•A comblike time-valve which comprises of a number of parallel comblike protrusions and interval channels is presented.•The time that the liquid takes to pass through the valve can be readily controlled by changing the number of the comblike protrusions.•The valve can delay the liquid flow from several tens of seconds to several minutes•This valve has a simple structure with a minimal line-width above 100 μm.Capillary-driven microfluidic devices can provide rapid on-site diagnostic results. It has gained more concerns over the years. Time-valve, which can provide enough reaction time for the target ligand and the test reagent, is an important module in the device. Traditional microfluidic valves usually have complicated and small line-width structures, which may limit their use in the mass production of the devices. Here, a comblike time-valve is presented. The valve comprises of a number of parallel comblike protrusions and interval channels. The time that the liquid takes to pass through the valve can be readily controlled by changing the number of the comblike protrusions. The effects of the valve's size parameters on flow time control have been studied. Results show that the valve can delay the liquid flow from several tens of seconds to several minutes, which will provide an accurate time control for the reaction between the target ligand and the test reagents. This time-valve has a simple structure with a minimal line-width above 100 μm. It can be readily fabricated and integrated onto a capillary-driven microfluidic device for mass production and quantitative diagnostics.Download high-res image (214KB)Download full-size image

The traversal rate for the liquid medium near a microfluidic channel edge is faster than that through the body of the channel, which makes the fluid front becomes concave rather than convex or flat. The concave front is unwished due to its influences on quantitative analysis accuracy and the possibility to generate air bubbles which will do harm to analysis process. Here, a method which can control the shape of fluid front in a microfluidic channel is presented. The channel edges that are parallel to the direction of flow are designed to three types of serrated shapes, including semicircle, triangle and trapezoid. The effects of their length ratio (r), peak distance (w) and phase mode (p) on meniscus curvature and flowing speed have been studied. Results have shown that the channel with serrated edges can generate convex fluid front, and the curvature of the fluid front as well as the flowing speed can be changed by adjusting r, w and p.

The leaf venation is considered to be an optimal transportation system with the mesophyll cells being divided by minor veins into small regions named areoles. The transpiration of water in different regions of a leaf fluctuates over time making the transportation of water in veins fluctuate as well. However, because of the existence of multiple paths provided by the leaf venation network and the pits on the walls of the vessels, the pressure field and nutrient concentration in the areoles that the mesophyll cells live in are almost uniform. Therefore, inspired by such structures, a microfluidic design of a novel cell culture chamber has been proposed to obtain a stable and uniform microenvironment. The device consists of a novel microchannel system imitating the vessels in the leaf venation to transport the culture medium, a cell culture chamber imitating the areole and microgaps imitating the pits. The effects of the areole and pit on flow fields in the cell culture chamber have been discussed. The results indicate that the bio-inspired microfluidic device is a robust platform to provide an in vivo like fluidic microenvironment.

In this paper, we present a new approach that is capable of fabricating nanochannels in a poly(methyl methacrylate) (PMMA) substrate. This method, which we call microchannel refill (MR), utilizes the refilling of glassy thermoplastics under thermal compression to reduce a microscopic channel to a nanochannel. It only has two main steps. First, a microchannel is fabricated in a PMMA substrate using normal hot embossing. Second, the microchannel is compressed under a certain temperature and pressure to obtain a nanochannel. We show that a nanochannel with a width as small as 132 nm (with a depth of 85 nm) can be easily produced by choosing the appropriate compression temperature, compression pressure, original microchannel width and original microchannel aspect ratio. Compared with most current nanochannel fabrication methods, MR is a quick, simple and cost-effective way to produce nanochannels in polymer substrates.

