Slab gel electrophoresis (SGE) is very common in biological experiment, but it is tedious, labor-intensive, skill-dependent, and relatively slow. Herein, we developed a compact SGE system based on a biochip. Such a system can resolve the DNA fragments while recording the DNA migration process. By electrophoresis of 50 bp DNA ladder, we found that the 16 DNA fragments could be resolved with high resolution less than 15 min. Furthermore, we have performed fast genetic diagnosis of periodontal pathogens in this compact SGE system by combining the polymerase chain reaction (PCR) technology. Experiments demonstrated that Porphyromonas gingivalis (P.g), Tannerela forsythia (T.f), and Treponema denticola (T.d) were diagnosed within short time, and the electrophoresis of P.g showed that the limit of detection of this system was about 6.4 ng/μl. Such a low cost system is easy to operate, and can greatly improve SGE efficiency in the biological experiment, especially for the labs in the third world countries.

Recent advances in additive manufacturing technologies have enabled fabrication of functional microscale devices using polymer-jet 3D printing. The class of polymer-jet printers (Stratasys, USA) offers broad range of inkjet 3D printers for various applications. In this study, we investigated the microscale features produced by the desktop, polymer-jet printer (Object30 Prime). The acrylic formulated, transparent photopolymer Veroclear is subjected for the test, and influence of the printing parameters over the feature dimensions are analysed. We found systemic deviation of the  printed microscale structures from the computer-aided design (CAD) of the structure. The deviation of the structure was explained in light of  two competing physical forces due to surface tension and gravity. Spreading of the resin and curvature formation are the two major phenomena that explains the deviation caused by the printing process. In this additive manufacturing process, the thickness of each layer is also known to affect the feature size of printed parts. The influence of layer thickness and interdependence of the design width over the printed heights are reported. Based on the observed limitation of the instrument, the suitability of the printer for producing microscale structures are discussed and some design considerations are provided.

We have been developing a compact and low-cost flow cytometry unit (Figure 1) suitable for a variety of water monitoring needs. We have been developing an integrated flow cytometry chip, which comprises a pre-treatment part and a sheath flow-forming part with a twisted microchannel structure, biological cells were successfully detected at the proposed chip [1][2]. We constructed a compact and low-cost monitoring unit with a light emitting diode (LED) based optical setup. In this presentation, we introduce the compact and low-cost flow cytometry unit and demonstrate the ability to measure the particles.

Figure 2 shows a schematic of flow cytometry chip and an image of the twisted flow cytometry chip. Figure 3 shows a photograph of the fabricated chip. The flow cytometry chip made of Polydimethylsiloxane (PDMS) and the sheath flow-forming part is twisted by 180 degrees (°). The length of the sheath flow channel was designed to be twisted by 90° at second junction and the sheath flow was formed. Figure 4 shows a schematic of the optical setup. A laser and a PMT of the conventional optical setup were changed to the LED and the optical sensor in the new setup. We assessed the detecting ability of the compact and low-cost flow cytometry unit using standard fluorescent particles.

Figure 5 shows a photograph of the compact and low-cost flow cytometry unit. The unit is a 60 mm cubic. Water including the fluorescent particles was used as the sample fluid. The flow rates of the sheath fluid and the sample fluid were set to 0.10 µl/sec and 0.017 µl/sec, respectively. The mean flow velocity at observation point is 1.3 mm/sec. Figure 6 shows the signals from particles. The signals of particles were successfully detected using the LED based optical setup.

In summary, we constructed the compact and low-cost flow cytometry unit for monitoring particles in water and the signal of particles were successfully detected.

Gecko's remarkable ability to attach and climb has attracted significant attentions for centuries. However, the nature of its fantastic climb ability ascribed to the intermolecular Van der Waals force is revealed only in recent years. A variety of biomimetic dry adhesives based on various materials have been fabricated via different methods. To achieve high adhesion, vertically aligned carbon nanotube-based dry adhesives have shown superior adhesion strength (~100 N/cm²) but their fabrication processes are typically expensive and cannot be easily controlled. On contrary, polymer-based dry adhesives can be fabricated in a simple and low-cost, yet their adhesion strength is significantly lower. The best one reported for polymer dry adhesive was less than 40 N/cm² in our survey so far. Herein, we propose a new strategy to achieve high-performance dry adhesive with high adhesion, high durability and low-cost based on polymer such as ethylene-vinyl acetate (EVA) and poly(dimethyl siloxane) (PDMS) with mushroom-shaped structures.

