Xianjue Chen

Optimising a vortex fluidic device for controlling chemical reactivity and selectivity

A vortex fluidic device (VFD) involving a rapidly rotating tube open at one end forms dynamic thin films at high rotational speed for finite sub-millilitre volumes of liquid, with shear within the films depending on the speed and orientation of the tube. Continuous flow operation of the VFD where jet feeds of solutions are directed to the closed end of the tube provide additional tuneable shear from the viscous drag as the liquid whirls along the tube. The versatility of this simple, low cost microfluidic device, which can operate under confined mode or continuous flow is demonstrated in accelerating organic reactions, for model Diels-Alder dimerization of cyclopentadienes, and sequential aldol and Michael addition reactions, in accessing unusual 2,4,6-triarylpyridines. Residence times are controllable for continuous flow processing with the viscous drag dominating the shear for flow rates >0.1u2005mL/min in a 10u2005mm diameter tube rotating at >2000u2005rpm.

Entrapment of Chlorella vulgaris cells within graphene oxide layers

Confinement of microalgae cells within layers of graphene oxide (GO) effectively reduces the rate of cell division, with the microalgal wrapping being more efficient in a vortex fluidic device than using mild sonication, as determined by the cell growth and the level of nitrate removal from the liquid effluent.

Nitrate uptake by p-phosphonic acid calix[8]arene stabilized graphene

In situ sonic probe exfoliated graphene sheets in the presence of various concentrations of p-phosphonic acid calix[8]arene are effective in removing nitrate from aquatic effluents, with the efficiency increasing for higher ratios of calixarene to graphite. Mild sonication of the nitrate-adsorbed material releases some nitrate ions back to the effluent.

Shear induced carboplatin binding within the cavity of a phospholipid mimic for increased anticancer efficacy

Vesicles 107u2009±u200919u2009nm in diameter, based on the self-assembly of tetra-para-phosphonomethyl calix[4]- arene bearing n-hexyl moieties attached to the phenolic oxygen centres, are effective in binding carboplatin within the cavity of the macrocycle under shear induced within a dynamic thin film in a continuous flow vortex fluidic device. Post shearing the vesicles maintain similar diameters and retain carboplatin within the cavity of the calixarene in a hierarchical structure, with their size and morphology investigated using DLS, TEM, SEM and AFM. Location of the carboplatin was confirmed using NMR, FTIR, ESI-MS and EFTEM, with molecular modelling favouring the polar groups of carboplatin hydrogen bonded to phosphonic acid moieties and the four member cyclobutane ring directed into the cavity of the calixarene. The loading efficiency and release profile of carboplatin was investigated using LC-TOF/MS, with the high loading of the drug achieved under shear and preferential released at pH 5.5, offering scope for anti-cancer drug delivery. The hierarchical structured vesicles increase the efficacy of carboplatin by 4.5 fold on ovarian cancer cells, lowered the IC50 concentration by 10 fold, and markedly increased the percent of cells in the S-phase (DNA replication) of the cell cycle.

Hierarchical patterning of multifunctional conducting polymer nanoparticles as a bionic platform for topographic contact guidance

The use of programmed electrical signals to influence biological events has been a widely accepted clinical methodology for neurostimulation. An optimal biocompatible platform for neural activation efficiently transfers electrical signals across the electrode-cell interface and also incorporates large-area neural guidance conduits. Inherently conducting polymers (ICPs) have emerged as frontrunners as soft biocompatible alternatives to traditionally used metal electrodes, which are highly invasive and elicit tissue damage over long-term implantation. However, fabrication techniques for the ICPs suffer a major bottleneck, which limits their usability and medical translation. Herein, we report that these limitations can be overcome using colloidal chemistry to fabricate multimodal conducting polymer nanoparticles. Furthermore, we demonstrate that these polymer nanoparticles can be precisely assembled into large-area linear conduits using surface chemistry. Finally, we validate that this platform can act as guidance conduits for neurostimulation, whereby the presence of electrical current induces remarkable dendritic axonal sprouting of cells.

Template-free assembly of three-dimensional networks of graphene hollow spheres at the water/toluene interface.

HYPOTHESISnThe Pickering emulsion system, generated by amphiphilic graphene oxide (GO) sheets trapped between water/toluene liquid interfaces, can be directly used for template-free formation of three-dimensional (3D) structure of GO hollow spheres.nnnEXPERIMENTSnThe method involves the formation of highly stable micron-sized Pickering emulsions via mild sonication of GO aqueous solution and toluene in the presence of polyvinyl alcohol (PVA), followed by direct freeze-drying of the mixture for preserving the unique 3D hollow spherical structures.nnnFINDINGSnThe 3D structure of interconnected GO hollow spheres, with a diameter in the range ∼2 to 10 μm, has been prepared. Transmission and scanning electron microscopy analyses confirmed the formation of the 3D structure directly from the Pickering emulsion system. The presence of PVA is critical in supporting the GO hollow spherical structures. Raman analysis confirmed the structural integrity of the GO in the 3D products.

Aqueous based synthesis of antimicrobial-decorated graphene

Ramizol® (1,3,5-tris[(1E)-2-(4-benzoic acid)vinyl]benzene) is a potent amphiphilic anti-microbial agent. It is essentially a planar molecule and can interact with the surface of graphene via extended π-π interactions. Herein we demonstrate the utility of Ramizol® in potentially acting as a molecular wedge to exfoliate graphene and stabilise it in water. The non-covalent attachment of Ramizol® on the graphene surface enables release of Ramizol® by altering the pH of the solution. Furthermore, the stabilised composite material demonstrates antibacterial activity against Staphylococcus aureus which leads to potential in biomedical applications with graphene acting as a drug carrier as well as enhancing the structural strength of the composite material.

Microencapsulation of bacterial strains in graphene oxide nano-sheets using vortex fluidics

Wrapping bacterial cells with graphene oxide sheets using a vortex fluidic device (VFD) effectively limits cellular growth for a certain time period whilst sustaining biological activity. This simple and benign method in preparing such a composite material relies on the shear within the film in the device without compromising the cellular viability. In principle, the process is scalable for large volumes, for operating the VFD(s) under continuous flow mode. Moreover, acquiring SEM images was possible without pre-coating the composite material with a metallic film, with limited charging effects. This establishes the potential for interfacing material with graphene oxide, which could be extended to more conductive graphene layers, as an effective approach for simplifying characterization using SEM.

Nitrate uptake by p-phosphonic acid or p-(trimethylammonium)methyl calix[8]arene stablized laminar materials

Graphite, BN, MoS2 and WS2 are readily exfoliated using probe sonication in the presence of p-(trimethylammonium)methyl-calix[8]arene resulting in few-layer laminar material. The positively charged material is effective in the removal of nitrate ions from waste effluent, as is the negatively charged corresponding material stablized by partially deprotonated p-phosphonic acid calix[8]arene, with scope for efficient recycling.