Chi Hwan Lee

• PhD
• Professor (Assistant) at Purdue University West Lafayette

Sustained‐release ocular drug delivery systems with minimal invasiveness are critical for managing eye diseases that cause blindness. An innovative platform is presented for painless and long‐term sustained ocular drug delivery utilizing controllably biodegradable silicon nanoneedles (Si NNs) conjugated with bevacizumab (Bev) integrated into a tear...

Conductive hydrogels, known for their biocompatibility and responsiveness to external stimuli, hold promise for biomedical applications like wearable sensors, soft robotics, and implantable electronics. However, their broader use is often constrained by limited toughness and environmental resilience, particularly under mechanical stress or extreme...

This review underscores the transformative potential of photonic nanomaterials in wearable health technologies, driven by increasing demands for personalized health monitoring. Their unique optical and physical properties enable rapid, precise, and sensitive real‐time monitoring, outperforming conventional electrical‐based sensors. Integrated into...

Electroluminescent (EL) films are promising light sources for flexible displays, wearable electronics, and soft machines. Traditional fabrication methods like thermal lamination, transfer printing, and screen printing are often labor‐intensive. To address these challenges, a mask‐free, fully printable alternating‐current electroluminescent (PACE) f...

Quasi‐3D plasmonic nanostructures are in high demand for their ability to manipulate and enhance light‐matter interactions at subwavelength scales, making them promising building blocks for diverse nanophotonic devices. Despite their potential, the integration of these nanostructures with optical sensors and imaging systems on a large scale poses c...

The increasing need for precise dietary monitoring across various health scenarios has led to innovations in wearable sensing technologies. However, continuously tracking food and fluid intake during daily activities can be complex. In this study, we present a machine-learning-powered smart neckband that features wireless connectivity and a comfort...

Advances in electroluminescent threads, suitable for weaving or knitting, have opened doors for the development of light-emitting textiles, driving growth in the market for flexible and wearable displays. Although direct embroidery of these textiles with custom designs and patterns could offer substantial benefits, the rigorous demands of machine e...

Conductive hydrogels, despite their significant potential, have faced historical limitations including vulnerability to dehydration, degradation of performance at extreme temperatures, and susceptibility to freezing in subzero conditions. Furthermore, the development of hydrogels that are both tough and stretchable, capable of maintaining performan...

Continuous real-time monitoring of biomarkers in interstitial fluid is essential for tracking metabolic changes and facilitating the early detection and management of chronic diseases such as diabetes. However, developing minimally invasive sensors for the in situ analysis of interstitial fluid and addressing signal delays remain a challenge. Here,...

Opioid-induced overdose is one of the leading causes of death among the US population under the age of 50. In 2021 alone, the death toll among opioid users rose to a devastating number of over 80,000. The overdose process can be reversed by the administration of naloxone, an opioid antagonist that rapidly counteracts the effects of opioid-induced r...

Smart, ultra-scaled, always-on wearable (and implantable) sensors are an exciting frontier of modern medicine. Among them, minimally invasive microneedles (MN) is an emerging technology platform for theragnostic applications. Compared to traditional continuous glucose measurement (CGM) devices, these MNs offer pain-less insertion and simple operati...

Inverse‐vulcanized polymeric sulfur has received considerable attention for application in waste‐based infrared (IR) polarizers with high polarization sensitivities, owing to its high transmittance in the IR region and thermal processability. However, there have been few reports on highly sensitive polymeric sulfur‐based polarizers by replication o...

Continuous monitoring of intraocular pressure, particularly during sleep, remains a grand challenge in glaucoma care. Here we introduce a class of smart soft contact lenses, enabling the continuous 24-hour monitoring of intraocular pressure, even during sleep. Uniquely, the smart soft contact lenses are built upon various commercial brands of soft...

Exosomes, a form of small extracellular vesicles, play a crucial role in the metastasis of cancers and thus are investigated as potential biomarkers for cancer diagnosis. However, conventional detection methods like immune‐based assay and microRNA analyses are expensive and require tedious pretreatments and lengthy analysis time. Since exosomes rel...

With the increasing use of soft and flexible electronics, there is a growing need to develop substrate materials that mitigate potential environmental risks associated with non‐degradable electronics waste from synthetic substrate materials. To address this issue, the authors develop a novel, 2D plant‐based substrate termed “sporosubstrate”, which...

