||Naotomo Tottori, Yasuhiko Muramoto, Hiraku Sakai, Takasi Nisisako, Nanoparticle separation through deterministic lateral displacement arrays in poly(dimethylsiloxane), Journal of Chemical Engineering of Japan, 10.1252/jcej.19we160, 53, 8, 414-421, 2020.08, We present size-based separation of nanopartides using deterministic lateral displacement (DLD) arrays in poly(dimethylsiloxane) (PDMS). Unlike conventional dry-etched silicon DLD devices for nanoparticle separation, our proposed devices are fabricated from PDMS by standard soft lithography. Using a DLD device having a critical diameter Dc of 0.7 pm, we could separate fluorescent polystyrene particles of diameters 1 and 0.5 pm. In addition, we could demonstrate solution exchange for 0.5-pm beads by using a DLD device having a smaller Dc of 0.3 pm. .
||Naotomo Tottori, Takasi Nisisako, Particle/cell separation using sheath-free deterministic lateral displacement arrays with inertially focused single straight input, Lab Chip, 10.1039/d0lc00354a, 20, 1999-2008, 2020.04, This paper proposes microfluidic particle separation by sheath-free deterministic lateral displacement (DLD) with inertial focusing in a single straight input channel. Unlike conventional DLD devices for size- based particle separation, in which sheath streams are used to focus the particles before the solution containing them reaches the DLD arrays, the proposed method uses inertial focusing to align the particles along the middle or the sidewalls of the straight rectangular input channel. The two-stage model of inertial focusing is applied to reduce the length of the side-focusing channel. The proposed method is demonstrated by using it to separate fluorescent polymer particles of diameters 13 and 7 μm, in the process of which the effect of the particle focusing regime on the separation performance is also investigated. Through middle focusing, the method is further used to separate MCF-7 cells (a model of circulating tumor cells (CTCs)) and blood cells, with ∼99.0% capture efficiency achieved..
||Yingzhe Liu, Naotomo Tottori, Takasi Nisisako, Microfluidic synthesis of highly spherical calcium alginate hydrogels based on external gelation using an emulsion reactant, Sensors and Actuators, B: Chemical, 10.1016/j.snb.2018.12.101, 283, 802-809, 2019.03, Alginate-based hydrogels are widely used in the biomedical and chemical fields, and their size and shape are significant to their applications like drug delivery and cell encapsulation. Here, we report a microfluidic external gelation process using an on-chip calcium chloride (CaCl2) emulsion reactant for producing highly spherical calcium alginate (Ca-alginate) hydrogel particles. The microfluidic channels were two serial cross-junctions fabricated on quartz glass. Monodisperse sodium alginate (Na-alginate) droplets with diameters greater or smaller than the opening (ranging from 176 μm to 225 μm) with a coefficient of variation (CV) less than 3% were successfully generated at the upstream cross-junction; they then reacted with the CaCl2 emulsion at the downstream cross-junction, forming Ca-alginate hydrogels. The effects of the fraction of the aqueous phase in the reactant CaCl2 emulsion and the flow rates of continuous and emulsion phases on the roundness of the obtained hydrogels were studied. By optimizing the parameters above, monodisperse spherical hydrogel particles were obtained with diameters ranging from 147 μm to 176 μm with CVs around 5%. The synthesis of magneto-responsive hydrogels with asymmetric Fe3O4 coatings was also demonstrated..
||Naotomo Tottori, Takasi Nisisako, Degas-Driven Deterministic Lateral Displacement in Poly(dimethylsiloxane) Microfluidic Devices, Analytical chemistry, 10.1021/acs.analchem.8b05587, 91, 4, 3093-3100, 2019.02, In this work, degas-driven microfluidic deterministic lateral displacement devices were fabricated from poly(dimethylsiloxane). Two device configurations were considered: One with a single input for the enrichment of particles and the other one with sheath inputs for the separation of particles based on their sizes. Using the single-input device, the characteristics of the degas-driven fluid through micropillars were investigated, and then selective enrichment of fluorescent polymer particles with diameters of around 13 μm mixed with similar 7 μm particles was demonstrated. Using the sheath-input device, the separation of 13 and 7 μm beads was achieved (the corresponding purities exceeded 92.62% and 99.98%, respectively). In addition, clusters composed of 7 μm beads (including doublets, triplets, and quadruplets) were fractionated based on their equivalent sizes. Finally, white blood cells could be separated from red blood cells at a relatively high capture efficiency (95.57%) and purity (86.97%)..
