Mechanistic Understanding of Sustained Viscoelasticity in Biodegradable Elastomers: Material Design and Constitutive Modeling

Achieving sustained viscoelasticity in biodegradable elastomers is critical for stable energy dissipation in clinical performance (e.g., sutures, patches, and strips). Yet rational material design and mechanistic understanding required to maintain this viscoelastic response during degradation have not been systematically investigated. Here, a framework integrating molecular design, experimental characterization, and constitutive modeling is proposed to elucidate the mechanisms underlying the sustained viscoelasticity of polyurethane elastomers (PUEs) during degradation. First, a multifunctional hard-segment design with tailored phase mixing and dense hydrogen bonding is implemented to ensure the sustained viscous response and high fracture strength even at later degradation stages (>80%). Subsequently, a domain-specific micromechanical model is developed, explicitly incorporating two distinct viscous mechanisms: short-term confinement-enhanced segmental friction and long-term dynamic dissociation of hydrogen-bonded clusters. By defining degradation as a physical internal state variable, the model quantitatively links microstructural evolution, specifically bond scission-induced friction loss and cluster loosening, to the macroscopic viscoelastic response. Finally, the model elucidates a fundamental compensatory mechanism wherein the robust hydrogen bonding in hard domains counterbalances network weakening, thereby preserving both viscous characteristics and fracture strength throughout the degradation process. This work provides both theoretical and practical guidance for the rational design of biodegradable PUEs.