June Won

Estimation of the thermocapillary force and its applications to precise droplet control on a microfluidic chip

Droplet control through the use of light-induced thermocapillary effects has recently garnered attention due to its non-intrusive and multifunctional nature. An important issue in droplet control is the estimation of the thermocapillary force. The purpose of the present study is to estimate the thermocapillary force and propose empirical equations between the force and simply measurable key parameters such as droplet diameter and power of heat source. In addition, we aim to shift the droplet trajectory and develop an on-demand droplet routing system based on the estimation of the thermocapillary force. We illuminated a continuous phase with a 532 nm laser beam to minimize possible damage or property changes to target molecules contained within droplets. A mixture of light-absorbing material and oleic acid was used for the continuous phase fluid, while deionized water (DI water) was used for the dispersed phase fluid. We proposed empirical equations to estimate the thermocapillary force, which was then applied to precise droplet shifting and routing. We found that the shifting distance was linearly proportional to the thermocapillary force, and that an on-demand droplet routing system resulted in a success rate greater than 95%.

Temporal change of photophobic step-up responses of Euglena gracilis investigated through motion analysis

The adaptation to a strong light is one of the essential characteristics of green algae, yet lacking relatively the information about the photophobic responses of Eukaryotic microalgae. We investigated the photophobic step-up responses of Euglena gracilis over a time course of several hours with alternated repetition of blue-light pulse illumination and spatially patterned blue-light illumination. Four distinctive photophobic motions in response to strong blue light were identified in a trace image analysis, namely on-site rotation, running and tumbling, continuous circular swimming, and unaffected straightforward swimming. The cells cultured in autotrophic conditions under weak light showed mainly the on-site rotation response at the beginning of blue-light illumination, but they acquired more blue-light tolerant responses of running and tumbling, circular swimming, or straightforward swimming. The efficiency of escaping from a blue-light illuminated area improved markedly with the development of these photophobic motions. Time constant of 3.0 h was deduced for the evolution of photophobic responses of E. gracilis. The nutrient-rich metabolic status of the cells resulting from photosynthesis during the experiments, i.e., the accumulation of photosynthesized nutrient products in balance between formation and consumption, was the main factor responsible for the development of photophobic responses. The reduction-oxidation status in and around E. gracilis cells did not affect their photophobic responses significantly, unlike the case of photophobic responses and phototaxis of Chlamydomonas reinhardtii cells. This study shows that the evolution of photophobic motion type of E. gracilis is dominated mainly by the nutrient metabolic status of the cells. The fact suggests that the nutrient-rich cells have a higher threshold for switching the flagellar motion from straightforward swimming to rotation under a strong light.

Dual-mode on-demand droplet routing in multiple microchannels using a magnetic fluid as carrier phase.

We present dual-mode, on-demand droplet routing in a multiple-outlet microfluidic device using an oil-based magnetic fluid. Magnetite (Fe3O4) nanoparticle-contained oleic acid (MNOA) was used as a carrier phase for droplet generation and manipulation. The water-in-MNOA droplets were selectively distributed in a curved microchannel with three branches by utilizing both a hydrodynamic laminar flow pattern and an external magnetic field. Without the applied magnetic field, the droplets travelled along a hydrodynamic centerline that was displaced at each bifurcating junction. However, in the presence of a permanent magnet, they were repelled from the centerline and diverted into the desired channel when the repelled distance exceeded the minimum offset allocated to the channel. The repelled distance, which is proportional to the magnetic field gradient, was manipulated by controlling the magnets distance from the device. To evaluate routing performance, three different sizes of droplets with diameters of 63, 88, and 102 μm were directed into designated outlets with the magnet positioned at varying distances. The result demonstrated that the 102-μm droplets were sorted with an accuracy of ∼93%. Our technique enables on-demand droplet routing in multiple outlet channels by simply manipulating magnet positions (active mode) as well as size-based droplet separation with a fixed magnet position (passive mode).

Autonomous oscillation/separation of cell density artificially induced by optical interlink feedback as designed interaction between two isolated microalgae chips

We demonstrate a designed interaction between two isolated cell populations of Euglena gracilis and Chlamydomonas reinhardtii, separately confined in two 25-square micro-aquariums of lab-on-chip size. The interaction was realized by interlinking two identical optical feedback systems, which measured the cell distribution. To analyze the cell populations, we measured the cell distribution in the 25 squares and irradiated the cells with a blue light pattern as an external stimulus. The cell distribution dataset was exchanged between the two systems. Governed by a designed interaction algorithm, the feedback systems produced a dynamic blue light illumination pattern that evoked the photophobic responses of both species. We also induced autonomous cell density oscillation and cell distribution separation and clustering, and analyzed how the types and diversities of the photophobic responses affected the oscillation period and separation and clustering. We conclude that artificial interlink feedback is a promising method for investigating diverse cell–cell interactions in ecological communities, and for developing soft-computing applications with living cells.

Bio-inspired neurocomputing with 256 noise oscillators simulating photo response of Euglena cells

Abstract We developed a bio-inspired neurocomputing approach based on our earlier biological neurocomputer, which leverages the survival strategies of living micro-algae cells (Euglena gracilis) to soft computing. Instead of using the real living cells, the bio-inspired neurocomputing in this study (namely, Euglena-inspired neurocomputing) mimics the photophobic responses of the cells using photo-responsive (PR) noise oscillators. The PR noise oscillators play the role of neurons during computation and their output signals are autonomously changed both by noise generation and firing of the neuron. The Euglena-inspired neurocomputing achieved a high performance in searching for multiple solutions continuously and autonomously for a combinatorial optimization problem, 16-city TSP as instance. We analyzed the temporal evolution of the computation and its dependence on the parameter set of the PR noise oscillators and identified the source of the high performance as the trade-off between noise amplitude and the reduction ratio of the oscillators. We next introduced two specific survival strategies observed in the real Euglena cells to PR noise oscillators, and elucidated their positive effects on the performance. The Euglena-inspired neurocomputing examined in this study can be used to address dynamically changing optimization problems, since the computation tracks changes in the imposed conditions by autonomous and non-converged searching for the solutions.

Facile moldless fabrication of disk-shaped and reed blood cell-like microparticles using photopolymerization of tripropylene glycol diacrylate

A facile method for the moldless fabrication of 2- or 3-dimensional microparticles is proposed by using a photopolymerization technique. Using only a monomer solution of tripropylene glycol diacrylate, a film mask and standard UV lithography equipment, we were able to fabricate microparticles of various shapes, such as disks, dimpled disks similar in shape to red blood cells, and slender gourd shapes, unlike previous moldless fabrication techniques requiring expensive and/or sophisticated equipment. The simple method could produce more than one million particles in a single batch, indicating that it can be applied to the mass production of polymer microparticles. Analyses of scanning electron micrographs and optical micrographs of the microparticles indicated that their size distribution was highly monodisperse. Detailed fabrication processes and statistics on the microparticle sizes are given in this paper.