Our publication in Nano Letters investigates the discrepancies between macrorheological and particle-based microrheological measurements in aqueous poly(ethylene oxide) (PEO) hydrogels. By analyzing hydrogels with varying PEO concentrations and chain lengths, we reveal that these deviations expose the nanoscopic viscoelastic properties at the particle–hydrogel interface. We show that an interfacial shell with distinct viscoelastic properties explains the experimental results by utilizing a generalized Stokes-Einstein relation and ruling out alternative explanations such as finite particle radius or surface-slip effects. Our approach provides insights into the nanoscopic interfacial rheology of hydrogels and can be extended to other viscoelastic materials. Robert F. Schmidt, Henrik Kiefer, Robert Dalgliesh, Michael Gradzielski, Roland R. Netz - Nano Lett. 24, 4758-4765 - Published April 9, 2024.