M.J. Kang

Randomized multicentre trial comparing external and internal pancreatic stenting during pancreaticoduodenectomy.

There is no consensus on the best method of preventing postoperative pancreatic fistula (POPF) after pancreaticoduodenectomy (PD). This multicentre, parallel group, randomized equivalence trial investigated the effect of two ways of pancreatic stenting after PD on the rate of POPF.

Portal vein patency after pancreatoduodenectomy for periampullary cancer.

The fate of the portal vein (PV) after pancreatoduodenectomy, especially its long‐term patency and associated complications, has received little attention. The aim of this study was to explore the long‐term patency rate of the PV after pancreatoduodenectomy, focusing on risk factors for PV stenosis/occlusion and associated complications.

Capillarity Guided Patterning of Microliquids

Soft lithography and other techniques have been developed to investigate biological and chemical phenomena as an alternative to photolithography-based patterning methods that have compatibility problems. Here, a simple approach for nonlithographic patterning of liquids and gels inside microchannels is described. Using a design that incorporates strategically placed microstructures inside the channel, microliquids or gels can be spontaneously trapped and patterned when the channel is drained. The ability to form microscale patterns inside microfluidic channels using simple fluid drain motion offers many advantages. This method is geometrically analyzed based on hydrodynamics and verified with simulation and experiments. Various materials (i.e., water, hydrogels, and other liquids) are successfully patterned with complex shapes that are isolated from each other. Multiple cell types are patterned within the gels. Capillarity guided patterning (CGP) is fast, simple, and robust. It is not limited by pattern shape, size, cell type, and material. In a simple three-step process, a 3D cancer model that mimics cell-cell and cell-extracellular matrix interactions is engineered. The simplicity and robustness of the CGP will be attractive for developing novel in vitro models of organ-on-a-chip and other biological experimental platforms amenable to long-term observation of dynamic events using advanced imaging and analytical techniques.

Live cell imaging compatible immobilization of Chlamydomonas reinhardtii in microfluidic platform for biodiesel research

This paper describes a novel surface immobilization method for live‐cell imaging of Chlamydomonas reinhardtii for continuous monitoring of lipid droplet accumulation. Microfluidics allows high‐throughput manipulation and analysis of single cells in precisely controlled microenvironment. Fluorescence imaging based quantitative measurement of lipid droplet accumulation in microalgae had been difficult due to their intrinsic motile behavior. We present a simple surface immobilization method using gelatin coating as the “biological glue.” We take advantage of hydroxyproline (Hyp)‐based non‐covalent interaction between gelatin and the outer cell wall of microalgae to anchor the cells inside the microfluidic device. We have continuously monitored single microalgal cells for up to 6 days. The immobilized microalgae remain viable (viability was comparable to bulk suspension cultured controls). When exposed to wall shear stress, most of the cells remain attached up to 0.1 dyne/cm2. Surface immobilization allowed high‐resolution, live‐cell imaging of mitotic process in real time‐which followed previously reported stages in mitosis of suspension cultured cells. Use of gelatin coated microfluidics devices can result in better methods for microalgae strain screening and culture condition optimization that will help microalgal biodiesel become more economically viable. Biotechnol. Bioeng. 2015;112: 494–501.

Fabrication of functional 3D multi-level microstructures on transparent substrates by one step back-side UV photolithography

This paper describes simple photolithography-based methods to fabricate multi-level three-dimensional (3D) microstructures without repeated processes using flexible and transparent film substrates such as polyethylene terephthalate (PET). When using a thin transparent film substrate, propagation of UV can be assumed to be near-field diffraction where wave property is more dominant than particle property. Using this phenomena, we patterned multi-level 3D SU-8 microstructures such as master molds for microfluidic neuron culture devices. PET film is compatible with SU-8 photoresist processing steps and exhibited good adhesion with patterned structures that were stable for more than 50 replica moldings. Advantages of the suggested method using PET are (1) simplified and faster fabrication of 3D structures with tunable thickness, (2) no requirement for mask alignment and repeated processes in fabricating multilayer structure, and (3) economical process with substrates that are ∼1000 times cheaper than Si wafers. To use PET based molds for soft lithography, we have designed an isothermal curing jig for replica molding with PDMS. Use of the PET substrate combined with back-side exposure can dramatically reduce fabrication time and cost. We believe that PET films can replace expensive Si based wafers for soft lithography master fabrication. Furthermore, they can be applied to the fabrication of microfluidic devices and complex multi-level high aspect ratio structures as an alternative to conventional photolithography.

PDMS microchannel surface modification with teflon for algal lipid research

This paper presents a simple method for modifying the polydimethylsiloxane (PDMS) microfluidic channels with Teflon for algal lipid research. When culturing and staining algae inside microfluidic devices, the small molecule dyes absorbed by the microchannel surface render it difficult for imaging and quantification. PDMS surface coated with Teflon-AF resists the absorption of hydrophobic dye molecules (i.e., BODIPY and Nile red) as confirmed using fluorescence microscopy. Here, we introduce a surface modification of PDMS microchannel using Teflon-AF using a procedure of filling and drying to directly treat the PDMS surface with perfluorinated materials. This method can be used to prevent the absorption of fluorescent probe and obtain clear fluorescence micrographs without background signal from absorbed dye molecules on PDMS microchannel. We confirmed that contact angle of Teflon-coated PDMS (116.4°) is higher than that of unmodified PDMS (106.1°) and thus more hydrophobic. Furthermore, Teflon-coated PDMS surface had ~80% of oxygen transfer rate compared to that of native PDMS and good transparency in all visible light regions. Based on these characteristics, we successfully validated the visualization and quantification of intracellular lipid droplets in microalgae C. reinhardtii using BODIPY. We believe that our new method will expand microfluidic applications on characterization of biological lipid with fluorescence probes and biochemical markers.

Microfluidic neural axon diode

Neural circuits, groups of neurons connected in directional manner, play a central role in information processing. Advances in neuronal biology research is limited by a lack of appropriate in vitro methods to construct and probe neuronal networks. Here, we describe a microfluidic culture platform that directs the growth of axons using “neural diode” structures to control neural connectivity. This platform is compatible with live cell imaging and can be used to (i) form pre-synaptic and postsynaptic neurons by directional axon growth and (ii) localize physical and chemical treatment to pre- or postsynaptic neuron groups (i.e. virus infection and etc.). The “neural diode” design consist of a microchannel that split into two branches: one is directed straight toward while the other returns back toward the starting point in a closed loop to send the axons back to the origin. We optimized the “neural diode” pattern dimension and design to achieve close to 70% directionality with a single unit of the “diode”. W...