Tunable rod-shaped microgels with surface grooves for hierarchical anisotropy in 3D bioprinted tissues

Accurate modeling of anisotropy is essential for understanding and replicating the behavior of structurally aligned tissues such as bone, muscle, heart, and ligaments, where cellular and extracellular matrix alignment critically influence function. Here, we introduce a scalable platform of anisotropic building blocks: rod-shaped microgels fabricated using a flow-focusing droplet microfluidic system with tunable surface topography. As microcarriers, the anisotropic microgels support enhanced cellular alignment and sarcomere maturation of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and mouse myoblasts (C2C12). These microgels are compacted into a shear-thinning bioink, enabling extrusion-based 3D printing. During extrusion bioprinting, the rod microgels align along the printing path, promoting macroscopic alignment that significantly increase the presentation of C2C12 differentiation markers. This multi-scale alignment, spanning subcellular, cellular, and construct levels, demonstrates the potential of surface-patterned anisotropic microgels as a modular, bottom-up strategy for engineering functional, hierarchically organized tissues.