Science
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Flexible Drug Delivery Microdevice to Advance Precision Medicine
(Schematic view of flexible microdevice: The flexible drug delivery device for controlled release fabricated via inorganic laser lift off.)
A KAIST research team has developed a flexible drug delivery device with controlled release for personalized medicine, blazing the path toward theragnosis.
Theragnosis, an emerging medical technology, is gaining attention as key factor to advance precision medicine for its featuring simultaneous diagnosis and therapeutics. Theragnosis devices including smart contact lenses and microneedle patches integrate physiological data sensors and drug delivery devices. The controlled drug delivery boasts fewer side-effects, uniform therapeutic results, and minimal dosages compared to oral ingestion. Recently, some research groups conducted in-human applications of controlled-release bulky microchips for osteoporosis treatment. However they failed to demonstrate successful human-friendly flexible drug delivery systems for controlled release.
For this microdevice, the team under Professor Daesoo Kim from the Department of Biological Science and Professor Keon Jae Lee from the Department of Materials Science and Engineering, fabricated a device on a rigid substrate and transferred a 50 µm-thick active drug delivery layer to the flexible substrate via inorganic laser lift off. The fabricated device shows mechanical flexibility while maintaining the capability of precise administration of exact dosages at desired times. The core technology is to produce a freestanding gold capping layer directly on top of the microreservoir with the drugs inside, which had been regarded as impossible in conventional microfabrication.
The developed flexible drug delivery system can be applied to smart contact lenses or the brain disease treatments by implanting them into cramped and corrugated organs. In addition, when powered wirelessly, it will represent a novel platform for personalized medicine. The team already proved through animal experimentation that treatment for brain epilepsy made progress by releasing anti-epileptic medication through the device.
Professor Lee believes the flexible microdevice will further expand the applications of smart contact lenses, therapeutic treatments for brain disease, and subcutaneous implantations for daily healthcare system. This study “Flexible Wireless Powered Drug Delivery System for Targeted Administration on Cerebral Cortex” was described in the June online issue of Nano Energy.
(Photo: The flexible drug delivery device for contolled relase attached on a glass rod.)
2018.08.13 View 8197 -
The MSE/CBE Int'l Workshop Explores Big Ideas in Emerging Materials
(KAIST President Sung-Chul Shin with scholars participated in the workshop)
The MSE/CBE International Workshop brought together editors from key academic journals in multidisciplinary materials science and scholars from leading universities at KAIST on Aug. 7.
The workshop hosted ten distinguished speakers in the fields of nanostructures for next-generation emerging applications, chemical and bio-engineering, and materials innovation for functional applications. They explored opportunities and challenges for reinventing novel materials that will solve complex problems.
(From left: Professor Buriak, Professor Swager and Professor Il-Doo Kim)
Speakers included: Chief Editor of Nature Materials Vincent Dusastre; Editor-in- Chief of ACS NANO and professor at UCLA Paul S. Weiss; Jillian M. Buriak, Editor-in-Chief of Chemistry of Materials; Associate Editor of Macromolecules and professor at MIT Timothy M. Swager; Coordinating Editor of Acta Materialia and Head of the Department of Materials Science and Engineering at MIT Christopher A. Schuh; Editor-in-Chief of Biotechnology Journal and Metabolic Engineering and Distinguished Professor at KAIST Sang-Yup Lee; Associate Editor of Energy Storage Materials and professor at KAIST Sang Ouk Kim; Professor Jeffrey C. Grossman at MIT; Professor Zhenan Bao at Stanford University; and Professor Hyuck Mo Lee, head of the Department of Materials Science and Engineering at KAIST.
Interdisciplinary materials research holds the key to building technological competitiveness in many industrial sectors extending from energy, environment, and health care to medicine and beyond. It has also been the bedrock of KAIST’s scholarship and research innovation. More than 200 faculty members in the field of materials science produce about 800 SCI papers every year. The two departments of materials science and chemical biomolecular engineering are leading KAIST’s global reputation, as they were both ranked 13th and 14th in the QS World University Ranking by Subject this year.
(Professor Il-Doo Kim fromt he Department of Materials Science Engineering)
Professor Il-Doo Kim from the Department of Materials Science Engineering has been the chair of this workshop from 2016. In hosting the second one this year, he said that he hopes this year’s workshop will inspire many materials scientists to have big ideas and work to make those big ideas get noticed in order to have a real impact.