Increasing demand of using everyday clothing in wearable sensing and display has synergistically advanced the field of electronic textiles, or e-textiles. A variety of types of e-textiles have been formed into stretchy fabrics in a manner that can maintain their intrinsic properties of stretchability, breathability, and wearability to fit comfortab...

Ocular drug delivery remains a grand challenge due to the complex structure of the eye. Here, we introduce a unique platform of ocular drug delivery through the integration of silicon nanoneedles with a tear-soluble contact lens. The silicon nanoneedles can penetrate into the cornea in a minimally invasive manner and then undergo gradual degradatio...

E‐Textiles In article number 2108021, Laurent Couetil, Martin Byung‐Guk Jun, Chi Hwan Lee, and co‐workers report how direct spray writing of functional nanomaterials into stretchy fabrics is enabled at sub‐millimeter resolution to produce e‐textiles with custom designs. The e‐textiles fit well various body sizes and shapes of large animals under am...

Increasing demand for wearable healthcare synergistically advances the field of electronic textiles, or e-textiles, allowing for the ambulatory monitoring of vital health signals. Despite great promises, the pragmatic deployment of e-textiles in clinical practice remains challenged due to the lack of a method in producing custom-designed e-textiles...

Swallowing is a critical function that enables humans to sustain life. When swallowing is compromised, the consequences can be devastating and include malnutrition, dehydration, respiratory compromise, and even death. Swallowing disorders (i.e., dysphagia) are very common in many disorders and diseases, such as stroke, ALS, Parkinson disease, and m...

Background: Skin mounted bioelectronics are difficult to integrate with the skin since biocompatible adhesives are not conductive or unsuitable for long-term use. Skin conformability is essential but strong adhesives can damage soft tissue in younger and frail individuals as well as the device during removal. Developing a noninvasive long-lasting b...

The increasing demand for minimal to noninvasive in situ analysis of body fluids, such as sweat, interstitial fluid, and tears, has driven rapid development of electrochemically active materials and wearable biosensors. The mechanically soft and deformable nature of these biosensors enables them to efficiently adapt to the geometric nonlinearity of...

The study of transparent daytime radiative cooling with no additional energy consumption is a promising area of research. Its applications include solar cells and building and automobile windows that are prone to heating issues. Ubiquitous applications necessitate the development of metamaterials with high mechanical flexibility in a scalable manne...

Large, distributed collections of miniaturized, wireless electronic devices1,2 may form the basis of future systems for environmental monitoring³, population surveillance⁴, disease management⁵ and other applications that demand coverage over expansive spatial scales. Aerial schemes to distribute the components for such networks are required, and—in...

The growing need for the implementation of stretchable biosensors in the body has driven rapid prototyping schemes through the direct ink writing of multidimensional functional architectures. Recent approaches employ biocompatible inks that are dispensable through an automated nozzle injection system. However, their application in medical practices...

Quasi-three-dimensionally designed metal-dielectric hybrid nanoantennas have provided a unique capability to control light at the nanoscale beyond the diffraction limit, which has enabled powerful optical manipulation techniques. However, the fabrication of these nanoantennas has largely relied on the use of nanolithography techniques that are time...

The global cost of diabetes care exceeds $1 trillion each year with more than $327 billion being spent in the United States alone. Despite some of the advances in diabetes care including continuous glucose monitoring systems and insulin pumps, the technology associated with managing diabetes has largely remained unchanged over the past several deca...

Electroretinogram examinations serve as routine clinical procedures in ophthalmology for the diagnosis and management of many ocular diseases. However, the rigid form factor of current corneal sensors produces a mismatch with the soft, curvilinear, and exceptionally sensitive human cornea, which typically requires the use of topical anesthesia and...

Large, distributed collections of miniaturized, wireless electronic devices may form the basis of future systems for environmental monitoring, population surveillance, disease management and other applications that demand coverage over expansive spatial scales. In this paper, we show that wind-dispersed seeds can serve as the bio-inspiration for un...

Recent technological advances of soft functional materials and their assembly into wearable (i.e., on-skin) biosensors lead to the development of ground-breaking biomedical applications ranging from wearable health monitoring to drug delivery and to human-robot interactions. These wearable biosensors are capable of unobtrusively interfacing with th...

