Living Hydrogels: Ultra-High-Molecular-Weight Hyaluronan and the Emergence of Adaptive Regenerative Macromolecules

Hyaluronan (HA) has traditionally been viewed as a structural component of the extracellular matrix, valued primarily for its viscoelastic, lubricating, and hydrating properties. However, accumulating evidence suggests that ultra-high-molecular-weight hyaluronan (UHMW-HA) functions far beyond passive tissue support, acting as a dynamic regulator of inflammation, mechanotransduction, immune homeostasis, cellular senescence, and regeneration. In this narrative review, we examine HA and specifically focus upon UHMW-HA operating as a “living hydrogel”, an adaptive regenerative macromolecule that continuously interacts with its microenvironment to shape tissue function and resilience. We examine evidence spanning evolutionary biology, glycobiology, biomaterials science, and regenerative medicine to examine how polymer size encodes biological activity and how UHMW-HA influences stem cell behaviour, extracellular matrix remodelling, and responses to injury and ageing. Attention is given to unique biological models, including the naked mole-rat, whose exceptional longevity and cancer resistance have been linked to abundant UHMW-HA, offering insights into the relationship between extracellular matrix architecture and organismal health. We further discuss how advances in synthetic biology and biomaterials engineering are enabling the development of next-generation HA-based hydrogels that mimic these adaptive properties for therapeutic applications in tissue engineering, in addition to potential roles in dynamically optimizing wound repair, and musculoskeletal rejuvenation, through precision medicine approaches. Finally, we argue that reclassifying UHMW-HA as a living regenerative material rather than an inert scaffold provides a new concept for designing bioinspired therapeutics and understanding extracellular matrix function. This review demonstrates HA-adaptive macromolecules as critical entities in future regenerative strategies and highlights the specific and unique potential of UHMW-HA to combine material science developments with enhancement of preferable biological outcome.