(KAIST President Sung-Chul Shin)
President Sung-Chul Shin, who is a physicist specializing in materials physics, expressed his keen interest in the workshop, saying innovative materials made of unthinkable and noble combinations will be the key factor in determining the competitiveness of new technology and new industries. He lauded international collaborations for making new materials and the scholarly passion to evaluate the materials’ characteristics that made this significant progress possible.
Dr. Vincent Dusastre, chief editor of Nature Materials, presented recent trends in materials for energy. He described how the rational design and improvement of materials’ properties can lead to energy alternatives which will compete with existing technologies. He pointed out that given the dramatic fundamental and practical breakthroughs that are taking place in the realization of solar cells with high energy-conversion efficiency, the improvement of batteries for electric vehicles and the grid is also a major challenge. He stressed, “Key advances in sustainable approaches beyond Li-ion batteries and control of redox processes are also greatly needed.”
Meanwhile, ACS NANO Editor-in-Chief Paul S. Weiss spoke on the importance of heterogeneity in the structure and function of molecules and nanoscale assemblies. He stressed that such extensiveness of multi-interdisciplinary research will accelerate a greater impact as indicated when the fields of neuroscience and microbiome converged with nanoscience and nanotechnology.
Editor-in-Chief of Chemistry of Materials Professor Jillian M. Buriak from the University of Alberta described how predictive models and machine learning can replace time consuming empirical device production and screening. By understanding and pinpointing the frustrating bottlenecks in the design of stable and efficient organic photovoltaics, much faster throughput can be obtained to enable a more direct pathway to stability, efficiency, and finally commercialization.
2018.08.13 View 10996 -
How to Trigger Innate Fear Response?
(Figure:This illustration describes how ACC-BLA circuit controls innate freezing response depending on its activity level.)
When animals encounter danger, they usually respond to the situation in one of two ways: to freeze or to flee. How do they make this quick decision in a life or death moment?
According to KAIST neuroscientists, there are two types of fear: learned versus innate. The latter is known to be induced without any prior experience and is thus naturally encoded in the brain. A research team under Professor Jin-Hee Han in the Department of Biological Sciences identified the brain circuit responsible for regulating the innate fear response.
The study, which appeared in the July 24 issue of Nature Communications represents a significant step toward understanding how the neural circuits in the prefrontal cortex create behavioral responses to external threats. This also represents a new paradigm in therapeutic development for fear-related mental disorders.
Responses of freezing or fleeing when facing external threats reflect behavioral and physiological changes in an instinctive move to adapt to the new environment for survival. These responses are controlled by the emotional circuit systems of the brain and the malfunction of this circuit leads to fear-related disorders.
The anterior cingulate cortex (ACC) is a sub-region within the prefrontal cortex, comprising a part of the brain circuitry that regulates behavioral and physiological fear responses. This area is capable of high-order processing of the perceived sensory information and conveys ‘top-down’ information toward the amygdala and brainstem areas, known as the response outlet.
Many studies have already demonstrated that the brain regions in the prefrontal cortex regulate the response against learned threats. However, it has been unknown how innate responses against fear are encoded in the neural circuits in the prefrontal cortex.
Dr. Jinho Jhang, the lead author of the study explains how the team achieved their key idea. “Many overseas studies have already proved that the prefrontal cortex circuit works to regulate the fear response. However, researchers have paid little attention to the innate response against predators. Professor Han suggested we do research on the instinctive fear response instead of the learned response. We particularly focused on the anterior cingulate region, which has been connected with memory, pain, and sympathy, but not the fear response itself. Since we turned in this new direction, we have accumulated some significant data,” said Dr. Jhang.
For this study, Professor Han’s team investigated how mice react when exposed to the olfactory stimuli of predators. Based on the results of optogenetic manipulation, neural circuit tracing, and ex vivo slice electrophysiology experiments, the team demonstrated that the anterior cingulate cortex and its projection input to the basolateral amygdala play a role in the inhibitory regulation of innate fear responses to predators’ odors in mice.
