Woeppel Kevin, Hughes Christopher, Herrera Angelica J, Eles James R, Tyler-Kabara Elizabeth C, Gaunt Robert A, Collinger Jennifer L, Cui Xinyan Tracy
Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States.
Center for the Neural Basis of Cognition, Pittsburgh, PA, United States.
Front Bioeng Biotechnol. 2021 Dec 7;9:759711. doi: 10.3389/fbioe.2021.759711. eCollection 2021.
Brain-computer interfaces are being developed to restore movement for people living with paralysis due to injury or disease. Although the therapeutic potential is great, long-term stability of the interface is critical for widespread clinical implementation. While many factors can affect recording and stimulation performance including electrode material stability and host tissue reaction, these factors have not been investigated in human implants. In this clinical study, we sought to characterize the material integrity and biological tissue encapsulation via explant analysis in an effort to identify factors that influence electrophysiological performance. We examined a total of six Utah arrays explanted from two human participants involved in intracortical BCI studies. Two platinum (Pt) arrays were implanted for 980 days in one participant (P1) and two Pt and two iridium oxide (IrOx) arrays were implanted for 182 days in the second participant (P2). We observed that the recording quality followed a similar trend in all six arrays with an initial increase in peak-to-peak voltage during the first 30-40 days and gradual decline thereafter in P1. Using optical and two-photon microscopy we observed a higher degree of tissue encapsulation on both arrays implanted for longer durations in participant P1. We then used scanning electron microscopy and energy dispersive X-ray spectroscopy to assess material degradation. All measures of material degradation for the Pt arrays were found to be more prominent in the participant with a longer implantation time. Two IrOx arrays were subjected to brief survey stimulations, and one of these arrays showed loss of iridium from most of the stimulated sites. Recording performance appeared to be unaffected by this loss of iridium, suggesting that the adhesion of IrOx coating may have been compromised by the stimulation, but the metal layer did not detach until or after array removal. In summary, both tissue encapsulation and material degradation were more pronounced in the arrays that were implanted for a longer duration. Additionally, these arrays also had lower signal amplitude and impedance. New biomaterial strategies that minimize fibrotic encapsulation and enhance material stability should be developed to achieve high quality recording and stimulation for longer implantation periods.
脑机接口正在被研发，用于帮助因受伤或疾病而瘫痪的患者恢复运动功能。尽管其治疗潜力巨大，但接口的长期稳定性对于广泛的临床应用至关重要。虽然许多因素会影响记录和刺激性能，包括电极材料稳定性和宿主组织反应，但这些因素尚未在人体植入物中进行研究。在这项临床研究中，我们试图通过取出植入物分析来表征材料完整性和生物组织包裹情况，以确定影响电生理性能的因素。我们检查了从两名参与皮层内脑机接口研究的人类参与者身上取出的总共六个犹他阵列。在一名参与者（P1）中，两个铂（Pt）阵列植入了980天，在第二名参与者（P2）中，两个Pt阵列和两个氧化铱（IrOx）阵列植入了182天。我们观察到，所有六个阵列的记录质量都遵循类似趋势，在P1中，峰峰值电压在最初30 - 40天内最初增加，此后逐渐下降。使用光学显微镜和双光子显微镜，我们观察到在参与者P1中植入时间较长的两个阵列上组织包裹程度更高。然后，我们使用扫描电子显微镜和能量色散X射线光谱来评估材料降解情况。发现Pt阵列的所有材料降解指标在植入时间较长的参与者中更为明显。对两个IrOx阵列进行了短暂的调查性刺激，其中一个阵列在大多数受刺激部位出现铱流失。记录性能似乎不受这种铱流失的影响，这表明IrOx涂层的附着力可能因刺激而受损，但金属层直到阵列取出时或之后才分离。总之，在植入时间较长的阵列中，组织包裹和材料降解都更为明显。此外，这些阵列的信号幅度和阻抗也较低。应该开发新的生物材料策略，以尽量减少纤维化包裹并提高材料稳定性，从而实现更长植入期的高质量记录和刺激。
