Muscle‐Inspired Fibers from Immunoglobulin Domains Combine Superior Mechanical Performance, Energy Damping, and Shape Memory Properties

ABSTRACT Animal muscle is an intriguing natural material whose mechanical properties arise from sequence‐diverse protein domains, many of which remain unexplored for material design. Among them, Immunoglobulin‐like (Ig) domains act as molecular springs that can unfold and refold repetitively without losing function, dissipating mechanical energy as heat, making them promising building blocks for next‐generation protein‐based materials (PBMs). In this study, we translate these molecular features to the macroscale by fabricating fibers from microbially‐synthesized Ig domains of various muscle proteins. Among them, Filamin‐derived Ig fibers ( M W = 123 kDa) exhibited a unique combination of high tensile strength (412 ± 22 MPa), high toughness (120 ± 17 MJ/m 3 ), remarkable mechanical stability (∼89%) under 90% humidity, high energy damping capacity (∼80%), and complete shape recovery (∼100%) over repeated loading–unloading cycles. Our results further revealed molecular mechanisms underlying these properties: (i) Ig domain hydrophobicity strongly correlates with fiber assembly and tensile strength, (ii) reversible unfolding–refolding of Ig domains enables efficient energy dissipation and self‐recovery, and (iii) hydrogen‐bonding networks within the amorphous matrix regulate humidity‐induced weakening. Together, these findings establish Ig domains as a new class of PBMs combining advantageous mechanical and physical properties, offering a versatile platform for developing advanced materials with tunable performance.