Characterization of surface micromachined metallic microneedles

The purpose of the paper is to provide quantitative characterization of metallic microneedles. Mechanical and fluid flow experiments were performed to evaluate the buckling force, the penetration force, and the pressure versus flow rate characteristics of the microneedles. The microneedle design variations characterized included varying the shaft lengths, varying the tip taper angles/geometries, and the inclusion of micromechanical barbs. The penetration force was found to range from 7.8 gF for a microneedle of shaft length 500 /spl mu/m, to 9.4 gF for a length of 1500 /spl mu/m, both with a tip taper angle of 30/spl deg/. Microneedles with a linear tip taper angle of 30/spl deg/ penetrated 95 +% of the time without failure. The microneedles with a 15/spl deg/ and 20/spl deg/ linear tip taper penetrated 10% and 25% of the time, respectively. The buckling force was found to be 98.4 gF for a 500 /spl mu/m long microneedle shaft, 72.3 gF for a needle of shaft length 1000 /spl mu/m, and 51.6 gF for a 1500 /spl mu/m long shaft. The results demonstrate that the penetration force was 7.9% of the buckling force for 500 /spl mu/m long shafts, 11.6% for a 1000 /spl mu/m long shaft, and 18.2% for a 1500 /spl mu/m long microneedle shafts. The microneedle fluid flow characteristics were studied. An inlet pressure of 49.0 Pa was required for a flow rate of 1000 /spl mu/L/h and 243.0 Pa for a flow rate of 4000 /spl mu/L/h using air as the fluid medium. For water, an average pressure of 30.0 kPa was required for a flow rate of 1000 /spl mu/L/h and 106.0 kPa for a flow rate of 4000 /spl mu/L/h.