Guangsheng Luo

In situ preparation of magnetic Fe3O4-chitosan nanoparticles for lipase immobilization by cross-linking and oxidation in aqueous solution.

A new and simple method has been proposed to prepare magnetic Fe(3)O(4)-chitosan (CS) nanoparticles by cross-linking with sodium tripolyphosphate (TPP), precipitation with NaOH and oxidation with O(2) in hydrochloric acid aqueous phase containing CS and Fe(OH)(2), and these magnetic CS nanoparticles were used to immobilize lipase. The effects on the sequence of adding NaOH and TPP, the reaction temperature, and the ratio of CS/Fe(OH)(2) were studied. TEM showed that the diameter of composite nanoparticles was about 80 nm, and that the magnetic Fe(3)O(4) nanoparticles with a diameter of 20 nm were evenly dispersed in the CS materials. Magnetic measurement revealed that the saturated magnetisation of the Fe(3)O(4)-CS nanoparticles could reach 35.54 emicro/g. The adsorption capacity of lipase onto nanoparticles could reach 129 mg/g; and the maximal enzyme activity was 20.02 micromol min(-1)mg(-1) (protein), and activity retention was as high as 55.6% at a certain loading amount.

Shear force induced monodisperse droplet formation in a microfluidic device by controlling wetting properties

Perpendicular flow is used to induce oil droplet breakup by using a capillary as water phase flow channel. It is a new route to produce monodisperse emulsions. The wetting properties of the fluids on the walls are exceedingly important parameters. Depending on the oil and water flow rates, different spatial distributions of the two phases as laminar, plugs, cobbles and drops, are obtained. The effects of two-phase flow rates on plugs and drop size are studied, and the different droplet formation mechanisms of plug flow and drop flow are discussed. Two quantitative equations utilized to predict the droplet size are developed.

Controllable gas-liquid phase flow patterns and monodisperse microbubbles in a microfluidic T-junction device

This letter describes the gas-liquid phase flow patterns and the mechanism of generation of monodisperse microbubbles in a T-junction microfluidic device using the crossflowing shear-rupturing technique. The bubble size is ranged from 100 to 500μm. The air phase states as isolate air slugs, “pearl necklaces,” periodic isolate bubbles, zig-zag bubble patterns, and multiple-bubble layer can be observed in the wider measured channel. The bubble size relates with the continuous phase flow velocity and viscosity as Vb∝1∕(μcuc), while being almost independent of surface tension γ and air phase flow rate Qg, for the conditions used in this work. The bubble formation mechanism by using the crossflowing shear-rupturing technique is different from the hydrodynamic flow focusing and both geometry-dominated breakup techniques. Our system provides independent control of both the size and volume fraction of dispersed bubbles.

Controllable preparation of nanoparticles by drops and plugs flow in a microchannel device.

Well controlled two-liquid-phase flows in a T-junction microchannel device have been realized. The system of H2SO4 and BaCl2, respectively, in two phases to form BaSO4 nanoparticles was used as a probe to characterize the microscale two-phase flow and transport conditions of a system with interphase mass transfer and chemical reaction. Nanoparticles with narrow size and good dispersibility were produced through drops or plugs flow in the microdevice. As a novel work, the influence of mass transfer and chemical reaction on interfacial tension and flow patterns was discussed based on the experiments. At the same time, the effect of the two-phase flow patterns on the nanoparticle size was also discussed. It was found that the increase of the amount of mass transfer and chemical reaction could change the flow patterns from plugs flow to drops flow. The drop diameter or plug length could be changed in a wide range. Accordingly, a new parameter of mu(0)u(c)/gamma(0)/Q(d) was defined to distinguish the flow patterns. The prepared nanoparticles ranged in size from 10 to 40 nm. Apparently, the particle size decreased with the increase of the drop diameter or plug length. Reasons were discussed based on the mass transfer direction and speed in drops and plugs flow patterns.

Microfluidic approach for rapid interfacial tension measurement.

A novel microfluidic approach to measure interfacial tension of immiscible fluids rapidly is reported. This method rests upon quantitative force balance analysis of drop formation dynamics in a coaxial microfluidic device. The values of interfacial tension for several two liquids without/with surfactants are measured. These measurements compare well with those measured by the commercial interfacial tensiometry. The viscosity of water phase fluid can also be accurately measured in the same microfluidic device. Several model systems with interfacial tension from 1.0 to 10.0 mN/m and water phase viscosity from 1.0 to 10.0 mPa.s are tested in this work.

Immobilization of lipase on methyl-modified silica aerogels by physical adsorption.

