Biology subjects

Giagka, V.

Publications and source records attributed to Giagka, V..

5 recordsLinked to original sources

bioRxiv2025

Ultrasonically Powered Neuromodulation Platform Intended for Spatially and Directionally Selective Electrical Stimulation

Vagus nerve stimulation (VNS), a well-established application of electrical neuromodulation, has been effective in treating dis-orders such as epilepsy and depression. Recent neuroscientific advancements have identified further potential in VNS, calling for technical advancements to explore these possibilities. To address this, we developed a neuromodulation platform that can perform both neural activity excitation and inhibition, to further explore spatially and directionally selective stimulation. The platform can be powered wirelessly through ultrasound and includes a charge balancing mechanism to enhance stimulation safety. The platform performs biphasic and monophasic voltage-controlled stimulation, using 6 electrodes for excitation and 2 for inhibition. The pulse width can be varied between 0 and 1500 {micro}s, and the pulse repetition rate between 1 Hz and 1 kHz for excitation and 1 kHz to 50 kHz for inhibition. The implemented charge balancing mechanism uses a digital PID controller to reduce the voltage offset at the stimulation site to values as low as 2 mV. The introduced neuromodulation platform provides a versatile experimental tool intended for, but not limited to, VNS in pre-clinical and clinical settings. It is designed using only commercially available components and is easily reproducible, allowing to explore the possibilities of VNS while identifying the necessary components and processes for developing a miniaturized version.

bioengineering↗

bioRxiv2025

Effects of Soft Encapsulation on the Receive Performance of PMUTs for Implantable Devices

Recent studies present ultrasound (US) as a promising candidate for powering implantable devices, requiring in-tegrated and encapsulated receivers to ensure longevity. Conventional hermetic packaging can hinder acoustic transmission, making polymer-based approaches desirable. This study evaluates how polymers commonly used for implants (i.e., thermoplastic polyurethane, parylene-C, medical-grade silicones, and polyimide) affect the receive performance of piezoelectric micromachined ultrasound transducers (PMUTs). Simulations and measurements between 1 and 7 MHz show transmission coefficients above 94 % for material thicknesses in the nm and m ranges. A theoretical analysis of the mechanical properties guides material selection for later PMUT encapsulation, focusing on polyurethane, parylene-C, and two medical-grade silicones (MED-1000, MED2-4213). In a complete system comprising encapsulated PMUTs, mechanical and acoustic properties, along with interface mismatch between the encapsulation and the PMUTs, influence the receive performance of the devices. Finite element modeling (FEM) and measurements evaluate the impedance and receive sensitivity of encapsulated PMUTs. The results show that residual stress or higher stiffness in some polymers, reduces the receive sensitivity, an effect not evident from only analysing the acoustic transmission through coatings. However, this study demonstrates that upon careful consideration of the acoustic and mechanical properties as well as thickness selection, polymers commonly used for implantable devices can effectively be used for PMUT encapsulation.

bioengineering↗

bioRxiv2024

Longevity of Implantable Silicon-ICs for Emerging Neural Applications: Evaluation of Bare Die and PDMS-Coated ICs After Accelerated Aging and Implantation Studies

Silicon integrated circuits (ICs) are central to the next-generation miniature active neural implants, whether packaged in soft polymers for flexible bioelectronics or implanted as bare die for neural probes. These emerging applications bring the IC closer to the corrosive body environment, raising reliability concerns, particularly for long-term clinical use. Here, we evaluated the long-term electrical and material stability of silicon-ICs from two foundries, after one-year accelerated in vitro and in vivo animal studies. The ICs featured various custom-designed test structures and were partially PDMS coated, creating two regions on each chip, uncoated "bare die" and "PDMS-coated". During the accelerated in vitro study, ICs were electrically biased and periodically monitored. Results demonstrated stable electrical performance for at least a year, suggesting that bare die ICs can function in the body for months. Despite electrical stability, material analysis revealed chemical and electrically driven degradation of the IC passivation in the bare die regions. In contrast, PDMS-coated regions revealed no such degradation, making PDMS a highly suitable encapsulant for ICs intended for years-long implantation. Based on the new insights, guidelines are proposed that may enhance the longevity of implantable ICs, significantly broadening their applications in the biomedical field.

neuroscience↗

bioRxiv2023

Surface modification of multilayer graphene neural electrodes by local printing of platinum nanoparticles using spark ablation

In this paper, we present the surface modification of multilayer graphene neural electrodes with platinum (Pt) nanoparticles (NPs) using spark ablation. This method yields an individually selective local printing of NPs on an electrode surface at room temperature in a dry process. NP printing is performed as a post-process step to enhance the electrochemical characteristics of graphene electrodes. The NP-printed electrode shows significant improvements in impedance, charge storage capacity (CSC), and charge injection capacity (CIC), versus the equivalent electrodes without NPs. Specifically, electrodes with 40% NP surface density demonstrate 4.5 times lower impedance, 15 times higher CSC, and 4 times better CIC. Electrochemical stability, assessed via continuous cyclic voltammetry (CV) and voltage transient (VT) tests, indicated minimal deviations from the initial performance, while mechanical stability, assessed via ultrasonic vibration, is also improved after the NP printing. Importantly, NP surface densities up to 40% maintain the electrode optical transparency required for compatibility with optical imaging and optogenetics. These results demonstrate selective NP deposition and local modification of electrochemical properties in neural electrodes for the first time, enabling the cohabitation of graphene electrodes with different electrochemical and optical characteristics on the same substrate.

neuroscience↗

bioRxiv2022

A robust backscatter modulation scheme for uninterrupted ultrasonic powering and back-communication of deep implants

Traditionally, implants are powered by batteries, which have to be recharged by an inductive power link. In the recent years, ultrasonic power links are being investigated, promising more available power for deeply implanted miniaturized devices. These implants often need to transfer back information. For ultrasonically powered implants, this is usually achieved with On-Off Keying based on backscatter modulation, or active driving of a secondary transducer. In this paper, we propose to superimpose subcarriers, effectively leveraging Frequency-Shift Keying, which increases the robustness of the link against interference and fading. It also allows for simultaneous powering and communication, and inherently provides the possibility of frequency domain multiplexing for implant networks. The modulation scheme can be implemented in miniaturized application specific integrated circuits, field programmable gate arrays, and microcontrollers. We have validated this modulation scheme in a water tank during continuous ultrasound and movement. We achieved symbol rates of up to 104 kBd, and were able to transfer data through 20 cm of water, with additional misalignment and during movements. This approach could provide a robust uplink for miniaturized implants that are located deep inside the body and need continuous ultrasonic powering.

bioengineering↗