Silicon as a ubiquitous contaminant in graphene derivatives with significant impact on device performance

Silicon-based contaminants are ubiquitous in natural graphite, and they are thus expected to be present in exfoliated graphene. Here, the authors show that such impurities play a non-negligible role in graphene-based devices, and use high-purity parent graphite to boost the performance of graphene sensors and supercapacitor microelectrodes

Fabrication and characterisation of conducting fibres for use in biomedical applications

Fabrication and characterisation of conducting biomaterials in 3-dimensional configuration for biomedical applications have been studied and is presented in this thesis. Different fibre spinning techniques (wet-spinning and electrospinning) were utilised to create multifunctional fibres to be employed for controlled drug delivery and cellular growth supports. Two different classes of organic conductors, namely conducting polymers and graphene, were utilised to induce and develop electrical and electrochemical features in the fibres for their potential applications in drug delivery and cell growth enhancement via electrical stimulation. Physical, mechanical, electrical, electrochemical and biological characterisations of the fibres were investigated. In chapter two, Poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS) and polypyrrole (Ppy) were utilised in conjugation with chitosan for fabrication of conducting biocompatible fibres using wet-spinning. Then, a layer of Ppy with an antibiotic drug Ciprofloxacin hydrochloride (Cipro) as a dopant for Ppy was produced on the PEDOT:PSS-CHI fibres. The wet-spinning of PEDOT:PSS in a chitosan coagulation bath was successfully carried out and the fibres were shown to have an electrical conductivity of 56 ± 7 S/cm with a modulus and strength of 2.0 ± 0.3 GPa and 99 ± 7 MPa, respectively. The PEDOT:PSS-CHI fibres were subsequently employed as an electrode for the electropolymerisation of Ppy.Cipro on their surfaces. Scanning electron microscopy (SEM) of the fibres showed the morphological differences between PEDOT:PSS and Ppy.Cipro layers, confirming the deposition of the Ppy.Cipro. Cyclic voltammograms of fibres exhibited that the Ppy.Cipro was electroactive and showed an oxidation and reduction peak at +0.2 V and -0.1 V, respectively. The conducting and electroactive fibres were utilised for controlling the release of Cipro using an electrochemical stimulation protocol. The results of electrical stimulation of fibres revealed that Cipro release could be tuned by utilizing the different redox states of PEDOT:PSS-CHI and Ppy.Cipro conducting polymers. The in vitro antibacterial studies on the fibres and released Cipro demonstrated that the drug did not lose its antibacterial property during electropolymerisation and electrochemically stimulated release processes. In vitro fluorescent staining images revealed that the fibres were not cytotoxic to B35 neuroblastoma cells, however, the cells tended to cluster together rather than attach to the fibres. Moreover, the results of a lactate dehydrogenase (LDH) test revealed that the Cipro concentrations released in this study did not have an adverse effect on B35 neural cell. In chapter three, the development of a novel and facile system of wet-electrospinning (combined electrospinning and wet-spinning) is presented. This new method was developed in order to improve the attachment behaviour of B35 neuroblastoma cells on wet-spun fibres containing conducting polymers. The process of fibre fabrication consists of simultaneously wet-spinning and electrospinning to form a structure composing of micro-size wet-spun fibres coated in nano-sized electrospun fibres. The new fibre configuration demonstrated increased B35 neuroblastoma cell attachment as well as promising electrochemical property. Extended electrospinning times resulted in a thick coating of poly(D,L-lactic-co-glycolic acid) (PLGA) around the PEDOT:PSS-CHIT fibres which hindered the electroactivity of this conducting inner core. This was attributed to the thick PLGA coating blocking any ions from solution interacting with the PEDOT:PSS. This result had implications on the ability to use these particular fibres in electrical stimulation experiments, and therefore shorter electrospinning times were investigated. Additionally, the release of Cipro from PLGA electrospun fibres has shown the potential of the fibres in drug delivery applications. In chapter four, fabrication and characterisation of graphene as an organic conductor in a wet-spun composite fibres structure was studied to induce and develop electrical conductivity and electrochemical activity in the fibres. The graphene dispersion exfoliated in N-Cyclohexyl-2-pyrrolidone (CHP) exhibited dispersion stability over an extended period of time. The free-standing graphene paper fabricated from the dispersion (thickness between 5.0 to 100 μm) demonstrated well-defined layered morphology of graphene. The TEM characterisations of CHP-exfoliated graphene showed that the graphene dispersion consisted of monolayer and few layers of graphene. Additionally, the blend of PLGA with graphene was fabricated using a wet-spinning system. The rheological characterisation of wet-spinning solutions showed that a concentration of 1.5 wt. % PLGA and above, dissolved in 5 mg/ml graphene dispersion in CHP, can provide viscosity of ≥ 0.023 Pa s which was found to be spinnable. The wet-spinning of graphene with the biocompatible PLGA was carried out successfully with the fibres demonstrating an electrical conductivity of 1.5 S/cm. The PLGA-graphene fibre showed electroactivity in phosphate buffered saline (PBS) when tested by cyclic voltammetry. The electrical conductivity measurements showed that, once the graphene content was greater than 11.1 wt. % (with respect to PLGA), electrical conductivity increased above the percolation threshold (~30 S/m) and increased to 150 S/m when the graphene content was 24.3 wt. %. The cytocompatibility tests and cryo-SEM images showed that C2C12 myoblast cells were metabolically active on the fibres and attached along the length of the fibres. Furthermore, the proliferation assessment over 72 hr on the fibres revealed that C2C12 cells proliferated along the fibres