Professor Han believes these results will extend the understanding of how instinctive fear responses can be encoded in our brain circuits. “Our findings will help to develop therapeutic treatments for mental disorders aroused from fear such as panic disorders and post-traumatic stress disorder,” said Professor Han.
2018.08.08 View 7352 -
A Breakthrough for Understanding Glioblastoma: Origin Cells for Deadly Brain Tumors Identified
Figure 1. The pattern of GBM genesis is similar to that of firework. The bottom canon represents the first occurrence of the SVZ mutated cell.
A new study by KAIST researchers identified where the mutation causing glioblastoma starts. According to the study, neural stem cells away from the tumor mass are the cells of origin that contain mutation drivers for glioblastoma, one of the most aggressive brain tumor. This breakthrough research, reported in Nature on August 1, gives insights for understanding why glioblastomas almost always grow back, even after surgery, and suggests novel ways to treat glioblastoma, which was previously thought to be incurable.
Like most cancers, glioblastoma is treated with surgery to remove as much of the tumor as possible, then radiation and chemotherapy. However, it almost always returns in less than a year and its median survival time is only 15 months. Precision therapeutic approaches targeting tumors themselves didn’t lead to any breakthroughs.
Professor Jeong Ho Lee’s team at the Graduate School of Medical Science and Engineering described direct genetic evidence through the deep sequencing of all triple-matched samples: normal SVZ tissue away from the tumor mass, tumor tissue, and normal cortical tissue. The research team studied 28 patients with glioblastomas and other types of brain tumors who underwent supra-total resection or other surgical resections of tumors, providing access to normal subventricular zone (SVZ) tissue (where neural stem cells are located) away from the tumor mass. The researchers used various deep and single cell sequencing technologies to conduct comparative DNA analysis on the samples from the patient’s SVZ tissue and tumors.
They reported that normal SVZ tissue away from the tumor in 56.3% of patients with glioblastoma already contained low-level glioblastoma driver mutations that were observed at high levels in their matching tumors. Furthermore, the research team generated a genome edited mouse carrying glioblastoma mutations in the SVZ and showed that neural stem cells with mutations migrate from the SVZ lead to the development of glioblastomas in distant brain regions. (See the image below)
Professor Lee conducted this study in collaboration with Professor Seok-Gu Kang of the Brain Tumor Center at Severance Hospital of Yonsei University. He said, “It’s easier to understand when we compare it to fireworks. Every flare flying around sky can be likened to cancer cells even though the fireworks are triggered on the ground. We found the trigger.” The identification of this mutation pathway of glioblastomas will lead to a new paradigm for therapeutic strategies. He added, “Now, we can focus on interrupting the recurrence and evolution of glioblastomas.”
Professor Lee has investigated mutations arising in the brain for a decade. He is developing innovative diagnostics and therapeutics for untreatable brain disorders including intractable epilepsy and glioblastoma at a tech-startup, SoVarGen. “All technologies we used during the research were transferred to the company. This research gave us very good momentum to reach the next phase of our startup,” he remarked.
Figure 2. Genetic analysis of tumor-free SVZ tissue and matching tumor tissue from GBM patients.
Figure 3. Glioma progression in genome edited mice carrying GBM mutations in the SVZ
2018.08.02 View 11532 -
A New Efficient Oxide Coating Technology to Improve Fuel Cells
A new efficient oxide coating technology that can be applied in less than five minutes could lead to dramatic improvements in the lifetime and performance of fuel cells. The fundamental principle behind this approach is maximizing the oxygen reduction reaction site of a platinum thin-film electrode, preventing the electrodes from aggregating at high temperatures.
Fuel cells have emerged as a clean electricity generation system that does not pollute the air. In particular, solid oxide fuel cells (SOFCs) are beginning to gain a great deal of attention due to their higher power generation efficiency compared to other fuel cells. It is also advantageous to use other power sources than expensive hydrogen fuel.
However, the high costs and insufficient lifetimes caused by high temperatures needed to operate the solid oxide fuel cells have remained significant challenges to commercialization.
Recently, attempts to lower the operating temperature (< 600°C) of these devices by introducing thin-film processes have drew attention of researchers, with the resulting products known as thin-film-based solid oxide fuel cells.
In order to create enhanced device performance at lower temperatures, the research team, led by Professor WooChul Jung in the Department of Materials Science and Engineering, applied and developed oxide coating technology to maximize the oxygen reduction reaction sites of a platinum thin-film electrode and to prevent platinum electrodes from thermal aggregating.
