Different fabrication methods of out-of-plane polymer hollow needle arrays and their variations

We demonstrate, in this paper, different methods for the fabrication of various out-of-plane hollow micro needle arrays through back side exposure. We validated the back side exposure to be capable of producing microstructures with taper angles experimentally. Then we found that the taper angles can be adjusted by changing the distance between the photo mask absorber and the photoresist. Solid micro needles can be fabricated by properly calculating the side wall tilting angle and the thickness of the photo resist, while hollow micro needles can be realized by one lithography step through appropriate combination of different back side exposure methods. In this paper, we also demonstrate the capability of fabricating a micro needle array on a flexible membrane for further medical applications.