||Naotomo Tottori, Takasi Nisisako, High-throughput production of satellite-free droplets through a parallelized microfluidic deterministic lateral displacement device, Sensors and Actuators, B: Chemical, 10.1016/j.snb.2018.01.112, 260, 918-926, 2018.05, We present a parallel numbering-up device for microfluidic production of satellite droplet-free emulsions. The device consists of two stacked layers made of polydimethylsiloxane (PDMS). The bottom layer combines eight parallel sets of a microfluidic droplet generator (MFDG) and deterministic lateral displacement (DLD) array for size-based separation of main and satellite droplets. The top layer has input reservoirs to supply both the disperse and continuous phases evenly to the eight channels of the bottom layer. We employed 3D flow simulations to find the reservoirs most suitable for equal inflow distribution. Water-in-oil (W/O) droplets comprised of main droplets (∼67 μm in diameter) and satellite droplets (1–20 μm) were generated in the parallelized MFDGs, and they were then completely separated through the DLD arrays having a critical diameter of Dc = 37.1 μm. Thus, we confirmed production of satellite droplet-free emulsion droplets at 0.2 ml/h, eight times the processing throughput of single device (= 0.025 ml/h) without decrease in performance..
||Naotomo Tottori, Takeshi Hatsuzawa, Takasi Nisisako, Separation of main and satellite droplets in a deterministic lateral displacement microfluidic device, RSC Advances, 10.1039/c7ra05852g, 7, 56, 35516-35524, 2017.01, A microfluidic droplet generator (MFDG) normally produces satellite droplets through break-off from the main droplet because of the Plateau-Rayleigh instability, resulting in contamination and/or poor size distribution of the products. Thus, we herein demonstrate the continuous, passive, and size-based separation of main and satellite droplets using the deterministic lateral displacement (DLD) array method. For the purpose of this study, we designed and employed microfluidic devices comprised of an upstream symmetric flow-focusing MFDG and a downstream DLD array composed of polydimethylsiloxane (PDMS). Initially, we produced water-in-oil (W/O) droplets containing main droplets of ∼61.1 μm diameter in addition to satellite droplets of 1-30 μm diameter in a hydrophobic MFDG, and we report the successful separation of the main and satellite droplets through a single-step DLD array with a critical diameter (Dc) of 37.1 μm. Furthermore, we demonstrated the generation and separation of single-phase or biphasic (i.e. Janus or core-shell) oil-in-water (O/W) main and satellite droplets using a hydrophilic MFDG and a DLD array. Finally, in addition to the removal of main and satellite W/O droplets, we also fractionated satellite droplets of different sizes into three groups (i.e., 21.4, 10.1, and 4.9 μm average diameter) using a device with three-step DLD arrays each having different Dc values (i.e., 37.1, 11.6, and 7.0 μm)..
||Naotomo Tottori, Takasi Nisisako, Jongho Park, Yasuko Yanagida, Takeshi Hatsuzawa, Separation of viable and nonviable mammalian cells using a deterministic lateral displacement microfluidic device, Biomicrofluidics, 10.1063/1.4942948, 10, 1, 2016.01, Here, we present a deterministic lateral displacement (DLD) microfluidic device that may be used for label-free, passive, and continuous separation of viable and nonviable mammalian cells. Cells undergoing apoptosis (programmed cell death) become smaller than normal viable cells due to shrinkage and fragmentation. We used this distinct difference in size to selectively isolate viable Jurkat cells from nonviable apoptotic cells and their remnants through a DLD array that is capable of size-based fractionation of microparticles. First, we calibrated our DLD devices by separating a mixture of larger (~15-μm) and smaller (~8-or ~10-μm) polystyrene beads that emulated viable and nonviable Jurkat cells, respectively. We then demonstrated the separation of viable and nonviable Jurkat cells by introducing their heterogeneous suspensions into two DLD devices with different design parameters. In a DLD device with a 20-μm gap, we collected viable cells at 100 ± 0% capture efficiency (n = 3), at a capture purity of 23.1 ± 4.8%, with 57.8 ± 8.1% removal efficiency of nonviable apoptotic cells and their remnants from the initial mixture solution. On a DLD device with a 23-μm gap, the capture purity of viable cells increased to 50.2 ± 15.0%, with 89.0 ± 3.5% removal efficiency of nonviable cells, and a lower capture efficiency of 48.2 ± 2.0% (n = 3). This first demonstration of label-free and passive separation of viable and nonviable cells by DLD illustrates its potential for, e.g., regenerative medicine and discovery of anti-cancer drugs..