Parylene-based implantable platinum-black coated wire microelectrode for orbicularis oculi muscle electrical stimulation.

A novel and simple process was proposed to fabricate a parylene-based platinum-black coated wire microelectrode for orbicularis oculi muscle electrical stimulation. Compared with conventional microelectrodes, wire microelectrodes would enable smaller wounds, increased ease of implantation, and improved cosmesis. Meanwhile, the circumferential electrode sites of this wire microelectrode fabricated by lift-off process would contribute to fully contact with tissue and reduction of electrode-tissue interface impedance. The width and the amount of electrode sites could be decided by the thickness and the amount of sacrificial layer, respectively. The platinum-black coatings were electroplated on electrode sites by applying a current pulse train in chloroplatinic acid solution with ultrasonic bath for further electrode-tissue interface impedance reduction and good mechanical stability of coatings. Electrode impedance at 1 kHz has been significantly reduced by 90%, and the cathodic charge storage capacity (CSCc) has been increased by 13 times. In addition, hematoxylin-eosin (HE) staining section of muscle demonstrated the good biocompatibility of this electroplated platinum-black. By applying a charge imbalanced biphasic stimulation waveform for orbicularis oculi muscle stimulation, the rabbits with facial paralysis rehabilitated the function of closing eyes. This kind of microelectrode will be promising for neuromuscular applications.

[Research on the electromyographic signals of orbicularis oculi muscle of rabbit].

OBJECTIVE: To study the features of electromyographic signals of orbicularis oculi muscle (OOM) of normal rabbits in various movement states, and to clarify relationships between functional actions of OOM and their electromyographic signals, hoping to obtain information concerning the electromyographic signals controlling OOM as reference for restoring the eye-closing function by artificial facial nerve prosthesis in patients with unilateral peripheral facial palsy. METHODS: The electromyographic signals were extracted from OOM of normal rabbits by implanted microelectrodes through upper and lower eyelids. Then the features of these electromyographic signals were analyzed in the time domain and the frequency domain. RESULTS: The peak values of the absolute electromyographic amplitude for natural continuous eye-opening event, natural continuous eye-closing state, natural eye-blinking movement and evoked eye-closing state were (28.8 ± 4.8) µV, (36.0 ± 4.7) µV, (398.8 ± 195.7) µV, and (715.4 ± 249.7) µV, respectively. The peak frequency values of the power spectrum density (PSD) of electromyographic signals for the four modes were (98 ± 17) Hz, (142 ± 22) Hz, (203 ± 58) Hz, and (349 ± 81) Hz, respectively. The electrical activities during the natural continuous eye-opening event and the natural continuous eye-closing state were stable and displayed low amplitudes. During the spontaneous blink state and the evoked eye-closing state, the electromyographic amplitudes markedly increased, and the increased level in the latter state was stronger than that in the former state. When rabbits continuously closed eyes or opened eyes, all of the peak values of the absolute voltage amplitudes were less than 50 µV. The absolute amplitude values of the starting site were between 50 µV and 60 µV during the spontaneous blink and the evoked eye-closing movements. The whole frequency band of the energy of PSD about OOM was between 0 Hz and 500 Hz, and the focus frequency range was between 20 Hz and 350 Hz.In the time domain, the difference was not significant for the electromyographic signals of OOM between the continuous eye-opening state and the continuous eye-closing movement (P > 0.05), but there were statistically significant differences in the other states for their pairwise comparisons (P < 0.05). In the frequency domain, there was no statistically significant difference for the peak frequency of PSD about the electromyographic signals when comparing the continuous eye-opening state with the continuous eye-closing event (P > 0.05). When comparing this item in the other movements with each other, however, the differences were statistically significant (P < 0.05). CONCLUSIONS: OOM relaxes when eyelid keeps continuously opening. The action of eyelid-closing is due to contraction of this muscle. Each state has its own features of the electromyographic signals for OOM, these features can be used as criteria for computers to judge and identify various movement states of OOM. However, it is difficult to distinguish the natural continuous eye-opening event from the natural continuous eye-closing state, based on the features of electromyographic signals in the time and frequency domain.