Spherical and cylindrical microencapsulation of living cells using microfluidic devices

Justin Cooper-White,Joung Sook Hong,신수정,이상훈,Edeline Wong 한국유변학회 2007 Korea-Australia rheology journal Vol.19 No.3

Microencapsulation of cells within microfluidic devices enables explicit control of the membrane thickness or cell density, resulting in improved viability of the transplanted cells within an aggressive immune system. In this study, living cells (3T3 and L929 fibroblast cells) are encapsulated within a semi-permeable membrane (calcium crosslinked alginate gel) in two different device designs, a flow focusing and a core-annular flow focusing geometry. These two device designs produce a bead and a long microfibre, respectively. For the alginate bead, an alginate aqueous solution incorporating cells flows through a flow focusing channel and an alginate droplet is formed from the balance of interfacial forces and viscous drag forces resulting from the continuous (oil) phase flowing past the alginate solution. It immediately reacts with an adjacent CaCl2 drop that is extruded into the main flow channel by another flow focusing channel downstream of the site of alginate drop creation. Depending on the flow conditions, monodisperse microbeads of sizes ranging from 50-200 m can be produced. In the case of the microfibre, the alginate solution with cells is extruded into a continuous phase of CaCl2 solution. The diameter of alginate fibres produced via this technique can be tightly controlled by changing both flow rates. Cell viability in both forms of alginate encapsulant was confirmed by a LIVE/DEAD cell assay for periods of up to 24 hours post encapsulation.

Shear-induced structure and dynamics of hydrophobically modified hydroxy ethyl cellulose (hmHEC) in the presence of SDS

Justin J. Cooper-White 한국유변학회 2002 Korea-Australia rheology journal Vol.14 No.4

Drop formation of Carbopol dispersions displaying yield stress, shear thinning and elastic properties in a flow-focusing microfluidic channel

홍정숙,Justin Cooper-White 한국유변학회 2009 Korea-Australia rheology journal Vol.21 No.4

The drop formation dynamics of a shear thinning, elastic, yield stress (τo) fluid (Carbopol 980 (poly(acrylic acid)) dispersions) in silicone oil has been investigated in a flow-focusing microfluidic channel. The rheological character of each solution investigated varied from Netwonian-like through to highly non-Newtonian and was varied by changing the degree of neutralization along the poly (acrylic acid) backbone. We have observed that the drop size of these non-Newtonian fluids (regardless of the degree of neutralisation) showed bimodal behaviour. At first we observed increases in drop size with increasing viscosity ratio (viscosity ratio=viscosity of dispersed phase (DP) / viscosity of continuous phase (CP)) at low flowrates of the continuous phases, and thereafter, decreasing drop sizes as the flow rate of the CP increases past a critical value. Only at the onset of pinching and during the high extensional deformation during pinch-off of a drop are any differences in the non-Newtonian characteristics of these fluids, that is extents of shear thinning,elasticity and yield stress (τo), apparent. Changes in these break-off dynamics resulted in the observed differences in the number and size distribution of secondary drops during pinch-off for both fluid classes, Newtonian-like and non-Newtonian fluids. In the case of the Newtonian-like drops, a secondary drop was generated by the onset of necking and breakup at both ends of the filament, akin to end-pinching behavior. This pinch-off behavior was observed to be unaffected by changes in viscosity ratio, over the range explored. Meanwhile, in the case of the non-Newtonian solutions, discrete differences in behaviour were observed, believed to be attributable to each of the non-Newtonian properties of shear thinning, elasticity and yield stress. The presence of a yield stress (τo), when coupled with slow flow rates or low viscosities of the CP, reduced the drop size compared to the Newtonian-like Carbopol dispersions of much lower viscosity. The presence of shear thinning resulted in a rapid necking event post onset, a decrease in primary droplet size and, in some cases, an increase in the rate of drop production. The presence of elasticity during the extensional flow imposed by the necking event allowed for the extended maintenance of the filament, as observed previously for dilute solutions of linear polymers during drop break-up.

