Microfluidic-mixer assisted 3D printing of functionally graded multimaterial hydrogels for engineering complex tissue interfaces

Abstract

Reconstructing complex tissue interfaces, such as the osteochondral junction, requires biomaterials capable of mimicking the native gradients in mechanical, biochemical, and structural properties. Traditional fabrication methods often are not able to achieve continuous and tunable transitions within a single construct. To overcome these limitations, we developed a novel microfluidic-assisted 3D printing platform where a high-efficiency passive micromixer with a flow-focusing junction (mix-ff-MPH) was used as a printhead. This technique enables the manufacturing of functionally graded porous hydrogels (FGPHs) with smooth gradients by real-time control of polymer composition and density during extrusion. By optimizing micromixer geometries, we achieved high mixing efficiency (mixing index ≥0.8), ensuring uniform integration of distinct bioinks such as gelatin methacrylate (GelMA) and dextran methacrylate (DexMA). The resulting constructs exhibit spatially controlled gradients in porosity and composition, confirmed by confocal microscopy and FTIR spectroscopy. When seeded with 3T3 fibroblasts, the scaffolds demonstrated region-specific cell adhesion and proliferation, highlighting the role of locally defined porosity and composition in guiding cellular behavior. This platform provides a versatile and precise method for fabricating graded hydrogels and holds significant promise for applications in tissue engineering, especially in addressing the long-standing challenge of replicating the intricate organization of native tissue interfaces.