The team succeeded in over-coating a platinum electrode with a new coating material called praseodymium-doped ceria (Pr,Ce)O2-, which has high conductivity for both electrons and oxygen ions and excellent catalytic properties for oxygen reduction reactions. As a result, electrode resistance was reduced by more than 1000 times, creating the potential for these electrodes to be used in high-temperature electrochemical cells.
In addition, they proposed that the high performance of thin-film-based oxide fuel cells’ oxygen electrodes could be realized through the nano-structuring of (Pr,Ce)O2-δ without any platinum.
Professor Jung said, “The electrode coating technology used in this study is of great technical value because of the utilization of affordable and mass-produced electrochemical deposition.” He added, “In the future, this technology will be feasible for replacing platinum electrodes in thin-film-based oxide fuel cells, and we expect that the affordable prices of this fuel cell will eventually boost market competitiveness.”
This research was described in Advanced Energy Materials in July and was featured as the Inside Front Cover and video abstract. It was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Korea Electric Power Corporation (KEPCO) Research Institute.
Figure 1. The change of electrode activity with and without overcoated (Pr,Ce)O2-δ nanostructures.
2018.07.18 View 7906 -
Mechanism Leading to Cortical Malformation from Brain-Only Mutations Identified
Focal malformations of cortical development (FMCDs) are a heterogeneous group of brain cortical abnormalities. These conditions are the most common causes of medically refractory epilepsy in children and are highly associated with intellectual disability, developmental delay, and autism-spectrum disorders. Despite a broad spectrum of cortical abnormalities in FMCDs, the defective migration of neuronal cells is considered a key pathological hallmark.
A research team led by Professor Jeong Ho Lee in the Graduate School of Medical Science and Engineering at KAIST has recently investigated the molecular mechanism of defective neuronal migration in FMCDs. Their research results were published online in Neuron on June 21, 2018.
The research team previously demonstrated that brain-only mutations in the mechanistic target of rapamycin (MTOR) gene causes focal cortical dysplasia, one major form of FMCDs leading to intractable epilepsy in children. However, the molecular mechanisms by which brain-only mutations in MTOR lead to cortical dyslamination and defective neuronal migration in FMCDs remain unclear.
To study the molecular mechanism of brain cortical dyslamination, the research team utilized patients’ brain tissues and modeled the MTOR mutation-carrying cell and animal models recapitulating the pathogenesis and symptoms of FMCD patients. By performing comprehensive molecular genetic experiments, they found that the formation of primary cilia, one of cellular organelles, was disrupted in MTOR mutation-carrying neurons and demonstrated that this ciliary disruption was a cause of cortical dyslamination in FMCDs.
MTOR mutations prevented degradation of the OFD1 protein, one of the negative regulators of ciliary formation. As a result, the OFD1 protein was abnormally accumulated in MTOR mutation-carrying neurons, causing focal cortical dyslamination. By suppressing the expression of the OFD1 protein, the research team was able to rescue the defective formation of primary cilia, leading to the restoration of cortical dyslamination and defective neuronal migration considerably.
Based on these results, the research team is carrying out further research to develop novel therapeutics for patients with FMCDs caused by brain-only mutations.
This work was supported by grants from the Suh Kyungbae Foundation and Citizens United for Research in Epilepsy.
The research paper is titled “Brain Somatic Mutations in MTOR Disrupt Neuronal Ciliogenesis, Leading to Focal Cortical Dyslamination.” (Digital Object Identifier #: 10.1016/j.neuron.2018.05.039)
Picture 1: The disrupted formation of primary cilia in brain tissues of FMCD mouse models and patients with FMCDs caused by brain somatic mutations in MTOR.
Picture 2: The rescue of defective ciliary formation in FMCD mouse models leading to the restoration of cortical dyslamination and defective neuronal migration.
2018.07.02 View 7999 -
Distinguished Professor Koh Donates His Ho-Am Prize Money
(From left: Distinguished Professor Gou Young Koh and KAIST President Sung-Chul Shin)
Distinguished Professor Gou Young Koh from the Graduate School of Medical Science and Engineering donated one hundred million KRW to KAIST that he received for winning the Ho-Am Prize.
