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pHEMA Encapsulated PEDOT-PSS-CNT Microsphere Microelectrodes for Recording Single Unit Activity in the Brain.

Castagnola E, Maggiolini E, Ceseracciu L, Ciarpella F, Zucchini E, De Faveri S, Fadiga L, Ricci D - Front Neurosci (2016)

Bottom Line: This enhancement significantly reduces the size of the implantable device though preserving excellent electrical performances.Moreover, the spherical shape of the electrode together with the surface area increase provided by the nanocomposite deposited on it, maximize the electrical contact and may improve recording stability over time.These results have a good potential to contribute to fulfill the grand challenge of obtaining stable neural interfaces for long-term applications.

View Article: PubMed Central - PubMed

Affiliation: Center for Translational Neurophysiology of Speech and Communication, Istituto Italiano di Tecnologia Ferrara, Italy.

ABSTRACT
The long-term reliability of neural interfaces and stability of high-quality recordings are still unsolved issues in neuroscience research. High surface area PEDOT-PSS-CNT composites are able to greatly improve the performance of recording and stimulation for traditional intracortical metal microelectrodes by decreasing their impedance and increasing their charge transfer capability. This enhancement significantly reduces the size of the implantable device though preserving excellent electrical performances. On the other hand, the presence of nanomaterials often rises concerns regarding possible health hazards, especially when considering a clinical application of the devices. For this reason, we decided to explore the problem from a new perspective by designing and testing an innovative device based on nanostructured microspheres grown on a thin tether, integrating PEDOT-PSS-CNT nanocomposites with a soft synthetic permanent biocompatible hydrogel. The pHEMA hydrogel preserves the electrochemical performance and high quality recording ability of PEDOT-PSS-CNT coated devices, reduces the mechanical mismatch between soft brain tissue and stiff devices and also avoids direct contact between the neural tissue and the nanocomposite, by acting as a biocompatible protective barrier against potential nanomaterial detachment. Moreover, the spherical shape of the electrode together with the surface area increase provided by the nanocomposite deposited on it, maximize the electrical contact and may improve recording stability over time. These results have a good potential to contribute to fulfill the grand challenge of obtaining stable neural interfaces for long-term applications.

No MeSH data available.


Related in: MedlinePlus

Representative SEM images of (A) a pHEMA encapsulated PEDOT-PSS-CNT microsphere after recordings in rat and (B) the higher magnification of the pHEMA surface after recordings in rat. (C) Magnification of the surface of a PEDOT-PSS-CNT coated microsphere (without pHEMA) after recordings in rat. (D) Example of magnitude impedance of a pHEMA encapsulated PEDOT-PSS-CNT coated microsphere before and after various recording sessions.
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Figure 5: Representative SEM images of (A) a pHEMA encapsulated PEDOT-PSS-CNT microsphere after recordings in rat and (B) the higher magnification of the pHEMA surface after recordings in rat. (C) Magnification of the surface of a PEDOT-PSS-CNT coated microsphere (without pHEMA) after recordings in rat. (D) Example of magnitude impedance of a pHEMA encapsulated PEDOT-PSS-CNT coated microsphere before and after various recording sessions.

