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Poly(3,4-ethylenedioxythiophene) (PEDOT) has emerged as a promising neural interface material, but the weak adhesion of PEDOT to substrates adversely affects its reliability and practical application. Although adhesive interfacial layers have been explored to enhance the adhesion of PEDOT, their poor conductivity seriously compromises the performance of neural electrodes. It is a great challenge to develop an adhesive interfacial layer with excellent electrical properties. Herein, utilizing the advantages of polyindole derivatives, conductive polymers which have various functional groups for potential interface bonding, a conductive, adhesive, and biocompatible poly(5-nitroindole) (PIN-5NO 2 ) interfacial layer is developed to enhance the adhesion of PEDOT to metal electrodes. The conjugated PIN-5NO 2 with its superior electrical property can be prepared by electropolymerization of 5-nitroindole; however, the electrografting of amino groups, which is reduced from nitro groups in 5-nitroindole can provide strong adhesion with the gold (Au) substrate. With PIN-5NO 2 as an adhesive interfacial layer, the resultant Au/PIN-5NO 2 /PEDOT electrode exhibits excellent electrochemical property, superb stability, and biocompatibility for high-performance neural interface. The in vivo evaluation of Au/PIN-5NO 2 / PEDOT electrocorticographic microelectrodes demonstrates superior capacity to capture the neural dynamics of the brain. The novel strategy would offer a new insight for the construction of high-performance neural electrodes with high stability for neural interface application.

Objective. To promote clinical applications of muscle-synergy-based neurorehabilitation techniques, this study aims to clarify any potential modulations of both the muscular compositions and temporal activations of forearm muscle synergies for multiple movements under variant force levels and arm positions. Approach. Two groups of healthy subjects participated in this study. Electromyography (EMG) signals were collected when they performed four hand and wrist movements under variant constraints—three different force levels for one group and five arm positions for the other. Muscle synergies were extracted from the EMGs, and their robustness across variant force levels and arm positions was separately assessed by evaluating their across-condition structure similarity, cross-validation, and cluster analysis. The synergies’ activation coefficients across the variant constraints were also compared, and the coefficients were used to discriminate the different force levels and the arm positions, respectively. Main results. Overall, the muscle synergies were relatively fixed across variant constraints, but they were more robust to variant forces than to changing arm positions. The activations of muscle synergies depended largely on the level of contraction force and could discriminate the force levels very well, but the coefficients corresponding to different arm positions discriminated the positions with lower accuracy. Similar results were found for all types of forearm movement analyzed. Significance. With our experiment and subject-specific analysis, only slight modulation of the muscular compositions of forearm muscle synergies was found under variant force and arm position constraints. Our results may shed valuable insights to future design of both muscle-synergy-based assistive robots and motor-function assessments.

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Pitch, as a sensation of the sound frequency, is a crucial attribute toward constructing a natural voice for communication. Producing intelligible sounds with normal pitches depend on substantive interdependencies among facial and neck muscles. Clarifying the interrelations between the pitches and the corresponding muscular activities would be helpful for evaluating the pitch-related phonating functions, which would play a significant role both in training pronunciation and in assessing dysphonia. In this study, the speech signals and the high-density surface electromyography (HD sEMG) signals were synchronously acquired when phonating [a:], [i:], and [ә:] vowels with increasing pitches, respectively. The HD sEMG energy maps were constructed based on the root mean square values to visualize spatiotemporal characteristics of facial and neck muscle activities. Normalized median frequency (nMF) and root-mean square (nRMS) were correspondingly extracted from the speech and sEMG recordings to quantitatively investigate the correlations between sound frequencies and myoelectric characteristics. The results showed that the frame-wise energy maps built from sEMG recordings presented that the muscle contraction strength increased monotonously across pitch-rising, with left-right symmetrical distribution for the face/neck. Furthermore, the nRMS increased at a similar rate to the nMF when there were rising pitches, and the two parameters had a significant correlation across different vowel tasks [(a:) (0.88 ± 0.04), (i:) (0.89 ± 0.04), and (ә:) (0.87 ± 0.05)]. These findings suggested the possibility of utilizing muscle contraction patterns as a reference for evaluating pitch-related phonation functions. The proposed method could open a new window for developing a clinical approach for assessing the muscular functions of dysphonia.

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