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3: a) Structure of neuron with axon, dendrites and synapses. b) Structure of a synaptic connection (from [10]). 

3: a) Structure of neuron with axon, dendrites and synapses. b) Structure of a synaptic connection (from [10]). 

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Implantable neural prosthetics devices offer, nowadays, a promising opportunity for the restoration of lost functions in patients affected by brain or spinal cord injury, by providing the brain with a non-muscular channel able to link machines to the nervous system. The long-term reliability of these devices constituted by implantable electrodes ha...

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... electrodes on soft substrate: There has been, therefore, a growing interest toward developing polymer-based implant materials ( Fig.1.13) that could be flexible enough to mimic living tissue and reduce the mechanical damage without evoking any adverse tissue reaction. In the last 20 years, polymer-based implants using, for example, polyimide [55,56,57,58], SU8 [59,60], BCB (benzocyclobutene) [58] and parylene [61,62,63,64,65,66,67] as both the structural and insulation material have been micromachined for both acute and chronic recordings [68]. The fabrication of these devices typically involves metal sites sandwiched by thin film of polymer using standard planar photolithographic techniques. [55]) and b) parylene (from ...
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... is the real part in phase with the potential and represent the resistive component of the current; Z", which represent the imaginary part out of phase, is related to the capacitive component of the current. The diagram which depict Z'/Z" is called Nyquist diagram and a typical example is shown in Fig.13. From the Nyquist diagram it could be possible to extract the values of the different components of the equivalent circuit. It is interesting to note that at high frequencies, Z(ω)= Z'(ω)= R s , represented by the intercept on the abscissa for (φ = 0 e Z"(ω)=0). For ω → 0, Z(ω) = R s + R p , the intercept on the abscissa at low ...
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... thickness of gold was 200 nm for both polyimide and parylene-based electrodes. The quality of the gold electrode surface has a noticeable influence on the homogeneity of the PEDOT:PSS deposition, as can be seen from Fig.3.13 and ...
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... plasma oxygen etching was performed as described above during a time duration (6 cycles of 15 min) long enough to allow the cutting of the 24 µm-thick layer of PXC. During the physical etching it is important to perform short cycles in order to avoid overheating of the sample and prevent Nickel cracking. The Ni layer was then chemically etched ( Fig.2.12.i). Finally the PXC on the edge of the Si wafer was scratched with tweezers and the electrode structures were easily peeled off from the Si surface, or released in a water bath ( Fig.2.13), keeping their planar shape. The details of the whole process are given in Table 2.2, whit the corresponding steps described in ...

Citations

... A wide range of conductive materials have been used as electrode interface materials including gold [8], platinum [9], iridium [10], titanium nitride [11], platinum-iridium alloys [12]. Recently conductive polymers such as PEDOT [13], poly(ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) [6], [14], polypyrrole (PPY)-modified CNTs (CNTs-PPY) [15], PEDOT/carbon nanotubes [16]- [17], polypyrrole/graphene oxide [18] were also used. ...
... The application of microelectrodes provides better spatial resolution with high density of recording sites but as the site diameter decrease the impedance increases resulting in low signal to noise ratio and poor recording quality. Recently, several groups developed or used various deposition techniques to obtain high surface area electrode 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t 15 interfaces. PEDOT:PSS coatings [43]- [46] was utilized due to its mixed electronic and ionic conductivity and high ionic mobility. ...
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Objective: Intracranial EEG (iEEG) or micro-electrocorticography (µECoG) microelectrodes offer high spatial resolution in recordings of neuronal activity from the exposed brain surface. Reliability of dielectric substrates and conductive materials of these devices are under intensive research in terms functional stability in biological environments. Approach. The aim of our study is to investigate the stability of electroplated platinum recording sites on 16-channel, 8 micron thick, polyimide based, flexible µECoG arrays implanted underneath the skull of rats. Scanning electron microscopy and electrochemical impedance spectroscopy was used to reveal changes in either surface morphology or interfacial characteristics. The effect of improved surface area (roughness factor = 23±0.12) on in vivo recording capability was characterized in both acute and chronic experiments. Main results. Besides the expected reduction in thermal noise and enhancement in signal-to-noise ratio (up to 39.8), a slight increase in the electrical impedance of individual sites was observed, as a result of changes in the measured interfacial capacitance. In this paper, we also present technology processes and protocols in details to use such implants without crack formation of the porous platinum surfaces. Significance. Our findings imply that black-platinum coating deposited on the recording sites of flexible microelectrodes (20 microns in diameter) provides a stable interface between tissue and device.&#13.
... However, implantation of soft and flexible structures into the brain is challenging as the precision and depth of implantation is compromised. Attempts to overcome this problem are done with the construction of various insertion aids in the forms of removable stiff-backbone stiffeners, additional layers of dissolvable materials or by piercing the tissue with other instruments prior to the implant placement (Takeuchi et al., 2005;Felix et al., 2013;Castagnola, 2014;Barz et al., 2015). ...
... Difficulties accounted during deposition of metals onto polymers are poor adhesion and mismatch in thermal and mechanical properties, causing metal films to crack when probes are subjected to high temperatures or significant strain (McClain et al., 2011). Both can be improved with the use of adhesion promoting layers and pre-roughening of polymer surface (Nakamura et al., 1996;Mercanzini et al., 2008;Castagnola, 2014). Rather than using physical deposition methods, metals can be applied a foils, which are integrated within a polymer sandwich by lamination. ...
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Implantable neural interfaces for central nervous system research have been designed with wire, polymer, or micromachining technologies over the past 70 years. Research on biocompatible materials, ideal probe shapes, and insertion methods has resulted in building more and more capable neural interfaces. Although the trend is promising, the long-term reliability of such devices has not yet met the required criteria for chronic human application. The performance of neural interfaces in chronic settings often degrades due to foreign body response to the implant that is initiated by the surgical procedure, and related to the probe structure, and material properties used in fabricating the neural interface. In this review, we identify the key requirements for neural interfaces for intracortical recording, describe the three different types of probes—microwire, micromachined, and polymer-based probes; their materials, fabrication methods, and discuss their characteristics and related challenges.