Mentions: To evaluate the ability of the pHEMA-encapsulated PEDOT-PSS-CNT microspheres to withstand the mechanical stress of brain implants, we investigated their morphology, surface composition and electrochemical properties after implanting them in the cerebral cortex of anesthetized animals to record the neural activity. Figures 5A,B shows an example of SEM image of the pHEMA-encapsulated PEDOT-PSS-CNT microsphere that was previously implanted in rat cortex. One can notice that the main visible consequence is the mere accumulation of tissue debris and erythrocytes on the hydrogel surface that are easily recognizable in the inset of Figure 5A. We have acquired SEM images at the same magnification of the hydrogel surface (Figure 5B) and of a non–encapsulated PEDOT-PSS-CNT microsphere (Figure 5C). Non–encapsulated PEDOT-PSS-CNT microsphere maintains, after the insertion and recording in rat brain, the typically rough and porous surface of the non-coated probe. Conversely, the pHEMA-encapsulated PEDOT-PSS-CNT microsphere keeps the smooth pHEMA surface morphology both before (Figure 3B) and after (Figure 5B) implant and recording. In order to verify that indeed pHEMA is still present after probe implant, we have performed EDS analysis of pHEMA-encapsulated microspheres prior and after implants, comparing results with spectra obtained from non-encapsulated PEDOT-PSS-CNT microspheres and from a reference sample of pHEMA. As we are dealing with a low density material—the hydrogel and the conductive polymer—made from low atomic number elements, one has to take into account that the penetration depth of the electron beam is several micrometers and can reach the underlying microsphere surface. Differences in detected composition between the pristine PEDOT-PSS-CNT devices and the pHEMA encapsulated ones regard mainly the relative amount of detected carbon, gold and sulfur. In the case of pristine PEDOT-PSS-CNT microspheres, one finds a significant sulfur signal that arises from PEDOT-PSS and also a high gold signal from the underlying gold-ball. A smaller sodium signal can also be attributed to PEDOT-PSS. When encapsulated with a pHEMA layer (dry thickness 6.49 ± 2.62 μm, average of 10 samples), gold and sulfur percentage significantly decrease due to the presence of the hydrogel layer that reduces the number of electrons reaching the underlying materials, while the oxygen and carbon signals have values similar to those of pure pHEMA (see Supplementary Table 1S and Supplementary Figure 2S for examples of such spectra). We have then performed EDS analysis on non-encapsulated PEDOT-PSS-CNT microspheres and pHEMA-encapsulated probes that have either been inserted three times in the rat cortex (acute experiment) or have been implanted for 28 days, comparing results with the analysis performed on pristine probes (Table 2). Examples of corresponding spectra are shown in Supplementary Figures 3S, 4S. Comparing the EDS analysis results for each kind of microsphere, we find that the characteristic signatures - higher S and smaller C values for PEDOT-PSS-CNT and the opposite for pHEMA - and preserved after implant. We also compared images and EDS spectra for the same pHEMA-encapsulated probes before and after implant, and an example of results are shown in the Supplementary Figure 5S. This is an indirect but convincing proof that both the PEDOT-PSS-CNT coating and the pHEMA layer withstand implant up to 28 days. Finally, Figure 5D reports an example of impedance magnitude spectra of a pHEMA-encapsulated PEDOT-PSS-CNT microsphere before and after several brain insertions and recording sessions, showing that the impedance is maintained well below 2 kΩ for frequencies above 10 Hz.


pHEMA Encapsulated PEDOT-PSS-CNT Microsphere Microelectrodes for Recording Single Unit Activity in the Brain.

Castagnola E, Maggiolini E, Ceseracciu L, Ciarpella F, Zucchini E, De Faveri S, Fadiga L, Ricci D - Front Neurosci (2016)