“Reservoir unsealed” and “boundary layer separation” are two main issues in the fabrication of a multilayer poly(methyl methacrylate) (PMMA) microfluidic chip. In this paper, embedded sacrificial layer bonding (ESLB) and laser edge welding (LEW) are presented to avoid them. ESLB is performed by inserting a sacrificial-layer into a reservoir to enhance the transfer of bonding pressure among different layers. LEW is performed by using CO2 laser to weld the edge of a bonded multilayer chip. By using these two methods, a three-layer microchip and a five layer micro-mixer are fabricated. Our results demonstrated that ESLB and LEW can be implemented readily in the fabrication of a multilayer thermoplastic microfluidic chip which may facilitate the development of sophisticated microfluidic systems.

To set up a point-of-care whole-blood immunoassay system, sample preparation and on-chip storage of conjugate reagents are indispensable functional units. Here, we merge these functions into a deposited microbead plug (DMBP) to simultaneously play the roles of a blood filter and a conjugate reagent carrier. The DMBP was easily fabricated by the use of natural deposition of beads without the need of weirs. Conjugate reagents (FITC labeled antibodies used here) were incorporated into the DMBP during the assembly of the DMBP. To demonstrate the ability of the DMBP, we constructed a DMBP-based microfluidic chip and used it for the detection of human IgG (hIgG). The DMBP enabled to remove blood cells from whole blood and provide the pure plasma for the downstream on-chip immunoreactions. The release of reconstituted FITC labeled antibodies from the DMBP was controlled in a passive fashion. Dry FITC labeled antibodies retained at least 81% of their activity after 60 days of storage at the room temperature. The DMBP presented here makes an important step towards the development of the self-contained, integrated, sample-to-answer microfluidic chips for point-of-care diagnostics.Highlights► A DMBP with the dual roles: a blood filter and a conjugate reagent carrier. ► DMBP is fabricated by the use of natural deposition of beads. ► Conjugate reagents are incorporated during the assembly of the DMBP. ► Dry conjugate reagents enable to be released from the DMBP in a controlled manner. ► Their activities are retained after 60 days of storage at the room temperature.

We present a deposited microbead plug (DMBP)-based microfluidic chip capable of performing plasma extraction and on-chip immunoassay. The DMBP used as a porous blood filter provides pure blood plasma without the contamination of blood cells or beads. Capillary-driven flow eliminates the requirement of external pumps. The human IgG and goat anti-human IgG sample-to-answer assay was performed in this chip within 600 s using only a 10 μl whole-blood sample. This easy-to-use, rapid, inexpensive, and disposable DMBP-based chip holds a great promise for point-of-care application.

We presented a deposited microbead plug (DMBP)-based microfluidic device capable of extracting plasma from whole blood by capillary forces. This device was fabricated by reversibly bonding a PDMS slab with a straight channel to a hydrophilic glass substrate. The DMBP was easily constructed at the inlet of the channel within 2 min by a method of natural deposition of microbeads without the need of weirs or photopolymerization. Capillary forces generated mainly on the hydrophilic glass substrate provided a driving force during the fabrication of the DMBP and plasma extraction, resulting in simplicity of operations. The DMBP only allows blood plasma to pass through but blocks blood cells, which was demonstrated experimentally using sheep blood. The DMBP enabled to remain in its initial configuration during plasma extraction. The high quality plasma was obtained without contamination of microbeads and blood cells. This easy-to-use, easy-to-integrate, disposable the DMBP-based microfluidic device has the potential to be integrated with on-chip bioanalytical units for the applications of point-of-care diagnostics.

Stomatal transpiration, which is an efficient way to carry water from the roots up to the leaves, can be described by “diameter-law”. According to the law, the flow rate induced by micropore transpiration far exceeded that induced by macroscale evaporation, and it can be controlled by opening (or closing) some micropores. In this research, a bio-inspired micropump based on stomatal transpiration is presented. The micropump is composed of three layers: the top layer is a 93 μm-thick PVC (polyvinylchloride) film with a group of slit-like micropores; the second layer is a PMMA sheet with adhesives to join the other two layers together; the third layer is a microporous membrane. Using this pump, controllable flow rates of 0.13–3.74 μl min−1 can be obtained. This micropump features high and adjustable flow-rates, simple structure and low fabrication cost. It can be used as a “plug and play” fluid-driven unit without any external power sources and equipment.

