Scaling-up of electropolishing for Ni micro-injection mould tools: Enhanced performance and throughput in microfluidic device fabrication

Precise miniature tooling is critical for the production of micro-electromechanical systems, microfluidics and micro-optics. Post-treating mould tools is critical for ensuring defect-free production in micro-injection moulding applications. In this study, large-scale electropolishing (EP) was implemented successfully to shape and polish 4-inch scale Ni mould tools, introducing a positive draft angle and increasing the fillet radius of the micro features. These geometric modifications reduced demoulding defects and facilitated smoother demoulding of polymer parts from Ni moulds. The upscaling of EP was investigated systematically, focusing on its impact on reducing friction and demoulding forces, using both polished and unpolished moulds. Polished moulds achieved a 9.22 ± 2.56% reduction in demoulding force and a decrease in the coefficient of friction from 0.3 to 0.2 compared to unpolished moulds. A mould tool life test, conducted over 1000 cycles, demonstrated the superior durability of electropolished moulds with high-quality cyclic olefin copolymer (COC) chips being produced. Furthermore, a microfluidic mould for a high-performance drug delivery system was fabricated via UV-lithography and electroforming. This mould was used in both polished and unpolished forms to produce microfluidic chips, which were tested subsequently for lipid nanoparticle synthesis and transfection efficiency. The polished moulds resulted in improved transfection efficiency and throughput. Overall, this study demonstrates that electropolished moulds can manufacture superior quality polymer components by reducing friction, demoulding forces and defects while also improving tool life. These findings provide valuable insights into the scalability of EP for enhancing mould performance and throughput in the fabrication of microfluidic devices.