Geometrical effects in mechanical characterizing of microneedle for biomedical applications

This paper proposes the design and implementation of MEMS (Micro Electro Mechanical Systems)-based in-plane silicon microneedles with explanation of integrated functionality for sensing the resistive forces offered by human skin. The proposed design dimensions are calculated by using the constraints of minimal microneedle dimension, force withstanding capabilities, and their relationship. The paper also proposes the novel fabrication process to realize the microneedles, along with the integrated sensors for sensing skin resistive forces at various depths. The idea of this microneedle prototype is based on the requirements of strength, robustness, minimal insertion pain, and tissue damage in patients. The fundamental constraints set the length of our proposed MEMS-based in-plane microneedle to be 600 mum. The design gives the optimal dimensions of length, width, and thickness both of microneedle and the channel running through it, while considering the influence of various mechanical forces. In addition, the skin also offers an opposing force on the microneedle, which changes with depth of microneedle, angle of insertion, and different layers of tissue penetrated. Three piezoelectric sensors are fabricated on the microneedle to give reliable skin resistance measurement for different insertion depth. Performance analysis is made to validate the proposed design approach for different microneedle geometries and sizes. (C) 2004 Elsevier B.V. All rights reserved.