Silke Seyock

Versatile Flexible Graphene Multielectrode Arrays

Graphene is a promising material possessing features relevant to bioelectronics applications. Graphene microelectrodes (GMEAs), which are fabricated in a dense array on a flexible polyimide substrate, were investigated in this work for their performance via electrical impedance spectroscopy. Biocompatibility and suitability of the GMEAs for extracellular recordings were tested by measuring electrical activities from acute heart tissue and cardiac muscle cells. The recordings show encouraging signal-to-noise ratios of 65 ± 15 for heart tissue recordings and 20 ± 10 for HL-1 cells. Considering the low noise and excellent robustness of the devices, the sensor arrays are suitable for diverse and biologically relevant applications.

Graphene transistors for interfacing with cells: towards a deeper understanding of liquid gating and sensitivity

This work is focused on the fabrication and analysis of graphene-based, solution-gated field effect transistor arrays (GFETs) on a large scale for bioelectronic measurements. The GFETs fabricated on different substrates, with a variety of gate geometries (width/length) of the graphene channel, reveal a linear relation between the transconductance and the width/length ratio. The area normalised electrolyte-gated transconductance is in the range of 1–2 mS·V−1·□ and does not strongly depend on the substrate. Influence of the ionic strength on the transistor performance is also investigated. Double contacts are found to decrease the effective resistance and the transfer length, but do not improve the transconductance. An electrochemical annealing/cleaning effect is investigated and proposed to originate from the out-of-plane gate leakage current. The devices are used as a proof-of-concept for bioelectronic sensors, recording external potentials from both: ex vivo heart tissue and in vitro cardiomyocyte-like HL-1 cells. The recordings show distinguishable action potentials with a signal to noise ratio over 14 from ex vivo tissue and over 6 from the cardiac-like cell line in vitro. Furthermore, in vitro neuronal signals are recorded by the graphene transistors with distinguishable bursting for the first time.

Graphene Multielectrode Arrays as a Versatile Tool for Extracellular Measurements

Graphene multielectrode arrays (GMEAs) presented in this work are used for cardio and neuronal extracellular recordings. The advantages of the graphene as a part of the multielectrode arrays are numerous: from a general flexibility and biocompatibility to the unique electronic properties of graphene. The devices used for extensive in vitro studies of a cardiac-like cell line and cortical neuronal networks show excellent ability to extracellularly detect action potentials with signal to noise ratios in the range of 45 ± 22 for HL-1 cells and 48 ± 26 for spontaneous bursting/spiking neuronal activity. Complex neuronal bursting activity patterns as well as a variety of characteristic shapes of HL-1 action potentials are recorded with the GMEAs. This paper illustrates that the potential applications of the GMEAs in biological and medical research are still numerous and diverse.

Interfacing neurons on carbon nanotubes covered with diamond

A recently discovered material, carbon nanotubes covered with diamond (DCNTs) was tested for its suitability in bioelectronics applications. Diamond shows advantages for bioelectronics applications (wide electro chemical window and bioinertness). This study investigates the effect of electrode surface shape (flat or three dimensional) on cell growth and behavior. For comparison, flat nanocrystalline diamond substrates were used. Primary embryonic neurons were grown on top of the structures and neither incorporated the structures nor did they grow in between the single structures. The interface was closely examined using focused ion beam (FIB) and scanning electron microscopy. Of special interest was the interface between cell and substrate. 5% to 25% of the cell membrane adhered to the substrate, which fits the theoretical estimated value. While investigating the conformity of the neurons, it could be observed that the cell membrane attaches to different heights of the tips of the 3D structure. However, the aspect ratio of the structures had no effect on the cell viability. These results let us assume that not more than 25% of cell attachment is needed for the survival of a functional neuronal cell.

How to image cell adhesion on soft polymers

Here, we present a method to investigate cell adhesion on soft, non-conducting polymers that are implant candidate materials. Neuronal cells were grown on two elastomers (polydimethylsiloxane (PDMS) and Ecoflex®) and prepared for electron microscopy. The samples were treated with osmium tetroxide (OsO4) and uranylacetate (UrAc). Best results can be achieved when the polymers were coated with a thin iridium layer before the cell culture. This was done to emphasize the usage of soft polymers as supports for implant electrodes. A good contrast and the adhesion of the cells on soft polymers could be visualized.

Rapid Prototyping of Ultralow-Cost, Inkjet-Printed Carbon Microelectrodes for Flexible Bioelectronic Devices

Gaining better understanding of the human brain using chip‐based devices and promoting the recovery of lost biological functionality through implants are long pursued endeavors driven by advances in material science, bioelectronics, and the advancing silicon technology. While conventional bioelectronic and neuroelectronic devices typically rely on cleanroom‐based processing, a rapid prototyping technique is proposed that is based on high‐resolution inkjet printing featuring nanoporous carbon electrodes that yield excellent cell–chip coupling. This study aims to overcome two major limitations of conventional approaches that make the development of neuroelectronic devices very challenging and limit a wider use within the research community as well as industry: high costs and lack of rapid prototyping capabilities. These challenges are addressed with an all‐printed, high‐resolution approach that makes use of flexible polymer substrates and is fabricated on a fully digital printing platform. The manufacturing of a chip consumes less than 60 min and costs a few cents per chip. This study introduces nanoporous carbon as a cell‐interfacing electrode material that features outstanding properties for extracellular recording of action potentials and stimulation indicating that the printed carbon chips have the means to be used as a versatile neuroelectronic tool for in vitro and in vivo studies.

Printed microelectrode arrays on soft materials: from PDMS to hydrogels

Microelectrode arrays (MEAs) provide promising opportunities to study electrical signals in neuronal and cardiac cell networks, restore sensory function, or treat disorders of the nervous system. Nevertheless, most of the currently investigated devices rely on silicon or polymer materials, which neither physically mimic nor mechanically match the structure of living tissue, causing inflammatory response or loss of functionality. Here, we present a new method for developing soft MEAs as bioelectronic interfaces. The functional structures are directly deposited on PDMS-, agarose-, and gelatin-based substrates using ink-jet printing as a patterning tool. We demonstrate the versatility of this approach by printing high-resolution carbon MEAs on PDMS and hydrogels. The soft MEAs are used for in vitro extracellular recording of action potentials from cardiomyocyte-like HL-1 cells. Our results represent an important step toward the design of next-generation bioelectronic interfaces in a rapid prototyping approach.Microelectrode arrays: ink-jet printing makes it simpleA cost-effective and simple approach to make soft microelectrode arrays has been developed using inkjet printing of carbon-based conductive ink. Prof Bernhard Wolfrum and his team from the Institute of Bioelectronics (ICS-8) at Forschungszentrum Jülich and the Munich School of Bioengineering at Technical University of Munich (TUM), Germany inkjet print functional sensor arrays on various soft substrates for bioelectronic applications. They print carbon nanoparticle conductive ink to fabricate high-resolution microelectrode arrays on PDMS and hydrogels. The soft microelectrode arrays are used for extracellular electrophysiological recordings of action potentials from HL-1 cells. The approach presented in their paper allows for rapid prototyping of disposable sensor array structures on a variety of soft substrates for in vitro as well as in vivo applications.