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.

A bstract This study was the first attempt to design, fabricate, and evaluate multi-material bone scaffolds composed of Ti6Al4V and akermanite (Ca₂Mg(Si₂O₇), Ak), produced via direct ink writing (DIW), followed by sintering. Two scaffold architectures were developed (i.e., monolithic and core-shell) aimed at combining the mechanical strength of the Ti alloy with the osteoinductive properties of Ak. Uniaxial compression testing demonstrated that the core-shell scaffolds exhibited higher relative-density-normalized elastic moduli (up to 7.65 ± 0.35 GPa) and yield strengths (up to 444.7 ± 8.1 MPa) than the monolithic designs, namely Ti6Al4V-only scaffolds (elastic modulus: 4.29 ± 0.18 GPa; yield strength: 230.9 ± 1.7 MPa) and 90% Ti6Al4V/10% Ak composite scaffolds (elastic modulus: 3.05 ± 0.08 GPa; yield strength: 24.7 ± 1.4 MPa).The enhanced mechanical performance was attributed to interfacial reinforcement and optimized material distribution. Bioactivity assays in r-SBF revealed surface Ca–P deposition on akermanite-containing scaffolds by SEM and EDS, a response not observed on Ti6Al4V only specimens. Complementary ICP-OES showed marked depletion of phosphate and calcium ions, consistent with rapid HAp nucleation and growth, and substantial silicon release in composite samples, a known pro-osteogenic stimulus. Cell culture assays further confirmed the cytocompatibility of the Ti6Al4V, composite and core-shell scaffolds for preosteoblasts. Furthermore, SEM imaging showed that all the scaffolds supported cell attachment and evidenced a distinct cell spatial distribution depending on scaffold composition and architecture. These results contribute to advancing the scaffold design for bone repair and regeneration by proposing DIW-fabricated Ti6Al7V/Ak core-shell scaffolds that show potential as customizable, load-bearing implants with improved mechanical properties and surface bioactivity relative to the Ti6Al4V scaffolds.

High-performance soft–hard interfaces are inherently difficult to fabricate due to the dissimilar mechanical properties of both materials, especially when connecting extremely soft biomaterials, such as hydrogels, to much harder biomaterials, such as rigid polymers. Nevertheless, there is significant clinical demand for synthetic soft–hard interfaces. Here, soft–hard interface geometries are proposed, designed with the aid of computational analyses and fabricated as 3D-printed hydrogel-to-polylactide (PLA) structures. Two primary interlocking geometries (i.e., anti-trapezoidal (AT) and double-hook (DH)) are used to study the envelope of 2.5D geometric interlocking designs, fabricated through hybrid 3D printing, combining pneumatic extrusion with fused deposition modeling. Finite-element analysis, uniaxial tensile tests, and digital image correlation (DIC) are used to characterize the geometries and identify parameters that significantly influence their mechanical performance. These findings reveal significant differences between geometric designs, where DH geometries performed significantly better than AT geometries, exhibiting a 190% increase in the maximum force, F_max, and a 340% increase in the fracture toughness, W. Compared to the control groups (i.e., flat, inset, and 90° interfaces), F_max and W values increased by 500%–990% and 350%–1200%, respectively. The findings of this study can serve as a guideline for the design and fabrication of efficient soft–hard interfaces with performances close to predicted values.