Hongsoo Choi

Daegu Gyeongbuk Institute of Science and Technology | DGIST · Department of Robotics Engineering

The past decade has seen an upsurge in the development of small‐scale magnetic robots for various biomedical applications. However, many of the reported designs comprise components with biocompatibility concerns. Strategies for fabricating biocompatible and degradable microrobots are required. In this study, polyvinyl alcohol (PVA)‐based magnetic h...

Magnetoelectric (ME) oxide materials can convert magnetic input into electric output and vice versa, making them excellent candidates for advanced sensing, data storage, and communication. However, their application has been limited to rigid devices due to their brittle nature. Here, flexible ME oxide composite (BaTiO3/CoFe2O4) thin film nanostruct...

Functional restoration by the re‐establishment of cellular or neural connections remains a major challenge in targeted cell therapy and regenerative medicine. Recent advances in magnetically powered microrobots have shown potential for use in controlled and targeted cell therapy. In this study, a magnetic neurospheroid (Mag‐Neurobot) that could for...

The shape recovery ability of shape-memory alloys vanishes below a critical size (~50 nm), which prevents their practical applications at the nanoscale. In contrast, ferroic materials, even when scaled down to dimensions of a few nanometers, exhibit actuation strain through domain switching, though the generated strain is modest (~1%). Here, we dev...

Dopamine (DA) homeostasis influences emotions, neural circuit development, cognition, and the reward system. Dysfunctions in DA regulation can lead to neurological disorders, including depression, developmental disorders, and addiction. DA homeostasis disruption is a primary cause of Parkinson's Disease (PD). Therefore, understanding the relationsh...

A vector hydrophone is an underwater acoustic sensor that can detect the direction of a sound source. Wide-band characteristics and high sensitivity enhance the performance of underwater surveillance systems in complex environments. A vector hydrophone comprising a triaxial piezoelectric accelerometer and spherical hydrophone was fabricated and tes...

Advanced flexible electronics and soft robotics require the development and implementation of flexible functional materials. Magnetoelectric (ME) oxide materials can convert magnetic input into electric output and vice versa, making them excellent candidates for advanced sensing, actuating, data storage, and communication. However, their applicatio...

Cell therapy refers to a treatment that involves the delivery of cells or cellular material by means of injection, grafting, or implantation in order to replace damaged tissue and restore its function, or to aid the body in fighting disease. However, limitations include poor targeting delivery and low therapeutic efficacy due to low cell survival....

A magneto-mechano-electric (MME) generator that converts an ambient magnetic field to available electricity has the potential as an autonomous power source for sensor networks without or supporting driving batteries. However, the output of a typical MME generator decreases when temperature changes lead to resonant frequency drift of the generator....

The shape recovery ability of shape-memory alloys vanishes below a critical size (~50nm), which prevents their practical applications at the nanoscale. In contrast, ferroic materials, even when scaled down to dimensions of a few nanometers, exhibit actuation strain through domain switching, though the generated strain is modest (~1%). Here, we deve...

Medical Robotics In article number 2102529 by Hongsoo Choi and co‐workers, a proposed electromagnetically controllable microrobotic system can help interventional medical practitioners optimally manipulate interventional devices such as guidewires for the treatment of cardiovascular diseases. The system can be teleoperated, protecting medical staff...

A great deal of research has focused on small‐scale robots for biomedical applications and minimally invasive delivery of therapeutics (e.g., cells, drugs, and genes) to a target area. Conventional fabrication methods, such as two‐photon polymerization, can be used to build sophisticated micro‐ and nanorobots, but the long fabrication cycle for a s...

Robotic magnetic manipulation systems offer a wide range of potential benefits in medical fields, such as the precise and selective manipulation of magnetically responsive instruments in difficult‐to‐reach vessels and tissues. However, more preclinical/clinical studies are necessary before robotic magnetic interventional systems can be widely adopt...

Hyperthermia therapy eliminates cancer cells by heating them above physiological temperatures. Superparamagnetic iron oxide nanoparticles (SPIONs) are promising for targeted hyperthermia therapy because of their excellent heating efficiency, biocompatibility, and active magnetic navigation. When exposed to a high-frequency alternating magnetic fiel...

