Design and Development of Microneedle Pads for Automated External Defibrillators (AEDs)

Abstract

With the prominent and life-threatening issue of sudden cardiac arrest (SCA), the demands for increased accessibility and effectiveness of AEDs continue to rise. Timely access to automated external defibrillators (AEDs) can vastly increase the chances of survival for someone who suffers an SCA. As we acknowledge the importance of AEDs, there is also a vested interest in improving the portability of defibrillators. Historically, they have been bulky and cumbersome to transport efficiently, particularly in non-traditional settings. The first step towards achieving this goal is reducing the patient’s transthoracic impedance (TI), which serves as a barrier preventing the optimal delivery of shock energy. One promising avenue involves advancing microneedle (MN) electrodes to tackle the electrode-skin barrier, a key element of TI that can be externally mitigated. The purpose of this study was to assess the feasibility and effectiveness of MN based AED electrodes through a functional proof of concept. An iterative design and experimentation approach was used to evaluate various electrode prototypes. A circuit for measuring interelectrode resistance was created to mimic the functionality of an operational AED, providing quantitative assessment of the resistance at the electrode-skin interface. Test specimens comprised of a multitude of animal skin samples, with a gradual transition to human cadaver mediums. The final pad iteration consisted of 8 arrays of microneedles, fabricated using bulk micromachining, and affixed to a flexible 3D-printed TPU base. Each cluster was made of gold-coated silicon, featuring 25 needles per cluster and a needle height of 0.7mm, resulting in a total conductive area of 13.52 cm2. Due to resource constraints, it was not feasible to manufacture an MN pad of equivalent size, which would have been eight times larger. Therefore, an extrapolated experimental approach was employed, where the performance of the 8 microneedle clusters was evaluated, and the behavior of the cluster numbers equivalent to the AED pad was inferred. In a direct pad comparison, the results indicated an average 20% reduction in human transthoracic skin resistance for a single MN pad. With increased efficiency, it was conjectured that the performance of an AED could be proportionally downscaled by 35%, resulting in the reduction in size and weight of all major components. Preliminary biocompatibility and safety evaluations concluded that the MN electrodes are safe and have the potential to improve safety compared to conventional methods. In the end, the advancement of AED microneedle electrodes makes a substantial impact in the field by further optimizing the effectiveness of AED defibrillation, improving portability, and consequently enhancing patient outcomes by raising the survival rate of sudden cardiac arrest.