A room temperature liquid metal based electroosmotic flow (EOF) pump has been proposed in this work. This low-cost EOF pump is convenient for both fabrication and integration. It utilizes polydimethylsiloxane (PDMS) microchannels filled with the liquid-metal as non-contact pump electrodes. The electrode channels are fabricated symmetrically to both sides of the pumping channel, having no contact with the pumping channel. To test the pumping performance of the EOF pump, the mean flow velocities of the fluid (DI water) in the EOF pumps were experimentally measured by tracing the fluorescent microparticles in the flow. To provide guidance for designing a low voltage EOF pump, parametric studies on dimensions of the electrode and pumping channels were performed in this work. According to the experimental results, the pumping speed can reach 5.93 μm s(-1) at a driving voltage of only 1.6 V, when the gap between the electrode and the pumping channel is 20 μm. Injecting a room temperature liquid metal into microchannels can provide a simple, rapid, low-cost but accurately self-aligned way to fabricate microelectrodes for EOF pumps, which is a promising method to achieve the miniaturization and integration of the EOF pump in microfluidic systems. The non-contact liquid electrodes have no influence on the fluid in the pumping channel when pumping, reducing Joule heat generation and preventing gas bubble formation at the surface of electrodes. The pump has great potential to drive a wide range of fluids, such as drug reagents, cell suspensions and biological macromolecule solutions.

A novel nanomagnesium hydroxide powder and three kinds of micro-Mg(OH) 2 , with different particle sizes, were chosen as fillers and mixed with ethylene-propylene-diene monomer rubber (EPDM) to form a series of composites by a traditional rubber-processing technique. The results showed that the mechanical properties of composites improved with decreasing particle size. The nanocomposites were far stronger than the microcomposites, which also supported the view that rubber reinforcement requires nanoreinforcement. The effect of particle size on the fire resistance of composites was investigated by cone calorimetry and limiting oxygen index analysis, which showed that the particle size of powder had an impact on the fire resistance of composites. For the composites filled with untreated powder, the peak value of heat release rate decreased and T ign increased with decreasing particle size. In conclusion, the fire resistance of nanocomposites was better than that of microcomposites. Surface modification of particles sometimes substantially improved the mechanical properties of nanocomposites, but had no effect on either the mechanical properties of microcomposites or the fire resistance of nanocomposites and flame retardance.

In the last few years, a new type of glucose-sensitive hydrogel (GSH) has been developed that shrinks with increasing glucose concentration due to the formation of reversible crosslinks The first osmotic swelling pressure results measured for any member of this new class of GSH are reported, so that their suitability for use in sensors combining pressure transducers and smart gels can be evaluated. Comparison is also made with results obtained for an older type of GSH that expands with increasing glucose concentration due to an increase in the concentration of counterions within the gel. The newer type of GSH exhibits both faster kinetics and weaker fructose interference, and therefore is more suitable for in vivo glucose sensing.

We investigate thin films of "smart" polymer hydrogels used to convert miniature pressure sensors into novel chemomechanical sensors. In this versatile sensing approach, a smart hydrogel is confined between a porous membrane and the diaphragm of a piezoresistive pressure transducer. An increase in the environmental analyte concentration, as sensed through the pores of the membrane, is detected by measuring the change in pressure exerted by the hydrogel on the pressure transducer diaphragm. We compare the response of such a sensor with the response of a free-swelling hydrogel identical to the one used within the sensor. The sensor and the free hydrogel are observed to have comparable mean response times. However, the time-dependent response curve of the sensor, unlike that of the free hydrogel, is highly asymmetric between swelling and deswelling, with a smaller time constant for deswelling. We also investigate novel methods for increasing sensor sensitivity, such as use of a two-layer membrane with a nanoporous polymer inner layer, and pre-loading of the hydrogel under pressure. In ionic strength response tests, use of an inner membrane increases sensor sensitivity without increasing mean response time, an effect that varies with membrane water fraction.

No abstract

We report new injectable and thermosensitive hydrogels from polycaprolactone-graft-polyethylene glycol (PCL-g-PEG). The PCL-g-PEG polymer aqueous solution was injectable and formed a physical hydrogel at human body temperature. The rheological properties, sol-gel transition mechanisms, and in vitro degradation properties of PCL-g-PEG hydrogels were investigated. Rheological results demonstrate that hydrogels with tunable storage moduli (G 0 ) that span four orders of magnitude, from 0.2 to 5500 Pa, can be obtained by varying polymer concentrations. Hydrophobic dye solubilization, dynamic light scattering, and X-ray diffraction results suggest that micelle aggregation and partial crystallization of the polycaprolactone segment lead to the sol-gel transition with increasing temperature. The degradation of PCL-g-PEG hydrogels was slow in the absence of the enzyme lipase, but can be substantially increased by lipase in a concentration-dependent manner. The PCL-g-PEG hydrogel has a low critical gelation concentration, high storage modulus, and easily handled solid morphology, representing great advantages over our previously developed structurally analogous PLGA-g-PEG. The results presented showcase the potential biomedical application of the versatile PCL-g-PEG hydrogels.

In this work, direct patterning of polydimethylsiloxane (PDMS) is demonstrated by the addition of a UV-sensitive photoinitiator benzophenone. As an improvement to our previous work, patterns with both positive and negative features have been fabricated on the same substrate. Infrared spectroscopy was used to investigate photocrosslinking behavior and reaction chemistry of this new photodefinable PDMS (photoPDMS) material. Several applications of the photoPDMS process have been successfully demonstrated. Multi-layer structures and multi-level microfluidic chips can be easily fabricated using this photopatterning process. Patterned PDMS thin films can also be removed from the underlying substrates and used as shadow masks for defining patterns on both planar and non-planar surfaces. The photopatternable PDMS was also found to be biocompatible once un-reacted benzophenone is extracted from the cured film. Overall, photoPDMS offers a number of critical advantages over conventional PDMS processing, including elimination of master template fabrication, ability to process under ambient light processing conditions, positive-acting tone, low cost, and rapid and easy fabrication.

We have developed a new ice valve to close or open liquid flow in a mini/micro channel. Unlike the traditionally used valve, no moving elements are needed in this normally open system. By freezing the working fluid running inside the channel using a thermoelectric cooling device (TECD), the flow can be blocked due to ice formation. If switching the TECD to heating, the frozen liquid becomes thawed and flow in the channel resumes its running state again. Several experiments were carried out to characterize the working performance of the ice valve for a micro tube. A theoretical model was established to analyze the time response constant of the ice valve. Without any leakage, being very clean, and easily controllable through electricity, this ice valve may find significant applications in microfluidics or nanofluidics.