Jongha Lee

Multifunctional wearable devices for diagnosis and therapy of movement disorders

Wearable systems that monitor muscle activity, store data and deliver feedback therapy are the next frontier in personalized medicine and healthcare. However, technical challenges, such as the fabrication of high-performance, energy-efficient sensors and memory modules that are in intimate mechanical contact with soft tissues, in conjunction with controlled delivery of therapeutic agents, limit the wide-scale adoption of such systems. Here, we describe materials, mechanics and designs for multifunctional, wearable-on-the-skin systems that address these challenges via monolithic integration of nanomembranes fabricated with a top-down approach, nanoparticles assembled by bottom-up methods, and stretchable electronics on a tissue-like polymeric substrate. Representative examples of such systems include physiological sensors, non-volatile memory and drug-release actuators. Quantitative analyses of the electronics, mechanics, heat-transfer and drug-diffusion characteristics validate the operation of individual components, thereby enabling system-level multifunctionalities.

Bioresorbable Electronic Stent Integrated with Therapeutic Nanoparticles for Endovascular Diseases

Implantable endovascular devices such as bare metal, drug eluting, and bioresorbable stents have transformed interventional care by providing continuous structural and mechanical support to many peripheral, neural, and coronary arteries affected by blockage. Although effective in achieving immediate restoration of blood flow, the long-term re-endothelialization and inflammation induced by mechanical stents are difficult to diagnose or treat. Here we present nanomaterial designs and integration strategies for the bioresorbable electronic stent with drug-infused functionalized nanoparticles to enable flow sensing, temperature monitoring, data storage, wireless power/data transmission, inflammation suppression, localized drug delivery, and hyperthermia therapy. In vivo and ex vivo animal experiments as well as in vitro cell studies demonstrate the previously unrecognized potential for bioresorbable electronic implants coupled with bioinert therapeutic nanoparticles in the endovascular system.

Ultra-Wideband Multi-Dye-Sensitized Upconverting Nanoparticles for Information Security Application

Multi-dye-sensitized upconverting nanoparticles (UCNPs), which harvest photons of wide wavelength range (450-975 nm) are designed and synthesized. The UCNPs embedded in a photo-acid generating layer are integrated on destructible nonvolatile resistive memory device. Upon illumination of light, the system permanently erases stored data, achieving enhanced information security.

Human eye-inspired soft optoelectronic device using high-density MoS 2 -graphene curved image sensor array

Soft bioelectronic devices provide new opportunities for next-generation implantable devices owing to their soft mechanical nature that leads to minimal tissue damages and immune responses. However, a soft form of the implantable optoelectronic device for optical sensing and retinal stimulation has not been developed yet because of the bulkiness and rigidity of conventional imaging modules and their composing materials. Here, we describe a high-density and hemispherically curved image sensor array that leverages the atomically thin MoS2-graphene heterostructure and strain-releasing device designs. The hemispherically curved image sensor array exhibits infrared blindness and successfully acquires pixelated optical signals. We corroborate the validity of the proposed soft materials and ultrathin device designs through theoretical modeling and finite element analysis. Then, we propose the ultrathin hemispherically curved image sensor array as a promising imaging element in the soft retinal implant. The CurvIS array is applied as a human eye-inspired soft implantable optoelectronic device that can detect optical signals and apply programmed electrical stimulation to optic nerves with minimum mechanical side effects to the retina.Soft and flexible optoelectronic devices may provide effective routes toward retinal implants for enhanced visual functions. Here, the authors fabricate a curved array of flexible MoS2-graphene photodetectors and demonstrate its potential application as ophthalmic imaging element in mouse models.

High-Resolution Spin-on-Patterning of Perovskite Thin Films for a Multiplexed Image Sensor Array

Inorganic-organic hybrid perovskite thin films have attracted significant attention as an alternative to silicon in photon-absorbing devices mainly because of their superb optoelectronic properties. However, high-definition patterning of perovskite thin films, which is important for fabrication of the image sensor array, is hardly accomplished owing to their extreme instability in general photolithographic solvents. Here, a novel patterning process for perovskite thin films is described: the high-resolution spin-on-patterning (SoP) process. This fast and facile process is compatible with a variety of spin-coated perovskite materials and perovskite deposition techniques. The SoP process is successfully applied to develop a high-performance, ultrathin, and deformable perovskite-on-silicon multiplexed image sensor array, paving the road toward next-generation image sensor arrays.

Calculation of CO2 laser beam absorptance as a function of temperature for steels by the numerical method

Temperature distributions were measured during the irradiation of a CO2 laser beam at one end of a rod-shaped specimen and at the centre of a thin plate-shaped specimen. Regarding the measured temperature distributions as one-dimensional and two-dimensional unsteady state heat transfer solutions, CO2 laser beam absorptances were calculated using a modified finite difference method. Temperature dependence of thermal properties, heat loss due to convection and latent heat during melting of the specimen were taken into account in this numerical calculation. Increasing the specimen temperature from room temperature to melting point, absorptances of STS304 stainless steel and SM45C steel were calculated as 8 ∼ 40% and 6 ∼ 41% for the one-dimensional calculation, and as 9.3 ∼ 41% and 5 ∼ 41% for the two-dimensional calculation, respectively. These calculated absortances were very close to theoretical values at relatively low temperature, which were calculated from the electrical resistivities of the specimens. Increasing the temperature of the specimens, absorptances increased considerably due to oxidation of the specimens. Regardless of specimen composition and specimen dimension, both absorptances showed nearly the same value of 41% at their melting points, in which the structures of both metals became amorphous phases.

High performance bio-integrated devices

In recent years, personalized electronics for medical applications, particularly, have attracted much attention with the rise of smartphones because the coupling of such devices and smartphones enables the continuous health-monitoring in patients’ daily life. Especially, it is expected that the high performance biomedical electronics integrated with the human body can open new opportunities in the ubiquitous healthcare. However, the mechanical and geometrical constraints inherent in all standard forms of high performance rigid wafer-based electronics raise unique integration challenges with biotic entities. Here, we describe materials and design constructs for high performance skin-mountable bio-integrated electronic devices, which incorporate arrays of single crystalline inorganic nanomembranes. The resulting electronic devices include flexible and stretchable electrophysiology electrodes and sensors coupled with active electronic components. These advances in bio-integrated systems create new directions in the personalized health monitoring and/or human-machine interfaces.