Compression pressure has significant influence on the performance of direct methanol fuel cell (DMFC) and the effect of compression is more significant for a DMFC than a proton exchange membrane fuel cell (PEMFC). But there are few data concerning the compression pressure on the performance of DMFCs. Loading history and feeding mode may also affect the optimal compression pressure for the DMFC. This paper investigates the influence of compression pressure on the DMFC. The effects of reload and air feeding mode are also examined. The optimal pressure of the DMFC is 1 MPa when the cell is assembled for the first time in forced convection mode. However, the optimum pressure decreases to 0.05 MPa when the cell is compressed again because of the residual strain of the GDL. The optimal pressure decreases to 0.5 MPa when the cell operates in air-breathing mode. Therefore, the optimum compression pressure for a DMFC strongly depends on the loading history and the feeding mode.

In land plants, water vapor diffuses into the air through the stomata. The loss of water vapor creates a water potential difference between the leaf and the soil, which draws the water upward. Quantitatively, the water potential difference is 1–2 MPa which can support a water column of 100–200 m. Here we present the design and operation of a biomimetic micropump. The micropump is mainly composed of a 48-μm thick metal screen plate with a group of 102-μm diameter micropores and an agarose gel sheet with nanopores of 100 nm diameter. The micropores in the screen plate imitate the stomata to regulate the flow rate of the micropump. The agarose gel sheet is used to imitate the mesophyll cells around the stomata. The lost of water from the nanopores in the gel sheet can generate a water potential difference (more than 30 kPa) which can drive solution flow in a microfluidic chip. Results have shown that a precise flow rate of 4–8 nl/min can be obtained by using this micropump, and its ultra-high flow rate is 113–126 nl/min. The advantages of this biomimetic micropump include adjustable flow rate, simple structure and low fabrication cost. It can be used as a “plug and play” fluid-driven unit in microfluidic chips without any external power sources or equipments.

In this study, we used a glass mold coated with TiN layer to fabricate submicron and nano-gratings on a PMMA (polymethylmethacrylate) film. The cavities on the mold, with sizes varying from 71 nm to 980 nm, was etched by ion beam. The deformation and filling modes of polymer during fabrication process were studied. Dual-peak deformations, which were considered as the characteristic filling modes of “viscous-dominant” polymer, were observed. Because our fabrication experiments were conducted near the glass transition temperature (Tg) of PMMA at which the polymer was “elastic–plastic-dominant”, the appearance of the dual-peak filling mode meant solid-state polymer might exhibit some characters of fluidic polymer at submicron and nano-scale. In addition, we presented a simple and effective mold release process at the end of this paper, which could reduce defects during molding release process.

With the dimensional reduction of micro-structure, the surface effects greatly influence the dimension precision and surface quality of micro-structure during micro-processing of thermoplastic materials. In this paper, the surface characteristics of several thermoplastic materials usually used in industry are investigated. The Axisymmetric Drop Shape Analysis (ADSA) method in nitrogen gas (N2) environment is adopted to measure the surface tensions of polymethylmethacrylate (PMMA), polystyrene (PS), polypropylene (PP), high-density polyethylene (HDPE) melt under different temperatures. The theoretical relationships between surface tension and temperature of polymer melts are obtained. The comparisons are made among different polymer melts according to the relationship of molecular dynamics. The static contact angles between polymer melts (PMMA, PS) and mold materials (silicon, nickel) under different temperatures are also measured in N2 environment using the ADSA method. The results indicate that the contact angle decreases with the increase of temperature and/or the increase surface energy of the mold material. This study provides relevant data to support for micro-injection molding and to optimize processing parameters.

