Xiao-Yang Kang

Graphene oxide doped conducting polymer nanocomposite film for electrode-tissue interface

One of the most significant components for implantable bioelectronic devices is the interface between the microelectrodes and the tissue or cells for disease diagnosis or treatment. To make the devices work efficiently and safely in vivo, the electrode-tissue interface should not only be confined in micro scale, but also possesses excellent electrochemical characteristic, stability and biocompatibility. Considering the enhancement of many composite materials by combining graphene oxide (GO) for its multiple advantages, we dope graphene oxide into poly(3,4-ethylenedioxythiophene) (PEDOT) forming a composite film by electrochemical deposition for electrode site modification. As a consequence, not only the enlargement of efficient surface area, but also the development of impedance, charge storage capacity and charge injection limit contribute to the excellent electrochemical performance. Furthermore, the stability and biocompatibility are confirmed by numerously repeated usage test and cell proliferation and attachment examination, respectively. As electrode-tissue interface, this biomaterial opens a new gate for tissue engineering and implantable electrophysiological devices.

Self-Closed Parylene Cuff Electrode for Peripheral Nerve Recording

We have designed, fabricated, and characterized a self-closed parylene cuff electrode for peripheral nerve recording, whose curliness and closeness is realized by the difference in self-stress of different parylene layers due to the heat treatments. Compared with the conventional cuff electrodes, the self-closed structure without any additional mechanical locking structure minimizes the mechanical structure of the cuff electrode. Moreover, the self-closed structure made of thin and flexible parylene film minimizes mechanical damage to the nerve and the surrounding tissues. The zero insertion force interface facilitates the connection of 16 channels with external circuits through the integrated parylene bonding pads. To reduce the impedance and increase the charge storage capacity of the electrode, the electrodeposited iridium oxide film is electrodeposited on the electrode sites. Using the fabricated self-closed parylene cuff electrode, acute neural recoding of 16 channels was performed on the rat sciatic nerve to verify the capability of recording the neural activities. The present self-closed parylene cuff electrode is promising to be used as an neural interface for peripheral nerve recording.

Optimization and electrochemical characterization of RF-sputtered iridium oxide microelectrodes for electrical stimulation

A reactively sputtered iridium oxide (IrOx) thin film has been developed as electrochemical modification material for microelectrodes to obtain high stability and charge storage capacity (CSC) in functional electrical stimulation. The effect of the oxygen flow and oxygen to argon ratio during sputtering process on the microstructure and electrochemical properties of the IrOx film is characterized. After optimization, the activated IrOx microelectrode shows the highest CSC of 36.15 mC cm−2 at oxygen flow of 25 sccm and oxygen to argon ratio of (2.5:1). Because the deposition process of the reactively sputtered iridium oxide is an exothermic reaction, it is difficult to form film patterning by the lift-off process. The lift-off process was focused on the partially carbonized photoresist (PR) and normal PR. The higher of the carbonization degree of PR reaches, the longer the immersion duration. However, the patterning process of the iridium oxide film becomes feasible when the sputtering pressure is increasing. The experimental results show that the iridium oxide films forms the pattern with the lowest duration of ultrasonic agitation when the deposition pressure is 4.2 Pa and pressure ratio between O2 and Ar pressure is 3:4.

Low-Voltage Transient/Biodegradable Transistors Based on Free-Standing Sodium Alginate Membranes

In this letter, we report a novel transient/ biodegradable transistor. The Al:ZnO (AZO) source, drain, and gate electrodes are directly self-assembled on the free-standing sodium alginate (SA) membrane by magnetron sputtering, and the SA membrane is used simultaneously as the substrates and dielectrics for the transistor. Due to the strong lateral electrostatic coupling effects of SA membrane, the transistor can operate at a low voltage of 1 V. Dissolution tests of the transistor in deionized water suggest its completely physical transience within 1 h.

Biodegradable Junctionless Transistors With Extremely Simple Structure

Biodegradable junctionless transistors with extremely simple structure are fabricated at room temperature. The free-standing sodium alginate membrane is used as both a substrate and a dielectric layer for the transistors. The source/drain electrodes and the channel region are made of one single patterned Al:ZnO (AZO) thin film. The proposed transistors can be operated at a low voltage of 1 V. Dissolution tests of those transistors in deionized water demonstrate their completely physical transience within 60 min. The operation mode of such transistors can effectively be tuned from the depletion mode to the enhancement mode by varying the thickness of the AZO film. Moreover, a resistor-loaded invertor was demonstrated by connecting those transistors in series with a 3 MΩ resistor.