The vision system of arthropods consists of a dense array of individual photodetecting elements across a curvilinear surface. This compound‐eye architecture could be a useful model for optoelectronic sensing devices that require a large field of view and high sensitivity to motion. Strategies that aim to mimic the compound‐eye architecture involve...

The growing need for the implementation of stretchable biosensors in the human body and organ systems has driven a new rapid prototyping scheme through the direct ink writing (DIW) of multidimensional functional architectures in an arbitrary shape and size to meet the requirement of adapting the geometric nonlinearity of a specific biological site....

“Living” cell sheets or bioelectronic chips have great potentials to improve the quality of diagnostics and therapies. However, handling these thin and delicate materials remains a grand challenge because the external force applied for gripping and releasing can easily deform or damage the materials. This study presents a soft manipulator that can...

Purpose Surface electromyography (sEMG) is often used for biofeedback during swallowing rehabilitation. However, commercially available sEMG electrodes are not optimized for the head and neck area, have rigid form, and are mostly available in large medical centers. We developed an ultrathin, soft, and flexible sEMG patch, specifically designed to c...

In recent years, the metallization of polymers has been intensely studied as it takes advantage of both plastics and metals. Laser direct writing (LDW) is one of the most widely used technologies to obtain metal patterns on polymer substrates. In LDW technology, different methods including injection-molding, drop-casting, dip coating, and spin coat...

Conventional melanoma therapies suffer from the toxicity and side effects of repeated treatments due to the aggressive and recurrent nature of melanoma cells. Less-invasive topical chemotherapies by utilizing polymeric microneedles have emerged as an alternative, but the sustained, long-lasting release of drug cargos remains challenged. In addition...

In recent years, the metallization of polymers has been intensely studied as it takes advantage of both plastics and metals. Laser direct writing (LDW) is one of the most widely used technologies to obtain metal patterns on polymer substrates. In LDW technology , different methods including injection-molding, drop-casting, dip coating, and spin coa...

Successful rehabilitation of oropharyngeal swallowing disorders (i.e., dysphagia) requires frequent performance of head/ neck exercises that primarily rely on expensive biofeedback devices, often only available in large medical centers. This directly affects treatment compliance and outcomes, and highlights the need to develop a portable and inexpe...

Amputees with prosthetic hands face challenges accomplishing ordinary tasks in daily life. An optimal set of materials, design layouts, and assembly schemes is presented for the construction of stretchable sensor circuits on an easy-to-wear rubber glove, allowing for the seamless integration with arbitrary prosthetic hands. A wristwatch unit provid...

Guided manipulation of light through periodic nanoarrays of three dimensional (3D) metal-dielectric patterns provides remarkable opportunities to harness light in a way that cannot be obtained with conventional optics, yet its practical implementation remains hindered by a lack of effective methodology. Here we report a novel 3D nanoassembly method...

Advances in printing materials and techniques for flexible and hybrid electronics in the domain of connected healthcare have enabled rapid development of innovative body‐interfaced health monitoring systems at a tremendous pace. Thin, flexible, and stretchable biosensors that are printed on a biocompatible soft substrate provide the ability to noni...

The liquid-assisted transfer printing is emerging as a competitive manufacturing technique in the delivery and assembly of thin film-layered functional materials and structures. In essence, this technique is underpinned by the detachment of thin films under a synergistic effect of external mechanical loading and interior chemical reaction at interf...

Real-time monitoring of cellular behaviors and functions with sensor-instrumented scaffolds can provide a profound impact on fundamental studies of the underlying biophysics and disease modeling. Although quantitative measurement of predictive data for in vivo tests and physiologically relevant information in these contexts is important, the long-t...

Miniaturization of electronic components and advances in flexible and stretchable materials have stimulated the development of wearable health care systems that can reflect monitor personal health status by health care professionals. New skin-mountable devices that offer seamless contact onto the human skin, even under large deformations by natural...

With approximately 48,000 attributed deaths in 2017, the opioid overdose is now the leading cause of death amongst Americans under the age of 50. The overdose process can be interrupted by the administration of naloxone, a safe and effective opiate antagonist that can reverse the effects of overdose and minimizing the delay in administering the ant...

Sensitive sensing Neonatal care, particularly for premature babies, is complicated by the infants' fragility and by the need for a large number of tethered sensors to be attached to their tiny bodies. Chung et al. developed a pair of sensors that only require water to adhere to the skin and allow for untethered monitoring of key vital signs (see th...

