Cp pnp bsg

The Young’s modulus E of the hydrogels was measured by nanoindentation using an atomic force microscope (NanoWizard, JPK Instruments, Berlin, Germany). The hydrogels were indented by a spherical colloidal probe that was attached to a silicon–nitride cantilever with a nominal spring constant of 0.08 N/m (CP-PNP-BSG; R = 5 $\mathsf{\mu }$ m, Olympus Optical) and an approach speed of 1 $\mathsf{\mu }$ m/s. Each cantilever was calibrated, and the spring constant was determined by thermal noise measurement [25 (link)]. The measured force–indentation curves were analyzed by nonlinear least-squares fitting to the Hertz model [22 ,26 (link),27 (link)] using a customized MATLAB (Mathworks) routine. The modified Hertz model equation for spherical indenter shapes to determine E was fitted as
$$F=4E{R}^{1/2}·{\left[3{(1-\nu )}^2\right]}^{-1}·{\delta }^{3/2},$$
where F is the force applied to the indenter, $\nu =0.5$ is Poisson’s ratio, and $\delta$ is the indentation depth [3 (link),28 (link)]. The average Young’s modulus of 50 independent indentation sites at two $100\times 100$
$\mathsf{\mu }$ m ${}^2$ areas was quantified for each hydrogel to ensure statistical significance.

The bulk elasticity of host-guest gels was measured by a Rheoner RE–33005 creep meter (Yamaden Ltd., Tokyo). The elasticity of host-guest gels near the surface was determined by nano-indentation with an atomic force microscope (NanoWizard, JPK Instruments, Berlin). As reported previously, the density of hydrated polymers near the surface is diffusive and thus cannot be treated like a clear boundary with a Gaussian roughness^{43 (link)–45 (link)}. In order to avoid the artifacts caused by indenting diffusive interface that has a larger length scale than the curvature radius of cantilevers (typically 20–30 nm), we indented the sample with a Pyrex-nitride spherical colloidal probe (R = 5 μm) attached to a silicon-nitride cantilever with a nominal spring constant of 0.08 N/m (CP-PNP-BSG; Olympus Optical). The Young’s modulus E of the gel was calculated from the nonlinear least-square fitting of the force-indentation curves^{46 (link),47 (link)}: $$F=4E{R}^{1/2}\cdot {\left[3{\left(1-\nu \right)}^2\right]}^{-1}\cdot {\delta }^{3/2}$$ where F is the force applied to the indenter, ν = 0.5 the Poisson’s ratio, and δ the indentation depth^{48 (link)}.
Unless stated otherwise, all the data points are from more than three independent measurements, and the error bars in each figure correspond to the standard deviations.