Fertala, N.; Uhlmann, K.; Grigoryev, E.; Seth, P.; Friedrichs, J.; Werner, C.; Balzani, D.

Viscoelastic hydrogels mimic the dynamic mechanical properties of native extracellular matrices, making them essential for biomedical applications. However, characterizing their scale-dependent mechanical properties remains challenging, despite their critical influence on cell-material interactions and biomaterial performance. Here, we present an integrated experimental-computational approach to quantify and model the viscoelastic behavior of interpenetrating polymer network hydrogels across micro- and macro-scales. Atomic force microscopy-based stress relaxation tests revealed that microgels exhibit rapid, localized relaxation, while macroscopic bulk gels displayed prolonged relaxation dominated by poroelastic effects. Finite element simulations accurately replicated experimental conditions, enabling the extraction of key parameters: instantaneous elastic modulus, relaxation modulus, and relaxation time constant. We further developed a novel analytical model to predict viscoelastic parameters from experimental data with minimal error (< 5%), significantly streamlining characterization. Our findings highlight the necessity of scale-specific mechanical analysis and provide a robust platform for designing biomaterials with tailored viscoelasticity for tissue engineering and regenerative medicine.