Light-addressable electrodeposition of cell-encapsulated alginate hydrogels for a cellular microarray using a digital micromirror device

Abstract

This paper describes a light-addressable electrolytic system used to perform an electrodeposition of calcium alginate hydrogels using a digital micromirror device (DMD). In this system, a patterned light illumination is projected onto a photoconductive substrate serving as a photo-anode to electrolytically produce protons, which can lead to a decreased pH gradient. The low pH generated at the anode can locally release calcium ions from insoluble calcium carbonate (CaCO(3)) to cause gelation of calcium alginate through sol-gel transition. By controlling the illumination pattern on the DMD, a light-addressable electrodeposition of calcium alginate hydrogels with different shapes and sizes, as well as multiplexed micropatterning was performed. The effects of the concentration of the alginate and CaCO(3) solutions on the dimensional resolution of alginate hydrogel formation were experimentally examined. A 3 × 3 array of cell-encapsulated alginate hydrogels was also successfully demonstrated through light-addressable electrodeposition. Our proposed method provides a programmable method for the spatiotemporally controllable assembly of cell populations into cellular microarrays and could have a wide range of biological applications in cell-based biosensing, toxicology, and drug discovery.

Light-Addressable Electrodeposition of Magnetically-Guided Cells Encapsulated in Alginate Hydrogels for Three-Dimensional Cell Patterning

“…The deposition solution, which contains soluble sodium alginate (80-120 mPa·S, Sigma-Aldrich), suspended cells labeled with magnetic particles (Fe3O4; 10 nm, Sigma-Aldrich), and insoluble calcium carbonate (CaCO3) nanoparticles (70 nm, Specialty Minerals, UK), was introduced into the microchamber (Figure 1a). We used CaCO3 nanoparticles (70 nm in diameter) as the calcium complex to drastically increase the sedimentation time to over 10 min and to ensure a homogeneous dispersion within the microchamber for the production of calcium alginate hydrogels with high shape fidelity [14]. The concentration of 2 wt % alginate solution was chosen for this study because they are optimal concentrations with suitably low viscosities for facilitating the homogeneous dispersion of the suspended cells and CaCO3 nanoparticles within the deposition solutions.…”

“…Our previous work [14] had successfully performed light-addressable micropatterning of cell-encapsulated alginate hydrogels and experimentally examined the effect of the illumination time of …”

“…This setup uses a modified commercial MP525P DMD projector (BENQ, Hsinchu, Taiwan) that is equipped with a mercury lamp unit as the light source. We modified the commercial DMD projector by simply removing the projection lens and the color filter wheel [14,21]. The structured light patterns of the DMD were controlled by a computer (C1), such as a rectangular shape.…”

“…The long period for encapsulated cells to be exposed with low pH and Ca 2+ ions at an anode can decrease cell viability. Our previous work showed that the cell viability for a single layer of the cell-encapsulated alginate hydrogel was over 95% at an applied voltage of 10 V for 15 s [14], but gradually decreased with increasing the illumination time of the light pattern, i.e., ~75% live cells at 10 V for 120 s and only ~35% live cells at 10 V for 240 s. Increasing the applied voltage from 20 to 40 V significantly decreased the cell viability, e.g., only ~35% live cells at 40 V for 15 s. To possess an acceptable cell viability for the first layer of cell-encapsulated alginate hydrogels, we need to control the overall illumination time of the light pattern at a preset voltage for the multiplex micropatterning. To avoid this issue, we can simply produce the first layer of the alginate hydrogel without cell encapsulation serving as the buffer layer.…”

“…Changing the pattern requires the re-design and re-fabrication of the photo-masks, microelectrodes and sometimes the chip structures themselves. Instead, our previous work [14] proposed an alternative approach to produce cell-encapsulated alginate hydrogels by utilizing a light-addressable electrolytic system to perform an electrodeposition of calcium alginate hydrogels using a digital micromirror device (DMD). The DMD provides spatiotemporal illumination pattern switching, which is used to achieve flexible electrode patterning for the dynamical and multiplexed electrodeposition of calcium alginate hydrogels.…”