Xiuqing Gong

Microfluidic Fabrication of Porous Polymer Microspheres: Dual Reactions in Single Droplets

We report the microfluidic fabrication of macroporous polymer microspheres via the simultaneous reactions within single droplets, induced by UV irradiation. The aqueous phase of the reaction is the decomposition of H(2)O(2) to yield oxygen, whereas the organic phase is the polymerization of NOA 61, ethylene glycol dimethacrylate (EGDMA), and tri(propylene glycol) diacrylate (TPGDA) precursors. We first used a liquid polymer precursor to encapsulate a multiple number of magnetic Fe(3)O(4) colloidal suspension (MCS) droplets in a core-shell structure, for the purpose of studying the number of such encapsulated droplets that can be reliably controlled through the variation of flow rates. It was found that the formation of one shell with one, two, three, or more encapsulated droplets is possible. Subsequently, the H(2)O(2) solution was encapsulated in the same way, after which we investigated its decomposition under UV irradiation, which simultaneously induces the polymerization of the encapsulating shell. Because the H(2)O(2) decomposition leads to the release of oxygen, porous microspheres were obtained from a combined H(2)O(2) decomposition/polymer precursor polymerization reaction. The multiplicity of the initially encapsulated H(2)O(2) droplets ensures the homogeneous distribution of the pores. The pores inside the micrometer-sized spheres range from several micrometers to tens of micrometers, and the maximum internal void volume fraction can attain 70%, similar to that of high polymerized high internal phase emulsion (polyHIPE).

Polydimethylsiloxane-based conducting composites and their applications in microfluidic chip fabrication.

This paper reviews the design and fabrication of polydimethylsiloxane (PDMS)-based conducting composites and their applications in microfluidic chip fabrication. Owing to their good electrical conductivity and rubberlike elastic characteristics, these composites can be used variously in soft-touch electronic packaging, planar and three-dimensional electronic circuits, and in-chip electrodes. Several microfluidic components fabricated with PDMS-based composites have been introduced, including a microfluidic mixer, a microheater, a micropump, a microdroplet controller, as well as an all-in-one microfluidic chip.

Manipulation of microfluidic droplets by electrorheological fluid

Microfluidics, especially droplet microfluidics, attracts more and more researchers from diverse fields, because it requires fewer materials and less time, produces less waste and has the potential of highly integrated and computer‐controlled reaction processes for chemistry and biology. Electrorheological fluid, especially giant electrorheological fluid (GERF), which is considered as a kind of smart material, has been applied to the microfluidic systems to achieve active and precise control of fluid by electrical signal. In this review article, we will introduce recent results of microfluidic droplet manipulation, GERF and some pertinent achievements by introducing GERF into microfluidic system: digital generation, manipulation of “smart droplets” and droplet manipulation by GERF. Once it is combined with real‐time detection, integrated chip with multiple functions can be realized.

Polydimethylsiloxane-integratable micropressure sensor for microfluidic chips.

A novel microfluidic pressure sensor which can be fully integrated into polydimethylsiloxane (PDMS) is reported. The sensor produces electrical signals directly. We integrated PDMS-based conductive composites into a 30 mum thick membrane and bonded it to the microchannel side wall. The response time of the sensor is approximately 100 ms and can work within a pressure range as wide as 0-100 kPa. The resolution of this micropressure sensor is generally 0.1 kPa but can be increased to 0.01 kPa at high pressures as a result of the quadratic relationship between resistance and pressure. The PDMS-based nature of the sensor ensures its perfect bonding with PDMS chips, and the standard photolithographic process of the sensor allows one-time fabrication of three dimensional structures or even microsensor arrays. The theoretical calculations are in good agreement with experimental observations.

