Disturbances in the propagation of the electrical wavefront can cause cardiac arrhythmia’s that can, in extreme cases, lead to cardiac arrest. By recording the electrical signals of the heart, a better understanding can be gained of the mechanisms behind cardiac arrhythmias. A method that can be used to investigate the state of the heart is electroanatomic mapping (EAM), where the local electrical activity is related to a point within a 3D anatomical reconstruction of the heart. By investigating the electrical activity, areas of scarring can be identified.
Currently, the electrical activity is recorded with a plaque multi-electrode array at the Erasmus MC. Local activation maps can be recorded during sinus rhythm (SR), and with the use of a reference electrode, total activation maps are generated. This can only be done during SR. During arrhythmia’s, this is no longer possible due to temporal variation in electrical activity. To investigate the activation maps during arrhythmia, an electrode array that can record the total activity of the ventricles was designed and developed in this thesis.
By studying the literature and with the help of medical experts, a requirement list was established. Different concept ideas were compared using a Harris profile to select the best design for further development.
From the Harris profile it was concluded that a 3D printed sock was the best design for the electrode array. An investigation of the effects of the pattern and thickness on the stiffness and fatigue life of the sock were performed with the help of tensile tests and fatigue tests. From the results of the tensile and fatigue tests, a decision for the design of the electrode array was made. A 3D printed sock with the optimized design and electrodes were used to make epicardial recordings on a porcine heart in an ex vivo heart perfusion setup. The electrical recordings were later analyzed and visualized on a 3D model of the heart.
Even though the resolution of the electrode array was lower than that of the epicardial mappings performed at the Erasmus MC, the results obtained from the electrode array looked promising. This is the first study that has developed a 3D printed electrode array the can record the electrical activity of the ventricular surface from multiple sites simultaneously. However, before the electrode array can be used for elucidating the mysteries behind epicardial activation during arrhythmia’s, further development is needed.

Ultrasound (US) neurostimulation, the non-pharmacological, reversible excitation or inhibition of the nervous system using ultrasonic waves, is emerging as a high interest topic in neurostimulation research. In the current project, an attempt was made to demonstrate US neuromodulation in a Lumbricus Terrestris model of evoked compound action potentials (eCAP). Hardware and software for the electrophysiological observation of local field potentials were designed and assembled. The resulting system was used to perform mechanical, electrical and both direct and indirect ultrasonic neurostimulation experiments. It was shown electrical stimulation could be performed reliably in-vivo and ex-vivo. Mechanical stimulation only functioned in-vivo. Additionally, power transfer experiments showed that deeply embedded CMUT devices can be used to harvest acoustic power and use this signal to stimulate an explanted Lumbricus Terrestris medial nerve cord. Direct ultrasound neurostimulation was however not observed, likely due to a combination of misalignment and incorrect acoustic pressure profiles.
As an additional project, a microfabrication step was designed and performed for the etching of high aspect-ratio silicon bulk structures for the backside venting of low frequency CMUT devices. A two-step process deep reactive ion etch (DRIE) was attempted where smaller features were first introduced into the silicon (phase A) and then advanced using a larger etch frame (phase B). It was shown that phase A etching could be performed adequately, resulting in high quality deep silicon etch profiles with minimal tapering and an excellent etch rate. However, phase B etching resulted in the consumption of side-walls and removal of previously etched features. It is likely some slight adjustments to the passivation stage of the DRIE process would result in successful completion of this fabrication step.
Acknowledgements

Microelectrode arrays (MEAs) are extensively used for measuring neural activity in-vitro given their ability to monitor several neurons simultaneously unlike techniques such as patch clamp. However, MEAs still have limitations in acquiring high spatial resolution data due to limited number of channels that can be parallelly scanned, the need for bulky anti-aliasing filters, and limitations in signal-to-noise ratio (SNR) arising from thermal noise. Commercially available MEAs rely on resistive or self-capacitive sensing scheme, but this research proposes a new approach to increase the number of sensing locations while reducing the channels and to increase SNR. Fundamental design aspects of a MEA such as the shape and size of electrodes are revisited. By employing traditional lithographic fabrication techniques, these arrays with various geometries are fabricated and characterized. Neural cultures are seeded on these novel MEAs to record neural activity in the electrical domain and concurrently Ca+2 Imaging is performed to correlate and verify the activity of a neuron.