In this work, methyl-modified silica aerogels, a new kind of macro-porous material with high porosity, were used as carriers to immobilize lipase by adsorption. SEM, TEM, nitrogen adsorption device, and thermogravimetric analysis were used to characterize the properties of modified aerogels. The surface area was 395.6 m(2)/g, and the average pore diameter was 68.72 nm. The contact angle of aerogel particles increased from 20.9 degrees to 99.2 degrees after methyl modification. Reaction characteristics of the material after enzyme loading were also discussed. The results showed that adsorption capacity could reach 67.42 mg/g; and the maximal enzyme activity was 19.87 micromol min(-1)mg(-1) (protein), and activity retention could reach 56.44%. It is worth mentioning that the amount of modified aerogels added had significant effects on the diameter of droplets and the mass transfer behavior of substrates in the reaction emulsion. Online microscope was used to visualize the droplets in the emulsion, where the aerogel particles were observed locating at the interface of oil and water. The average diameter of droplets reached the minimum when 0.06 g of modified aerogels was added into the reaction emulsion which contained 10 ml of oil and 10 ml of phosphate buffer solution. The phenomenon was resulted from the wettability of methyl-modified silica aerogels.

A Novel Microfluidic Approach for Monodispersed Chitosan Microspheres with Controllable Structures

A novel and simple approach to prepare monodispersed chitosan microspheres with relative small size and controlled structures was developed by combining the solidification methods of solvent extraction and chemical crosslinking in a capillary-embedded microfluidic decive. The microspheres with different structures are used in the field of protein drug controlled release and immobilization lipases and they show different release profiles and good stability, respectively.

Polyethylenimine-impregnated siliceous mesocellular foam particles as high capacity CO2 adsorbents

Siliceous mesostructured cellular foams (MCF) impregnated with polyethylenimine (PEI) of various molecular weights and structures were evaluated as CO2 adsorbents. The MCF solid support consisted of a well-defined interconnected three-dimensional mesoporous structure with large cell diameter of 30.3 nm and large window diameter of 11.3 nm, filled with polyethylenimine up to 70 weight percent or about 22.3% nitrogen atom by weight of the adsorbents. While other mesoporous solid supports lost their porosity after PEI impregnation, our MCF solid support maintained its pore volume over the range of 1.12 to 1.64 cm3 g−1. The importance of the porosity of PEI-impregnated MCF adsorbents for high capacity CO2 adsorbents was demonstrated. The highest CO2 sorption capacity (180.6 mg-CO2/g-adsorbent or 393.6 mg-CO2/g-PEI at 75 °C) was obtained for silica supports loaded with 50 weight percent branched PEI with average molecular weight of 600 g mol−1. Under dry atmospheric CO2 gas, this adsorbent reached the theoretical CO2 capacity of 0.50 mole-CO2 per mole-nitrogen within less than about 8 min, making this adsorbent one of the most effective CO2 adsorbents reported. Repeated multiple sorption cycles demonstrated good stability of this adsorbent for CO2 capture. The initial sorption kinetics determined the overall CO2 sorption capacity, which was limited by the formation of a carbamate layer as a result of the CO2–PEI complexation that due to inhibition of CO2 diffusion; the kinetics of “ionic” gelation of the impregnated PEI by CO2 controlled the overall performance of the CO2 adsorbents. At 75 °C, the operating temperature favored the molecular mobility of PEI and unrestricted diffusion of CO2 to allow the theoretical CO2 capacity of the PEI to be attained. Lower temperatures limited the mobilities of PEI and CO2 and the kinetics of “ionic” gel formation dominated, causing a lowered overall performance of the CO2 adsorbents. Overall, this study points to the importance of interconnected porous channel networks to optimize the performance of PEI-impregnated mesoporous silica particles.

Immobilization of penicillin G acylase on macro-mesoporous silica spheres

In this study, macro-mesoporous silica spheres were prepared with a micro-device and used as the support for the immobilization of penicillin G acylase (PGA). To measure the enzymatic activity, the silica spheres with immobilized PGA were placed into a packed-bed reactor, in which the hydrolysis of penicillin G was carried out. The influences of the residence time, the initial concentration of the substrate, the accumulation of the target product 6-aminopenicillanic acid, and the enzyme loading amount on the performance of the immobilized PGA were investigated. The introduction of macropores increased the enzyme loading amount and decreased the internal mass transfer resistance, and the results showed that the enzyme loading amount reached 895 mg/g (dry support), and the apparent enzymatic activity achieved up to 1033 U/g (dry support). In addition, the immobilized PGA was found to have great stability.

Controllable microfluidic production of gas-in-oil-in-water emulsions for hollow microspheres with thin polymer shells

Here we developed a simple and novel one-step approach to produce G/O/W emulsions with high gas volume fractions in a capillary microfluidic device. The thickness of the oil layer can be controlled easily by tuning the flow rates. We successfully used the G/O/W emulsions to prepared hollow microspheres with thin polymer shells.