Fig. 2: Characterization of soft PDMS substrates.
From: The role of elasticity on adhesion and clustering of neurons on soft surfaces
PDMS surfaces were mechanically characterized using conventional elongation tests (a) and micro-indentation techniques (b) to find the elasticity of the substrate as a function of the ratio of liquid PDMS phase to the binding agent \(r\): the larger the value of \(r\), the smaller the value of elasticity. While results from the elongation test and micro-indentation of samples are consistent, however the latter overestimates the values of elasticity of a factor of \(1.3\) (c). Using laser interferometry, we measured the topography of PDMS surface represented here in the form of a linear and 2D density plot (d) and of a 3D plot (e). The average (\({{{{{\rm{Ra}}}}}}\)) and root mean square (\({{{{{\rm{Rrms}}}}}}\)) values of roughness were determined from morphological data. Values of \({{{{{\rm{Ra}}}}}}\) greater than \(0\) (\({{{{{\rm{Ra}}}}}} \sim 20{nm}\)) evidence that at the nanoscale the PDMS surface is not flat (f). For different surface-preparations the values of \({{{{{\rm{Ra}}}}}}\) deviate marginally from the central value \({{{{{\rm{Ra}}}}}} \sim 20{nm}\) (g). Contact angle (CA) measurements of samples indicate the PDMS surface is moderately hydrophilic with values of \({CA} < 80^{\circ}\) for all considered PDMS/curing agent ratios and values of elasticity \(E < 2.65{MPa}\) (h). Data in Fig. 2f are quantitatively described by a whisker box plot, where the lower and upper boundary corresponds to the 25% and 75% quartiles of the distribution, while the central band marks the median value (sample size\(\sim\)50). Data in Fig. 2g are represented by mean ± standard deviation (sample size\(=\)10).
