Probing research on implant electrodes

Heart, cochlear, spinal-cord and deep-brain stimulators all deliver therapeutic stimuli through electrodes implanted in the human body. Researchers are looking for ways to miniaturise and improve these electrodes for better health outcomes.

Implants could be made smaller, longer lasting and more effective if a surfacing technique could be developed that reduces the electrode impedance and also avoids activating the body's natural defences so that impedance stays low. Immune reactions and the development of scar tissue can reduce the effective surface area of the electrodes and limit both the therapeutic stimulus and the battery life of the implant. Surface roughening technology is not used in implants as it is observed that the advantage of the increased surface area is lost over extended periods of time. This is sometimes attributed to cells in scar tissue 'clogging' the induced pores.

However, since surface roughening treatments are used as anti-fouling protection for boats, it is clear that not all surface roughness approaches invite the same outcome.

University of Waikato researchers from the Faculty of Science and Engineering, including Professor Jonathan Scott, Dr Ray Cursons, Dr Gregory Jacobsen and PhD student Mark Jones, are working to explain what happens when electrodes degrade in the body and to develop a way to improve the electrode surface area without it becoming susceptible to the body's natural defences. Professor Scott and Mark Jones have developed an objective method of characterising electrode impedance through the use of a newly-developed fractional capacitor model of the electrode-electrolyte interface. Applying this should help the team to understand exactly how the electrode impedance is affected by various biological events.

The potential number of beneficiaries for this implant research is large and growing. More than 325,000 people worldwide use cochlear implants to overcome profound deafness. About 100 New Zealanders receive cochlear implants every year. Numbers of patients using deep-brain stimulators have also grown as the treatment has gained approval for more conditions, from essential tremor to Parkinson's disease.