Multifunctional conducting polymer fibres for drug delivery applications

Advances in the fabrication of neuroprosthetic electrodes have attracted considerable interest from biomedical researchers. These electrodes are incorporated into a neuroprosthetic device capable of, electrically stimulating and recording of neuron activity. Critical to the successful application of these electrodes is their biocompatibility, stable conductivity, lower impedance and flexibility whilst maintaining appropriate mechanical properties [1]

Electrical Stimulation with a Conductive Polymer Promotes Neurite Outgrowth and Synaptogenesis in Primary Cortical Neurons in 3D

Deficits in neurite outgrowth and synaptogenesis have been recognized as an underlying developmental aetiology of psychosis. Electrical stimulation promotes neuronal induction including neurite outgrowth and branching. However, the effect of electrical stimulation using 3D electrodes on neurite outgrowth and synaptogenesis has not been explored. This study examined the effect of 3D electrical stimulation on 3D primary cortical neuronal cultures. 3D electrical stimulation improved neurite outgrowth in 3D neuronal cultures from both wild-Type and NRG1-knockout (NRG1-KO) mice. The expression of synaptophysin and PSD95 were elevated under 3D electrical stimulation. Interestingly, 3D electrical stimulation also improved neural cell aggregation as well as the expression of PSA-NCAM. Our findings suggest that the 3D electrical stimulation system can rescue neurite outgrowth deficits in a 3D culturing environment, one that more closely resembles the in vivo biological system compared to more traditionally used 2D cell culture, including the observation of cell aggregates as well as the upregulated PSA-NCAM protein and transcript expression. This study provides a new concept for a possible diagnostic platform for neurite deficits in neurodevelopmental diseases, as well as a viable platform to test treatment options (such as drug delivery) in combination with electrical stimulation

Combined wet-spinning and electrospinning: novel and facile method to fabricate micro-nano scale conducting fibres

One of the main challenges in tissue engineering is to design and fabricate an appropriate 3D extra cellular matrix (ECM) with capability to tune the in vivo environment in conjugation with additional requirements for cells enhancement. The composition, topology and artichectures of ECM are critical to achieve the desirable functionality of tissue or organ to be regenerated [1]

Formation and processability of liquid crystalline dispersion graphene oxide

Rational control over the formation and processability, and consequently final properties of graphene oxide liquid crystalline dispersions has been a long-standing goal in the development of bottom-up device fabrication processes. Here we report, the principal conditions through which such levels of control can be exercised to fine-tune dispersion properties for further processing

