Fabrication of taper hollow metallic microneedle array for portable drug delivery system

In this paper, we demonstrated the detailed fabrication process of taper hollow metallic microneedle array through 2-layer SU-8 thick photoresist based backside exposure and Nickel electroplating techniques. We got microneedles with length in the range of 300 μm to 450 μm, and sharp tips with cone angles in the range of 4.6° to 5.7°. It was found that backside exposure through transparent glass substrate and the first layer of exposed SU-8 photoresist had many advantages. First, we could get more strong microneedles with bottom diameter larger than bore diameter on the mask. Besides, the ratio of the inner diameter of microneedle tip to the bore diameter on the mask was defined as R_d, which was less than 1. It presented the sharpness of microneedles. The microneedle would be sharper when the thickness of the exposed SU-8 photoresist layer increase. If the second SU-8 layer was backside exposed insufficiently, ultra sharp microneedles with smooth profile could be fabricated by adjusting the current density of electroplating. Finally, UV glue was applied to bond an array of nickel microneedles to a glass slide, which could bond microneedle array and glass firmly and seal the gap sufficiently.