Se Youn Cho

Microporous Carbon Nanoplates from Regenerated Silk Proteins for Supercapacitors

Novel carbon-based microporous nanoplates containing numerous heteroatoms (H-CMNs) are fabricated from regenerated silk fibroin by the carbonization and activation of KOH. The H-CMNs exhibit superior electrochemical performance, displaying a specific capacitance of 264 F/g in aqueous electrolytes, a specific energy of 133 Wh/kg, a specific power of 217 kW/kg, and a stable cycle life over 10000 cycles.

Carbonization of a stable β-sheet-rich silk protein into a pseudographitic pyroprotein

Silk proteins are of great interest to the scientific community owing to their unique mechanical properties and interesting biological functionality. In addition, the silk proteins are not burned out following heating, rather they are transformed into a carbonaceous solid, pyroprotein; several studies have identified potential carbon precursors for state-of-the-art technologies. However, no mechanism for the carbonization of proteins has yet been reported. Here we examine the structural and chemical changes of silk proteins systematically at temperatures above the onset of thermal degradation. We find that the β-sheet structure is transformed into an sp2-hybridized carbon hexagonal structure by simple heating to 350 °C. The pseudographitic crystalline layers grew to form highly ordered graphitic structures following further heating to 2,800 °C. Our results provide a mechanism for the thermal transition of the protein and demonstrate a potential strategy for designing pyroproteins using a clean system with a catalyst-free aqueous wet process for in vivo applications.

Sodium-Ion Storage in Pyroprotein-Based Carbon Nanoplates

Pyroprotein-based carbon nanoplates are fabricated from self-assembled silk proteins as a versatile platform to examine sodium-ion storage characteristics in various carbon environments. It is found that, depending on the local carbon structure, sodium ions are stored via chemi-/physisorption, insertion, or nanoclustering of metallic sodium.

Influence of cellulose nanofibers on the morphology and physical properties of poly(lactic acid) foaming by supercritical carbon dioxide

AbstractThe foaming process of poly(lactic acid) (PLA)/cellulose nanofiber (CNF) nanocomposites using supercritical CO2 as a foaming agent was studied with various CNF contents. CNFs were obtained by sonication, and their morphology was examined by transmission electron microscopy. According to the CNF content, the changes in the rheological and the thermal properties of the nanocomposites were studied through viscometry and differential scanning calorimetry. The viscosity of the composites increased with increasing CNF content. The effects of the CNF content on the foam properties and morphologies were evaluated. Compared to neat PLA foam, the PLA/CNF nanocomposite foams exhibited decreased cell size as well as increased cell density and foam density due to the improved viscous properties.

Multiwalled Carbon Nanotubes-Embedded Electrospun Bacterial Cellulose Nanofibers

Multiwalled carbon nanotubes (MWCNTs) were embedded in electrospun bacterial cellulose (BC) nanofibers, which were prepared using an electrospinning method. In this study, Gluconacetobacter xylinum BRC5 was employed to produce a hydrogel-like bacterial cellulose (BC) sheet. BC was difficult to process in the solution stat because of the large concentration of intra- or inter-molecular hydrogen bonds. In this study, an ionic liquid, 1-allyl-3-methyl-imidazolium chloride, was used to dissolve BC. To form BC nanofibers, 5 wt% BC solutions both with and without MWCNTs were electrospun. Scanning electron microscopy and transmission electron microscopy showed that the MWCNTs were embedded and well aligned along the fiber axis. The crystalline polymorph transformed from cellulose I (pristine BC) to cellulose II (electrospun regenerated BC fibers). Moreover, the tensile strength and modulus of the MWCNT-embedded electrospun BC nanofibers increased by approximately 290% and 280%, respectively. Additionally, the thermal stability and electrical conductivity of the MWCNT-embedded electrospun BC nanofibers also increased compared to pristine BC.