Professor Koh, who is widely renowned for angiogenesis, was appointed as the 2018 laureate of the 28th Ho-Am Prize for demonstrating the effective reduction of tumor progression and metastasis via tumor vessel normalization.
He made the donation to the Graduate School of Medical Science and Engineering, where he conducted his research. “As a basic medical scientist, it is my great honor to receive this prize for the recognition of my research outcome. I will give impetus to research for continuous development,” Professor Koh said.
Professor Koh also received the 5th Asan Award in Medicine in 2012 and the 7th Kyung-Ahm Award in 2011. He was also the awardee of the 17th Wunsch Medical Award. He has donated cash prizes to the school every time he is awarded.
KAIST President Sung-Chul Shin said, “I would like to express my gratitude to the professor for his generous donation to the school. It will be a great help fostering outstanding medical scientists.
Professor Koh received his MD-PhD from the Medical School of Chonbuk National University. After finishing his post-doctoral program at Cornell University and Indiana State University, he was appointed as a professor at Chonbuk National University and POSTECH. Currently, he holds the position of distinguished professor at KAIST and director of the IBS Center for Vascular Research.
2018.06.20 View 5086 -
KAIST Team Develops Flexible Blue Vertical Micro LEDs
A KAIST research team developed a crucial source technology that will advance the commercialization of micro LEDs.
Professor Keon Jae Lee from the Department of Materials Science and Engineering and his team have developed a low cost production technology for thin-film blue flexible vertical micro LEDs (f-VLEDs).
In CES 2018, micro LED TV was spotlighted as a strong candidate for replacing the active-matrix organic light-emitting diode (AMOLED) display. Micro LED is a sub-100 um light source for red, green and blue light, which has advantages of outstanding optical output, ultra-low power consumption, fast response speed, and excellent flexibility.
However, the current display industry has utilized the individual chip transfer of millions of LED pixels, causing high production cost. Therefore, the initial market of micro LED TV will be estimated to ~ a hundred thousand dollars for global premium market.
To widely commercialize micro LEDs for mobile and TV displays, the transfer method of thin film micro LEDs requires a one-time transfer of one million LEDs. In addition, highly efficient thin-film blue micro LED is crucial for a full-color display.
The team developed thin-film red f-VLED in previous projects, and now has realized thousands of thin-film blue vertical micro LEDs (thickness < 2 μm) on plastics using a one-time transfer.
The blue GaN f-VLEDs achieved optical power density (~30 mW/mm2) three times higher than that of lateral micro LEDs, and a device lifetime of 100,000 hours by reducing heat generation. These blue f-VLEDs could be conformally attached to the curved skin and brains for wearable devices, and stably operated by wirelessly transferred electrical energy.
Professor Lee said, “For future micro LEDs, the innovative technology of thin-film transfer, efficient devices, and interconnection is necessary. We plan to demonstrate a full-color micro LED display in smart watch sizes by the end of this year. ”
This research “ Monolithic Flexible Vertical GaN Light‐Emitting Diodes for a Transparent Wireless Brain Optical Stimulator ” led by a PhD candidate Han Eol Lee was published in the June 2018 issue of Advanced Materials.
Figure 1. Schematic image of wireless thin-film blue f-VLED arrays on the brain surface
Figure 2. Photo of high-performance and high-density blue f-VLED arrays
2018.06.18 View 8310 -
Professor YongKeun Park Wins the 2018 Fumio Okano Award
(Professor Park)
Professor YongKeun Park from the Department of Physics won the 2018 Fumio Okano Award in recognition of his contributions to 3D display technology development during the annual conference of the International Society for Optics and Photonics (SPIE) held last month in Orlando, Florida in the US.
The Fumio Okano Best 3D Paper Prize is presented annually in memory of Dr. Fumio Okano, a pioneer and innovator of 3D displays who passed away in 2013, for his contributions to the field of 3D TVs and displays. The award is sponsored by NHK-ES.
Professor Park and his team are developing novel technology for measuring and visualizing 3D images by applying random light scattering. He has published numerous papers on 3D holographic camera technology and 3000x enhanced performance of 3D holographic displays in renowned international journals such as Nature Photonics, Nature Communications, and Science Advances. His technology has drawn international attention from renowned media outlets including Newsweek and Forbes.
