Esma Ismailova

In vivo recordings of brain activity using organic transistors

In vivo electrophysiological recordings of neuronal circuits are necessary for diagnostic purposes and for brain-machine interfaces. Organic electronic devices constitute a promising candidate because of their mechanical flexibility and biocompatibility. Here we demonstrate the engineering of an organic electrochemical transistor embedded in an ultrathin organic film designed to record electrophysiological signals on the surface of the brain. The device, tested in vivo on epileptiform discharges, displayed superior signal-to-noise ratio due to local amplification compared with surface electrodes. The organic transistor was able to record on the surface low-amplitude brain activities, which were poorly resolved with surface electrodes. This study introduces a new class of biocompatible, highly flexible devices for recording brain activity with superior signal-to-noise ratio that hold great promise for medical applications.

Highly Conformable Conducting Polymer Electrodes for In Vivo Recordings

Electronic devices that interface with living tissue have become a necessity in clinics to improve diagnosis and treatments. Devices such as cardiac pacemakers and cochlear implants stimulate and monitor electrically active cells, restoring lost function and improving quality of life. On a more fundamental level, most breakthroughs in our understanding of the basic mechanisms of information processing in the brain have been obtained by means of recordings from implantable electrodes. [ 1–3 ] Materials science is playing a pivotal role in this fi eld. For example, state-of-the-art implantable electrodes are microfabricated devices that contain high-density arrays of metal sites on a silicon shank (silicon probes). [ 4 ] Still, as neuroscience continues to advance and more options for electrical intervention become a reality for patients (ocular implants, deep-brain stimulation for epilepsy and Parkinson’s disease), [ 5 ] there is a tremendous need for developing advanced materials solutions for the biotic/abiotic interface. One such example is the necessity to develop electrodes that can conform to the curvilinear shapes of organs (e.g., the surface of the brain or its sulci) and form high-quality electrical contacts. Such surface electrodes are needed for electrocorticography (ECoG), which is increasingly used for functional mapping of cognitive processes before certain types of brain surgery (e.g., tumors) or for diagnosis purposes (e.g., epilepsy). [ 6 ] Placed on the somatosensory cortex, surface electrode arrays are also being used in brain-machine interfaces, an assistive technology for people with severe motor disabilities. [ 7 ] In contrary to silicon probes that penetrate the brain and cause tissue damage, these arrays are placed on the surface of the brain and are hence less invasive.

Wearable Keyboard Using Conducting Polymer Electrodes on Textiles

A wearable keyboard is demonstrated in which conducting polymer electrodes on a knitted textile sense tactile input as changes in capacitance. The use of a knitted textile as a substrate endows stretchability and compatibility to large-area formats, paving the way for a new type of wearable human-machine interface.

Direct patterning of organic conductors on knitted textiles for long-term electrocardiography

Wearable sensors are receiving a great deal of attention as they offer the potential to become a key technological tool for healthcare. In order for this potential to come to fruition, new electroactive materials endowing high performance need to be integrated with textiles. Here we present a simple and reliable technique that allows the patterning of conducting polymers on textiles. Electrodes fabricated using this technique showed a low impedance contact with human skin, were able to record high quality electrocardiograms at rest, and determine heart rate even when the wearer was in motion. This work paves the way towards imperceptible electrophysiology sensors for human health monitoring.

Localized Neuron Stimulation with Organic Electrochemical Transistors on Delaminating Depth Probes.

Organic electrochemical transistors are integrated on depth probes to achieve localized electrical stimulation of neurons. The probes feature a mechanical delamination process which leaves only a 4 μm thick film with embedded transistors inside the brain. This considerably reduces probe invasiveness and correspondingly improves future brain-machine interfaces.

