Ultrasound-transparent neural interfaces for multimodal interaction

We are very excited to share our latest publication on the topic of Ultrasound transparent neural interfaces for multimodal interaction, recently published in Nature Portfolio npj Flexible Electronics in collaboration with the groups of David Maresca and Valeria Gazzola.

Schematic illustration of the concept of ultrasound-compatible neural electrodes. (1) Importance of multimodal sensing and stimulation, (2) Challenges of ultrasound wave propagation,(3) Design method for ultrasound transparent neuralelectrodes

Structure and acoustic modeling ofpolymer-based electrodes.

Here, we introduce a framework for designing flexible, metal-based neural interfaces that remain acoustically transparent, enabling integration with functional and focused ultrasound technologies. We combine theory, simulations, and experiments to show how common implant materials and practical metal thicknesses can achieve high ultrasound transmission. Importantly, we demonstrate in vivo compatibility with functional ultrasound imaging (fUSI),
with undistorted signal transmission and robust visualization of subcortical activation through a neural interface. This work lays the foundation for multimodal neural interfaces that bridge electrophysiology, imaging and neuromodulation.

Functional ultrasound Doppler imaging of mice brain through a flexible neural interface.

A special shout-out goes to Raphael Panskus, who led this impressive work.

This was an invited contribution to the special collection “Conformable
Brain-Computer and Brain-Machine Interfaces” edited by Xinxia Cai, Jeffrey R Capadona,
Maria Asplund and Ulrich Hofmann.

Get the full paper here

Cite this paper: R. Panskus, A. I. Velea, L. Holzapfel, C. Pavlou, Q. Li, C. Qin, F. M. Nelissen, R. Waasdorp, D. Maresca, V. Gazzola, and V. Giagka, “Ultrasound Transparent Neural Interfaces for Multimodal Interaction,” npj Flexible Electronics, 2026. doi: 10.1038/s41528-025-00517-1.

Interview with Bioelectronics Drop

Vasiliki Giagka was recently interviewed by Bioelectronics Drop as part of the new video series Bioelectronics Talk, which features leading researchers in biomedical engineering. In this interview, she talked about research, neuroelectronics, the European neurotechnology landscape and more. The interview is released soon on Youtube and Spotify and we hope you will enjoy it as much as we did!

Talk @ MRS in Boston

Vasiliki Giagka recently returned to MRS in Boston, where she kicked off a session on neuroelectronic interfaces with a talk on robust and conformal hybrid electronics. In addition, the group’s work NanoBlooms was selected among the 50 finalists of the Science as Art competition.

These beautiful blooms were created during a Friday afternoon experiment of Maria Camarena Perez while experimenting with the graphene growth on molybdenum catalysts and are planted on a SiO2 “soil”.

Beyond Acoustic Transparency: The Role of Polymer Encapsulation

Ultrasound is a powerful modality for wireless powering of implantable devices. But packaging remains a major challenge: hermetic cases often block acoustic transmission, while soft polymer encapsulation may alter device performance.

Schematic illustration of the implantable MUT receiver and its layered structure

In our recent work at IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control (UFFC), we investigated how implant-grade polymer coatings such as thermoplastic polyurethane, parylene-C, and medical-grade silicones affect the receive performance of piezoelectric micromachined ultrasonic transducers (PMUTs).

Key findings:

All tested coatings were highly acoustically transparent (>94% transmission).
But performance depends not only on acoustic transparency, but also on mechanical effects: stiffness, residual stress and fleixural rigidity of the coating.
Softer materials (e.g. silicones) preserve sensitivty even at larger thicknesses.
Stiffer coatings (e.g., parylene-C) can reduce sensitivity, unless applied in very thin layers.

Test structures and encapsulation methods. (a) Top-view of the PMUT array layout. (b) Description
of the encapsulation processes.

Acoustic characterisation of materials. (a) Simulated transmission coefficients through several polymer thicknesses
(b) Measured transmission coefficients juxtaposed against simulations.

Our results provide a framework for selecting encapsulation strategies that balance long-term stability and ultrasonic performance, enabling more reliable and miniaturized implantable devices.

