Multi-material interface printing of a magneto-responsive hydrogel scaffold with tuned stiffness

Osteochondral tissue engineering remains a significant challenge due to the complex biochemical and mechanical gradients between cartilage and subchondral bone. In this study, we present the development of a 3D-printed, multi-material magnetic hydrogel scaffold with tunable stiffness. To achieve this, we formulated a gelatin-alginate hydrogel matrix with various levels of embedded iron oxide magnetic particles (MPs) to create controlled hard-soft interfacial regions. The optimal composition (i.e . , 2.5% gelatin, 5% alginate, and 10% (w/v) MPs) demonstrated magnetorheological behavior, including increased effective Young’s modulus from 159 to 172 kPa and decreased viscosity from 175 to 145 kPa·s under a static magnetic field. Later, we evaluated scaffold printability through filament collapse, fusion, and porous scaffold tests, identifying a Gel:Alg ratio of 1:2 as optimal for structural fidelity. Mechanical and rheological characterizations confirmed that MPs significantly enhanced stiffness and responsiveness to magnetic fields. A checkered scaffold design enabled the fabrication of alternating hard and soft regions, and a bi-layered scaffold demonstrated improved interfacial adhesion. Micro-computed tomography provided quantitative evidence of magnetic field-induced particle redistribution within the hydrogel, confirming internal reorganization beyond bulk mechanical response. Importantly, in vitro live/dead assays confirmed that scaffold fabrication and magnetic functionality did not adversely affect cell viability. This platform offers a tunable, bioactive, and magneto-responsive scaffold architecture with potential for osteochondral repair or other applications requiring dynamic interface tissue engineering. • Development of a 3D-printed multi-material magnetic hydrogel with spatially controlled stiffness. • Optimized gelatin–alginate (1:2) with 10% iron oxide balances printability and magneto-responsive stiffening. • µCT analysis demonstrates direction-specific particle redistribution under magnetic stimulation. • Tensile testing confirms mechanically stable integration between magnetic and non-magnetic regions. • In vitro studies show cytocompatibility, supporting potential use in osteochondral tissue engineering.