Supersoft yet tough bottlebrush polymers via dynamic domain exchange

Biological tissues exhibit a unique combination of supersoft mechanics and high toughness, a property pairing rarely achieved in synthetic solids. Replicating this duality in solvent-free synthetic polymers remains a fundamental challenge, as the strategies required for supersoftness and high toughness are inherently incompatible. Here, we present a bottlebrush polymer design strategy featuring unique dynamic domain exchange behavior that simultaneously achieves tissue-level softness and high fracture toughness. Our BBPs form physically crosslinked, dynamic networks with suppressed entanglements and dynamic domain exchange under deformation, allowing rapid network reconstruction and efficient energy dissipation under strain. As a result, the material exhibits tissue-like softness (E≈40 kPa), ultra-high stretchability (~1,300%), and exceptional toughness (~9,300 J m⁻²). This unique combination enables conformal yet mechanically robust integration with biological tissue, significantly reducing foreign-body responses and sustaining long-term in vivo stability.