Vertically ordered arrays of silicon nanoneedles (Si NNs), due to their nanoscale dimension and low cytotoxicity, could enable minimally invasive nanoinjection of biomolecules into living biological systems such as cells and tissues. Although production of these Si NNs on a bulk Si wafer has been achieved through standard nanofabrication technology...

Significance The ability to endow the surface of existing objects with desired electronic features enables many emerging applications such as Internet of Things (IoT). Despite significant progress in the optimization of thin-film materials and construction schemes, the realization of high-performance thin-film electronics on arbitrary place through...

Emerging transfer printing methods provide means to build a range of mechanically flexible and wearable bioelectronics, opening up a new prospect in the field of biomedical technologies. The mechanical flexibility allow the devices to intimately integrate with biological systems such as biological cells, tissues, and/or the skin at their length sca...

An important pathway for cost-effective light energy conversion devices, such as solar cells and light emitting diodes, is to integrate III-V (e.g., GaN) materials on Si substrates. Such integration first necessitates growth of high crystalline III-V materials on Si, which has been the focus of many studies. However, the integration also requires t...

By using subliming materials, Bong Hoon Kim, John A. Rogers, and co-workers successfully design dry electronic systems that undergo timed self-destruction. As described in article number 1606008, sublimation causes mechanical fragmentation and disintegration of the devices. The concept is promising for such diverse fields as biomedical implants, en...

The recent emergence of materials for electronic systems that are capable of programmable self-destruction and/or bio/eco-resorption creates the potential for important classes of devices that cannot be easily addressed using conventional technologies, ranging from temporary biomedical implants to enviromentally benign environmental monitors to har...

Mechanically reinforced skin-electronics are presented by exploiting networked nanocomposite elastomers where high quality metal nanowires serve as conducting paths. Theoretical and experimental studies show that the established skin-electronics exhibit superior mechanical enhancements against crack and delamination phenomena. Device applications i...

Biology is soft and curvilinear, whereas wafer-based electronics are rigid and planar. The mechanical mismatch impedes the effective integration of electronic systems with biological tissues or skins, paving the way for the construction of device materials (i.e., semiconducting composites) onto soft, biocompatible elastomers with the ability to be...

Photoelectrochemical (PEC) water splitting devices rely on light-absorbers to absorb sunlight, and the photogenerated electrons and holes further react with water to generate hydrogen and oxygen. Fabricating light-absorbers on textured substrates offers alternative routes for optimizing their PEC performance. Textured substrates would greatly enhan...

Here we report multilayer stacking of films of quantum dots (QDs), for the purpose of tailoring the energy band alignment between charge transport layers and light emitting layers of different colors in quantum dot light-emitting diodes (QD LED) for maximum efficiency in full color operation. The performance of QD LEDs formed by transfer printing c...

Wearable sensors have the potential to enable longitudinal, objective health monitoring in patients with chronic diseases, including cardiac rhythm disorders, neurological and movement disorders, diabetes, and pain. However, conventional wearable devices are typically comprised of rigid, packaged electronics, which may compromise overall signal fid...

Many procedures in modern clinical medicine rely on the use of electronic implants in treating conditions that range from acute coronary events to traumatic injury. However, standard permanent electronic hardware acts as a nidus for infection: bacteria form biofilms along percutaneous wires, or seed haematogenously, with the potential to migrate wi...

On-demand, localized release of drugs in precisely controlled, patient-specific time sequences represents an ideal scenario for pharmacological treatment of various forms of hormone imbalances, malignant cancers, osteoporosis, diabetic conditions and others. We present a wirelessly operated, implantable drug delivery system that offers such capabil...

Electronic systems that enable programmable transformation of functional behaviors by remote control or by autonomous responses to user-defined circumstances create unusual engineering opportunities, where physical changes in the hardware induce desired changes in operation. This paper presents materials and device architectures for technologies of...

The isolation of the two-dimensional semiconductor molybdenum disulphide introduced a new optically active material possessing a band gap that can be facilely tuned via elastic strain. As an atomically thin membrane with exceptional strength, monolayer molybdenum disulphide subjected to biaxial strain can embed wide band gap variations overlapping...

Human skin-like core/shell material encapsulating structures for wearable electronics serve to minimize interface stresses and mechanical constraints on natural body motions, with ability to strain isolate the active devices. On page 3698, Y. Huang, J. A. Rogers, and co-workers show how integrating emerging commercial classes of stretchable electro...

