In-plane single-crystal-silicon microneedles for minimally invasive microfluid systems

This paper reports an in-plane single-crystal-silicon microneedle array, its mechanical safety, its integration with a polydimethylsiloxane (PDMS) microfluid chip, as well as in vitro and ex vivo test results. The fabricated microneedle arrays have buried microchannels, which are fabricated by using the processes of anisotropic dry etching, isotropic dry etching, and trench-refilling. The microchannel diameter is about 20μm. Several needle dimensions and shapes were investigated, and the microneedle shape was optimized using mechanical strength analysis. A 100μm wide, 100μm thick, and 2mm long microneedle shaft with the tip taper angle 30° and the isosceles triangle tip shape is strong enough to endure 0.248mNm of out-of-plane bending moment and 6.28N of in-plane buckling load. Then, the microneedle array is integrated with a PDMS microfluid chip. The microneedle integrated microfluid chip is tested in vitro, by injecting black ink into a methanol-filled petridish, and Rhodamine B dye into 1% agarose gel through microchannels of the integrated microneedle. The integrated microfluid chip is also tested ex vivo, by injecting Rhodamine B dye into a chicken breast flesh. In this ex vivo test, the penetration force was measured. For the optimized microneedle shaft, the penetration force was 80.9mN, and this force is less than 1.3% of the buckling force, which is 6.28N.