidity-sensing. (a) Distributions of cell area for hMSCs plated on micropost arrays of different rigidities (rigid:L= 0.97 m,k= 1,556 nN/m; medium:L= 6.1 m,k= 18.16 nN/m; soft:L= 12.9 m,k= 1.90 nN/m). Gaussian functions (red curves) were used for fitting, and red bars centered on the mean and indicated peak widths. (bc) Total FA area (b) and total number of FA sites (c) per single hMSCs plotted against hMSC area, for three different micropost arrays as indicated. Each data point represents an individual cell (n =322 cells). Data trends are plotted as Gaussian-weighted moving averages (red curves) one s.d. (pink regions), and are compared with the linear least square fitting (dark yellow lines, slope NVP-BAW2881 values are indicated). (d) Quantification of FA area and traction force for hMSCs (top).