Fig. 6. Schematic representation of different fabrication methods: (a) template-based fabrication where the mould is on the bottom side and the demoulded cilia on the top side with the base material made of either the same as cilia material or a different one. (b) The template free fabrication based on MEMS processes like thin film deposition, photolithography and etching, accompanied by other chemical treatment processes are used to mostly fabricate in-plane flap-shaped cilia structures. The source element shown here may either be a UV source or a source for metal coating etc. The mask may either be a separate unit or one deposited on the device surface itself. (c) The poles in the self assembly process are permanent or electro magnets used to align and assemble magnetic cilia structures, or can form an electric field aligning conducting material. (d) In 3D printing, the nozzle dispenses a material to form the cilia while, optionally (‘4D’), an external magnetic field imposes alignment of magnetic particles in the cilia during fabrication. (e) In cilia pulling, the pulling posts shown here may either be formed by solid structures (mostly PDMS) or by electrodes, which pull out hairlike structures from a liquid precursor film either by direct contact or by a localized electric field. (f) In part assembly, different units of the entire cilia structure are assembled to form a fully functional unit.