Representative SEM images of (A) a pHEMA encapsulated PEDOT-PSS-CNT microsphere after recordings in rat and (B) the higher magnification of the pHEMA surface after recordings in rat. (C) Magnification of the surface of a PEDOT-PSS-CNT coated microsphere (without pHEMA) after recordings in rat. (D) Example of magnitude impedance of a pHEMA encapsulated PEDOT-PSS-CNT coated microsphere before and after various recording sessions.
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Figure 5: Representative SEM images of (A) a pHEMA encapsulated PEDOT-PSS-CNT microsphere after recordings in rat and (B) the higher magnification of the pHEMA surface after recordings in rat. (C) Magnification of the surface of a PEDOT-PSS-CNT coated microsphere (without pHEMA) after recordings in rat. (D) Example of magnitude impedance of a pHEMA encapsulated PEDOT-PSS-CNT coated microsphere before and after various recording sessions.
Mentions: To evaluate the ability of the pHEMA-encapsulated PEDOT-PSS-CNT microspheres to withstand the mechanical stress of brain implants, we investigated their morphology, surface composition and electrochemical properties after implanting them in the cerebral cortex of anesthetized animals to record the neural activity. Figures 5A,B shows an example of SEM image of the pHEMA-encapsulated PEDOT-PSS-CNT microsphere that was previously implanted in rat cortex. One can notice that the main visible consequence is the mere accumulation of tissue debris and erythrocytes on the hydrogel surface that are easily recognizable in the inset of Figure 5A. We have acquired SEM images at the same magnification of the hydrogel surface (Figure 5B) and of a non–encapsulated PEDOT-PSS-CNT microsphere (Figure 5C). Non–encapsulated PEDOT-PSS-CNT microsphere maintains, after the insertion and recording in rat brain, the typically rough and porous surface of the non-coated probe. Conversely, the pHEMA-encapsulated PEDOT-PSS-CNT microsphere keeps the smooth pHEMA surface morphology both before (Figure 3B) and after (Figure 5B) implant and recording. In order to verify that indeed pHEMA is still present after probe implant, we have performed EDS analysis of pHEMA-encapsulated microspheres prior and after implants, comparing results with spectra obtained from non-encapsulated PEDOT-PSS-CNT microspheres and from a reference sample of pHEMA. As we are dealing with a low density material—the hydrogel and the conductive polymer—made from low atomic number elements, one has to take into account that the penetration depth of the electron beam is several micrometers and can reach the underlying microsphere surface. Differences in detected composition between the pristine PEDOT-PSS-CNT devices and the pHEMA encapsulated ones regard mainly the relative amount of detected carbon, gold and sulfur. In the case of pristine PEDOT-PSS-CNT microspheres, one finds a significant sulfur signal that arises from PEDOT-PSS and also a high gold signal from the underlying gold-ball. A smaller sodium signal can also be attributed to PEDOT-PSS. When encapsulated with a pHEMA layer (dry thickness 6.49 ± 2.62 μm, average of 10 samples), gold and sulfur percentage significantly decrease due to the presence of the hydrogel layer that reduces the number of electrons reaching the underlying materials, while the oxygen and carbon signals have values similar to those of pure pHEMA (see Supplementary Table 1S and Supplementary Figure 2S for examples of such spectra). We have then performed EDS analysis on non-encapsulated PEDOT-PSS-CNT microspheres and pHEMA-encapsulated probes that have either been inserted three times in the rat cortex (acute experiment) or have been implanted for 28 days, comparing results with the analysis performed on pristine probes (Table 2). Examples of corresponding spectra are shown in Supplementary Figures 3S, 4S. Comparing the EDS analysis results for each kind of microsphere, we find that the characteristic signatures - higher S and smaller C values for PEDOT-PSS-CNT and the opposite for pHEMA - and preserved after implant. We also compared images and EDS spectra for the same pHEMA-encapsulated probes before and after implant, and an example of results are shown in the Supplementary Figure 5S. This is an indirect but convincing proof that both the PEDOT-PSS-CNT coating and the pHEMA layer withstand implant up to 28 days. Finally, Figure 5D reports an example of impedance magnitude spectra of a pHEMA-encapsulated PEDOT-PSS-CNT microsphere before and after several brain insertions and recording sessions, showing that the impedance is maintained well below 2 kΩ for frequencies above 10 Hz.

Bottom Line: This enhancement significantly reduces the size of the implantable device though preserving excellent electrical performances.Moreover, the spherical shape of the electrode together with the surface area increase provided by the nanocomposite deposited on it, maximize the electrical contact and may improve recording stability over time.These results have a good potential to contribute to fulfill the grand challenge of obtaining stable neural interfaces for long-term applications.

View Article: PubMed Central - PubMed

Affiliation: Center for Translational Neurophysiology of Speech and Communication, Istituto Italiano di Tecnologia Ferrara, Italy.

ABSTRACT
The long-term reliability of neural interfaces and stability of high-quality recordings are still unsolved issues in neuroscience research. High surface area PEDOT-PSS-CNT composites are able to greatly improve the performance of recording and stimulation for traditional intracortical metal microelectrodes by decreasing their impedance and increasing their charge transfer capability. This enhancement significantly reduces the size of the implantable device though preserving excellent electrical performances. On the other hand, the presence of nanomaterials often rises concerns regarding possible health hazards, especially when considering a clinical application of the devices. For this reason, we decided to explore the problem from a new perspective by designing and testing an innovative device based on nanostructured microspheres grown on a thin tether, integrating PEDOT-PSS-CNT nanocomposites with a soft synthetic permanent biocompatible hydrogel. The pHEMA hydrogel preserves the electrochemical performance and high quality recording ability of PEDOT-PSS-CNT coated devices, reduces the mechanical mismatch between soft brain tissue and stiff devices and also avoids direct contact between the neural tissue and the nanocomposite, by acting as a biocompatible protective barrier against potential nanomaterial detachment. Moreover, the spherical shape of the electrode together with the surface area increase provided by the nanocomposite deposited on it, maximize the electrical contact and may improve recording stability over time. These results have a good potential to contribute to fulfill the grand challenge of obtaining stable neural interfaces for long-term applications.

No MeSH data available.


Related in: MedlinePlus