Neural Interface And MRI-Related Study Of Carbon Nanotube Yarns Electrode

Background and objectives:Electrodes made from precious metals such as platinum-iridium (Pt-Ir) have been widely used to stimulate or record in the deep brain to study the function or treat disorders of the nervous system. However, metal electrode has some major disadvantage, such as disintegration and peeling-off of the chemical coating layer after long term of implantation. In addition, the shadow and safety issue under MRI is another major concern of metal electrodes. Therefore, a new generation of electrode made from a biocompatible, non-metal material is urgently needed in clinical practice. The carbon nanotube yarns (CNTY) material has good electrochemical characteristics with high strength and flexibility. Published and preliminary data demonstrated that CNTY material has a good biocompatibility with neural tissue in vitro and in vivo, while producing almost no shadow in Magnetic Resonance Imaging (MRI). These results indicated that CNTY might be ideal material to make deep brain electrodes.Materials and Methods:We implanted electrodes made from CNTY or Pt-Ir (as control) in the brain of rats and rabbits, and observed the general condition of animals. Histological studies included hematoxylin&eosin (HE) staining and immunohistochemical staining for CD68(a microphage marker), GFAP (maker for activated astrocytes) and NeuN (a neuronal maker). The extends of neuronal damage and inflammation were compared for1week,6weeks and12weeks after implantation of different types of electrodes to determine the biocompatibility of CNTY electrode. The MRI of T1and T2phase were also performed and compared for1week and12weeks after implantation of different types of electrodes. In addition, we tried to implant active electrode made from CNTY or Pt-Ir, and collected preliminary data for the electrode resistance, stimulator voltage and the body weight or animals after active stimulation.Results:The histochemical study revealed an excellent biocompatibility of CNTY electrode. HE staining showed that the CNTY electrode produced a significantly narrower band of non-neuronal area immediately around the electrode as compared to the Pt-Ir electrode, suggesting a good neural compatibility. Immunohistochemical staining indicated that the CNTY electrode resulted in significantly less CD68-positive macrophages, and similar level of GFAP expression as compared to the Pt-Ir electrode. The preliminary results of NeuN staining also indicated a better survival rate of neurons surrounding the CNTY electrode, suggesting a less sever acute and chronic inflammatory response after implantation compared to Pt-Ir electrode. The MRI studies after1week and12weeks of implantation indicated that:compared with Pt-Ir electrode, the CNTY electrode produced almost no shadow in either T1or T2phase, revealing a clear image of surrounding tissue. In addition, preliminary data suggested that implantation of active electrode made from CNTY or Pt-Ir resulted in no obvious difference in the electrode resistance, stimulator voltage or the body weight or animals.Conclusions:This study demonstrated that CNTY electrode has a better biocompatibility as compared to the traditional Pt-Ir electrode, and produced almost no shadow under MRI. For the first time, using a full-size electrode implanted to the deep brain of animalin vivo, we have proved that the CNTYelectrode is superior to the Pt-Ir electrode in terms of monitoring the electrode position and detecting the abnormality in the surrounding tissue. The CNTY electrode may serve as an ideal implantable electrode to be used clinically to stimulate or record in the central nervous system.