Chung-Soo Kim

Cellulose nano whiskers from grass of Korea

Polymer composites form a fascinating interdisciplinary area by bringing together biology and material science for wide verity of applications ranging from construction to biomedical technology. A deliberate interest in the development of eco-friendly material motivated the efforts toward research on cellulose composites due to its cheap, sustainable, recyclable, degradable nature and remarkable reinforcing properties at 167.5 GPa of Young’s modulus along the chain axis per theoretical estimations. The use of natural fiber for technical applications like automobile industry is restricted due to its incompatibility with generally hydrophobic host matrix and increase in weight of resulting products which provide a poor cost performance ratio. After resolving the incompatibility issues up to a satisfactory extent by adequate modification either in host or filler, it was assumed that dispersion and material properties may be enhanced with reduction in the size and increase in surface area by introducing nano fillers. Nano size (5-20 nm cross sections with length to several μm depending on source) rod like cellulose crystallites particles, known as cellulose nano whiskers (CNW), can be extracted from laterally stabilized fibrils bundle by removing amorphous region through controlled acid hydrolysis. These whiskers have been employed in reinforcing several polymers, which result in comparatively better mechanical properties. Nevertheless, such fibers have conquered many obstacles against industrial practices due to time consuming preparation procedure with very low yield, commercial unavailability, and most importantly, comparative higher cost through expensive source such as tunicate, bacterial, algal (valonia), brown algae (Oomycota) and commercially available microcrystalline cellulose. The low yield and availability of raw materials of these sources generally inhibit the penetration of this tremendous reinforcer for the development of daily use biodegradable products. The current attempt was made to obtain the cellulose nano whiskers from the cheapest source, grass of Koera for the first time, which may further broaden the use of these bio fillers ranging from commodity to constructive applications.

Characteristics and Prognostic Implications of High-Risk HPV-Associated Hypopharyngeal Cancers

Background High-risk human papillomavirus (HPV) is an oncogenic virus that causes oropharyngeal cancers, and it has a favorable outcome after the treatment. Unlike in oropharyngeal cancer, the prevalence and role of high-risk HPV in the etiology of hypopharyngeal squamous cell carcinoma (HPSCC) is uncertain. Objective The aim of the present study was to evaluate the effect and prognostic significance of high-risk HPV in patients with HPSCC. Methods The study included 64 subjects with HPSCC who underwent radical surgery with or without radiation-based adjuvant therapy. Primary tumor sites were the pyriform sinus in 42 patients, posterior pharyngeal wall in 19 patients, and postcricoid area in 3 patients. High-risk HPV in situ hybridization was performed to detect HPV infection. Results The positive rate of high-risk HPV in situ hybridization was 10.9% (7/64). There was a significant difference in the fraction of positive high-risk HPV among pyriform sinus cancer (16.7%), posterior pharyngeal wall cancer (0%), and postcricoid area cancer (0%) (p = 0.042). The laryngoscopic examination revealed a granulomatous and exophytic appearance in 85.7% (6/7) of patients with high-risk HPV-positive pyriform sinus cancer, but in only 31.4% (11/35) of patients with high-risk HPV-negative pyriform sinus cancer (p = 0.012). Significant correlations were found between positive high-risk HPV and younger age (p = 0.050) and non-smoking status (p = 0.017). HPV-positive patients had a significantly better disease-free survival (p = 0.026) and disease-specific survival (p = 0.047) than HPV-negative patients. Conclusions High-risk HPV infection is significantly related to pyriform sinus cancer in patients with HPSCC.

Evaluation of morphological architecture of cellulose chains in grass during conversion from macro to nano dimensions

Abstract The cellulose nanowhiskers (CNW) are of imminent importance in the development of ecofriendly green material for environment. Morphological study of their structure was carried out after extraction from grass. The controlled alkali and acid hydrolysis after soxhlet extraction of bleached fiber in ethanol and water provided a mixture of micro/nano fiber which can be further converted into CNW by mechanical treatment. Width of obtained CNW were found to be ~10-65 nm with length of several nanometers as evidenced by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The changes in dimensions during alkali treatment, bleaching and acid hydrolysis of grass exhibited an interesting architecture and clarify the phenomenon of separation of nano level fibrils from the matrix of hemicellulose and lignin which starts after swelling of fibers and opening from middle followed by splitting from each other. The nanofibers were embedded in the matrix surrounded by amorphous layers. The size of fibers was directly associated with the extent of treatments. The crystalline part of fiber was intact during hydrolysis which must be attributed to easy removal of amorphous region by penetration of hydronum ions from acid. The results of SEM and TEM were correlated with the Scanning Ion Microscopy (SIM) which showed a direct evidence of breaking of thick fiber strands resulting in the formation of sharp edged crystalline entities composed of cellulose crystals.

