Bioelectronics
Department of Microelectronics

Andrada Velea

Publications

  1. Feasibility Study for a High-Frequency Flexible Ultrasonic Cuff for High-Precision Vagus Nerve Ultrasound Neuromodulation
    Cornelis van Damme; Gandhika K. Wardhana; Andrada Iulia Velea; Vasiliki Giagka; Tiago L. Costa;
    IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control,
    2024. DOI: 10.1109/TUFFC.2024.3381923
    document

  2. Non-monolithic fabrication of thin-film microelectrode arrays on PMUT transducers as a bimodal neuroscientific investigation tool
    Andrada I. Velea; Joshua Wilson; Astrid Gollhardt; Cyril B. Karuthedath; Abhilash S. Thanniyil; Vasiliki Giagka;
    In IEEE (Ed.), in Proc. 45th Int. Conf. of the IEEE Engineering in Medicine and Biology (EMBC) 2023, July 2023,
    July 2023.
    document

  3. Multilayer CVD graphene electrodes using a transfer-free process for the next generation of optically transparent and MRI-compatible neural interfaces
    Nasim Bakhshaee; Merlin Palmar; Andrada Iulia Velea; Chiara Coletti; Sebastian Weingaertner; Frans Vos; Wouter A. Serdijn; Sten Vollebregt; Vasiliki Giagka;
    Microsystems & Nanoengineering,
    Volume 8, Issue 107, pp. 1-14, Sep 2022. DOI: 10.1038/s41378-022-00430-x
    Abstract: ... Multimodal platforms combining electrical neural recording and stimulation, optogenetics, optical imaging, and magnetic resonance (MRI) imaging are emerging as a promising platform to enhance the depth of characterization in neuroscientific research. Electrically conductive, optically transparent, and MRI-compatible electrodes can optimally combine all modalities. Graphene as a suitable electrode candidate material can be grown via chemical vapor deposition (CVD) processes and sandwiched between transparent biocompatible polymers. However, due to the high graphene growth temperature (≥ 900 °C) and the presence of polymers, fabrication is commonly based on a manual transfer process of pre-grown graphene sheets, which causes reliability issues. In this paper, we present CVD-based multilayer graphene electrodes fabricated using a wafer-scale transfer-free process for use in optically transparent and MRI-compatible neural interfaces. Our fabricated electrodes feature very low impedances which are comparable to those of noble metal electrodes of the same size and geometry. They also exhibit the highest charge storage capacity (CSC) reported to date among all previously fabricated CVD graphene electrodes. Our graphene electrodes did not reveal any photo-induced artifact during 10-Hz light pulse illumination. Additionally, we show here, for the first time, that CVD graphene electrodes do not cause any image artifact in a 3T MRI scanner. These results demonstrate that multilayer graphene electrodes are excellent candidates for the next generation of neural interfaces and can substitute the standard conventional metal electrodes. Our fabricated graphene electrodes enable multimodal neural recording, electrical and optogenetic stimulation, while allowing for optical imaging, as well as, artifact-free MRI studies.

    document

  4. Towards a miniaturized cuff implant for highly selective US neuromodulation of peripheral nerves
    A. Velea; W. A. Serdijn; V. Giagka;
    In Proc International Winterschool on Bioelectronics (BioEl) 2022, Tirol, Austria, Mar. 2022.,
    2022.
    document

  5. UV and IR laser-patterning for high-density thin-film neural interfaces
    Andrada Velea; Joshua Wilson; Anna Pak; Manuel Seckel; Sven Schmidt; Stefan Kosmider; Nasim Bakhshaee; Wouter Serdijn; Vasiliki Giagka;
    In IEEE European Microelectronics and Packaging Conference (EMPC) 2021,
    Online, September 2021.
    document

  6. Wafer-scale Graphene-based Soft Implant with Optogenetic Compatibility
    A.I. Velea; S. Vollebregt; G.K. Wardhana; V. Giagka;
    In Proc. IEEE Microelectromech. Syst. (MEMS) 2020,
    Vancouver, Canada, IEEE, Jan. 2020.
    document

  7. Soft, flexible and transparent graphene-based active spinal cord implants for optogenetic studies
    A. Velea; S. Vollebregt; V. Giagka;
    In proc. 13th International Symposium on Flexible Organic Electronics (ISFOE20) 2020,
    Thessaloniki, Greece, July 2020.
    document

  8. Flexible, graphene-based active implant for spinal cord stimulation in rodents
    A.I. Velea; S. Vollebregt; V. Giagka;
    In Book of Abstracts, SAFE 2019,
    Delft, the Netherlands, July 4-5 2019.
    document

  9. Towards a Microfabricated Flexible Graphene-Based Active Implant for Tissue Monitoring During Optogenetic Spinal Cord Stimulation
    A.I. Velea; S. Vollebregt; V. Giagka;
    In Book of Abstracts, IEEE Nanotech. Mater. Dev. Conf. (NMDC) 2019,
    Stockholm, Sweden, IEEE, Oct. 2019.
    Abstract: ... Our aim is to develop a smart neural interface with transparent electrodes to allow for electrical monitoring of the site of interest during optogenetic stimulation of the spinal cord. In this work, we present the microfabrication process for the wafer-level development of such a compact, active, transparent and flexible implant. The transparent, passive array of electrodes and tracks have been developed using graphene, on top of which chips have been bonded using flip-chip bonding techniques. To provide high flexibility, soft encapsulation, using polydimethylsiloxane (PDMS) has been used. Preliminary measurements after the bonding process have shown resistance values in the range of kΩ for the combined tracks and ball-bonds.

    document

  10. Towards a Microfabricated Flexible Graphene-Based Active Implant for Tissue Monitoring During Optogenetic Spinal Cord Stimulation
    A.I. Velea; S. Vollebregt; T. Hosman; A. Pak; V. Giagka;
    In Proceedings IEEE Nanotechnology Materials and Devices Conference (NMDC) 2019,
    Stockholm, Sweden, Oct. 2019.
    Abstract: ... This work aims to develop a smart neural interface with transparent electrodes to allow for electrical monitoring of the site of interest during optogenetic stimulation of the spinal cord. In this paper, a microfabrication process for the wafer-level development of such a compact, active, transparent and flexible implant is presented. Graphene has been employed to form the transparent array of electrodes and tracks, on top of which chips have been bonded using flip-chip bonding techniques. To provide high flexibility, soft encapsulation, using polydimethylsiloxane (PDMS) has been used. Making use of the "Flex-to-Rigid" (F2R) technique, cm-size graphene-on-PDMS structures have been suspended and characterized using Raman spectroscopy to qualitatively evaluate the graphene layer, together with 2-point measurements to ensure the conductivity of the structure. In parallel, flip-chip bonding processes of chips on graphene structures were employed and the 2-point electrical measurement results have shown resistance values in the range of kΩ for the combined tracks and ball-bonds.

    document

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