Get the full paper

Cite this paper: A. I. Velea, R. Panskus, B. Szabo, V. A. -L. Oppelt, L. Holzapfel, C. B. Karuthedath, A. T. Sebastian, T. Stieglitz, A. S. Savoia, and V. Giagka, “Effects of Soft Encapsulation on the Receive Performance of PMUTs for Implantable Devices,” IEEE Trans. Ultrasonics, Ferroelectrics, and Frequency Control (UFFC), vol. 72, no. 9, pp. 1282-1292, Sept. 2025, doi: 10.1109/TUFFC.2025.3592740.

Project Kickoff: DUSTIN

This project explores a new approach to the treatment of autoimmune diseases through a miniaturized, wireless, and battery-free implant. Developed in collaboration with the Fraunhofer Institutes IMS, ENAS, IZM, and ITEM, the system is designed to stimulate small nerve branches deep inside the body, directly at the target site and without systemic side effects.

By enabling precise stimulation of even the smallest nerve branches, this technology opens up new therapeutic possibilities beyond conventional drug-based treatments. It also highlights the potential of interdisciplinary research at the intersection of microelectronics, ultrasound technology, and biomedical engineering.

Project members from left: Tatjana Fedtschenko, Andrada Velea, Stefan Bol, Kira Heinrich, Dr. Ulrich Froriep, Dr. Nooshin Saeidi, Prof. Karsten Seidl, Lukas Holzapfel, Karman Selvam

Within the project, Fraunhofer IMS develops the microchip for control, stimulation and wireless communication, Fraunhofer ENAS contributes micro-electromechanical ultrasound transducers for energy and data transfer, Fraunhofer IZM develops biocompatible and flexible housings and electrodes, and Fraunhofer ITEM evaluates the system under realistic testing conditions.

The project is funded by the PREPARE program of the Fraunhofer-Gesellschaft.

More information is available here.

How Soft Encapsulation Enables Long-Term Reliability of Silicon IC Implants

Our latest paper, “On the longevity and inherent hermeticity of silicon-ICs: evaluation of bare-die and PDMS-coated ICs after accelerated aging and implantation studies,” is now published in Nature Communications Portfolio.

Silicon integrated circuits (ICs) are at the heart of next-generation brain-computer interfaces BCIs and active neural implants. A key question driving our work: How do we ensure these tiny, powerful chips remain reliable in the body’s corrosive environment for decades?

In our study, we evaluated the inherent hermeticity of CMOS ICs and explored PDMS as a lightweight, accessible encapsulation material to enhance their longevity in vivo.

Schematic illustrations of silicon-IC test structures (dimensions not to scale). (a) A wire-bonded IC partially coated with PDMS. (b) A cross-sectional schematic demonstrating the multilayer stack of a representative 6-metal CMOS process. (c-e) Schematic of implemented test structures in silicion-IC, from simple to more advanced.

Key findings:

Foundry-fabricated CMOS exhibit inherent hermeticity, and can maintain their functionality in the body for at least 12 months unprotected. However, the outer nitride layers gradually degrade over time.
PDMS encapsulation acts as a soft moisture-permeable coating, preventing nitride dissolution, inhibiting ion ingress, and extending implantable IC lifetimes to decades.
Accelerated aging models in PBS alone are insufficient for bare die ICs but remain valid for PDMS-encapsulated chips, thanks to the material’s protective properties.

Positive mode ToF-SIMS depth profiles analyzing the ionic barrier performance of the exposed passivation layers after 7 and 12 months implantation in rat.

This publication represents 4+ years of interdisciplinary effort, including in vitro and in vivo studies, to bring CMOS technology closer to its full potential in bioelectronics. There is a wealth of information in the paper, including guidelines for designing state-of-the-art polymer-packaged neurotechnologies.

We believe these findings will contribute to advancing the clinical relevance of neurotechnologies, paving the way for minimally invasive, reliable brain-machine interfaces and active neuroelectronic implants.

Get the full paper

Cite this paper: K. Nanbakhsh, A. Shah Idil, C. Lamont, C. Dusco, O. C. Akgun, D. Horvath, K. Toth, D. Meszena, I. Ulbert, F. Mazza, T. G. Constandinou, W. A. Serdijn, A. Vanhoestenberghe, N. Donaldson, and V. Giagka, “On the Longevity and Inherent Hermeticity of Silicon-ICs: Evaluation of Bare-Die and PDMS-Coated ICs After Accelerated Aging and Implantation Studies,” Nat. Commun., vol. 16, no. 12, Jan. 2025. doi: 10.1038/s41467-024-55298-4.