Shear-induced structure and dynamics of hydrophobically modified hydroxy ethyl cellulose (hmHEC) in the presence of SDS

Tirtaatmadija, Viyada,Cooper-white, Justin J.,Gason, Samuel J. The Korean Society of Rheology 2002 Korea-Australia rheology journal Vol.14 No.4

The interaction between hydrophobically modified hydroxyethyl cellulose (hmHEC), containing approximately 1 wt% side-alkyl chains of $C_{16}$, and an anionic sodium dodecyl sulphate (SDS) surfactant was investigated. For a semi-dilute solution of 0.5 wt% hmHEC, the previously observed behaviour of a maximum in solution viscosity at intermediate SDS concentrations, followed by a drop at higher SDS concentrations, until above the cmc of surfactant when the solution resembles that of the unsubstituted polymer, was confirmed. Additionally, a two-phase region containing a hydrogel phase and a water-like supernatant was found at low SDS concentrations up to 0.2 wt%, a concentration which is akin to the critical association concentration, cac, of SDS in the presence of hmHEC. Above this concentration, SDS molecules bind strongly to form mixed micellar aggregates with the polymer alkyl side-chains, thus strengthening the network junctions, resulting in the observed increase in viscosity and elastic modulus of the solution. The shear behaviour of this polymer-surfactant complex during steady and step stress experiments was examined In great detail. Between SDS concentrations of 0.2 and 0.25 wt%, the shear viscosity of the hmHEC-polymer complex network undergoes shear-induced thickening, followed by a two-stage shear-induced fracture or break-up of the network. The thickening is thought to be due to structural rearrangement, causing the network of flexible polymers to expand, enabling some polymer hydrophobic groups to be converted from intra- to inter-chain associations. At higher applied stress, a partial local break-up of the network occurs, while at even higher stress, above the critical or network yield stress, a complete fracture of the network into small microgel-like units, Is believed to occur. This second network rupture is progressive with time of shear and no steady state in viscosity was observed even after 300 s. The structure which was reformed after the cessation of shear is found to be significantly different from the original state.

Facile and controllable incorporation of gold nanoparticles within one-dimensional self-assemblies of hyperbranched polymers

Li, Haiqing,Cooper-White, Justin J.,Kim, Il The Royal Society of Chemistry 2013 SOFT MATTER Vol.9 No.21

<P>Using a mono-pyrene terminated hyperbranched polyglycidol (mPTHP) as a building block, one-dimensional (1D) mPTHP and mPTHP/gold nanoparticle (Au NP) nanostructures are fabricated in the presence of HAuCl<SUB>4</SUB>. By simply mixing mPTHP and different concentrations of aqueous HAuCl<SUB>4</SUB> solution at room temperature, mPTHP nanofibers and nanotubes are obtained through Au(<SMALL>III</SMALL>) ion induced self-assembly processes. Upon elevating the reaction temperature from room temperature to 60 °C, Au NPs are <I>in situ</I> generated within 1D mPTHP assemblies <I>via</I> an analogous “polyol process”, forming mPTHP/Au NP hybrid nanofibers and nanotubes. Careful control of the HAuCl<SUB>4</SUB> concentration enables <I>in situ</I> generated Au NPs to be either distributed along the center-line of nanofibers or symmetrically aligned into a double-line along the nanofibers and the inner surface of nanotubes. Further investigation reveals that the involvement of a small amount of NaBr in the reaction system of mPTHP and different amounts of HAuCl<SUB>4</SUB> results in the formation of <I>pseudo</I>-nanotubes decorated with double-lined Au NP chains along their inner surfaces. Moreover, the size of Au NPs can be effectively tuned in terms of HAuCl<SUB>4</SUB> concentration. All 1D mPTHP and mPTHP/Au NP nanostructures described in our current work are achieved through one-pot aqueous reactions in the absence of any additional reducing agents, surfactants and organic solvents, so that they are facile, green and low-cost strategies. To the best of our knowledge, this is the first example to synthesize 1D hyperbranched polymer/metal NP hybrid nanostructures with controllable spatial distribution of NPs using such a facile and green protocol.</P> <P>Graphic Abstract</P><P>A facile and green protocol has been developed to <I>in situ</I> generate and controllably align Au nanoparticles within the one-dimensional self-assembled nanostructures of hyperbranched polymers. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3sm50768h'> </P>

Inertio-elastic mixing in a straight microchannel with side wells

Hong, Sun Ok,Cooper-White, Justin J.,Kim, Ju Min American Institute of Physics 2016 APPLIED PHYSICS LETTERS Vol.108 No.1

A general and efficient method for decorating graphene sheets with metal nanoparticles based on the non-covalently functionalized graphene sheets with hyperbranched polymers.