This brief presents a novel tracking control algorithm for a micro-robot based on dynamics and positional measurements. The algorithm improves the tracking performance and response time. We designed a two-degree-of-freedom (TDOF) control, which is widely utilized in industrial servo systems, for a micro-robot. Our TDOF control prevents undesirable...

Magnetic field mapping is tedious; a magnetometer probe collects magnetic field data in a point-by-point manner within a two-dimensional (2D) or three-dimensional (3D) space. Magnetometer arrays accelerate this process by replacing point-by-point mapping with plane-by-plane mapping. When mapping a large space, a motorized stage is additionally requ...

Animals detect and discriminate countless environmental chemicals for their well-being and survival. Although a single chemical can trigger opposing behavioral responses depending on its concentration, the mechanisms underlying such a concentration-dependent switching remain poorly understood. Here, we show that C. elegans exhibits either attractio...

Microrobots In article number 2100801 by Sung Won Kim, Hongsoo Choi, and co-workers, a magnetically powered stem cell-based microrobot (named Cellbot) is proposed for the minimally invasive targeted delivery of stem cells to the brain via the intranasal passage. The Cellbot is developed by internalizing superparamagnetic iron oxide nanoparticles in...

Vector hydrophones based on a micro-electro-mechanical system (MEMS) hold great promise for underwater communications, due to their potential for miniaturization and mass production. Piezoelectric materials have recently been utilized in the fabrication of MEMS-based vector hydrophones, as less power is typically required for their operation. Here,...

Targeted stem cell delivery with microrobots has emerged as a potential alternative therapeutic strategy in regenerative medicine, and intranasal administration is an effective approach for minimally invasive delivery of therapeutic agents into the brain. In this study, a magnetically powered stem cell‐based microrobot (“Cellbot”) is used for minim...

Poly(vinylidene fluoride) (PVDF) and its copolymers have been extensively utilized owing to their fascinating properties such as thermal stability, chemical resistance, and mechanical robustness. However, their lack of microbial resistance is considered a drawback that limits their adoption as biomedical materials. In this study, to overcome this p...

Implantable sensors can be used to monitor biomechanical strain continuously. However, three key challenges need to be addressed before they can be of use in clinical practice: the structural mismatch between the sensors and tissue or organs should be eliminated; a practical suturing attachment process should be developed; and the sensors should be...

Neutrophil-based microrobots accomplish the mission of crossing the blood-brain barrier for targeted drug delivery.

Automatic catheter and guidewire segmentation plays an important role in robot-assisted interventions that are guided by fluoroscopy. Existing learning based methods addressing the task of segmentation or tracking are often limited by the scarcity of annotated samples and difficulty in data collection. In the case of deep learning based methods, th...

To fundamentally solve the bottleneck of Von Neumann’s computing architecture, a neuromorphic thin-film transistor (NTFT) employing Pb(Zr, Ti)O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (PZT) was investigated. The indium gallium zinc oxide (IGZO) channel back gate TFT structure was chosen...

Therapeutic agents, such as drugs and cells, play an essential role in virtually every treatment of injury, illness, or disease. However, the conventional practices of drug delivery often result in undesirable side effects caused by drug overdose and off‐target delivery. In the case of cell delivery, the survival rate of the transplanted cells is e...

Microrobots for targeted drug delivery are of great interest due to their minimal invasiveness and wireless controllability. Here, a magnetically driven porous degradable microrobot (PDM) is reported that consists of a 3D printed helical soft polymeric chassis made of a poly(ethylene glycol) diacrylate and pentaerythritol triacrylate matrix contain...

There has been a great deal of interest in the development of technologies for actively manipulating neural networks in vitro, providing natural but simplified environments in a highly reproducible manner in which to study brain function and related diseases. Platforms for these in vitro neural networks require precise and selective neural connecti...

This brief presents a high voltage modular supply multiplying pulser in a 0.18-$\mu m$ BCD CMOS process. Two prototypes of the pulser were implemented for target loads of 55pF and 1nF, and generated up to 1MHz and 28.7V pulse from 1.2 and 5V supplies. Proposed modular based stepwise pulse generation achieved a peak power reduction of 75.4% relative...

