Eunpyo Choi

Open-loop position control of a polymer cable–driven parallel robot via a viscoelastic cable model for high payload workspaces

A polymer cable–driven parallel robot has a wide range of potential industrial applications by virtue of its light actuator dynamics, high payload capability, and large workspace. However, due to a viscoelastic behavior of polymer cable and difficulty in actual cable length measurement, there have been inevitable position and tracking control accuracy problems such as pick and place a high payload application. In this article, to overcome control problem, we propose a model-based open-loop control with the cable elongation compensation via experimentally driven cable model and switching control logic without additional Cartesian space feedback signal. The approach suggests a five-element cable model that is made with series combination of a linear spring and two Voigt models as a function of payload and cable length that are available to be measured in real-time. Experimental results show that using the suggested method, the cable length error due to viscoelastic effect can be compensated, and thus the position control accuracy of the polymer cable–driven parallel robot improved remarkably especially in gravity direction.

A Polymer Cable Creep Modeling for a Cable-Driven Parallel Robot in a Heavy Payload Application

A polymer cable driven parallel robot can be an effective system in many fields due to its fast dynamics, high payload capability and large workspace. However, creep behavior of polymer cables may yield a posture control problem, especially in high payload pick and place application. The aim of this paper is to predict creep behavior of polymer cables by using different mathematical models for loading and unloading motion. In this paper, we propose a five-element model of the polymer cable that is made with series combination of a linear spring and two Voigt models, to portray experimental creep in simulation. Ultimately, the cable creep can be represented by payloads and cable length estimated according to the changes of actual payloads and cable lengths in static condition.

Dual tumor-targeted multifunctional magnetic hyaluronic acid micelles for enhanced MR imaging and combined photothermal-chemotherapy

Multifunctional polymeric micelles were developed as a promising dual tumor-targeted drug delivery platform for magnetic resonance (MR) imaging and combined photothermal-chemotherapy. HA-C16 copolymers were synthesized via peptide formation process with subsequent co-encapsulation of therapeutic agent docetaxel (DTX) and superparamagnetic iron oxide nanoparticles (SPIONs) to form the multifunctional micelles. The micelles exhibited uniform nanosize and remarkable colloidal stability in aqueous solution. The sustained drug release behavior from HA micelles was observed over the test period. Moreover, the specific targeting capability based on CD44 recptor-mediated endocytosis and the enhanced targeting efficacy by in presence of external magnetic field were investigated. The clustered SPIONs within micelles exerted excellent contrast effect with high r2 relaxivity in MR phantom test. Furthermore, the multifunctional micelles could readily convert light to heat to hyperthermia temperature upon near infrared light irradition and induce photothermal ablation to breast cancer cells. The combined photothermal therapy with DTX-mediated chemotherapy of the developed multifunctional polymeric micells could generate a synergistic therapeutic effect. Based on these findings, the resulting multifunctional micelles may provide high potential for multimodality theragnosis of cancer.

Folate receptor-targeted liposomal nanocomplex for effective synergistic photothermal-chemotherapy of breast cancer in vivo

An effective nanoparticle-based drug delivery platform holds great promise for non-invasive cancer therapy. This study explores the breast tumor regression in vivo by synergistic photothermal-chemotherapy based on liposomal nanocomplex (folic acid-gold nanorods-anticancer drug-liposome). The proposed liposomal nanocomplex can enhance the tumor targeting by functionalizing folic acid (FA) molecules on the surface of liposome that encapsulates both gold nanorods (AuNRs) and the doxorubicin (DOX) to combine the photothermal therapy and the chemotherapy, respectively. Herein, 7-nm gold nanorods were fabricated and co-encapsulated with DOX into nanoliposomes functionalized with FA, with an average diameter of 154 nm, for active targeting to the cancer cells. The experimental results showed that the FA targeting liposomes had better cellular uptake than the non-targeting liposomes (AuNRs-DOX-LPs). Especially, upon 5 min exposure to near infrared (NIR) irradiation (808 nm) triggered DOX release could be achieved to 46.38% in 60 min at pH 5.5. In addition, in vitro cell proliferation assays indicated that, with synergistic photothermal-chemotherapy, the targeting liposomes could significantly enhance the toxicity towards the cancer cells with the IC50 value of 1.90 ± 0.12 μg mL-1. Furthermore, in vivo experiments on the breast tumor-bearing mice showed that the targeting liposomes could effectively inhibit the growth of the tumors using the combined strategy.