We report a simple, versatile, and wafer-scale water-assisted transfer printing method (WTP) that enables the transfer of nanowire devices onto diverse nonconventional substrates that were not easily accessible before, such as paper, plastics, tapes, glass, polydimethylsiloxane (PDMS), aluminum foil, and ultrathin polymer substrates. The WTP method...

This paper presents materials and core/shell architectures that provide optimized mechanical properties in packages for stretchable electronic systems. Detailed experimental and theoretical studies quantitatively connect the geometries and elastic properties of the constituent materials to the overall mechanical responses of the integrated systems,...

Hard and soft structural composites found in biology provide inspiration for the design of advanced synthetic materials. Many examples of bio-inspired hard materials can be found in the literature; far less attention has been devoted to soft systems. Here we introduce deterministic routes to low-modulus thin film materials with stress/strain respon...

Here we demonstrate materials and operating conditions that allow for high resolution printing of layers of quantum dots (QDs) with precise control over thickness and sub-micron lateral resolution, with capabilities for use as an active layer of QD light-emitting diode (LED). The shapes and thicknesses of the QD patterns exhibit systematic dependen...

Electronics that are capable of destroying themselves, on demand and in a harmless way, might provide the ultimate form of data security. This paper presents materials and device architectures for triggered destruction of conventional microelectronic systems by means of microfluidic chemical etching of the constituent materials, including silicon,...

Fabricating thin film solar cells (TFSCs) on flexible substrates will not only broaden the applications of solar cells, but also potentially reduce the installation cost. However, a critical challenge for fabricating flexible TFSCs on flexible substrates is the incompatibility issues between the thermal, mechanical and chemical properties of these...

This paper presents materials, device designs, and physical/electrical characteristics of a form of nanotube electronics that is physically transient, in the sense that all constituent elements dissolve and/or disperse upon immersion into water. Studies of contact effects illustrate the ability to use water soluble metals such as magnesium for sour...

Doping nanowires (NWs) is of crucial importance for a range of applications due to the unique properties arising from both impurities incorporation and nanoscale dimensions. However, existing doping methods face the challenge of simultaneous control over the morphology, crystallinity, dopant distribution and concentration at the nanometer scale. He...

We report a scalably-synthesized WO3/BiVO4 core/shell nanowire photoanode in which BiVO4 is the primary light-absorber and WO3 acts as an electron conductor. These core/shell nanowires achieve the highest product of light absorption and charge separation efficiencies among BiVO4-based photoanodes to date and, even without an added catalyst, produce...

We report a new flame reduction method to generate controllable amount of oxygen vacancies in TiO2 nanowires that leads to nearly three times improvement in the photoelectrochemical (PEC) water-splitting performance. The flame reduction method has unique advantages of a high temperature (>1000 (o)C), ultra-fast heating rate, tunable reduction envir...

Peel-and-stick process, or water-assisted transfer printing (WTP), represents an emerging process for transferring fully fabricated thin-film electronic devices with high yield and fidelity from a SiO2/Si wafer to various non-Si based substrates, including papers, plastics and polymers. This study illustrates that the fundamental working principle...

An electro-assisted method is developed to transfer silicon (Si) wire arrays from the Si wafers on which they are grown to other substrates while maintaining their original properties and vertical alignment. First, electro-assisted etching is used to form a sacrificial porous Si layer underneath the Si wires. Second, the porous Si layer is separate...

Recent density-functional theory calculations suggest that codoping TiO2 with donor-acceptor pairs is more effective than monodoping for improving photoelectrochemical water-splitting performance because codoping can reduce charge recombination, improve material quality, enhance light absorption and increase solubility limits of dopants. Here we re...

Fabrication of thin-film solar cells (TFSCs) on substrates other than Si and glass has been challenging because these nonconventional substrates are not suitable for the current TFSC fabrication processes due to poor surface flatness and low tolerance to high temperature and chemical processing. Here, we report a new peel-and-stick process that cir...

Polycrystalline Si (poly-Si) thin-film, due to its low Si consumption, low substrate cost and good stability, is an attractive candidate for cost-effective solar cells, but the as-deposited poly-Si typically has a columnar structure with grain boundaries in between, severely limiting the efficiency of the poly-Si. Here, we report a micropillar poly...