The i-Rheo Framework: A Unified Approach to Broadband Rheology and Microrheology of Soft Matter from Molecular Simulations to Biomechanics

Linear viscoelasticity provides a time-invariant mechanical fingerprint of materials and underpins predictive descriptions of their response to external deformation. The corresponding material functions reflect the hierarchy of inter- and intra-molecular interactions governing structure and dynamics across multiple scales, from atomistic motions to macromolecular and mesoscopic rearrangements. Access to linear viscoelastic properties over the widest possible frequency range therefore offers unique insight into the mechanisms controlling the behaviour of soft matter and complex fluids. However, obtaining reliable broadband viscoelastic spectra remains experimentally and analytically challenging owing to instrumental limitations, finite measurement windows, discrete data sampling, and the shortcomings of conventional transformation procedures. This Review/Perspective examines the evolution of the i-Rheo Framework, a model-free methodology for extracting broadband viscoelastic properties directly from finite experimental or simulated datasets without imposing predefined constitutive models. Originally developed to transform creep-compliance measurements into the complex shear modulus, the framework has subsequently been extended to bulk rheology, passive and active microrheology, optical tweezers, atomic force microscopy, macro-indentation, biomechanics, rheo-optical measurements, and molecular simulations. The recent development of i-Rheo-Tempo further establishes a reversible connection between time- and frequency-domain representations, providing a unified analytical framework for multiscale viscoelastic characterisation across soft-matter physics.