Long term performance of porous platinum coated neural electrodes

Abstract

Over the last several years, there has been a growing interest in neural implants for the study and diagnostics of neurological disorders as well as for the symptomatic treatment of central nervous system related diseases. One of the major challenges is the trade-off between small electrode sizes for high selectivity between single neurons and large electrode-tissue interface areas for excellent stimulation and recording properties. This paper presents an approach of increasing the real surface area of the electrodes by creating a surface microstructure. Two major novelties let this work stand out from existing approaches which mainly make use of porous coatings such as platinum black or iridium oxide, or Poly(3,4-ethylenedioxythiophene) (PEDOT). Roughening is carried out by a dry etching process on the silicon electrode core before being coated by a sputtered platinum layer, eliminating complicated deposition processes as for the materials described above. The technology is compatible with any commonly used coating material. In addition, the surface roughening is compatible with high aspect ratio penetrating electrode arrays such as the well-established Utah electrode array, whose unique geometry presents a challenge in the surface modification of active electrode sites. The dry etching process is well characterized and yields a high controllability of pore size and depth. This paper confirms the superior electrochemical properties including impedance, charge injection capacity, and charge storage capacity of surface engineered electrode arrays compared to conventional arrays over a period of 12 weeks. Furthermore, mechanical stability of the modified electrodes was tested by implantation in the brain of a recently deceased rat. In conclusion, the larger interface surface of the electrodes does not only decrease the impedance which should lead to enhanced Signal to noise ratio (SNR) for recording purposes, but also yields higher charge injection capacities, which improve the stimulation characteristics of the implants.

Characterizing Longitudinal Changes in the Impedance Spectra of In-Vivo Peripheral Nerve Electrodes

“…For the IrOx arrays, these spectra were similar to one that have been chronically implanted for at least 30 days [ 11 ], or to the uncoated sputtered iridium oxide films (SIROF) sites [ 12 ], and are thus likely aging sites, with the iridium oxide flaking off, damage to the tips, and/or a complex interaction with the encapsulation sheath. For the platinum arrays, the mixed category was the most prevalent group for all of the timepoints, and the spectra were similar to those previously characterized in vitro [ 14 , 15 ].…”

“…For the platinum arrays, the phase spectrum for the predominant mixed group initially presented with a U-shaped minimum in middle frequencies, similar to that of Pt UEAs previously shown in vitro [ 14 , 15 ]. As time progresses, this minimum flattens out and a high-frequency peak develops.…”

“…Thus, these changes are likely due the foreign body response, although the aging of the electrode may also contribute. The magnitude spectra are similar [ 14 , 15 ] or much lower than a previous study [ 19 ], with the latter difference potentially arising from the large error bars presented with the mean. Over time, we found that the impedance decreased at low frequencies (<100 Hz) and increased at very high frequencies (1 MHz).…”

Acousto-Plasmonic Sensing Assisted by Nonlinear Optical Interactions in Bimetallic Au-Pt Nanoparticles

“…In contrast, the absorption of platinum NPs (Pt NPs) presents resonances in the ultraviolet region [ 15 ], taking advantage of their ability for high-energy photon manipulation to be considered for batteries and fuel cells developments [ 16 ]. Pt NPs may give rise to new photo-thermal agents [ 17 ] that may be assisted by biostability and adhesion properties that are strongly attractive for nano/micro-engineered systems for neurological diagnostic [ 18 ]. Additionally, the electronic properties of Pt NPs make them useful for building optical signal processing devices, such as circuits and electrodes of multilayer ceramic capacitors [ 19 ].…”

Hybrid Chemomechanical Promotion of PEDOT Adhesion onto Flexible Microelectrode Arrays for Chronic Neural Stimulation

“…The challenge in doing so is to enhance the electrical charge storage capacity (CSC) of ultra-small electrode sites (<50um). Even though there are multiple approaches to enhance CSC of existing inorganic coating technologies [2][3][4][5], conductive polymers promise significantly better cellular agreement [6][7][8] while they maintain superior CSC, high flexibility, and lasting biocompatibility [9]. Among them, Poly3,4-ethylenedioxythiophene (PEDOT) stands out as the most established and investigated in literature to date.…”