He has established two startups to commercialize his technology. Tomocube specializes in 3D imaging microscopes using holotomographic technology and the company exports their products to several countries including the US and Japan. The.Wave.Talk is exploring technology for examining pre-existing bacteria anywhere and anytime.
Professor Park’s innovations have already been recognized in and out of KAIST. In February, he was selected as the KAISTian of the Year for his outstanding research, commercialization, and startups. He was also decorated with the National Science Award in April by the Ministry of Science and ICT and the Hong Jin-Ki Innovation Award later in May by the Yumin Cultural Foundation.
Professor Park said, “3D holography is emerging as a significant technology with growing potential and positive impacts on our daily lives. However, the current technology lags far behind the levels displayed in SF movies. We will do our utmost to reach this level with more commercialization."
2018.05.31 View 8991 -
Platinum Catalyst Has Price Lowed and Durability Doubled
(Professor Cho in the Department of Materials Science and Engineering)
Professor EunAe Cho in the Department of Materials Science and Engineering reported a fuel cell catalyst that shows 12 times higher performance and twice the durability than previously used platinum catalyst.
Fuel cells, eco-friendly power generators, are said to be running air purifiers. A hydrogen vehicle powered by fuel cells can allegedly purify more than 98 percent of the particulate matter and ultrafine particles from the amount of air that 70 adults breathe.
Despite this peculiarity, the high price of platinum, which is used as an electrode catalyst, remains a big challenge to accelerating commercialization. In addition, recently developed ‘nano-structured platinum catalysts’ have not yet commercialized due to its meager oxygen reduction reaction and durability in fuel cell.
Addressing all those challenges, Professor Cho’s team reported a platinum catalyst costing 30 percent less but boasting 12 times higher performance.
The research team, to this end, combined the platinum with nickel, then applied various metallic elements for making the most efficient performance. Among others, they found that the addition of gallium can modulate the oxygen intermediate binding energy, leading to enhanced catalytic activity of the oxygen reduction reaction.
They made octahedron nanoparticle platinum-nickel alloy and could efficiently achieve 12-times high performance with the platinum catalyst by adding gallium to the surface of octahedron.
Existing fuel cell catalysts have issues in practical fuel cell applications. However, Professor Cho’s team experimentally proved the high performance of the catalyst even in the fuel cell, and is expected to be practically applied to the existing procedure.
First author JeongHoon Lim said their work demonstrates the gallium-added octahedral nanoparticles can be utilized as a highly active and durable oxygen reduction reaction catalyst in practical fuel cell applications. It will make it feasible for the mass production of the catalysts.
Professor Cho also said, “Our study realized the two main goals: an affordable price and increased performance of fuel cells. We hope this will make a contribution to the market competitiveness of fuel cell electric vehicles.”
This research was described in Nano Letters in April and was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP), the National Research Foundation (NRF), and the Agency for Defense Development (ADD).
(Figure: HAADF STEM images with EDX analyses and line scanning profiles of (a) Ga-PtNi/C and (b) PtNi/C during the voltage-cycling tests. The composition changes of Ni, Pt, and Ga atoms in the nanoparticles were determined by EDX (inset in the EDX mapping results)).
2018.05.15 View 6857 -
Capillary Forces at Work for Lithium-Sulfur Batteries
Professor Do Kyung Kim from the KAIST Department of Materials Science and Engineering and his team succeeded in developing high-areal-capacity lithium sulfur batteries (Li-S batteries) by capturing polysulfide with carbon nanofibers. This research will provide new batteries to replace existing lithium rechargeable batteries, shifting the commercialization of related technologies ahead.
Electrical vehicles and large-scale energy storage systems necessitate the development of batteries with high energy density and cost effectiveness, and Li-S batteries are known to be one of the promising alternatives to the predominant lithium ion batteries.
With six times as much energy density, Li-S batteries theoretically thrust electric vehicle to twice the distance of lithium ion batteries. Therefore, they have been spotlighted as next-generation lithium rechargeable batteries because they can go up to 400km once charged.
However, several issues make it challenging to readily commercialize Li-S batteries. The low electrical conductivity of sulfur, volumetric expansion and contraction of the battery during charge and discharge, and permanent damage of the electrode caused by the dissolution of the lithium polysulfide into the electrolyte – known as the “shuttle effect” – are three of the biggest obstacles to commercial-grade Li-S batteries.
