Sheng-Yang Tseng

A microfluidic chip with a U-shaped microstructure array for multicellular spheroid formation, culturing and analysis

Multicellular spheroids (MCS), formed by self-assembly of single cells, are commonly used as a three-dimensional cell culture model to bridge the gap between in vitro monolayer culture and in vivo tissues. However, current methods for MCS generation and analysis still suffer drawbacks such as being labor-intensive and of poor controllability, and are not suitable for high-throughput applications. This study demonstrates a novel microfluidic chip to facilitate MCS formation, culturing and analysis. The chip contains an array of U-shaped microstructures fabricated by photopolymerizing the poly(ethylene glycol) diacrylate hydrogel through defining the ultraviolet light exposure pattern with a photomask. The geometry of the U-shaped microstructures allowed trapping cells into the pocket through the actions of fluid flow and the force of gravity. The hydrogel is non-adherent for cells, promoting the formation of MCS. Its permselective property also facilitates exchange of nutrients and waste for MCS, while providing protection of MCS from shearing stress during the medium perfusion. Heterotypic MCS can be formed easily by manipulating the cell trapping steps. Subsequent drug susceptibility analysis and long-term culture could also be achieved within the same chip. This MCS formation and culture platform can be used as a micro-scale bioreactor and applied in many cell biology and drug testing studies.

Cell patterning via diffraction-induced optoelectronic dielectrophoresis force on an organic photoconductive chip

A laser diffraction-induced dielectrophoresis (DEP) phenomenon for the patterning and manipulation of individual HepG2 cells and polystyrene beads via positive/negative DEP forces is reported in this paper. The optoelectronic substrate was fabricated using an organic photoconductive material, TiOPc, via a spin-coating process on an indium tin oxide glass surface. A piece of square aperture array grid grating was utilized to transform the collimating He-Ne laser beam into the multi-spot diffraction pattern which forms the virtual electrodes as the TiOPc-coating surface was illuminated by the multi-spot diffraction light pattern. HepG2 cells were trapped at the spot centers and polystyrene beads were trapped within the dim region of the illuminated image. The simulation results of light-induced electric field and a Fresnel diffraction image illustrated the distribution of trapped microparticles. The HepG2 morphology change, adhesion, and growth during a 5-day culture period demonstrated the cell viability through our manipulation. The power density inducing DEP phenomena, the characteristics of the thin TiOPc coating layer, the operating ac voltage/frequency, the sandwiched medium, the temperature rise due to the ac electric fields and the illuminating patterns are discussed in this paper. This concept of utilizing laser diffraction images to generate virtual electrodes on our TiOPc-based optoelectronic DEP chip extends the applications of optoelectronic dielectrophoretic manipulation.

Light-driven manipulation of picobubbles on a titanium oxide phthalocyanine-based optoelectronic chip

Microbubbles have a variety of applications in science and biological technology. Here, we demonstrate the manipulation of the picoliter gas bubble (picobubble) based on the optoelectronic-mechanism. The organic photoconductive material, titanium oxide phthalocyanine (TiOPc), was developed to make the light-sensitive substrate of this optoelectronic chip. The virtual electrodes are formed by projecting the dynamic light pattern onto TiOPc layer for generating the desired nonuniform electric field. The picobubble suspended in silicone oil can be manipulated with the velocity of 40–50 μm/s. The driving force up to 160 pico-Newtons could be generated for manipulating a gas bubble of 300 picoliters.

A miniaturized optically-induced fluorescence-activated cell sorter

We integrate the concept of liquid light-driven approach and a cell fluorescent detection system to sort different labeled color HepG2 and 3T3 cells. The optoelectroosmosis flow (OEOF) method would drive the liquid and reverse the flow direction immediately only with light pattern movement. A dielectrophoresis (DEP) force is applied to focal the moving cells as a line. A LabVIEW program would detect the fluorescent cell color and switch the projected light pattern automatically to manipulate the mobile cell real-time. After the OEOF operation, the selected cell is able to push a lateral displacement with 120µm distance against original direction. Based on these four features, this article demonstrates a potential for cells sorting with light driving approaches.

NUSAS: Negative pressure driving HEPG2/3T3 cells mixing/gradient co-culture inside U trapper array on rapid multicellular Spheroid Assembling System

This article presents a Negative-pressure-powered U-trapper of Spheroid Assembling System (NUSAS) and four unique features are addressed: (1) Negative pressure powered medium driving, (2) HepG2/3T3 gradient distribution and mixing co-culture, (3) Cell trapping effect via gravity force and liquid flow co-activation, and (4) Large area of U trapper array. The development of in vitro liver device benefits liver toxicology and metabolism.[1,2] However, due to the complexity of human liver tissue, it has been rarely discussed what kind of hepatocyte to fibroblast ratio has nearest performance to a real liver tissue. Here, we culture liver/fibroblast cells with gradient ratio as multicellular assembling spheroids simultaneously to find this ratio. These results based on our efficient approaches give us meaningful foundations to investigate biomedical character of 3D HepG2/3T3 artificial tissue in different mixing cell conditions.

Controlling the transverse momentum distribution of a light field via azimuth division of a hologram in holographic optical tweezers

This study proposes a method for creating a light field with controlled distribution of transverse momentum (TM) by displaying a hologram only in an azimuth region that centers at θ(0) and has a range of Δθ of a spatial light modulator in holographic optical tweezers. This study utilized ray optics to analyze the TM of the resultant field, revealing that the direction of the TM is determined by the center angle of the azimuth region and that the magnitude of the TM is proportional to sin(Δθ/2), without regarding the intensity. The relationship was verified experimentally. In addition, this study demonstrated moving particles along a designed path and depleting particles by the fields.

Organic photoconductive dielectrophoresis by using titanium oxide phthalocyanine for micro-particles manupulation

This paper reports our updating development for the organic photoconductive dielectrophoresis (OPDEP) by using titanium oxide phthalocyanine (TiOPc) material for the manipulation of micro-objects. The advantages of organic photoconductive material include non-toxicity, low cost, easy coating fabrication, flexibility, panchromaticity and high photosensitivity [1]. TiOPc has the high photoconductivity and the optical absorptions in the near infrared region (550 – 850 nm) to be a candidate of the light-sensitive charge generation layer. OPDEP chip is easily mass-produced by using a spin-coating process. Here, we demonstrate two kinds of the manipulations of micro-particles on our OPDEP chip. Firstly, the trapping and movement of single micro-particle is achieved by the ring shaped virtual electrode. Secondly, the steel rim shaped virtual electrode is designed to rotate micro-particles and characterize the OPDEP induced force.