Fig. 2: SMFS and MD simulations of the friction between PEG and CD.
From: Rapidly damping hydrogels engineered through molecular friction
a Schematic diagram of the AFM-based SMFS experiments of the friction between PEG and CD. mPEG-SH (10 kDa) was linked to the cantilever tip via APTES and SMCC. F indicates the pulling force. b Typical force‒displacement curves for the friction between PEG and α-CD or β-CD at a pulling speed of 200 nm s−1. c Force histograms of frictions between PEG and α-CD or β-CD at a pulling speed of 200 nm s−1. The Gaussian fitting shows average frictional forces of 26 ± 10 pN (n = 107) and 19 ± 9 pN (n = 122), respectively. d, e Dynamic force spectroscopy experiments of sliding frictions between PEG and α-CD (d) or β-CD (e) at various pulling speeds (200, 400, 800, 1600, and 3200 nm s−1). Frictional forces between PEG and α-CD or β-CD are both pulling speed dependent. The dashed line indicates the linear fitting of the frictional forces and pulling speeds. The diffusion speeds at zero pulling forces were determined to be 23 nm s−1 for α-CD and 26 nm s−1 for β-CD. Values represent the mean and standard deviation (sample size n = 107, 76, 77, 60 and 81 in d, respectively; sample size n = 122, 86, 75, 140, and 62 in e, respectively). f Cartoon representation of pulling a PEG (n = 34) through the ring of CD in a typical MD simulation. All the force fields of molecules were generated based on the general AMBER force field (GAFF) and Antechamber. F indicates the pulling force. g Typical curves of work vs pulling distance (top) and force vs pulling distance (bottom) in α-CD and water. PEG was first pulled through a α-CD ring and then pulled in water. h, i Frictional force between PEG and α-CD (h) or β-CD (i) at different pulling speeds (1−14 m s−1) predicted by MD simulations. Values represent the mean and standard deviation (sample size n = 10 for the frictional forces at each pulling speed).
