Mechanical Failure Analysis of Needles, for Micro-needle Array Dry-electrodes

J. K. Radhakrishnan; V. C. Padaki; U. K. Singh

doi:10.14429/dlsj.2.12282

J. K. Radhakrishnan Defence Bioengineering and Electromedical Laboratory, Bengaluru -560 093, India
V. C. Padaki Defence Bioengineering and Electromedical Laboratory, Bengaluru -560 093, India
U. K. Singh Defence Bioengineering and Electromedical Laboratory, Bengaluru -560 093, India

DOI: https://doi.org/10.14429/dlsj.2.12282

Abstract

Dry electrodes, which have an array of vertically aligned conducting micro-needles over a conducting substrate/base are most suitable for long-term continuous monitoring of EEG-signal, and overcomesthe disadvantages of conventional wet electrodes. A crucial design requirement for thesemicro-needlearrays, is the choice of the needle material with suitable mechanical strength to penetrate the skin without mechanical failure. This paper gives, the results of mechanical failure analysis of different needle materials that have been typically used/proposed for invasive use. A conical needle with 150μ width at the base and 10μ width at the tip, and length in the range 10μ - 200μ was taken up for calculation. The Critical load for failure, falls in the following descending order for the selected materials: viz., Carbon Nanofibre (CNF), Titanium-alloy (Ti 6-4), Single Crystal Silicon, Nickel, Tungsten, Platinum-Iridium (Pt90 percent-Ir10 percent), Stainless Steel (SS304),Poly Methyl Methacrylate (PMMA), Polyimide, Polycarbonate, Gold, Silver, Photoresist-SU8, Polyurethane and Poly DiMethylSiloxane (PDMS).Taking the most accepted value of 0.1N as the penetration force required for needle penetration into skin, it is seen that for a needle length of 100μ, the following materials, Carbon Nanofibre (CNF), Titanium-alloy (Ti 6-4), Single Crystal Silicon, Nickel, Tungsten, Platinum -Iridium (Pt90 percent-Ir10 percent) andStainless Steel (SS304), can penetrate the skin without mechanical failure.

Author Biographies

J. K. Radhakrishnan, Defence Bioengineering and Electromedical Laboratory, Bengaluru -560 093, India

Dr J.K. Radhakrishnan, obtained his MSc and PhD in Physics,
from Bharathiar University, Coimbatore. He is presently the Head,
Department of Sensor Technology, Defence Bio-Engineering and Electro-medical Laboratory, Bengaluru. He is working on development
of Sensors for Aeromedical and Biomedical Applications

V. C. Padaki, Defence Bioengineering and Electromedical Laboratory, Bengaluru -560 093, India

Dr V.C. Padaki has obtained his MSc in Physics, from Bangalore
University, and PhD in Physics from Indian Institute of Science,
Bengaluru. He retired as Director, Defence Bio-Engineering and
Electro-medical Laboratory (DEBEL) and presently working as
DRDO fellow at DEBEL, Bengaluru. He was involved in development
of aero-medical life support systems, protective equipment and
biomedical devices for the services.

U. K. Singh, Defence Bioengineering and Electromedical Laboratory, Bengaluru -560 093, India

Dr U K Singh completed his MSc and MTech in Computer Science
from DAVV, Indore and obtained his PhD in Soft Computing from
University of Hyderabad. Currently working as Director, Defence
Bioengineering and Electromedical Laboratory, Bengaluru. Prior
to this assignment, he was Project Director (Weapon Systems) for
Ballistic Missile Programme at Hyderabad. He is a recipient of
DRDO Award for Path-breaking Research/Outstanding Technology
development and Laboratory Scientist of the Year Award (Lab level-
DRDO Award).