Direct electrodeposition of Graphene enhanced conductive polymer on microelectrode for biosensing application

Engineering of neural interface with nanomaterials for high spatial resolution neural recording and stimulation is still hindered by materials properties and modification methods. Recently, poly(3,4-ethylene-dioxythiophene) (PEDOT) has been widely used as an electrode-tissue interface material for its good electrochemical property. However, cracks and delamination of PEDOT film under pulse stimulation are found which restrict its long-term applications. This paper develops a flexible electrochemical method about the co-deposition of graphene with PEDOT on microelectrode sites to enhance the long-term stability and improve the electrochemical properties of microelectrode. This method is unique and profound because it co-deposits graphene with PEDOT on microelectrode sites directly and avoids the harmful post reduction process. And, most importantly, significantly improved electrochemical performances of the modified microelectrodes (compared to PEDOT-GO) are demonstrated due to the large effective surface area, good conductivity and excellent mechanical property of graphene. Furthermore, the good mechanical stability of the composites is verified by ultrasonication and CV scanning tests. In-vivo acute implantation of the microelectrodes reveals the modified microelectrodes show higher recording performance than the unmodified ones. These findings suggest the composites are excellent candidates for the applications of neural interface.

Fabrication and degradation characteristic of sputtered iridium oxide neural microelectrodes for FES application

This paper shows the fabrication process of the reactively sputtered iridium oxide film (SIROF) microelectrodes under different oxygen flows and characters the electrochemical performances of the iridium oxide neural microelectrodes which are suffered from stimulus-evoked degradation. The SIROF microelectrodes prepared under 25 sccm oxygen flow shows the least degradation from continuous electrical stimulation (two million phases). That the charge storage capacity is only decreased by 9.6 % and the 1 kHz impedance is only increased by 4.23 %. Hence, the 25 sccm one can be an ideal microelectrode modification material for electrical stimulation with the least degradation.

Biotic and abiotic molecule dopants determining the electrochemical performance, stability and fibroblast behavior of conducting polymer for tissue interface

Because the growth activities of cells considerably depend on the surface characteristics of tissue culture substrates, tissue–substrate interface is a crucial factor in modulating the behavior of cells in tissue engineering. Conducting polymers with excellent biocompatibility act as ideal tissue interface material because they can be facilely fabricated into multiple structures, patterned to undergo electrical stimulation and modified with different dopants. Meanwhile, the performance of conducting polymers is significantly influenced by the characteristics of negatively charged dopants. Herein, six kinds of biotic and abiotic molecules with electronegative groups are used as counterions to dope poly(3,4-ethylenedioxythiophene) (PEDOT). A comprehensive evaluation of the properties of PEDOT, including electrochemistry, electrical stimulation, stability and biocompatibility is provided for further comparison and analysis. This work would reinforce our understanding of the dopant-dependent performance of conducting polymers for tissue engineering and applications in electrophysiological recording and stimulation.

Flexible intramuscular micro tube electrode combining electrical and chemical interface

With the rapidly developed micromachining technology, various kinds of sophisticated microelectrodes integrated with micro fluidic channels are design and fabricated for not only electrophysiological recording and stimulation, but also chemical drug delivery. As many efforts have been devoted to develop rigid microprobes for neural research of brain, few researchers concentrate on fabrication of flexible microelectrodes for intramuscular electrophysiology and chemical interfacing. Since crude wire electrodes still prevail in functional electrical stimulation (FES) and electromyography (EMG) recording of muscle, here we introduce a flexible micro tube electrode combining electrical and chemical pathway. The proposed micro tube electrode is manufactured based on polymer capillary, which provide circumferential electrode site contacting with electro-active tissue and is easy to manufactured with low cost.

Fabrication and electrochemical comparison of SIROF-AIROF-EIROF microelectrodes for neural interfaces

Iridium oxide has been widely used in neural recording and stimulation due to its good stability and large charge storage capacity (CSC). In general, the iridium oxide film used in the electrophysiological application can be grouped into three principal classifications: sputtering iridium oxide film (SIROF), activated iridium oxide film (AIROF) and electrodeposited iridium oxide film (EIROF). Although these kinds of iridium oxide all can remarkably reduce the impedance and increase the CSC of the microelectrode, they also exhibit markedly differences in electrochemical performances. After activation, the CSC of EIROF is 68.20 mC/cm2, which is 88.7 % larger than that of the SIROF and 67.6 % larger than that of the AIROF. The impedance at 1 kHz of the three kinds of iridium oxide microelectrode is around 4000 ohm, it is acceptable for the neural interface application. The phase at 1 kHz of the AIROF microelectrode is the largest which is -6.1 degree, about 22.6 % of the SIROF and 44.5 % of the EIROF.