COMMUNICATION: Multi-site incorporation of bioactive matrices into MEMS-based neural probes

Methods are presented to incorporate polymer-based bioactive matrices into micro-fabricated implantable microelectrode arrays. Using simple techniques, hydrogels infused with bioactive molecules are deposited within wells in the substrate of the device. This method allows local drug delivery without increasing the footprint of the device. In addition, each well can be loaded individually, allowing spatial and temporal control over diffusion gradients in the microenvironment of the implanted neural interface probe. In vivo testing verified the following: diffusion of the bioactive molecules, integration of the bioactive molecules with the intended neural target and concurrent extracellular recording using nearby electrodes. These results support the feasibility of using polymer gels to deliver bioactive molecules to the region close to microelectrode shanks. This technique for microdrug delivery may serve as a means to intervene with the initial phases of the neuroinflammatory tissue response to permanently implanted microelectrode arrays.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49187/2/jne5_4_l03.pd

Spatial characterization of interictal high frequency oscillations in epileptic neocortex

Interictal high frequency oscillations (HFOs), in particular those with frequency components in excess of 200 Hz, have been proposed as important biomarkers of epileptic cortex as well as the genesis of seizures. We investigated the spatial extent, classification and distribution of HFOs using a dense 4 × 4 mm2 two dimensional microelectrode array implanted in the neocortex of four patients undergoing epilepsy surgery. The majority (97%) of oscillations detected included fast ripples and were concentrated in relatively few recording sites. While most HFOs were limited to single channels, ∼10% occurred on a larger spatial scale with simultaneous but morphologically distinct detections in multiple channels. Eighty per cent of these large-scale events were associated with interictal epileptiform discharges. We propose that large-scale HFOs, rather than the more frequent highly focal events, are the substrates of the HFOs detected by clinical depth electrodes. This feature was prominent in three patients but rarely seen in only one patient recorded outside epileptogenic cortex. Additionally, we found that HFOs were commonly associated with widespread interictal epileptiform discharges but not with locally generated ‘microdischarges’. Our observations raise the possibility that, rather than being initiators of epileptiform activity, fast ripples may be markers of a secondary local response

Sonochemical and soft-chemical intercalation of lithium ions into MnO 2 polymorphs

Abstract We explored routes for the synthesis of LiMn 2 O 4 spinel from five different polymorphs of MnO 2 as the manganese source. These included a and b-MnO 2 and three types of c MnO 2 (electrochemically produced EMD, and two types of chemically produced CMD). The synthesis included a lithiation step by mild reduction of the MnO 2 with glucose in a LiOH solution, followed by calcination of the lithiated product. This route was shown in a previous study to produce highly pure, nanocrystalline LiMn 2 O 4 . The effect of the application of ultrasound radiation in the lithiation step on the quality of the products was also explored. It was found that the degree of lithiation, the purity of the Li x Mn 2 O 4 spinel phase obtained and its electrochemical behavior as a Li insertion electrode material depend strongly on the nature of the MnO 2 material in terms of crystal structure and morphology. The effect of ultrasound radiation was found to be detrimental. A very good electrochemical performance (capacity, stability) in repeated Li intercalation-deintercalation cycling was obtained with LiMn 2 O 4 originating from nanometric CMD. The tools for this study included XRD, TEM, surface area measurements (BET method), atomic absorption and standard electrochemical techniques (voltammetry, chronopotentiometry)