Distortion-Free Sensing of Neural Activity Using Graphene Transistors.

Graphene solution-gated field-effect transistors (g-SGFETs) are promising sensing devices to transduce electrochemical potential signals in an electrolyte bath. However, distortion mechanisms in g-SGFET, which can affect signals of large amplitude or high frequency, have not been evaluated. Here, a detailed characterization and modeling of the harmonic distortion and non-ideal frequency response in g-SGFETs is presented. This accurate description of the input-output relation of the g-SGFETs allows to define the voltage- and frequency-dependent transfer functions, which can be used to correct distortions in the transduced signals. The effect of signal distortion and its subsequent calibration are shown for different types of electrophysiological signals, spanning from large amplitude and low frequency cortical spreading depression events to low amplitude and high frequency action potentials. The thorough description of the distortion mechanisms presented in this article demonstrates that g-SGFETs can be used as distortion-free signal transducers not only for neural sensing, but also for a broader range of applications in which g-SGFET sensors are used.

High-resolution mapping of infraslow cortical brain activity enabled by graphene microtransistors.

Recording infraslow brain signals (<0.1 Hz) with microelectrodes is severely hampered by current microelectrode materials, primarily due to limitations resulting from voltage drift and high electrode impedance. Hence, most recording systems include high-pass filters that solve saturation issues but come hand in hand with loss of physiological and pathological information. In this work, we use flexible epicortical and intracortical arrays of graphene solution-gated field-effect transistors (gSGFETs) to map cortical spreading depression in rats and demonstrate that gSGFETs are able to record, with high fidelity, infraslow signals together with signals in the typical local field potential bandwidth. The wide recording bandwidth results from the direct field-effect coupling of the active transistor, in contrast to standard passive electrodes, as well as from the electrochemical inertness of graphene. Taking advantage of such functionality, we envision broad applications of gSGFET technology for monitoring infraslow brain activity both in research and in the clinic.

Full-bandwidth electrophysiology of seizures and epileptiform activity enabled by flexible graphene microtransistor depth neural probes.

Mapping the entire frequency bandwidth of brain electrophysiological signals is of paramount importance for understanding physiological and pathological states. The ability to record simultaneously DC-shifts, infraslow oscillations (<0.1 Hz), typical local field potentials (0.1-80 Hz) and higher frequencies (80-600 Hz) using the same recording site would particularly benefit preclinical epilepsy research and could provide clinical biomarkers for improved seizure onset zone delineation. However, commonly used metal microelectrode technology suffers from instabilities that hamper the high fidelity of DC-coupled recordings, which are needed to access signals of very low frequency. In this study we used flexible graphene depth neural probes (gDNPs), consisting of a linear array of graphene microtransistors, to concurrently record DC-shifts and high-frequency neuronal activity in awake rodents. We show here that gDNPs can reliably record and map with high spatial resolution seizures, pre-ictal DC-shifts and seizure-associated spreading depolarizations together with higher frequencies through the cortical laminae to the hippocampus in a mouse model of chemically induced seizures. Moreover, we demonstrate the functionality of chronically implanted devices over 10 weeks by recording with high fidelity spontaneous spike-wave discharges and associated infraslow oscillations in a rat model of absence epilepsy. Altogether, our work highlights the suitability of this technology for in vivo electrophysiology research, and in particular epilepsy research, by allowing stable and chronic DC-coupled recordings.

Predictive factors of Boston Type I Keratoprosthesis outcomes: A long-term analysis.

PURPOSE: To study the long-term visual- and device retention-related outcomes and complications of the Boston Type I Keratoprosthesis (KPro). METHODS: Single-center, retrospective cohort study of all patients undergoing KPro implantation from February 2007 to April 2014 with at least 5 years of follow-up. RESULTS: 68 eyes from 65 patients underwent KPro implantation during the study period. At 5 and 10 years, the probability of maintaining or improving visual acuity (VA) was 75.0% and 66.7%, respectively, and the probability of KPro retention was 89.2% and 89.2%, respectively. Initial device retention rate at 10 years was significantly lower in those with underlying ocular surface disease (46.8% [30.6-63.2] vs 75.8% [61.0-90.7], P = 0.03), while other baseline characteristics showed no significant association. Final VA was more likely to be stable or improved in patients with fewer failed grafts (2 [1-6] vs 3 [1-6], P < 0.01), and a final VA of 20/200 or better was more likely in primary KPro eyes (44.8% [26.7-62.9] vs 19.4% [6.5-32.3], P = 0.03). Combined KPro-vitrectomy eyes were more likely to have stable or improved final VA than non-vitrectomy eyes (88.5% [76.2-100.0] vs 64.1% [49.1-79.1], P = 0.04). All complications had increasing incidence beyond 5 years; in particular, corneal melt, surgical glaucoma interventions, and endophthalmitis tended to have late presentations, with 79.0%, 78.6%, and 88.9% of these complications occurring beyond one year, respectively. CONCLUSIONS: KPro devices show favorable long-term visual and retention outcomes in select patients. Careful long-term, multidisciplinary follow-up is warranted to address potential complications.