Electroformation on 3D Chip with "Holes" and "Inlands"

Uniform deposited lipid film is a crucial factor in the electroformation of monodisperse vesicles. Methods of the lipid-film formation adopted in previous studies include dropping, spin-coating, or dipping by using size-controllable stamps.

         According to the stamp-based method, two novel chips are designed by fabricating cylindrical "holes" and "inlands" array on the substrate, respectively. Lipid film is formed on these chips by using dropping or dipping methods. It should be noted, though, that the film thickness on the two chips are different due to distinct formation methods, it has a negligible impact on the result of vesicle size distribution.

         Numerical simulation shows that the electric field is focused on the bottom due to these irregular structures ("holes" and "inlands"), specifically "holes", which also result in a stronger electroosmotic flow (EOF) without doubt. Experiments results demonstrate that the number of lipid vesicles formed on each chip decrease with the decrease of the diameter of cylindrical microstructures. However, this dependence becomes very weak when the diameter decreases to 100 um (this value is also depended on some other conditions such as the applied electric field). Optimal formation effect can be achieved when the diameter is about 40 um. In addition, these results are also affected by the distance between two substructures which is set at 20 um finally.