Li, Haiqing,Han, Lina,Cooper-White, Justin J,Kim, Il RSC Pub 2012 Nanoscale Vol.4 No.4

<P>Multipyrene terminated hyperbranched polyglycidol (mPHP) has been synthesized and used to non-covalently functionalize pristine graphene sheets (GSs) through π-π stacking interactions. Mediated by the mPHP layer, a variety of metal nanoparticles (Au, Ag and Pt) were in situ generated and deposited onto the surface-modified GS, yielding versatile GS/mPHP/metal nanohybrids. As typical examples, by simply controlling the concentration of HAuCl(4) used, Au nanostructures ranging from isolated spheres to a continuous film were created and coated onto the surface-modified GS. The studies on the fluorescence properties of resulting GS/mPHP/Au hybrid nanostructures reveal that the GS and controllable content of Au components in the hybrids can effectively quench the fluorescence emission of mPHP in a controlled manner. Further investigation indicates that GS/mPHP/Au hybrids are promising surface enhanced Raman scattering (SERS) substrates. The SERS activities of these hybrids depend on the contents and form of the Au. The GS/mPHP/Au hybrid containing continuous Au films exhibits the strongest SERS activity. GS/mPHP/Au hybrids are also used as efficient heterogeneous catalysts for the reduction of 4-NP, and demonstrate excellent catalytic performance. The detailed reaction kinetics and the reusability of such catalysts have also been investigated.</P>

Drop formation of Carbopol dispersions displaying yield stress, shear thinning and elastic properties in a flow-focusing microfluidic channel

Hong, Joung-Sook,Cooper-White, Justin The Korean Society of Rheology 2009 Korea-Australia rheology journal Vol.21 No.4

The drop formation dynamics of a shear thinning, elastic, yield stress ($\tau_o$) fluid (Carbopol 980 (poly(acrylic acid)) dispersions) in silicone oil has been investigated in a flow-focusing microfluidic channel. The rheological character of each solution investigated varied from Netwonian-like through to highly non-Newtonian and was varied by changing the degree of neutralization along the poly (acrylic acid) backbone. We have observed that the drop size of these non-Newtonian fluids (regardless of the degree of neutralisation) showed bimodal behaviour. At first we observed increases in drop size with increasing viscosity ratio (viscosity ratio=viscosity of dispersed phase (DP)/viscosity of continuous phase (CP)) at low flowrates of the continuous phases, and thereafter, decreasing drop sizes as the flow rate of the CP increases past a critical value. Only at the onset of pinching and during the high extensional deformation during pinch-off of a drop are any differences in the non-Newtonian characteristics of these fluids, that is extents of shear thinning, elasticity and yield stress ($\tau_o$), apparent. Changes in these break-off dynamics resulted in the observed differences in the number and size distribution of secondary drops during pinch-off for both fluid classes, Newtonian-like and non-Newtonian fluids. In the case of the Newtonian-like drops, a secondary drop was generated by the onset of necking and breakup at both ends of the filament, akin to end-pinching behavior. This pinch-off behavior was observed to be unaffected by changes in viscosity ratio, over the range explored. Meanwhile, in the case of the non-Newtonian solutions, discrete differences in behaviour were observed, believed to be attributable to each of the non-Newtonian properties of shear thinning, elasticity and yield stress. The presence of a yield stress ($\tau_o$), when coupled with slow flow rates or low viscosities of the CP, reduced the drop size compared to the Newtonian-like Carbopol dispersions of much lower viscosity. The presence of shear thinning resulted in a rapid necking event post onset, a decrease in primary droplet size and, in some cases, an increase in the rate of drop production. The presence of elasticity during the extensional flow imposed by the necking event allowed for the extended maintenance of the filament, as observed previously for dilute solutions of linear polymers during drop break-up.

Palladium nanoparticles decorated carbon nanotubes: facile synthesis and their applications as highly efficient catalysts for the reduction of 4-nitrophenol

Li, Haiqing,Han, Lina,Cooper-White, Justin,Kim, Il The Royal Society of Chemistry 2012 GREEN CHEMISTRY Vol.14 No.3

<P>Two completely green and facile strategies have been developed to decorate Pd nanoparticles onto carbon nanotubes (CNT) sidewalls <I>via</I> non-covalent interactions assisted with newly synthesized hyperbranched polymers (PiHPs). The resultant CNT/PiHP/Pd heterogeneous catalysts exhibit ultrahigh catalytic reactivity towards the reduction of 4-nitrophenol.</P> <P>Graphic Abstract</P><P>Two facile strategies have been developed to decorate Pd nanoparticles onto CNT sidewalls <I>via</I> non-covalent interactions assisted with newly synthesized hyperbranched polymers (PiHPs). The resultant CNT/PiHP/Pd heterogeneous catalysts exhibit ultrahigh catalytic reactivity towards the reduction of 4-nitrophenol. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2gc16359d'> </P>

Deformation and Break-up of a Drop in Contraction Flow

Malcolm R. Davidson,Justin Cooper-White 한국전산유체공학회 2003 한국전산유체공학회 학술대회논문집 Vol.2003 No.10