Cellulose Nanowhisker-incorporated Poly(Lactic Acid) Composites for High Thermal Stability

In this study, biodegradable composites were prepared using cellulose nanowhiskers and poly(lactic acid). For processing at high temperature over 200 °C, cellulose nanowhiskers were prepared by ultra-sound treatment, with the high thermal stability of natural cellulose. The nanowhiskers were confirmed using transmission electron microscopy, X-ray diffraction, and thermo-gravimetric analysis. Surface modification of the cellulose nanowhiskers was performed to increase the adhesion between hydrophilic nanofillers and hydrophobic polymer matrix. The dynamic mechanical thermal analysis of the composites showed better reinforcing effect of the modified cellulose nanocrystals. The effects of cellulose nanowhiskers on the biodegradability of poly(lactic acid) were studied using a microbial oxidative degradation analyzer.

Long-Lasting Nb2O5-Based Nanocomposite Materials for Li-Ion Storage

Advanced nanostructured hybrid materials can help us overcome the electrochemical performance limitations of current energy storage devices. In this study, three-dimensional porous carbon nanowebs (3D-CNWs) with numerous included orthorhombic Nb2O5 (T-Nb2O5) nanoparticles were fabricated using a microbe-derived nanostructure. The 3D-CNW/T-Nb2O5 nanocomposites showed an exceptionally stable long-term cycling performance over 70 000 cycles, a high reversible capacity of ∼125 mA h g-1, and fast Li-ion storage kinetics in a coin-type two-electrode system using Li metal. In addition, energy storage devices based on the above nanocomposites achieved a high specific energy of ∼80 W h kg-1 together with a high specific power of ∼5300 W kg-1 and outstanding cycling performance with ∼80% capacitance retention after 35 000 cycles.

A transparent artificial dura mater made of silk fibroin as an inhibitor of inflammation in craniotomized rats.

OBJECT To improve the safety of dura repair in neurosurgical procedures, a new dural material derived from silk fibroin was evaluated in a rat model with a dura mater injury. METHODS The authors prepared new, transparent, artificial dura mater material using silk fibroin from the silkworm, Bombyx mori. The cytotoxic and antiinflammatory effects of the artificial dura mater were examined in vitro and in vivo by histological examination, western blotting, and reverse transcription polymerase chain reaction analyses. RESULTS The novel artificial dura mater was not cytotoxic. However, it efficiently reduced cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase expression as well as the expression of the proinflammatory cytokines IL-1β, IL-6, and tumor necrosis factor-α. Cerebrospinal fluid leakage did not occur after repair of the brain of craniotomized rats with the artificial dura mater material. CONCLUSIONS The new artificial dura mater described in this study appears to be safe for application in neurosurgical procedures and can efficiently inhibit inflammation without side effects or CSF leakage. Although the long-term effects of this artificial dura mater material need to be validated in larger animals, the results from this study indicate that it is suitable for application in neurosurgery.

Carbon nanofibers prepared by the carbonization of self-assembled cellulose nanocrystals

AbstractIn this study, we fabricated fibrous carbon materials by using self-assembled cellulose nanocrystal fibers as the precursor. Cellulose nanocrystals at low concentrations, which were isolated from commercial microcystallline cellulose by a sulfuric acid treatment, were self-assembled into fibrous cellulose particles during the frozen process. After a stabilization process, the cellulose nanocrystal fibers were carbonized at 1,000 °C. Field-emission scanning electron microscopy, Raman spectroscopy, and wide-angle X-ray diffraction analysis were used to confirm the formation of amorphous carbon fibers from the cellulose nanocrystal fibers.

Carbon aerogels based on regenerated silk proteins and graphene oxide for supercapacitors

AbstractCarbon aerogels based on regenerated silk proteins and graphene oxide (GO) were prepared by a flash freezing/lyophilization process followed by carbonization. Hydrophilic blocks of ampiphilic silk proteins showed strong interactions with the oxygen functional groups of GO through intermolecular hydrogen bonds, resulting in silk-protein-coated GO nanoplates. The silk-protein-coated GO nanoplates were assembled into 3D cryogels by the gelation of the silk proteins after a flash freezing/lyophilization process. The cryogels based on GO and silk proteins, which contained numerous nitrogen heteroatoms, were successfully transformed to carbon aerogels after crystallization by a methanol treatment. Consequently, the nitrogen-enriched carbon aerogels exhibited a high capacitance of 298 F/g because of significant contributions from the pseudocapacitive effects. A specific energy of 63 W h/kg, specific power of 20 kW/kg, and stable cycle life of over 5,000 cycles were achieved.