P.C. Nalam
University at Buffalo,
United States
Keywords: hydrogels, viscoelasticity, colloidal roughness
Summary:
Extremely soft hydrogels, with stiffnesses in the range of a few tens of kilopascals, exhibit mechanical characteristics comparable to biological cells, making them ideal platforms to study nanomechanical and nanorheological behavior. Colloid-probe force spectroscopy is widely employed to probe the mechanical response of such materials; however, the influence of frequency-dependent viscoelasticity and probe roughness on the measured elastic properties remains insufficiently understood. This work investigates the nanorheology of soft hydrogels using direct-drive force modulation atomic force microscopy (AFM), focusing on off-resonance frequency response and its implications for accurately capturing intrinsic viscoelastic behavior. Special attention is given to the effects of adhesion hysteresis arising from dangling polymer chains, analogous to cellular interfaces, which alter contact mechanics at high resonance frequencies. Additionally, the inherent nanoscale roughness of colloidal probes interacting with highly hydrated, compliant hydrogel surfaces is analyzed in terms of elastic deformation of contact perimeter and polymer chain interactions per unit area. The findings highlight critical experimental considerations for measuring soft viscoelastic contacts, offering guidelines for reliable nanomechanical characterization of hydrogels in contexts ranging from tissue engineering to contact lens materials.