Investigations into insertion force of electrochemically micro-textured hypodermic needles

Abstract

Electrochemical micro-machining (ECMM) is being a widely used process for replicating multiple micro-structures for micro-texturing due to its heat-free and zero tool wear processing. This paper outlines an experimental study of the tribological behavior of medical hypodermic needles. The real surface contact area of textured needles is calculated and related to insertion force. Insertion force of textured needles is investigated by puncturing and inserting in a hydrogel sample with and without castor oil. An electrochemical micro-machining process is extended for machining of micro-dimples, circular micro-grooves, and linear micro-channels on curved metallic surfaces for creating micro-textures. Insertion force of micro-textured needle is recorded using a load cell, and comparison of it with untextured needles shows the significance of micro-textures. From the experimental study, it is witnessed that micro-textures developed on the needle decreased the insertion force and changed the behavior of fracturing of the hydrogel as compared to the needle without textures. The needle with circular micro-channels (grooves) confirmed the minimum insertion force compared to other micro-textured needles. Reduction in insertion force with respect to micro-dimples, parallel micro-channels, and circular micro-channels are 5.6, 25.5, and 37.8%, respectively. Calculation and analysis of surface area in all the three micro-textured needles support the reason of reducing the force in the case of circular micro-channels. In the case of circular micro-channels, contact area decreases more and fracture in the lateral direction is minimal; hence, insertion force recorded is minimum.