This study presents the fabrication and characterization of a piezoelectric micromachined ultrasonic transducer (pMUT; radius: 40 μm) using a patterned aluminum nitride (AlN) thin film as the active piezoelectric material. A 20 × 20 array of pMUTs using a 1 μm thick AlN thin film was designed and fabricated on a 2 × 2 mm2 footprint for a high fill...

Background: Clinically, steroids have been used for hearing preservation both topically and systemically during cochlear implantation. Objective: This study compared steroid efficacy for hearing preservation among different types of delivery modes using an animal experiment. Materials and methods: For 76 guinea pigs, topical and systemic delivery m...

Neurodegenerative diseases generally result in irreversible neuronal damage and neuronal death. Cell therapy shows promise as a potential treatment for these diseases. However, the therapeutic targeted delivery of these cells and the in situ provision of a suitable microenvironment for their differentiation into functional neuronal networks remain...

In article number 1901697 by Hongsoo Choi and co‐workers, a drug‐loaded micro‐robot can be attached to a target micro‐tissue by swimming in a corkscrew motion with magnetic torque under a rotating magnetic field. The needle‐type micro‐robot has the potential to improve targeted drug delivery to a micro‐tissue in vitro in physiological fluid environ...

A needle‐type microrobot (MR) for targeted drug delivery is developed to stably deliver drugs to a target microtissue (MT) for a given period time without the need for an external force after affixing. The MRs are fabricatedby 3D laser lithography and nickel (Ni)/titanium oxide (TiO2) layers are coated by physical vapor deposition. The translationa...

This research focuses on the development of a flexible tactile sensor array consisting of aluminum nitride (AlN) based on micro-electro-mechanical system (MEMS) technology. A total of 2304 tactile sensors were integrated into a small area of 2.5 × 2.5 cm2. Five hundred nm thick AlN film with strong c-axis texture was sputtered on Cr/Au/Cr (50/50/5...

Magnetic actuation techniques and microrobots have attracted considerable interest due to their potential applications in biomedicine. Interventional techniques have emerged as a minimally invasive approach to treat a wide range of vascular diseases. The current practice of interventional procedures is, however, limited by manual control of interve...

Underwater sensors that detect the distance and direction of acoustic sources are critical for surveillance monitoring and target detection in the water. Here, we propose an axial vector sensor that utilizes a small (~1 cm3) compressive-type piezoelectric accelerometer using piezoelectric single crystals. Initially, finite element analysis (FEA) wa...

In article number 1900739 by Hongsoo Choi, Dong‐Pyo Kim, and co‐workers, biocompatible ceramic microrobots are developed for cell delivery for the first time. The microrobots are fabricated by 3D laser lithography, and magnetic nanoparticles are immobilized on the surface of the microrobots to manipulate the movement of the microrobots by an extern...

Objective: Interventional ultrasound imaging is a prerequisite for guiding implants and treatment within the hearts and blood vessels. Due to limitations on the catheter's diameter, interventional ultrasonic transducers have side-looking structures although forward-looking imaging may provide more intuitive and real time guidance in treating disea...

A silicon carbonitride (SICN) ceramic microrobot, biocompatible and magnetically activable, is developed for the delivery of viable cells to defective tissue by sequential steps of microstructuring, magnetization, and cell loading. The ceramic carrier of porous cylindrical framework is fabricated by 3D laser lithography using a photocurable precera...

In cochlear implants, the electrode insertion trauma during surgery can cause damage residual hearing. Preserving the residual hearing is an important challenge and the localized administration of drugs, such as steroids, is one of the most promising ways, but remains a challenge. Here, a microscaffold cochlear electrode array (MiSCEA) consisting o...

An artificial tactile system has attracted tremendous interest and intensive study, since it can be applied as a new functional interface between humans and electronic devices. Unfortunately, most previous works focused on improving the sensitivity of sensors. However, humans also respond to psychological feelings for sensations such as pain, softn...

Microrobots facilitate targeted therapy due to their small size, minimal invasiveness, and precise wireless control. A degradable hyperthermia microrobot (DHM) with a 3D helical structure is developed, enabling actively controlled drug delivery, release, and hyperthermia therapy. The microrobot is made of poly(ethylene glycol) diacrylate (PEGDA) an...

For the safety and efficacy of in vivo therapy using electromagnetic actuated microrobots, position tracking performance is crucially important. However, it is difficult to manipulate the microrobots accurately and rapidly due to the nonlinear and complex dynamics of the microrobots and highly limited magnetic force of the actuator. In this paper,...