While there have been numerous attempts to curb, avoid, or alleviate these issues — such as the physical encapsulation of sulfur using various metal oxides or carbonaceous matrices — most of them entail utilizing zero-dimensional (0D) carbon materials. This encapsulation method has been somewhat effective in enhancing the electrical conductivity of sulfur while simultaneously tolerating some volumetric alterations and suppressing the shuttle effect. The downside of 0D carbon material-based encapsulation methods is their complicated synthetic processing and the limited mass loading of sulfur.
With this in mind, the team set out to employ one-dimensional (1D) carbon materials instead. Unlike the 0D case, 1D carbon materials render a large surface area and a long-range conduction path for electrons and lithium ions. Being 1D also solves the undesirable high-contact resistance problem frequently encountered by 0D carbon material-based encapsulation.
The key to developing the proposed material was to exploit the capillary force to decrease the energy associated with the dissolution of polysulfides. As such, carbon nanofibers (CNFs) were found to be suitable for high-areal-capacity lithium-sulfur batteries since capillary force acting between CNFs can take advantage of the high electrical conductivity with the suppressed dissolution of sulfides.
The research findings show that sulfur was successfully contained in between the CNFs by wetting due to the capillary force without the need for complicated synthetic processing, as in the 0D case. The research results indicate that the sulfur contained per unit area (mg/cm2) is five times greater for the newly implemented method, which then enabled the lithium-sulfur battery to achieve an areal capacity of 7 mAh/cm2, which amounts to as much as at most seven times that of conventional lithium ion batteries.
First author Jong Hyuk Yun stated that the unprecedented methods utilized in this study will help further and widen the progress of lithium batteries in general. Meanwhile, Professor Kim said, “This study brought us closer to commercial-grade high-capacity Li-S batteries, which are applicable for a wide variety of products, including electric vehicles, unmanned aerial vehicles (UAVs), and drones.”
This research, led by PhD candidate Yun, was published in the 18th issue of this year’s Nano Letters.
Figure 1. Electrochemical reaction leading to the containment of the sulfur within the carbon nanofiber and the corresponding specific capacity of the battery over a number of charge-discharge cycles
Figure 2. SEM images of the first discharged electrode containing lithium sulfide at the junction between the nanofibers, and the first charged electrode
Figure 3. carbon nanofiber effectively absorbing liquid based lithium polysulfide
2018.05.14 View 7244 -
New Material for Generating Energy-Efficient Spin Currents
(Professor Byong-Guk Park (left) and Professor Kab-Jin Kim)
Magnetic random access memory (MRAM) is emerging as next-generation memory. It allows information to be kept even without an external power supply and its unique blend of high density and high speed operation is driving global semiconductor manufacturers to develop new versions continuously.
A KAIST team, led by Professor Byong-Guk Park in the Department of Materials Science and Engineering and Professor Kab-Jin Kim in the Department of Physics, recently has developed a new material which enables the efficient generation of a spin current, the core part of operating MRAM. This new material consisting of ferromagnet-transition metal bilayers can randomly control the direction of the generated spin current unlike the existing ones.
They also described a mechanism for spin-current generation at the interface between the bottom ferromagnetic layer and the non-magnetic spacer layer, which gives torques on the top magnetic layer that are consistent with the measured magnetization dependence.
When applying this to spin-orbit torque magnetic memory, it shows the increased efficiency of spin torque and generation of the spin current without an external magnetic field. High-speed operation, the distinct feature of spin-orbit torque-based MRAM that carries its non-volatility, can significantly reduce the standby power better than SRAM.
This new material will expect to speed up the commercialization of MRAM. The research team said that this magnetic memory will further be applied to mobile, wearable, and IoT devices.
This study, conducted in collaboration with Professor Kyung-Jin Lee from Korea University and Dr. Mark Stiles from the National Institute of Standards and Technology in the US, was featured in Nature Materials in March. The research was funded by the Creative Materials Discovery Program of the Ministry of Science and ICT.
(Figure: Ferromagnet-transition metal bilayers which can randomly control the direction of the generated spin current)
2018.05.11 View 8810