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Xiong G.M.,Nanyang Technological University | Yuan S.,University of Sichuan | Wang J.K.,Nanyang Environmental and Water Research Institute NEWRI | Wang J.K.,Nanyang Technological University | And 4 more authors.
Acta Biomaterialia | Year: 2015

Hemocompatibility, anti-inflammation and anti-thrombogenicity of acellular synthetic vascular grafts remains a challenge in biomaterials design. Using electrospun polycaprolactone (PCL) fibers as a template, a coating of polypyrrole (PPy) was successfully polymerized onto the fiber surface. The fibers coated with heparin-doped PPy (PPy-HEP) demonstrated better electroactivity, lower surface resistivity (9-10-fold) and better anti-coagulation response (non-observable plasma recalcification after 30 min vs. recalcification at 8-9 min) as compared to fibers coated with pristine PPy. Red blood cell compatibility, measured by% hemolysis, was greatly improved on PPy-HEP-coated PCL in comparison to uncoated PCL (3.9 ± 2.1% vs. 22.1 ± 4.1%). PPy-HEP-coated PCL fibers also exhibited higher stiffness values (6.8 ± 0.9 MPa vs. 4.2 ± 0.8 MPa) as compared to PCL fibers, but similar tensile strengths. It was also observed that the application of a low alternating current led to a 4-fold reduction of platelet activation (as quantitated by CD62p expression) for the PPy-HEP-coated fibers as compared to non-stimulated conditions. In parallel, a reduction in the leukocyte adhesion to both pristine PPy-coated and PPy-HEP-coated fibers was observable with AC stimulation. Overall, a new strategy involving the use of hemocompatible conducting polymers and electrical stimulation to control thrombogenicity and inflammatory responses for synthetic vascular graft designs was demonstrated. © 2015 Acta Materialia Inc. Source

Xiong G.M.,Nanyang Technological University | Do A.T.,Nanyang Technological University | Wang J.K.,Nanyang Environmental and Water Research Institute NEWRI | Wang J.K.,Nanyang Technological University | And 3 more authors.
Journal of Biological Engineering | Year: 2015

Background: Directing cell behaviour using controllable, on-demand non-biochemical methods, such as electrical stimulation is an attractive area of research. While there exists much potential in exploring different modes of electrical stimulation and investigating a wider range of cellular phenomena that can arise from electrical stimulation, progress in this field has been slow. The reasons for this are that the stimulation techniques and customized setups utilized in past studies have not been standardized, and that current approaches to study such phenomena rely on low throughput platforms with restricted variability of waveform outputs. Results: Here, we first demonstrated how a variety of cellular responses can be elicited using different modes of DC and square waveform stimulation. Intracellular calcium levels were found to be elevated in the neuroblast cell line SH-SY5Y during stimulation with 5 V square waves and, stimulation with 150 mV/mm DC fields and 1.5 mA DC current resulted in polarization of protein kinase Akt in keratinocytes and elongation of endothelial cells, respectively. Next, a miniaturized stimulation device was developed with an integrated cell chamber array to output multiple discrete stimulation channels. A frequency dividing circuit implemented on the device provides a robust system to systematically study the effects of multiple output frequencies from a single input channel. Conclusion: We have shown the feasibility of directing cellular responses using various stimulation waveforms, and developed a modular stimulation device that allows for the investigation of multiple stimulation parameters, which previously had to be conducted with different discrete equipment or output channels. Such a device can potentially spur the development of other high throughput platforms for thorough investigation of electrical stimulation parameters on cellular responses. © 2015 Xiong et al. Source

Chan Y.Y.,Nanyang Technological University | Chan Y.Y.,Nanyang Environmental and Water Research Institute NEWRI | Eng A.Y.S.,Nanyang Technological University | Pumera M.,Nanyang Technological University | And 2 more authors.
ChemElectroChem | Year: 2015

The drop-casting method for the suspension of nanomaterials on conducting surfaces is a commonly used procedure for evaluating the electrochemical properties of the drop-cast materials. In this study, we pinpoint a key limitation of the method, which may lead to misinterpretation of the obtained data, especially when evaluating heterogeneous electron-transfer rates. The electrochemical responses recorded at 1mm-diameter copper electrodes modified with porous layers of drop-cast multiwalled carbon nanotubes (MWCNTs) in 0.1M Na2SO4 aqueous solutions were examined. Standard amounts of the MWCNTs that are typically used for the drop-casting procedure (1mg MWCNT in 1mL of dimethylformamide) were deposited drop wise on the surface of the copper electrodes. Layers of MWCNTs were progressively built up on the electrode surface by varying the number of drops from 0 to 10. The ability of the MWCNTs to cover and prevent diffusion to the base copper electrode was assessed by performing oxidative cyclic (CV) and linear-sweep voltammetry (LSV) experiments in the presence of aggressive SO42- supporting electrolyte, where a large oxidative current indicated the occurrence of corroding copper metal. It was demonstrated that a total of 10 drops of the coating solution (equivalent to 640μgcm-2 of MWCNTs per unit area) was still insufficient in providing complete coverage over the underlying electrode surface (as a corrosion current was still observed), even though considerably lower CNT loadings have been applied in many literature reports. The electrochemical results indicate that, for experiments that utilize the drop-casting procedure to modify electrode surfaces, it cannot be assumed that the base electrode, nor the pore structure of the coating material, does not significantly contribute to the overall observed voltammetric response. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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