Multimodal X-ray imaging reveals hierarchical fibre mechanics

Fibrous materials, ranging from connective tissues^1-4 to engineered composites^5-8, are vital to many biological and man-made systems, optimized to withstand complex in operando or in vivo loading. The load-bearing capacity of intervertebral discs (IVDs) of the spine depends on a hierarchical extracellular matrix, where plywood-like lamellae of collagen fibres in the annulus fibrosus contain nanometre-scale fibrils built from staggered triple-helical monomers^4,9,10. How intact IVDs couple fibril-scale mechanics to fibre-scale organization under load remains unresolved. Here we introduce TomoSAXS, a full-field 3D small-angle X-ray scattering tomography that maps fibril-to-fibre mechanics across an intact tissue. We show that intrafibrillar molecular pre-strain (D-period stagger) is lamellar textured and tightly correlated with microscale fibre strain. Pre-strain is inversely related to fibril strain and its variability, consistent with load-sharing through molecular unwinding. Radial strain bridges and high-curvature zones at the annulus fibrosus-nucleus pulposus interfaces emerge as critical regulators of local mechanics. These findings reveal concerted fibril-fibre interactions that sustain mechanical equilibrium in the IVD, preserving elasticity and shape. More broadly, TomoSAXS establishes a platform to visualize nanoscale-to-microscale matrix mechanics across biological and synthetic fibrous materials, with applications in ageing and disease, therapeutic evaluation and the design of bio-based and bio-inspired materials.