Hierarchical platinum–iridium neural electrodes structured by femtosecond laser for superwicking interface and superior charge storage capacity

The interfacial performance of implanted neural electrodes is crucial for stimulation safety and the recording quality of neuronal activity.This paper proposes a novel surface architecture and optimization strategy for the platinum–iridium(Pt–Ir)electrode to optimize electrochemical performance and wettability.A series of surface micro/nano structures were fabricated on Pt–Ir electrodes with different combinations of four adjustable laser-processing parameters.Subsequently,the electrodes were characterized by scanning electron microscopy,energy-dispersive X-ray spectroscopy,cyclic voltammetry,electrochemical impedance spectroscopy,and wetting behavior.The results show that electrode performance strongly depends on the surface morphology.Increasing scanning overlap along with moderate pulse energy and the right number of pulses leads to enriched surface micro/nano structures and improved electrode performance.It raises the maximum charge storage capacity to 128.2 mC/cm^(2) and the interface capacitance of electrodes to 3.0×10^(4)μF/cm^(2) for the geometric area,compared with 4.6 mC/cm^(2) and 443.1μF/cm2,respectively,for the smooth Pt–Ir electrode.The corresponding optimal results for the optically measured area are 111.8 mC/cm^(2) and 2.6×10^(4)μF/cm^(2),which indicate the contribution of fner structures to the ablation profle.The hierarchical structures formed by the femtosecond laser dramatically enhanced the wettability of the electrode interface,giving it superwicking properties.A wicking speed of approximately 80 mm/s was reached.Our optimization strategy,leading to superior performance of the superwicking Pt–Ir interface,is promising for use in new neural electrodes.

Polyurethane/poly(vinyl alcohol) hydrogel coating improves the cytocompatibility of neural electrodes

Neural electrodes,the core component of neural prostheses,are usually encapsulated in polydimethylsiloxane（PDMS）.However,PDMS can generate a tissue response after implantation.Based on the physicochemical properties and excellent biocompatibility of polyurethane（PU）and poly（vinyl alcohol）（PVA）when used as coating materials,we synthesized PU/PVA hydrogel coatings and coated the surface of PDMS using plasma treatment,and the cytocompatibility to rat pheochromocytoma（PC12）cells was assessed.Protein adsorption tests indicated that the amount of protein adsorption onto the PDMS substrate was reduced by 92%after coating with the hydrogel.Moreover,the PC12 cells on the PU/PVA-coated PDMS showed higher cell density and longer and more numerous neurites than those on the uncoated PDMS.These results indicate that the PU/PVA hydrogel is cytocompatible and a promising coating material for neural electrodes to improve their biocompatibility.

Establishment of a Refined Brain Model for Evaluating Implantation Behavior of Neural Electrode and Research of its Simulated Behavior

The long-term reliability of the neural electrode is closely related to its implantation behavior.In orderto realize the quantitative research of the implantation behavior in a low-cost and accurate way,a refined brainmodel containing meninges is proposed.First,the expected simulation material was selected through measuringthe elastic modulus based on the method of atomic force microscope indentation technique.As a result,the 2%(mass fraction)agarose gel simulated the gray and white matter,the 7:1(volume ratio)polydimethylsiloxane(PDMS)sheet simulated the pia mater,and the polyvinyl chloride(PVC)film simulated the dura mater.Second,based on designing a three-layer structure mold,the brain model was prepared by inverted pouring to realizea flat implantation surface.Finally,the simulation behavior of the brain model was investigated with the ratbrain as a reference.For mechanical behavior of implantation,the implantation force experienced two peaks bothin the brain model and the rat brain,maximum values of which were 10.17 mN and 7.69 mN respectively.Thelarger implantation force in the brain model will increase the strength requirement for the electrode,but reducethe risk of buckling of that in practical application.For humoral dissolution behavior,the dissolution rates ofthe polyethylene glycol(PEG)coating of the electrode in the brain model and rat brain were 7000μm3/s and5600μm3/s,respectively.The faster dissolution rate in the brain model will cause the larger thickness of thecoating design but provide sufficient implantable time in practical application.The establishment of the brainmodel and the research of its simulated behavior are beneficial to the size design of the electrode substrate andcoating,and research of the implantation mechanism,and further increase the functional life of the electrode.

Biocompatibility of Implantable Electrodes Coated with PVA Films in the Brain of Rats: a Histological Evaluation

The biocompatibility of silicone rubber （SR） based electrodes coating with poly （vinyl alcohol） （PVA） films after implanted in the brain of rats was investigated. Twenty-two Wistar rats were used and implanted with SR electrodes and PVA/PAA films coated electrodes in left and right cerebral cortex respectively. After 4 and 8 weeks, the expression of glial fibrillary acidic protein （GFAP, a specific marker of astrocytes） and cluster of differentiation 68 （CD68, a specific marker of macrophages） were evaluated by immunohistochemistry. After 8 weeks, GFAP and CD68 expressions around PVA electrodes were significantly lower than those around SR electrodes in every stratified area （0-50 μm, 50-100 μm, 100 μm from further up to the electrode-tissue interface）. The resuits show that PVA coating can reduce the expressions of GFAP and CD68, suggesting the PVA coating can improve the biocompatibility of the SR while it is implanted in brain.

Flexible and biocompatible nanopaper-based electrode arrays for neural activity recording

Advances in neural electrode technologies can have a significant impact on both fundamental and applied neuroscience. Here, we report the development of flexible and biocompatible neural electrode arrays based on a nanopaper substrate. Nanopaper has important advantages with respect to polymers such as hydrophilicity and water wettability, which result in significantly enhanced biocompatibility, as confirmed by both in vitro viability assays and in vivo histological analysis. In addition, nanopaper exhibits high flexibility and good shape stability. Hence, nanopaper-based neural electrode arrays can conform to the convoluted cortical surface of a rat brain and allow stable multisite recording of epileptiform activity in vivo. Our results show that nanopaper-based electrode arrays represent promising candidates for the flexible and biocompatible recording of the neural activity.

Platinum Wire Implants Coated with PEDOT/Carbon Nanotube Conducting Polymer Films in the Brain of Rats: A Histological Evaluation

Platinum （Pt） implants coated with poly （3, 4-ethylenedioxythiophene）/carbon nanotube （PEDOT/CNT） composite films were implanted into the brain of rats, and the brain response was evaluated 6 weeks after the implantation. The surface morphology of Pt implants with and without the PEDOT/CNT coating was studied using scanning electron microscopy （SEM）. After 6 weeks post-implantation, the expression of laminin （vascular endothelial marker） and neuronal nuclei （NeuN, neuronal marker） were evaluated by immnohistochemistry. It is revealed that the obvious improvements of the surface density of blood vessels and neurons aound the Pt implants with the coating, which were evidenced by laminin and NeuN staining in the zone within the distance of 150 μm to the implant interface. These results suggest the PEDOT/CNT composite films can improve the biocompatibility of the Pt electrodes while it is implanted in brain.