Organic electrode coatings for next-generation neural interfaces

Traditional neuronal interfaces utilize metallic electrodes which in recent years have reached a plateau in terms of the ability to provide safe stimulation at high resolution or rather with high densities of microelectrodes with improved spatial selectivity. To achieve higher resolution it has become clear that reducing the size of electrodes is required to enable higher electrode counts from the implant device. The limitations of interfacing electrodes including low charge injection limits, mechanical mismatch and foreign body response can be addressed through the use of organic electrode coatings which typically provide a softer, more roughened surface to enable both improved charge transfer and lower mechanical mismatch with neural tissue. Coating electrodes with conductive polymers or carbon nanotubes offers a substantial increase in charge transfer area compared to conventional platinum electrodes. These organic conductors provide safe electrical stimulation of tissue while avoiding undesirable chemical reactions and cell damage. However, the mechanical properties of conductive polymers are not ideal, as they are quite brittle. Hydrogel polymers present a versatile coating option for electrodes as they can be chemically modified to provide a soft and conductive scaffold. However, the in vivo chronic inflammatory response of these conductive hydrogels remains unknown. A more recent approach proposes tissue engineering the electrode interface through the use of encapsulated neurons within hydrogel coatings. This approach may provide a method for activating tissue at the cellular scale, however, several technological challenges must be addressed to demonstrate feasibility of this innovative idea. The review focuses on the various organic coatings which have been investigated to improve neural interface electrodes

Materials for neural interfaces

The treatment of disorders of the nervous system poses a major clinical challenge. Development of neuromodulation (i.e., interfacing electronics to nervous tissue to modulate its function) has provided patients with neuronal-related deficits a new tool to regain lost function. Even though, in principle, electrical stimulation and recording by interfacing technology is simple and straightforward, each presents different challenges. In stimulation, the challenge lies in targeting the effects of stimulation on precise brain regions, as each region specializes for particular functions on a millimeter scale. In practice, our experience with deep brain stimulation for treating Parkinson's disease reveals that stimulation of larger regions of the brain can be relatively well tolerated. However, the task of fabricating an ideal electrode that performs reliably for long periods of time has been daunting. The primary obstacle in successful interfacing comes from integration of electrodes ("foreign” material) into the nervous system (biological material). The second tier of complexity is added by the need for the electrodes to "sense” signals emanating from individual neurons, an estimated microenvironment of 10 to 20 microns in diameter. Materials design and technology impact electrode design—with their size, shape, mechanical properties, and composition all being actively optimized to enable chronic, stable recordings of neural activity. The articles in this issue discuss designing interfacing technology to "listen to the nervous system” from a materials perspective. These include identification of materials with a potential for in vivo development, electrodes with various material types, including natural nanocomposites, and optical neural interfacin

Nanomaterials for Neural Interfaces

This review focuses on the application of nanomaterials for neural interfacing. The junction between nanotechnology and neural tissues can be particularly worthy of scientific attention for several reasons: (i) Neural cells are electroactive, and the electronic properties of nanostructures can be tailored to match the charge transport requirements of electrical cellular interfacing. (ii) The unique mechanical and chemical properties of nanomaterials are critical for integration with neural tissue as long-term implants. (iii) Solutions to many critical problems in neural biology/medicine are limited by the availability of specialized materials. (iv) Neuronal stimulation is needed for a variety of common and severe health problems. This confluence of need, accumulated expertise, and potential impact on the well-being of people suggests the potential of nanomaterials to revolutionize the field of neural interfacing. In this review, we begin with foundational topics, such as the current status of neural electrode (NE) technology, the key challenges facing the practical utilization of NEs, and the potential advantages of nanostructures as components of chronic implants. After that the detailed account of toxicology and biocompatibility of nanomaterials in respect to neural tissues is given. Next, we cover a variety of specific applications of nanoengineered devices, including drug delivery, imaging, topographic patterning, electrode design, nanoscale transistors for high-resolution neural interfacing, and photoactivated interfaces. We also critically evaluate the specific properties of particular nanomaterials—including nanoparticles, nanowires, and carbon nanotubes—that can be taken advantage of in neuroprosthetic devices. The most promising future areas of research and practical device engineering are discussed as a conclusion to the review.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/64336/1/3970_ftp.pd

Live demonstration: a public engagement platform for invasive neural interfaces

Neural interfaces, and more specifically ones ofthe invasive/implantable variety, today are a topic of muchcontroversy, often making the general public uncomfortable andintimidated. We have thus devised a bespoke interactive demoto help people understand brain implants and their need inthe age of wearable devices, with the secondary objective ofintroducing the wireless cortical neural probe that we, at NGNI(Next Generation Neural Interfaces) lab, are developing

