**5. Conclusions**

This work presents the novel design of a low-cost ECAM system for printing mesoscale metal parts. With the proposed microfluidic system, i.e., the fountain pen feed system, which is composed of a semi-open main channel and comb structure, a stable mesoscale meniscus can be obtained during the printing process without liquid leaking or meniscus breaking. Two materials, copper and nickel, were attempted to print. It is believed that some other metals that can be electrodeposited from aqueous electrolytes, such as Ag and Ti, can be printed through the same ECAM system. The investigation of the surface roughness of the printed structures shows that the surface smoothness can be controlled by manipulating the applied potential and printing strategy. Various structures were also printed and an example of a copper circuit printed on the non-conductive PET substrate was achieved to provide a possible application using the proposed ECAM system. The presented work demonstrates the possibility to control the meniscus and electrolyte flow by designing an appropriate microfluidic system and provides a foundation for future work on designing more sophisticated microfluidic systems to achieve higher printing precisions and satisfactory material properties for the fabrication of functional electronics.

**Author Contributions:** Conceptualization, Y.Y.; validation, P.L., Y.G., Y.W., and J.C.; formal analysis, P.L. and Y.G.; investigation, P.L. and Y.G.; writing–original draft preparation, P.L. and Y.Y.; writing–review and editing, P.L., Y.G., Y.W., J.C., and Y.Y.; and supervision, Y.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external fund.

**Conflicts of Interest:** The authors declare no conflict of interest.
