Electron transfer processes occurring on platinum neural stimulating electrodes: pulsing experiments for cathodic-first, charge-imbalanced, biphasic pulses for 0.566 ⩽ k ⩽ 2.3 in rat subcutaneous tissues

Deciphering platinum dissolution in neural stimulation electrodes: Electrochemistry or biology?

Platinum (Pt) is the metal of choice for electrodes in implantable neural prostheses like the cochlear implants, deep brain stimulating devices, and brain-computer interfacing technologies. However, it is well known since the 1970s that Pt dissolution occurs with electrical stimulation. More recent clinical and in vivo studies have shown signs of corrosion in explanted electrode arrays and the presence of Pt-containing particulates in tissue samples. The process of degradation and release of metallic ions and particles can significantly impact on device performance. Moreover, the effects of Pt dissolution products on tissue health and function are still largely unknown. This is due to the highly complex chemistry underlying the dissolution process and the difficulty in decoupling electrical and chemical effects on biological responses. Understanding the mechanisms and effects of Pt dissolution proves challenging as the dissolution process can be influenced by electrical, chemical, physical, and biological factors, all of them highly variable between experimental settings. By evaluating comprehensive findings on Pt dissolution mechanisms reported in the fuel cell field, this review presents a critical analysis of the possible mechanisms that drive Pt dissolution in neural stimulation in vitro and in vivo. Stimulation parameters, such as aggregate charge, charge density, and electrochemical potential can all impact the levels of dissolved Pt. However, chemical factors such as electrolyte types, dissolved gases, and pH can all influence dissolution, confounding the findings of in vitro studies with multiple variables. Biological factors, such as proteins, have been documented to exhibit a mitigating effect on the dissolution process. Other biological factors like cells and fibro-proliferative responses, such as fibrosis and gliosis, impact on electrode properties and are suspected to impact on Pt dissolution. However, the relationship between electrical properties of stimulating electrodes and Pt dissolution remains contentious. Host responses to Pt degradation products are also controversial due to the unknown chemistry of Pt compounds formed and the lack of understanding of Pt distribution in clinical scenarios. The cytotoxicity of Pt produced via electrical stimulation appears similar to Pt-based compounds, including hexachloroplatinates and chemotherapeutic agents like cisplatin. While the levels of Pt produced under clinical and acute stimulation regimes were typically an order of magnitude lower than toxic concentrations observed in vitro, further research is needed to accurately assess the mass balance and type of Pt produced during long-term stimulation and its impact on tissue response. Finally, approaches to mitigating the dissolution process are reviewed. A wide variety of approaches, including stimulation strategies, coating electrode materials, and surface modification techniques to avoid excess charge during stimulation and minimise tissue response, may ultimately support long-term and safe operation of neural stimulating devices.

Bioelectronic Neural Interfaces: Improving Neuromodulation Through Organic Conductive Coatings

Integration of bioelectronic devices in clinical practice is expanding rapidly, focusing on conditions ranging from sensory to neurological and mental health disorders. While platinum (Pt) electrodes in neuromodulation devices such as cochlear implants and deep brain stimulators have shown promising results, challenges still affect their long-term performance. Key among these are electrode and device longevity in vivo, and formation of encapsulating fibrous tissue. To overcome these challenges, organic conductors with unique chemical and physical properties are being explored. They hold great promise as coatings for neural interfaces, offering more rapid regulatory pathways and clinical implementation than standalone bioelectronics. This study provides a comprehensive review of the potential benefits of organic coatings in neuromodulation electrodes and the challenges that limit their effective integration into existing devices. It discusses issues related to metallic electrode use and introduces physical, electrical, and biological properties of organic coatings applied in neuromodulation. Furthermore, previously reported challenges related to organic coating stability, durability, manufacturing, and biocompatibility are thoroughly reviewed and proposed coating adhesion mechanisms are summarized. Understanding organic coating properties, modifications, and current challenges of organic coatings in clinical and industrial settings is expected to provide valuable insights for their future development and integration into organic bioelectronics.

Smart Graphene-Based Electrochemical Nanobiosensor for Clinical Diagnosis: Review

The technological improvement in the field of physics, chemistry, electronics, nanotechnology, biology, and molecular biology has contributed to the development of various electrochemical biosensors with a broad range of applications in healthcare settings, food control and monitoring, and environmental monitoring. In the past, conventional biosensors that have employed bioreceptors, such as enzymes, antibodies, Nucleic Acid (NA), etc., and used different transduction methods such as optical, thermal, electrochemical, electrical and magnetic detection, have been developed. Yet, with all the progresses made so far, these biosensors are clouded with many challenges, such as interference with undesirable compound, low sensitivity, specificity, selectivity, and longer processing time. In order to address these challenges, there is high need for developing novel, fast, highly sensitive biosensors with high accuracy and specificity. Scientists explore these gaps by incorporating nanoparticles (NPs) and nanocomposites (NCs) to enhance the desired properties. Graphene nanostructures have emerged as one of the ideal materials for biosensing technology due to their excellent dispersity, ease of functionalization, physiochemical properties, optical properties, good electrical conductivity, etc. The Integration of the Internet of Medical Things (IoMT) in the development of biosensors has the potential to improve diagnosis and treatment of diseases through early diagnosis and on time monitoring. The outcome of this comprehensive review will be useful to understand the significant role of graphene-based electrochemical biosensor integrated with Artificial Intelligence AI and IoMT for clinical diagnostics. The review is further extended to cover open research issues and future aspects of biosensing technology for diagnosis and management of clinical diseases and performance evaluation based on Linear Range (LR) and Limit of Detection (LOD) within the ranges of Micromolar µM (10^-6), Nanomolar nM (10^-9), Picomolar pM (10^-12), femtomolar fM (10^-15), and attomolar aM (10^-18).

Electrochemistry of Graphene Nanoplatelets Printed Electrodes for Cortical Direct Current Stimulation

Possible risks stemming from the employment of novel, micrometer-thin printed electrodes for direct current neural stimulation are discussed. To assess those risks, electrochemical methods are used, including cyclic voltammetry, square-wave voltammetry, and electrochemical impedance spectroscopy. Experiments were conducted in non-deoxidized phosphate-buffered saline to better emulate living organism conditions. Since preliminary results obtained have shown unexpected oxidation peaks in 0–0.4 V potential range, the source of those was further investigated. Hypothesized redox activity of printing paste components was disproven, supporting further development of proposed fabrication technology of stimulating electrodes. Finally, partial permeability and resulting electrochemical activity of underlying silver-based printed layers of the device were pointed as the source of potential tissue irritation or damage. Employing this information, electrodes with corrected design were investigated, yielding no undesired redox processes.

Current perspectives on the safe electrical stimulation of peripheral nerves with platinum electrodes

This review details some peripheral nervous system (PNS) targets and electrode designs used for electrical stimulation. It investigates limitations in current knowledge of safe electrical stimulation and possible future electrode developments. Current PNS targets are large, leading to poor resolution and off-target side-effects. Most clinical devices are platinum or platinum/iridium embedded in an insulation material. Their safety is usually guided by the Shannon plot, which is not valid for the PNS. New electrode designs are needed to target smaller nerve fibers, enabling higher resolution electrical therapies with fewer off-target side-effects. Damage can occur through biological and electrochemical mechanisms. Greater mechanistic understanding is required to ensure safe and efficacious, long-term electrical stimulation with new electrode materials, geometries and stimulation waveforms.