Figure 1 shows the EVA-based dry adhesive fabrication process obtained by soft replication. As shown in part I, mushroom-shaped Si template were obtained using deep reactive ion etching (DRIE) after patterning SiO₂ cap on Si. The fabrication complexity and cost of the initial master template can be further reduced by replacing the Si master with the dual-layer resist master, where inverse mushroom-shaped micro-cavities were fabricated in two resist layers, as shown in part II. Part III shows the fabrication of mushroom-shaped EVA dry adhesives by soft replication process. PDMS was dispensed on the as-fabricated master and cured in an oven. Afterward, the vinyl acetate ethylene emulsion was spin-coated on the PDMS mold and cured to form the EVA film. Then the film was grafted in the vapor phase to achieve hydrophobicity. Figure 2 shows typical mushroom-shaped microstructures of Si and dual-layer resist templates by a scanning electron microscope (SEM). The SiO₂ cap of the Si templates were 400 nm thick with undercut varied from 2 μm to 3 μm while the cap thickness of the dual-layer resist templates is 1.5 μm with undercut varied from 500 nm to 5 μm.

A low-force mechanical testing system was used to measure the pull-off forces of EVA and PDMS samples, illustrated in Figure 3. After applying a preload to samples to ensure full contact with the glass slide, we lifted the motorized stage with speed of 0.03 nm/s and the recorded the maximum pull-off force, which indicates the adhesion force of dry adhesive. As shown in Figure 4, the adhesion force for all samples is quite small without applied preload, while the adhesion forces of both patterned and flat dry adhesives significantly increase with applied preload, due to the increment of effective contact area. We noticed that the adhesion forces of EVA patterned samples are 10 times higher than those PDMS counterpart, and its maximum adhesion force reached up to ~ 25.0 N (~ 70.0 N/cm2) with mushroom-shaped microstructure，which is the best record for polymer dry adhesives by far, and can be further increased by optimizing geometric designs. Following our previous work on superlyophobic surfaces, mushroom-shaped EVA dry adhesives present excellent superlyophobic performances as well, as seen in Figure 5, which is suitable for self-cleaning and durable uses. In addition, their superior flexible, stretchable characteristics and low-cost, facile fabrication process shed new lights for the practical applications.

In this study, methods for fabrication of functionalized microfluidic systems using inkjet printing are presented. By surface modifications and inkjet printing, we have successfully fabricated microfluidic devices with microchannels, electrodes and droplet dispersion components. Owing to the desirable features of inkjet printing such as direct additive manufacturing, the methods presented in this paper are fast and easy to use in comparison with conventional fabrication methods.

To fabricate PDMS-based microfluidic channels, here we use a special surface modification, the superhydrophobic coating, to enhance the water-repelling property of the substrate and allow direct inkjet patterning. In this practice, The PDMS is first superhydrophobically coated using a commercially available spray. Then the pigment ink is printed and dried to form durable hydrophilic pattern for liquid template attachment. Through dispensing aqueous liquid on the substrate, liquid templates are self-shaped on the hydrophilic symbols. Finally, by molding on the liquid template, enclosed PDMS microchannels can be obtained directly. Besides the advantages such as rapidness and inexpensiveness, such technique is capable of layer-by-layer fabrication, enabling multilayer fabrication of microfluidic structures without manual alignment and bonding.

Apart from the microfluidic channels, inkjet printing is also capable of fabricating electrodes inside microchannels directly while conventional methods are not. For microelectrode patterning on PDMS substrate, a chemical reagent as the wettability and adhesion promoter was employed. (3-Mercaptopropyl) trimethoxysilane (MPTMS), a coupling agent of noble metal to Si-based materials, was used to modify the PDMS. The surface modification improves the surface wettability of PDMS, which decreases the evaporation time of the silver droplet solvent and effectively avoids the coalescence of adjacent droplets. Besides, the modification also provides a tight bonding between the silver patterns and PDMS. The resulting printed silver patterns exhibited good compactness, conductivity and excellent adhesion to PDMS. The work here was used to fabricate a three-electrode electrochemical sensor on PDMS successfully and the sensor was sealed in the microchannel of a microfluidic system, forming an integrated lab-on-a-chip biosensing system.

Beside aforementioned methods of constructing microfluidic components, we have also succeeded in fabricating droplet dispersion devices using inkjet printing. Similar to the liquid-template method of the microchannel fabrication, superhydrophobic substrate and hydrophilic inks were employed for Rayleigh instability induced droplet dispersion. Compared with previously reported droplet generation devices, the method proposed in this work is capable of pre-depositing reagents at the site of each droplet, and is able to trigger specific reactions such as recombinase polymerase amplification (RPA), leading to a simpler solution to controlled reactions. Meanwhile, this device no longer requires complicated droplet-generating structures and cumbersome peripheral devices, which makes it a perfect candidate for point-of-care testing (POCT)

In conclusion, we have fabricated multiple microfluidic devices with inkjet printing technique. The fabrication for a fully inkjet-printed functionalized microfluidic system is still ongoing and the results will be presented on the conference.

