Development of a smart needle integrated with an impedance sensor to determine needle to nerve proximity for nerve blocking (anaesthetic) procedures

Abstract

This research was undertaken with the aim of developing novel fabrication processes to enable integration of a two-electrode system to a hypodermic needle and therefore fabrication of a smart needle. The concept was conceived with the intention of addressing a currently unmet clinical need for a regional anaesthetic procedure, ultrasound guided peripheral nerve block (USgPNB). The technique USgPNB refers to a set of medical procedures which block nerve impulse conduction, provide anaesthesia and pain relief to facilitate surgical operations or are performed to treat acute or chronic pain. The location of the needle tip relative to the target nerve is crucial to the safe and effective practice of USgPNB. By developing a smart needle, a hypodermic needle integrated with an impedance sensor, bioimpedance can be measured at the needle tip. Bioimpedance has been used to differentiate between tissue type and therefore has the potential to identify the tissue type located at the needle tip, identifying needle location within the body. Accurate identification of tissue at the needle tip could provide valuable objective information and inform high stakes procedural decisions prior to injection of local anesthetic in close proximity to neural structures. To allow for accurate and specific bioimpedance recording at the needle tip a novel smart needle device was designed and fabricated. This thesis describes novel approaches to fabricating a two-electrode system directly and in-directly to the surface of a hypodermic needle. The impedance sensor was fabricated by a range a different processing steps including reactive ion etching, parylene C vapour deposition and various metal deposition techniques such as electron beam evaporation and sputtering. The main research challenge of this work was the alteration of conventional MEMs fabrication techniques, traditionally used on flat, very smooth substrates, into processes that can fabricate electrical components onto 3D, curved (round), rough, stainless-steel, hypodermic needle substrates. One of the merits of the electrode fabrication route developed herein is its potential to be transferable to rougher needles, including those with inbuilt grooves or bumps which are becoming desirable for nerve block procedures. As a result, very robust, reliable smart needle prototype devices were fabricated, characterised and demonstrated to provide bioimpedance data of live tissues in an animal model. Addressing the research challenge has contributed new knowledge to microfabrication processes.