Artin Petrossians

Materials and Fractal Designs for 3D Multifunctional Integumentary Membranes with Capabilities in Cardiac Electrotherapy

Advanced materials and fractal design concepts form the basis of a 3D conformal electronic platform with unique capabilities in cardiac electrotherapies. Fractal geometries, advanced electrode materials, and thin, elastomeric membranes yield a class of device capable of integration with the entire 3D surface of the heart, with unique operational capabilities in low power defibrillation. Co-integrated collections of sensors allow simultaneous monitoring of physiological responses. Animal experiments on Langendorff-perfused rabbit hearts demonstrate the key features of these systems.

Electrodeposition and Characterization of Thin-Film Platinum-Iridium Alloys for Biological Interfaces

An efficient platinum-iridium thin film alloy electrodeposition method has been evaluated to modify the surface of platinum or gold microelectrodes that are being developed for neural recording and stimulation applications. A large number of electrodeposition process variables have been investigated in terms of how they affected the properties of the electrodeposited films. Three sets of Pt-Ir films of a certain composition were electroplated on gold substrates using a potential cycling technique and characterized using microscopy, elemental analysis, nanoindentation, and electrochemical techniques to evaluate the repeatability of the electrodeposition process. Deposition rates were estimated by determining film mass and thickness as a function of deposition time. The surface morphology of the Pt-Ir films was characterized using scanning electron microscopy (SEM) and the chemical composition was determined using wavelength dispersive spectroscopy (WDS). Nanoindentation measurements showed that the hardness of the electroplated Pt-Ir thin films was nearly 100% higher than that of a Pt foil. The electrochemical properties of the films were evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) and compared with those of pure Pt, pure Ir and 80-20% Pt-Ir foils. The final electroplating process resulted in 60-40% Pt-Ir alloys. The film thickness increased with electrodeposition time at a rate of 16.5 nm/min and stable films with up to 500 nm thickness were obtained. Characterization by SEM and EIS revealed that the real surface area of the Pt-Ir films was much larger than that of pure Pt and increased significantly with increasing deposition time.

Surface modification of neural stimulating/recording electrodes with high surface area platinum-iridium alloy coatings

High-surface area platinum-iridium alloys were electrodeposited by on Pt and Au microelectrodes using a potential sweep technique. Detailed investigations of the structure and morphology and the electrochemical properties of the electrodeposited Pt-Ir alloy coatings were performed. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for the determination of the surface morphology and the chemical composition of the Pt-Ir coatings, respectively. The elemental analysis by EDS showed a nearly 60–40% Pt-Ir composition of the coatings. The electrochemical properties of the Pt-Ir coatings were evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV and EIS measurements revealed that the Pt-Ir coated electrodes exhibit significantly increased charge storage capacity and real surface area compared to uncoated Pt electrodes. Charge injection experiments of the Pt-Ir coated microelectrodes revealed low potential excursions, indicating high charge injection capabilities within safe potential limits.

Reduction of Edge Effect on Disk Electrodes by Optimized Current Waveform

Rectangular pulses applied to disk electrodes result in high current density at the edges of the disk, which can lead to electrode corrosion and tissue damage. We explored a method for reducing current density and corrosion, by varying the leading edge of the current pulse. Finite-element modeling and mathematical analysis were used to predict an optimal waveform that reduces current density at the edge while also maintaining short pulse duration. An approximation of the optimized waveform was implemented experimentally and applied to platinum disk electrodes. Surface analysis using energy-dispersive spectroscopy showed significant reduction of corrosion on the periphery of these electrodes after pulsing, compared to those pulsed with the control rectangular waveform.

Strategies to improve stimulation efficiency for retinal prostheses

Retinitis Pigmentosa (RP) is a degenerative disease of the retina that leads to vision loss. Retinal prostheses are being developed in order to restore functional vision in patients suffering from RP. We conducted in-vivo experiments in order to identify strategies to efficiently stimulate the retina. We electrically stimulated the retina and measured electrically evoked potentials (EERs) from the superior colliculus of rats. We compared the strength of EERs when voltage-controlled and current-controlled pulses of varying pulse width and charge levels were applied to the retina. In addition to comparing EER strength, we evaluated improvement in power efficiency afforded by a high surface area platinum-iridium material. Voltage-controlled pulses were more efficient than current-controlled pulses when the pulses have a short duration (<; 1 ms) and current-controlled pulses were more efficient than voltage-controlled pulses when the pulse width was greater than 1 ms. The high surface area platinum-iridium stimulation electrode consumed power significantly lower than a standard platinum-iridium electrode.

Improved electrode material for deep brain stimulation

Deep brain stimulation (DBS) devices have been implanted for treatment of basic tremor, Parkinsons disease and dystonia. These devices use electrodes in contact with tissue to deliver electrical pulses to targeted cells, to elicit specific therapeutic responses. In general, the neuromodulation industry has been evolving towards smaller, less invasive electrodes. However, current electrode materials do not support small sizes without severely restricting the stimulus output. Hence, an improved electrode material will benefit present and future DBS systems. In this study, five DBS leads were modified using a cost-effective and materials-efficient process for applying an ultra-low impedance platinum-iridium alloy coating. One DBS lead was used for insertion test and four DBS leads were chronically pulsed for 12 weeks. The platinum-iridium alloy significantly improved the electrical properties of the DBS electrodes and was robust to insertion into brain and to 12 weeks of chronic pulsing.

Nanotechnology for Packaging

The use of implantable microelectronic devices for treatment of medical conditions, e.g. movement disorders, deafness and urinary incontinence has increased steadily over the years [1]. These devices use microelectronic components to sense biological activities in the im‐ planted patient. The microelectronic components must be protected from the surrounding tissue using insulating (hermetic) packaging material. This packaging prevents the aqueous saline environment of the body from corroding, short-circuiting and contaminating the internal electronics. Microelectronic packages must incorporate some electrically conducting elements that bridge through the protective packaging to allow the internal microelectronics to sense (or stimulate) the surrounding external environment. These conductive elements are called interconnects or feed-throughs.

Electrodeposition of platinum-iridium alloy nanowires for hermetic packaging of microelectronics

An electrodeposition technique was applied for fabrication of dense platinum-iridium alloy nanowires as interconnect structures in hermetic microelectronic packaging to be used in implantable devices. Vertically aligned arrays of platinum-iridium alloy nanowires with controllable length and a diameter of about 200 nm were fabricated using a cyclic potential technique from a novel electrodeposition bath in nanoporous aluminum oxide templates. Ti/Au thin films were sputter deposited on one side of the alumina membranes to form a base material for electrodeposition. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were used to characterize the morphology and the chemical composition of the nanowires, respectively. SEM micrographs revealed that the electrodeposited nanowires have dense and compact structures. EDS analysis showed a 60:40% platinum-iridium nanowire composition. Deposition rates were estimated by determining nanowire length as a function of deposition time. High Resolution Transmission Electron Microscopy (HRTEM) images revealed that the nanowires have a nanocrystalline structure with grain sizes ranging from 3 nm to 5 nm. Helium leak tests performed using a helium leak detector showed leak rates as low as 1 × 10-11 mbar L s-1 indicating that dense nanowires were electrodeposited inside the nanoporous membranes. Comparison of electrical measurements on platinum and platinum-iridium nanowires revealed that platinum-iridium nanowires have improved electrical conductivity.