Dalrymple Ashley N, Robles Ulises A, Huynh Mario, Nayagam Bryony A, Green Rylie A, Poole-Warren Laura A, Fallon James B, Shepherd Robert K
Bionics Institute, St. Vincent's Hospital, Melbourne, VIC, Australia.
J Neural Eng. 2020 Apr 9;17(2):026018. doi: 10.1088/1741-2552/ab7cfc.
Evaluate electrochemical properties, biological response, and surface characterization of a conductive hydrogel (CH) coating following chronic in vivo stimulation.
Coated CH or uncoated smooth platinum (Pt) electrode arrays were implanted into the cochlea of rats and stimulated over a 5 week period with more than 57 million biphasic current pulses. Electrochemical impedance spectroscopy (EIS), charge storage capacity (CSC), charge injection limit (CIL), and voltage transient (VT) impedance were measured on the bench before and after stimulation, and in vivo during the stimulation program. Electrically-evoked auditory brainstem responses were recorded to monitor neural function. Following explant, the cochleae were examined histologically and electrodes were examined using scanning electron microscopy.
CH coated electrodes demonstrated a bench-top electrochemical advantage over Pt electrodes before and after the electrical stimulation program. In vivo, CH coated electrodes also had a significant advantage over Pt electrodes throughout the stimulation program, exhibiting higher CSC (p= 0.002), larger CIL (p = 0.002), and lower VT impedance (p < 0.001). The CH cohort exhibited a greater tissue response (p= 0.003) with small deposits of particulate material within the tissue capsule. There was no loss in auditory neuron density or change in neural response thresholds in any cochleae. Examination of the electrode surface revealed that most CH electrodes exhibited some coating loss; however, there was no evidence of corrosion in the underlying Pt.
CH coated electrodes demonstrated significant electrochemical advantages on the bench-top and in vivo and maintained neural function despite an increased tissue response and coating loss. While further research is required to understand the cause of the coating loss, CH electrodes provide promise for use in neural prostheses.
评估导电水凝胶（CH）涂层在慢性体内刺激后的电化学特性、生物学反应和表面特征。
将涂有CH或未涂覆的光滑铂（Pt）电极阵列植入大鼠耳蜗，并在5周内用超过5700万个双相电流脉冲进行刺激。在刺激前后在实验台上以及在刺激程序进行期间在体内测量电化学阻抗谱（EIS）、电荷存储容量（CSC）、电荷注入极限（CIL）和电压瞬变（VT）阻抗。记录电诱发听觉脑干反应以监测神经功能。取出后，对耳蜗进行组织学检查，并使用扫描电子显微镜检查电极。
在电刺激程序前后，涂有CH的电极在实验台上显示出比Pt电极更好的电化学优势。在体内，在整个刺激程序中，涂有CH的电极也比Pt电极具有显著优势，表现出更高的CSC（p = 0.002）、更大的CIL（p = 0.002）和更低的VT阻抗（p < 0.001）。CH组表现出更大的组织反应（p = 0.003），组织囊内有少量颗粒物质沉积。在任何耳蜗中，听觉神经元密度均未降低，神经反应阈值也未改变。对电极表面的检查表明，大多数CH电极都有一定程度的涂层损失；然而，没有证据表明底层Pt有腐蚀。
涂有CH的电极在实验台和体内均显示出显著的电化学优势，尽管组织反应增加和涂层损失，但仍能维持神经功能。虽然需要进一步研究以了解涂层损失的原因，但CH电极在神经假体中的应用前景广阔。
