Redesign and Flow Characterization of Microcapsules through Hollow 3D-Printed Microneedles

Traditional bulk cavity microneedles suffer from stagnant zones and internal wall collisions that damage suspended cell carriers. This research computationally optimized and experimentally validated a novel multi-planar, branched hollow microneedle chamber to minimize dead volume and protect sensitive payloads. By replacing the traditional bulk cavity with a symmetric six-peripheral nozzle architecture, COMSOL simulations confirmed the elimination of central stagnation zones. Low fluid velocities (0.05 m/s) maintained streamline alignment, while higher velocities (0.32 m/s) induced wall impacts, a drift completely mitigated by high-viscosity fluids.

Arrays fabricated via SLA 3D printing demonstrated consistent cross-unit nozzle diameters, despite a 27.8% average print shrinkage. Payload extrusion was empirically validated using fluorescent alginate microcapsules, establishing a linear calibration range (R² = 0.9778) to dynamically track volume fractions, with internal payload retention limited to 10% to 20%. Biomechanical testing on tissue phantoms verified structural integrity for reliable puncture under a 7.8 ± 0.7 N peak force.

This novel design resolves historical flow imbalances and operates at shear-protective flow rates of 1.53 to 7.54 mL/min, substantially lower than the 12 mL/min literature standard. This gentle transport environment establishes a robust framework for advancing microencapsulated cell-based therapies, with future translational optimization required to align these workflows with clinical infusion rates that minimize patient discomfort.