Mechanical characterization of surface micromachined microneedle array

This paper will report on the mechanical characterization of hollow metallic microneedles. The characterization will include the affects of design variations on the buckling and penetration force of these microneedles, and on the fluid flow characteristics. Needles of five different tip geometry and three different taper angles were designed. The taper angle varies between 15° and 30°. The lengths of the needle shaft tested were 500 μm, 1000 μm and 1500 μm respectively. Microneedles were fabricated using an extension of the work reported earlier. A simple horizontal loading set up consisting of a load cell and a micromanipulator was designed. A rigid orthogonal surface was used in order to study the buckling force, while a mechanically "skin-like" material was used to determine the penetration force. The buckling force was found to vary between 54 gF and 100 gF for needles with shaft lengths of 1500 and 500 μm, respectively. The penetration force was found to be independent of shaft length and was approximately 8 gF. While the needle tips with 15° taper angle failed, the needles with 20° taper angle performed better but experienced a 50% tip failure rate. The flow rate of the microneedles was characterized over a range of 0 - 100 psi using distilled water and air as the fluid media