Direct methanol fuel cell (DMFC), with benefits such as high energy efficiency, quick start capability and instantaneous refueling, is a promising power source to meet the ever-increasing power demand for portable electronic products. In this paper, a novel CO2-driven fuel-feed device was produced and equipped in a passive 8-cell DMFC twin-stack for long-term operation. It was shown that this fuel-feed device was capable of supplying methanol solution continuously in response to the change in discharging current of the stack. Stainless steel sheet was photochemically etched as current collectors based on MEMS techniques. Series interconnections between two neighbor cells were realized in banded configuration which avoided the external connection. TiN-plated mesh was placed between current collector and membrane electrode assembly (MEA), which was used to lessen the internal resistance of the stack. A peak power density of 16.9 mW cm−2 was achieved with 4 M methanol at ambient temperature and passive operation. The stack equipped with the fuel feed device successfully powered a sensor node for 39 h with the consumption of 80 ml of 4 M methanol.

CO2 laser is a quick and cheap method for the fabrication of microfluidic chip. However, bulges will form at the rim of the laser ablation zone due to the thermal stress induced by great temperature gradient. The bulges will result in bonding problems, microchannels clogging and electrophoresis sample leak. The method to eliminate the bulges still requires further investigation. In this paper, the formation process of the bulges was recorded synchronously. The relationship between laser fabrication parameters and the height of bulge was established. The effects of the extruding direction of the plate on the forming of the bulge were evaluated. A simple method of “two times of laser cutting” is presented to eliminate the bulges. Results showed that the laser fabrication parameters, such as output power of laser beam and laser beam moving speed, have significant influence on the forming of bulge. The height of bulge also has relationship with the extruding direction of the commercial plate. The method of two times of laser cutting is an effective and simple way to eliminate the bulges.

The emphasis of this paper lies in the fabrications of an eight-layer chip for liquid mixing and a seven-layer chip for liquid sample dilution. In this paper, the microchannels, fabricated by CO2 laser, constructed three-dimensional serpentine channel networks for liquid sample operation. The eight-layer mixing chip used the “F”-shape mixing units to achieve splitting and recombination mixing. Furthermore, mixing was enhanced by chaotic flow induced by three-dimensional serpentine channel path. The seven-layer dilution chip created eight diluted fluid streams mixed in same volumetric proportions. Prior to thermal bonding, the polymethylmethacrylate (PMMA) substrates were treated by oxygen plasma to improve their surface properties. The increased surface properties served to reduce thermal bonding temperature and pressure, which minimized the deformation of microchannel. The mixing and diluting experiments showed high levels of mixing and diluting performances were obtained with the chips.

Thermal bonding is an important technique to fabricate polymer electrophoresis microchip. However, the metal electrodes deposited on polymer substrate can readily fracture during the thermal bonding. In this paper, poly(ethylene terephthalate) (PET) was exploited to fabricate the electrophoresis microchip with an integrated gold electrode for amperometric detection. The fracture of the gold electrode was studied through FEA (finite element analysis) simulations, the potentially risk positions on the electrode were shown. The calculation results were tested by bonding experiments and were proven to be consistent with the experiments. Besides, an optimal bonding temperature for PET chip was also presented based on FEA simulations and bonding experiments. Considering the low surface properties of PET, oxygen plasma-assisted thermal bonding technique was used to enhance bonding. Upon treated for 150 s, the PET substrates could be thermally bonded at 62 °C without electrode fracture. The fabricated PET chips were demonstrated for detection of standard glucose solution. Satisfactory reproducibility was achieved, and the RSD values of peak height and migration time of the PET CE chips were 0.51% and 2.17%, respectively.

To investigate the basic mechanism of hot embossing, a series of experiments were conducted by using male die with micro-features. With online and outline methods, the polymer flow behavior during microembossing was observed. A hot embossing method without vacuum to achieve high replication accuracy was presented. Orthogonal experiment was used to establish the relationship between hot embossing conditions and replication accuracy. The results of the present work implied that during hot embossing cycle, the increasing temperature and pressure stage will determine the replication accuracy of microchannel in depth, and the replication accuracy of width and shape was determined by maintaining temperature and pressure stage. The replication accuracy depends strongly on the processing conditions. By using new hot embossing method, the replication accuracy has reached about 99%.