Water Transport-Modulated Highly Compressive Hydrogel for Total Biomimetic Sensing Intervertebral Disc.

Degenerative disc disease (DDD) affects millions globally, with artificial total disc replacement (A-TDR) emerging as a key surgical intervention to restore spinal function and mobility. Current implantable prostheses incorporating multi-component architectures to replicate the functional heterogeneity of natural intervertebral discs (IVD) face challenges in achieving mechanical and physiological compatibility. Inspired by the natural IVD's structure, where a soft nucleus pulposus (NP) is encased by a tough annulus fibrosus (AF), a water transport-modulated directional annealing casting (DAC) approach has been developed to construct bulk hydrogels with tunable mechanical properties (up to ≈36.69 MPa compressive strength with ≈5.35 MPa modulus). This strategy enables the fabrication of an integrated hydrogel-based IVD (H-IVD) with biomechanically gradient structures, featuring a high-strength AF region (compressive modulus ≈2.77 MPa) seamlessly transitioning to a compliant NP core (modulus ≈0.26 MPa) while maintaining physiological water content throughout. The H-IVD exhibits excellent biocompatibility and load-bearing capacity, with inherent stress-sensing capabilities enabling dynamic functional assessment of spinal biomechanics. Furthermore, this integrated design strategy demonstrates broad applicability for engineering various dimensionally-controlled biomimetic tissues, from simple 1D structures to complex 3D organs requiring precise spatial control of material properties.