PEDOT:TOS with PEG: a biofunctional surface with improved electronic characteristics

Devices based on conducting polymers offer great promise for interfacing with cells. Here, we use vapour phase polymerisation to create a biofunctional composite material of the conducting polymer poly(3,4-ethylenedioxythiophene):tosylate (PEDOT:TOS) and the biologically relevant poly(ethylene glycol) (PEG). On the addition of PEG, electroactivity of the PEDOT is maintained, conductivity is increased, and its performance as the active material in a transistor is unaffected. Both direct and indirect biocompatibility tests prove that PEDOT:TOS and PEDOT:TOS:PEG are biocompatible and nontoxic to mammalian cells. A functionalised PEG (PEG(COOH)) was additionally introduced into PEDOT:TOS to showcase the potential of this material for use in applications requiring biofunctionalisation.

Cholinium-based ion gels as solid electrolytes for long-term cutaneous electrophysiology

Cholinium-based bio-ion gels were prepared by photopolymerization of poly(cholinium lactate methacrylate) network within cholinium lactate ionic liquid. The rheological and thermal properties as well as ionic conductivity of ion gels of different compositions were measured. As indicated by rheological measurements, the ion gels show the properties of gel materials which become soft by increasing the amount of free ionic liquid. Cholinium ion gels with various composition of free ionic liquid vs. methacrylic network show glass transitions between −40° and −70 °C and thermal stability up to 200 °C. The ionic conductivity of these gels increases from 10−8 to 10−3 S cm−1 at 20 °C by varying the amount of free ionic liquid between 0 and 60 wt%, respectively. Low glass transition temperature and enhanced ionic conductivity make the cholinium-based ion gels good candidates to be used as a solid electrolytic interface between the skin and an electrode. The ion gels decrease the impedance with the human skin to levels that are similar to commercial Ag/AgCl electrodes. Accurate physiologic signals such as electrocardiography (ECG) were recorded with ion gels assisted electrodes for a long period of time (up to 72 h) with a remarkable stability. The low toxicity and superior ambient stability of cholinium ionic liquids and ion gels make these materials highly attractive for long-term cutaneous electrophysiology and other biomedical applications.

Engineering hydrophilic conducting composites with enhanced ion mobility

Ion mobility has a direct influence on the performance of conducting polymers in a number of applications as it dictates the operational speed of the devices. We report here the enhanced ion mobility of poly(3,4-ethylene dioxythiophene) after incorporation of gelatin. The gelatin-rich domains were seen to provide an ion pathway through the composites.

Nanostructured conducting polymers for stiffness controlled cell adhesion

UNLABELLED We propose a facile and reproducible method, based on ultra thin porous alumina membranes, to produce cm(2) ordered arrays of nano-pores and nano-pillars on any kind of substrates. In particular our method enables the fabrication of conducting polymers nano-structures, such as poly[3,4-ethylenedioxythiophene]:poly[styrene sulfonate] ( PEDOT PSS). Here, we demonstrate the potential interest of those templates with controlled cell adhesion studies. The triggering of the eventual fate of the cell (proliferation, death, differentiation or migration) is mediated through chemical cues from the adsorbed proteins and physical cues such as surface energy, stiffness and topography. Interestingly, as well as through material properties, stiffness modifications can be induced by nano-topography, the ability of nano-pillars to bend defining an effective stiffness. By controlling the diameter, length, depth and material of the nano-structures, one can possibly tune the effective stiffness of a (nano) structured substrate. First results indicate a possible change in the fate of living cells on such nano-patterned devices, whether they are made of conducting polymer (soft material) or silicon (hard material).

Orientation selectivity with organic photodetectors and an organic electrochemical transistor

Neuroinspired device architectures offer the potential of higher order functionalities in information processing beyond their traditional microelectronic counterparts. Here we demonstrate a neuromorphic function of orientation selectivity, which is inspired from the visual system, with a combination of organic photodetectors and a multi-gated organic electrochemical transistor based on poly(3,4ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The device platform responds preferably to different orientations of light bars, a behaviour that resembles orientation selectivity of visual cortex cells. These results pave the way for organic-based neuromorphic devices with spatially correlated functionalities and potential applications in the area of organic bioelectronics.