Yerin Shin

Soft actuators have recently been widely studied due to their significant advantages including light weight, continuous deformability, high environment adaptability, and safe human-robot interactions. In this study, we designed electrically responsive poly(sodium 4-vinylbenzenesulfonate/2-hydroxyethylmethacrylate/acrylamide) (P(VBS/HEMA/AAm)) and poly(sodium 4-vinylbenzenesulfonate/2-hydroxyethyl methacrylate/acrylic acid) (P(VBS/HEMA/AAc)) hydrogels. A series of P(VBS/HEMA/AAm) and P(VBS/HEMA/AAc) hydrogels were prepared by adjusting the monomer composition and cross-linking density to systemically analyze various factors affecting the actuation of hydrogels under an electric field. All hydrogels exhibited more than 65% gel fraction and a high equilibrium water content (EWC) of more than 90%. The EWC of hydrogels gradually increased with decreasing cross-linker content and was also influenced by the monomer composition. The mechanical properties of hydrogels were proportional to the cross-linking density. Particularly, hydrogels showed bending deformation even at low voltages below 10 V, and the electrically responsive bending actuation of hydrogels can be modulated by cross-linking density, monomer composition, applied voltage, ion strength of the electrolyte solution, and geometrical parameters of the hydrogel. By controlling these factors, hydrogels showed a fast response with a bending of more than 100° within a minute. In addition, hydrogels did not show significant cytotoxicity in a biocompatibility test and exhibited more than 84% cell viability. These results indicate that P(VBS/HEMA/AAm) and P(VBS/HEMA/AAc) hydrogels with fast response properties even under a low electric field have the potential to be used in a wide range of soft actuator applications.

Electroactive hydrogels that exhibit large deformation in response to an electric field have received significant attention as a potential actuating material for soft actuators and artificial muscle. However, their mechanical actuation has been limited in simple bending or folding due to uniform electric field modulation. To implement complex movements, a pre-program, such as a hinge and a multilayer pattern, is usually required for the actuator in advance. Here, we propose a reprogrammable actuating method and sophisticated manipulation by using multipolar three-dimensional electric field modulation without pre-program. Through the multipolar spatial electric field modulator, which controls the polarity/intensity of the electric field in three-dimensions, complex three-dimensional (3D) actuation of single hydrogels are achieved. Also, air bubbles generated during operation in the conventional horizontal configuration are not an issue in the proposed new vertical configuration. We demonstrate soft robotic actuators, including basic bending mechanics in terms of controllability and reliability, and several 3D shapes having positive and negative curvature can easily be achieved in a single sheet, paving the way for continuously reconfigurable materials.

In this paper, randomness of ring-oscillator-based True Random Number Generators (TRNGs) on Field Programmable Gate Arrays (FPGAs) are analyzed according to the number of constituent inverters and the number of ring oscillators. A typical ring oscillator is composed of an odd number of inverter chain, in which the output of the last inverter is fed back to the input of the first inverter. TRNG utilizes a different jitter caused by PVT variations as an entropy source. To evaluate ring-oscillator-based TRNG on FPGAs, we implement various TRNGs with different numbers of constituent inverters and ring oscillators on Xilinx Spartan-3 FPGA, and the randomness is evaluated by the NIST SP 800-22 test. According to experimental results, it shows that TRNG with the smaller number of constituent inverters and the larger number of ring oscillators provides the stronger randomness.

Natural killer (NK) cells are a subset of innate lymphoid cells playing an important role in immune surveillance and early defense against infection and cancer. They recognize and directly kill infected or transformed cells. At the same time, they produce various cytokines and chemokines to regulate other immune cells. NK cell activity can be a useful marker for health screenings because impaired NK cell functions may indicate a more susceptible environment for infection or tumor development. Currently, most NK cell activity assays are focused on measuring either cytokine secretion, in particular, interferon γ (IFN-γ), or cytotoxicity against target cells such as K562, thus only providing partial information on NK cell activity. In order to develop a comprehensive test for measuring NK cell function, cytotoxicity and cytokine secretion ability should be measured simultaneously. In addition, current NK cell assays are performed by stimulating NK cells with cocktails of cytokines, antibody-coated beads, or live target cells. In this study, we developed multifunctional microparticles for NK cell activity assay (MNAs) that allow simultaneous stimulation and sensing various NK cell activities, including cytokine secretion and cytotoxicity. The surfaces of MNAs are decorated with multiple functional biomolecules, including antibodies that stimulate NK cells by engaging NK cell activating receptors, antibodies that can capture cytokines secreted by NK cells, and a peptide sensor that reacts with granzyme B, a key molecule released by NK cells for cytotoxicity. The performances of MNAs are assessed using flow cytometry and live cell imaging. NK cell activity is measured by simply mixing MNAs with NK cells and performing flow cytometry, and the results are comparable to those measured by standard NK cell activity assays.