Multifunctional Nanobiomaterials for Neural Interfaces

Neural electrodes are designed to interface with the nervous system and provide control signals for neural prostheses. However, robust and reliable chronic recording and stimulation remains a challenge for neural electrodes. Here, a novel method for the fabrication of soft, low impedance, high charge density, and controlled releasing nanobiomaterials that can be used for the surface modification of neural microelectrodes to stabilize the electrode/tissue interface is reported. The fabrication process includes electrospinning of anti-inflammatory drug-incorporated biodegradable nanofibers, encapsulation of these nanofibers by an alginate hydrogel layer, followed by electrochemical polymerization of conducting polymers around the electrospun drug-loaded nanofibers to form nanotubes and within the alginate hydrogel scaffold to form cloud-like nanostructures. The three-dimensional conducting polymer nanostructures significantly decrease the electrode impedance and increase the charge capacity density. Dexamethasone release profiles show that the alginate hydrogel coating slows down the release of the drug, significantly reducing the burst effect. These multifunctional materials are expected to be of interest for a variety of electrode/tissue interfaces in biomedical devices.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/61888/1/573_ftp.pd

Implantable devices for optical neural interfaces

pre-printOptical neural control requires light delivery techniques dependent on the experimental goal and biological model. Several light sources and neural interfaces have been implemented featuring one or more of the fol- lowing criteria: deep illumination, specific and/or com- prehensive access, spectral control, temporal precision, high resolution patterning. We've developed 3D needle- type waveguide arrays as potentially compact neural interfaces for light transmission of as much as 90% of input light to depths >1mm in tissue; various experimental paradigms are easily accommodated as the arrays can be modified to project different illumination volumes at defined depths, wavelengths and patterns

Electronic, Optical, and Magnetic Neural Interfaces

Mammalian nervous system contains billions of neurons that exchange electrical, chemical and mechanical signals. Our ability to study this complexity is limited by the lack of technologies available for interrogating neural circuits across their diverse signaling modalities without inducing a foreign-body reaction. My talk will describe neural interface strategies pursued in my group aimed at mimicking the materials properties and transduction mechanisms of the nervous system. Specifically, I will discuss (1) Fiber-based probes for multifunctional interfaces with the brain and spinal cord circuits; (2) Magnetic nanotransducers for minimally invasive neural stimulation; and (3) Active scaffolds for neural tissue engineering and interrogation. Fiber-drawing methods can be applied to create multifunctional polymer-based probes capable of simultaneous electrical, optical, and chemical probing of neural tissues in freely moving subjects[1]. Similar engineering principles enable ultra-flexible miniature fiber-probes with geometries inspired by nerves, which permit simultaneous optical excitation and recording of neural activity in the spinal cord allowing for optical control of lower limb movement[2]. Furthermore, fiber-based fabrication can be extended to design of scaffolds that direct neural growth[3] and activity[4] facilitating repair of damaged nerves. Molecular mechanisms of action potential firing inspire the development of materials-based strategies for direct manipulation of ion transport across neuronal membranes. For example, hysteretic heat dissipation by magnetic nanomaterials can be used to remotely trigger activity of neurons expressing heat-sensitive ion channels. Since the alternating magnetic fields in the low radiofrequency range interact minimally with the biological tissues, the magnetic nanoparticles injected into the brain can act as transducers of wireless magnetothermal deep brain stimulation[5, 6]. Similarly, local hysteretic heating allows magnetic nanoparticles to disrupt protein aggregates associated with neurodegenerative disorders[7]. 1. Canales, A., Jia, X., Froriep, U.P., Koppes, R.A., Tringides, C.M., Selvidge, J., Hou, C., Wei, L., Fink, Y., Anikeeva, P., Multifunctional fibers for simultaneous optical, electrical and chemical interrogation of neural circuits in vivo. Nature Biotechnology, 2015. 33(3): p. 277-284. 2. Lu, C., Froriep, U.P., Canales, A., Koppes, R.A., Caggiano, V., Selvidge, J., Bizzi, E., Anikeeva, P., Polymer fiber probes enable optical control of spinal cord and muscle function in vivo. Advanced Functional Materials, 2014. 24(42): p. 6594-6600. 3. Koppes, R.A., Park, S., Hood, T., Jia, X., Poorheravi, N.A., Achyuta, A.K.H., Fink, Y. Anikeeva, P., Thermally drawn fibers as nerve guidance scaffolds. Biomaterials, 2016. 81: p. 27-35. 4. Park, S., Koppes, R. A., Froriep, U. P., Jia, X., Achyuta, A. K. H., McLaughlin, B. L., Anikeeva, P., Optogenetic control of nerve growth. Scientific Reports, 2015. 5. 5. Chen, R., Romero, G., Christiansen, M.G., Mohr, A., Anikeeva, P., Wireless magnetothermal deep brain stimulation. Science, 2015. 347(6229): p. 1477-1480. 6. Romero, G., Christiansen, M.G., Stocche Barbosa, L., Garcia, F., Anikeeva, P., Localized Excitation of Neural Activity via Rapid Magnetothermal Drug Release. Advanced Functional Materials, 2016. 7. Loynachan, C.N., Romero, G., Christiansen, M.G., Chen, R., Ellison, R., O\u27Malley, T.T., Froriep, U.P., Walsh, D.M., Anikeeva, P., Targeted Magnetic Nanoparticles for Remote Magnetothermal Disruption of Amyloid-β Aggregates. Advanced Healthcare Materials, 2015. 4(14): p. 2100-2109