In Situ Fabrication of Complex Hollow Nickel Microstructures via Filament-Guided Electrolyte-Column Electrodeposition

Complex hollow metallic microstructures are essential for microelectromechanical systems (MEMS), lab-on-a-chip microfluidics, and bio-integrated devices, yet their fabrication remains challenging because geometric complexity, microscale precision, and high aspect ratios must be satisfied simultaneously. This study proposes filament-guided electrolyte-column electrodeposition (FG-ECD), which couples a removable filament template with a nozzle-confined electrolyte column to define internal channels in situ during localized metal growth, thereby avoiding the collapse risks associated with conventional template removal routes. A two-dimensional axisymmetric multiphysics model reveals that the embedded filament reorganizes the electrolyte into a stable annular flow and shifts the cathodic current density maximum from the substrate toward the advancing dome front, establishing a self-consistent, quasi-stable localized reaction zone, while a parametric sweep shows that the total current scales the current density magnitude without altering its spatial profile. Experiments demonstrate that a current of 3.6 mA produces smooth dome front growth at approximately 20 μm/min, whereas 5.5 mA triggers sustained hydrogen evolution and a transition to cellular deposition. Under optimized conditions, straight, 540° spiral, and R-shaped dual-channel hollow nickel microstructures were fabricated with continuous, collapse-free internal channels of 50 ± 5 μm, aspect ratios exceeding 10:1, and dimensional accuracy within ±35 μm. FG-ECD provides a low-temperature processing route for complex hollow metallic architectures and offers process regulation principles based on co-regulation of the flow field and current density for electrochemical microfabrication.