Magnetic microrobots were developed for three-dimensional culture and the precise delivery of stem cells in vitro, ex vivo, and in vivo. Hippocampal neural stem cells attached to the microrobots proliferated and differentiated into astrocytes, oligodendrocytes, and neurons. Moreover, microrobots were used to transport colorectal carcinoma cancer ce...

Theories suggest that ancient Egyptians believed that the bones of gods were made of iron. Indeed, iron has been suggested as a key material in implantable biodegradable medical devices. In article number 1805006, Sangwon Kim, Bradley J. Nelson, Salvador Pané, and co‐workers describe how to manufacture three‐dimensional fully iron magnetic microrob...

Biocompatibility and high responsiveness to magnetic fields are fundamental requisites to translate magnetic small‐scale robots into clinical applications. The magnetic element iron exhibits the highest saturation magnetization and magnetic susceptibility while exhibiting excellent biocompatibility characteristics. Here, a process to reliably fabri...

A particular challenge in intravascular treatments is the control of submillimeter guidewires. This requires a new microrobotics approach. A soft magnetic microrobot consisting of 1) a flexible polydimethylsiloxane (PDMS) body, 2) two permanent magnets, and 3) a micro-spring connector designed and controlled in any 2D arbitrary paths. The proposed...

Here, we develop a flexible microrobot enhancing the steerability of a conventional guidewire. To improve steerability, a microrobot is attached to the tip of the guidewire and guided using an external magnetic field generated by an electromagnetic coil system. The flexible microrobot is fabricated via replica-molding and features a body made of po...

Magnetically driven microrobots have been widely studied for various biomedical applications in the past decade. An important application of these biomedical microrobots is heart disease treatment. In intravascular treatments, a particular challenge is the submillimeter-sized guidewire steering; this requires a new microrobotic approach. In this st...

The energy harvesting by utilizing the piezoelectric effect for the conversion of oscillatory mechanical energy to useful electrical energy has been promising for self-powered devices. The output power can be controlled by designing the size and shape of the constituents of the harvester. This study demonstrates the effect of Ti plate (elastic laye...

Magnetically actuated soft robots may improve the treatment of disseminated intravascular coagulation. Significant progress has been made in the development of soft robotic systems that steer catheters. A more challenging task, however, is the development of systems that steer sub-millimeter-diameter guidewires during intravascular treatments; a no...

Animals change sensory responses and their eventual behaviors, depending on their internal metabolic status and external food availability. However, the mechanisms underlying feeding state-dependent behavioral changes remain undefined. Previous studies have shown that Caenorhabditis elegans hermaphrodite exhibits avoidance behaviors to acute exposu...

A capsule‐type microrobot exhibits “Pick‐and‐Drop” (P&D) motion for possible drug and cell transport via a corkscrew motion. Drugs or cells can be encapsulated in the microrobot's container by the P&D motion or attached to the surface of the cap, which can be used as a cell supporting structure. This work is discussed in article number 1700985 by H...

Micro-electromechanical system (MEMS) technologies were used to develop a thickness-mode piezoelectric micromachined ultrasonic transducer (Tm-pMUT) annular array utilizing a lead magnesium niobate-lead zirconate titanate (PMN-PZT) single crystal prepared by the solid-state single-crystal-growth method. Dicing is a conventional processing method fo...

This paper presents a novel Adaptive Genetic Algorithm for optimal path planning of multiple nanoparticles during the nanomanipulation process. The proposed approach determines the optimal manipulation path in the presence of surface roughness and environment obstacles by considering constraints imposed on the nanomanipulation process. In this rese...

Magnetically manipulated biodegradable microrobots that encapsulate drugs from the outset are produced in a novel, simple way using UV-laser micro-machining. This method enables multiple microrobots to be produced rapidly, without the need for post-drug encapsulation or polymerization by light exposure, which may cause the drug compound to denature...

Intravascular microrobots have emerged as a promising tool for vascular diseases. They can be wirelessly and precisely manipulated with a high degree of freedom. Previous studies have evaluated their drilling performance and locomotion, and showed the feasibility of using microrobots for biomedical applications in two-dimensional space. However, it...