High-Performance Graphene-Fiber-Based Neural Recording Microelectrodes

Fabrication of flexible and free-standing graphene-fiber- (GF-) based microelectrode arrays with a thin platinum coating, acting as a current collector, results in a structure with low impedance, high surface area, and excellent electrochemical properties. This modification results in a strong synergistic effect between these two constituents leading to a robust and superior hybrid material with better performance than either graphene electrodes or Pt electrodes. The low impedance and porous structure of the GF results in an unrivalled charge injection capacity of 10.34 mC cm −2 with the ability to record and detect neuronal activity. Furthermore, the thin Pt layer transfers the collected signals along the microelectrode efficiently. In vivo studies show that microelectrodes implanted in the rat cerebral cortex can detect neuronal activity with remarkably high signal-to-noise ratio (SNR) of 9.2 dB in an area as small as an individual neuron

Electrical stimulation using conductive polymer polypyrrole counters reduced neurite outgrowth of primary prefrontal cortical neurons from NRG1-KO and DISC1-LI mice

Deficits in neurite outgrowth, possibly involving dysregulation of risk genes neuregulin-1 (NRG1) and disrupted in schizophrenia 1 (DISC1) have been implicated in psychiatric disorders including schizophrenia. Electrical stimulation using conductive polymers has been shown to stimulate neurite outgrowth of differentiating human neural stem cells. This study investigated the use of the electroactive conductive polymer polypyrrole (Ppy) to counter impaired neurite outgrowth of primary pre-frontal cortical (PFC) neurons from NRG1-knock out (NRG1-KO) and DISC1-locus impairment (DISC1-LI) mice. Whereas NRG1-KO and DISC1-LI exhibited reduced neurite length and number of neurite branches compared to wild-type controls, this was not apparent for cultures on electroactive Ppy. Additionally, the use of the Ppy substrate normalised the synaptophysin and PSD95 protein and mRNA expression whereas both are usually reduced by NRG1-KO or DISC1-LI. Our findings support the utility of Ppy mediated electrical stimulation to prevent the reduction of neurite outgrowth and related synaptic protein expression in the primary PFC neurons from NRG1-KO and DISC1-LI mice, providing proof-of-concept for treating neurodevelopmental diseases including schizophrenia

3D textile structures with integrated electroactive electrodes for wearable electrochemical sensors

2020, 2020 The Textile Institute. Common textile fabrication techniques have been utilised as scalable and cost-effective production methods for fabricating flexible 3D textile electrode platforms. These textile structures may be readily integrated with electroactive electrodes that can potentially carry out electrochemical detection in wearable devices. Here we demonstrate that conductive fibre or yarn-based electrodes can be readily incorporated into knitted and braided textile structures for electrochemical detection. Due to the poor nature of these commodity-based conducting yarns and fibres surface modification utilising electrodeposition of conducting polypyrrole and or gold nanoparticles was demonstrated to enhance the device performance

Conductive composite fibres from reduced graphene oxide and polypyrrole nanoparticles

Continuous composite fibres composed of polypyrrole (PPy) nanoparticles and reduced graphene oxide (rGO) at different mass ratios were fabricated using a single step wet-spinning approach. The electrical conductivity of the composite fibres increased significantly with the addition of rGO. The mechanical properties of the composite fibres also improved by the addition of rGO sheets compared to fibres containing only PPy. The ultimate tensile strength of the fibres increased with the proportion of rGO mass present. The elongation at break was greatest for the composite fibre containing equal mass ratios of PPy nanoparticles and rGO sheets. L929 fibroblasts seeded onto fibres showed no reduction in cell viability. To further assess toxicity, cells were exposed to media that had been used to extract any aqueous-soluble leachates from developed fibre. Overall, these composite fibres show promising mechanical and electrical properties while not significantly impeding cell growth, opening up a wide range of potential applications including nerve and muscle regeneration studies