Study On Microneedle Based On Moving LIGA Lithography Technology

MEMS based microneedles have been the focus of study in bio-MEMS field recently. Microneedles are generally fabricated by fine machining technology, with diameter and length in micrometers. The diameter of the microneedle is taller than 100μm and diameter is 30-80μm. Firstly, the microneedles should be sharp enough so that they can penetrate the outer layer of skin, create pathways for drug into the epidermis layer. And release drug in proper depth. In order to withstand the pressure from different direction during skin penetration and drug delivery, the strength of microneedles should have enough strength. Microneedles have been made by silicon, metal and polymer. Silicon surface adsorb protein to promote adhesion of white blood cells and microneedles, which would lead to stress response. Therefore, Silicon cannot be applied to human therapy directly. However, polymer is widely used due to its low cost and the ease of mass fabrication.Based on structures, the microneedles are classified as in-plane microneedles and out-of-plane microneedles. As for in-plane microneedles, the microneedle shaft is parallel to the substrate surface and their length can be accurately controlled during the fabrication process. However, it is difficult to fabrication in-plane microneedle arrays with two dimensional geometry. In out-of-plane microneedles, the shaft is perpendicular to the substrate surface and it is easier to fabricate. Through those high aspect ratio process technology, such as DRIE (Deep Reaction Ion Etch) and LIGA technology, the shaft can be produced out of the substrate.In this paper, the main research was on out-of-plane microneedle based on Moving LIGA lithography technology. In order to penetrate the skin easily and feel painless, enough stiffness and sharp tip are needed. With conventional LIGA technology; only vertical sidewalls micro structures can be obtained. To obtain beveled sidewalls, some processes are improved and moving LIGA is presented. Compared to LIGA technology, PMMA are exposed by X-ray twice and the second exposure is perpendicular to the first one through turning the resist stage during the second exposure. With isosceles triangle mask pattern, 3-dimensional micro needle arrays with pyramids-like sidewalls were fabricated based on Moving LIGA technology. Besides, the cross section of micro needles was similar to the mask pattern.However, the tip width of 3-D micro needle based on Moving LIGA mask lithography was discovered to be different from designed mask needle tip width. In order to control the needle tip size, MATLAB is utilized to analyze important fabrication parameters, including mask shape and tilting effect, developing time and exposure does. Among these parameters, the tilting effect refers to the impact caused by the mask pattern tilt. The experiments were also carried out, in which different shape masks with the same needle tip width was employed.Finally, ANSYS was employed to analyze the strength of microneedle. Besides, based on PDMS transfer and electroplating technology, metallic microneedle array and microneedle mold was fabricated from the PMMA original mold.