Geometric Parameter Calibration for a Cable-Driven Parallel Robot Based on a Single One-Dimensional Laser Distance Sensor Measurement and Experimental Modeling

A cable-driven parallel robot has benefits of wide workspace, high payload, and high dynamic response owing to its light cable actuator utilization. For wide workspace applications, in particular, the body frame becomes large to cover the wide workspace that causes robot kinematic errors resulting from geometric uncertainty. However, appropriate sensors as well as inexpensive and easy calibration methods to measure the actual robot kinematic parameters are not currently available. Hence, we present a calibration sensor device and an auto-calibration methodology for the over-constrained cable-driven parallel robots using one-dimension laser distance sensors attached to the robot end-effector, to overcome the robot geometric uncertainty and to implement precise robot control. A novel calibration workflow with five phases—preparation, modeling, measuring, identification, and adjustment—is proposed. The proposed calibration algorithms cover the cable-driven parallel robot kinematics, as well as uncertainty modeling such as cable elongation and pulley kinematics. We performed extensive simulations and experiments to verify the performance of the suggested method using the MINI cable robot. The experimental results show that the kinematic parameters can be identified correctly with 0.92 mm accuracy, and the robot position control accuracy is increased by 58%. Finally, we verified that the developed calibration sensor devices and the calibration methodology are applicable to the massive-size cable-driven parallel robot system.

Reverese electrodialysis based nanofluidic power generator with multiple cells

In this study, we propose a nanofluidic power generator inspired by an electrical eel to harness ion concentration gradient by reverse electrodialysis (RED). The key element for nanofluidic device, cation-exchange NCNM (CE-NCNM) and anion-exchange NCNM (AE-NCNM) constructed by self-assembled nanoparticles with hydroxyl and amine groups, respectively, enable high ionic current through 3-dimensional nanochannel networks for efficient power generation. The system performance is investigated by changing the number of serially stackable cells and intermembrane distance between cells.

Development of hyaluronic acid microcargo for therapeutic bacteriobots

Recently, bacteria-based microrobots (Bacteriobots), which consist of the microbeads as cargos of drugs, and attenuated bacteria as actuators and sensors, were proposed for cancer therapeutic microrbots. A new type of bacteriobots were prepared and investigated against tumors. The hyaluronic acid (HA) microbeads were crosslinked with divinyl sulfone (DVS) to form HA microbeads with diameter of 10 μm. Moreover, docetaxel (DTX) loaded nanoparticles were encapsulated into the microbeads. Hyaluronidase (HAse) was used to control the degradation of HA microbeads and the release of entrapped DTX. The in vitro anticancer ability of HA microbeads was investigated against 4T1, CT26, showed high cell cytotoxicity to tumor cells. The anticancer efficacy was also enhanced by degrading HA microbeads with HAse. The bacteriobots were prepared by attaching bacteria onto the surface of HA microbeads. The bacteriobots showed high motion ability and excellent tumor therapeutic effect than that of drug encapsulated microbeads. Consequently, those results demonstrated that the HA microbead with HAse could be excellent microcargo for a therapeutic bacteriobot in cancer therapy.

Development of direct patterning and visualization system for fabrication of hydrogel microstructure

In this study, we developed a direct patterning system based on infinity-corrected optics for light-induced fabrication of hydrogel microstructures, while still visualizing the fabrication process in real time by integrating the objective lens and red LED system. The optical projection system for reducing the size of patterns from film mask to desired substrate was optimized through the theoretical calculation and the numerical simulation. Then the optic system was integrated with macro and micro manipulation stage for direct patterning of hydrogel. To demonstrate the proposed patterning and visualizing system, the UV-curable hydrogel was patterned in micro-scale and observed simultaneously.