Logic control of microfluidics with smart colloid

We report the successful realization of a microfluidic chip with switching and corresponding inverting functionalities. The chips are identical logic control components incorporating a type of smart colloid, giant electrorheological fluid (GERF), which possesses reversible characteristics via a liquid-solid phase transition under external electric field. Two pairs of electrodes embedded on the sides of two microfluidic channels serve as signal input and output, respectively. One, located in the GERF micro-channel is used to control the flow status of GERF, while another one in the ither micro-fluidic channel is used to detect the signal generated with a passing-by droplet (defined as a signal droplet). Switching of the GERF from the suspended state (off-state) to the flowing state (on-state) or vice versa in the micro-channel is controlled by the appearance of signal droplets whenever they pass through the detection electrode. The output on-off signals can be easily demonstrated, clearly matching with GERF flow status. Our results show that such a logic switch is also a logic IF gate, while its inverter functions as a NOT gate.

A simple method of fabricating mask-free microfluidic devices for biological analysis

We report a simple, low-cost, rapid, and mask-free method to fabricate two-dimensional (2D) and three-dimensional (3D) microfluidic chip for biological analysis researches. In this fabrication process, a laser system is used to cut through paper to form intricate patterns and differently configured channels for specific purposes. Bonded with cyanoacrylate-based resin, the prepared paper sheet is sandwiched between glass slides (hydrophilic) or polymer-based plates (hydrophobic) to obtain a multilayer structure. In order to examine the chips biocompatibility and applicability, protein concentration was measured while DNA capillary electrophoresis was carried out, and both of them show positive results. With the utilization of direct laser cutting and one-step gas-sacrificing techniques, the whole fabrication processes for complicated 2D and 3D microfluidic devices are shorten into several minutes which make it a good alternative of poly(dimethylsiloxane) microfluidic chips used in biological analysis researches.

Copolymer solution-based “smart window”

The authors report the design of a prototype smart window based on the phenomenon of the thermally induced aggregation of triblock copolymer poly (ethylene oxide)–poly (propylene oxide)–poly (ethylene oxide) (EPE). Fluorescein isothiocyanate was used to label EPE and study aggregation phenomenon at different temperatures. The cloud point could be tuned by mixing EPE with sodium dodecyl sulfate (SDS) and varying the concentration of the latter. The light transmittance at different temperatures was studied as a function of SDS concentration.

Giant electrorheological fluid comprising nanoparticles: Carbon nanotube composite

We have fabricated suspensions exhibiting the giant electrorheological (GER) effect comprising nanoparticles—multiwall carbon nanotubes (MCNTs) composite particles dispersed in silicone oil. This type of GER fluids display dramatically enhanced antisedimentation characteristic without sacrificing the yield stress. The nanoparticles-nanotubes composites were fabricated by modifying the coprecipitation method with MCNTs and urea-coated barium titanyl-oxylate (BTRU) nanoparticles as the components. The composite solid particles are denoted MCNT-BTRU. In the best cases, stabilized suspensions with MCNT-BTRU particles dispersed in silicone oil have been maintained for several months without any appreciable sedimentation being observed. Both the sedimentary and rheological properties of the MCNT-BTRU suspension were systematically studied and compared with their BTRU counterparts. Yield stress as high as 194 kPa was obtained in the MCNT-BTRU suspensions. The MCNT-BTRU based GER fluids, with their antisedimentat...

Synthesis of Biomaterials Utilizing Microfluidic Technology

Recently, microfluidic technologies have attracted an enormous amount of interest as potential new tools for a large range of applications including materials synthesis, chemical and biological detection, drug delivery and screening, point-of-care diagnostics, and in-the-field analysis. Their ability to handle extremely small volumes of fluids is accompanied by additional benefits, most notably, rapid and efficient mass and heat transfer. In addition, reactions performed within microfluidic systems are highly controlled, meaning that many advanced materials, with uniform and bespoke properties, can be synthesized in a direct and rapid manner. In this review, we discuss the utility of microfluidic systems in the synthesis of materials for a variety of biological applications. Such materials include microparticles or microcapsules for drug delivery, nanoscale materials for medicine or cellular assays, and micro- or nanofibers for tissue engineering.