Microfluidics is a multidisciplinary technology which enables the face-lift crossing a wide range of applications such as life science research, point-of-care diagnostics and personal medicine. Polymer materials, especially thermoplastics, are dominating this emerging market due to the low material cost and the ease of mass production. This talk reports the new development of major fabrication technologies for making polymer, especially thermoplastic microfluidic chips, including micro tooling, injection molding, bonding and surface treatment. The talk also discusses about the key challenges in fulfilling the needs of next generation microfluidic products.

An improved fabrication process for realization of vertical comb capacitors is proposed, which can suppress the lateral etching problem in the normal silicon-on-glass process due to the heat conduction problem during the over etching. An out-of-plane electrostatic actuator with in-situ position sensing comb capacitors was fabricated to verify the feasibility of the proposed process. The total range of the open-loop static actuation is measured to be 13μm with the maximum actuation voltage of 32 volts.

We describe a process to fabricate simple (2D, planar) and complex (3D, non-planar) microfluidic devices using molds consisting of polyvinyl alcohol (PVA) fabricated with fused deposition modeling (FDM) 3D printer. Our approach successfully created leak-free, closed microfluidic devices in various commercial polymers, which are both photo and heat curable. The fabrication process requires only water to remove the sacrificial mold, and fabrication of microfluidic hydrogels are easily demonstrated. The approach we describe here offers a rapid and simple route to create channels with complex three-dimensional architecture.

Figure. 1 describes the schematics of the steps required in the sacrificial molding. Figure. 2 shows that sacrificial molding of FDM 3D printed microfluidic mold is suitable for use with hard polymers such as rigid polyurethane, epoxy, and thiolene-based polymers. It is also compatible for use with soft polymers like flexible polyurethane and PDMS. Water-soluble FDM 3D printed PVA mold was stable in hydrogels like TG gelatin and PEGDA. To demonstrate the versatility of the technique, we fabricated and demonstrated application of 3D staggered herringbone based chaotic mixers (Figure. 3) and modular perfusion grid of interconnected microchannels (Figure. 4).

At present, the capability to directly fabricate closed microfluidic channel, 3D microfluidic design or 3D design with undercut structures may be achieved by stereolithography1 and a combination of laminated object manufacturing and soft lithography2. Although recently, FDM was also used to produce entire reaction-wares incorporating fluidic circuit by printing polypropylene3. Alternatively, other methods may be employed albeit with additional assembly steps to achieve such feat. Even so, 3D microfluidic geometry is still difficult to achieve with these printing techniques.

The versatility of fabrication of FDM printed microchannels by sacrificial molding can be useful in fabricating microchannels in soft, biomimetic matrixes (e.g. hydrogels). In addition, the wide selection of the various polymers for the materials of the channels encourages opportunities to build chemically resistant microchannels to support relevant applications.

Microfluidics has been developing for two decades, and most of the microfluidic applications were developed on flat microfluidic platforms. In this study, we used a 3-axis micromilling machine, which was commonly used in many laboratories and factories, to manufacture adjustable microlens on three-dimensional substrates. From the experiments, it is clear that several factors were critical to the quality of the micro features on the three-dimensional substrate, including the plan of the cutting path, the profile of the cutting tool, and the depth of cut. After carefully planning the cutting path with UG software and accumulating experience, we could successfully manufacture precise micro features on a three-dimensional polymeric substrate, which could be bonded with another piece of polymeric substrate by solvent bonding or used as a mold insert to fabricate micro features on the PDMS substrates by PDMS casting technique. To clearly demonstrate this fabrication process, we designed and fabricated an PDMS-based adjustable microlens on semi-sphere PMMA substrate and red food dye was used to show there had no leakage after bonding.

Photonic materials were originated from the inspiration of the nature, such as the feather of peacock, the wing of butterfly and the skin of chameleon. Due to their special optical properties, photonic materials have been wisely explored in various research fields like communication, sensors and display devices. Here, we would like to present our recent research on responsive photonic crystals, including bio-inspired fabrications, biosensing and display devices. By incorporating stimuli-responsive polymers into photonic crystals, the resulting responsive photonic crystals can be used for biosensing, displays and photonic paper. Based on this progress, we believe responsive photonic crystals will find great practical applications, such as wearable device, portable detecting device and information storage.