Aerodynamically focused nanoparticle (AFN) printing: novel direct printing technique of solvent-free and inorganic nanoparticles.

Aerodynamically focused nanoparticle (AFN) printing was demonstrated for direct patterning of the solvent-free and inorganic nanoparticles. The fast excitation-purge control technique was proposed and investigated by examining the aerodynamic focusing of nanoparticles and their time-scale, with the analytical and experimental approaches. A series of direct patterning examples were demonstrated with Barium Titanate (BaTiO3) and Silver (Ag) nanoparticles onto the flexible and inflexible substrates using the AFN printing system. The capacitor and flexible conductive line pattern were fabricated as the application examples of the proposed technique. The results presented here should contribute to the nanoparticle manipulation, patterning, and their applications, which are intensely being studied nowadays.

Relationship between extracapsular spread and FDG PET/CT in oropharyngeal squamous cell carcinoma

Abstract Conclusion: Median maximum standardized uptake (SUVmax) cut-off values of FDG PET/CT higher than 3.85 were found to be associated with a greater risk cervical lymph node metastasis with extracapsular spread (ECS) in patients with oropharyngeal squamous cell carcinoma (OPSCC). Objectives: The purpose of this study was to evaluate the use of FDG PET/CT for the identification of ECS and to establish its histologic correlates in OPSCC. Methods: The medical records of 78 patients who underwent FDG PET/CT for OPSCC before surgery were reviewed. Results: ECS was present in 42% (42/69) of dissected necks and in 51% (54/106) of dissected cervical levels. The SUVmax values of cervical lymph nodes with and without ECS were found to be significantly different (6.73 ± 3.78 vs 3.02 ± 2.24, p < 0.001). The SUVmax cut-off value for differentiating necks with ECS from those without ECS was 3.85. The presence of ECS (p = 0.036) and median SUVmax (using 3.85 as a cut-off) (p = 0.037) were found to have a significant adverse effect on 5-year disease-specific survival by univariate analysis. The multivariate analysis showed a significant association of 5-year disease-specific survival with ECS (hazard ratio (HR) = 32.3 in cervical metastasis with ECS, p = 0.012; and HR = 19.6 in cervical metastasis without ECS, p = 0.024).

Flexible ceramic-elastomer composite piezoelectric energy harvester fabricated by additive manufacturing

As a renewable energy harvesting method, interest in piezoelectric energy harvesting has increased significantly. Despite the piezoelectric energy-harvesting technology expanding its area to the flexible (elastic, amendable) devices, striking use or application of the technology is hardly found in the market. Here, we report a novel flexible piezoelectric energy harvester fabricated by using an additive manufacturing process, which enables both effective and customized manufacturing technique. By taking advantages of additive manufacturing, further application of the piezoelectric energy-harvesting technology is highly expected. Particles of BaTiO3, a ceramic with a large piezoelectric constant, were mixed with polyether block amide elastomer to form a flexible piezoelectric composite. The energy harvester was fabricated using an additive manufacturing process, by printing the piezoelectric composite on a laser-patterned flexible Indium-tin-oxide–coated polyethylene terephthalate substrate. Performance of fabricated energy harvester was evaluated by applying a mechanical stress to the energy harvester; voltage and current output were 2 V and 40 nA, respectively. An analytical model of the piezoelectric energy harvester was developed and discussed to explain the form of the voltage waveforms in response to the applied stress.

Energy Analysis of Micro-drilling Process Used to Manufacture Printed Circuit Boards

Energy savings are becoming a new focus in the industrial sector because of environmental concerns. In order to establish an energy-saving strategy for micro-drilling, it is necessary to consider all aspects of the drilling procedure, including the post-drilling process. This study analyzed micro-drills with diameters of 400 μm. Process parameters, such as the rotational speed of the spindle and in-feed, were controlled, and the energy consumption of each process was measured. Operators can use the results to make decisions on process parameters and whether to perform a de-burring process. Ultimately, an effective energy-saving strategy can be devised for micro-drilling.

Preparation and structural evaluation of nano reinforced composites from cellulose whiskers of grass and biodegradable polymer matrix

Biocomposites of polylactic acid with cellulose whiskers from grass were prepared and reinforced with nanolayer-filled ionomer (Surlyn®). Three types of polymer composites were fabricated by filling the whiskers in polylactic acid at 5, 10, and 15% concentration. The analysis of resulting products was conducted by monitoring the functional group variation, crystallinity, and thermal behavior. The addition of clay-filled ionomer appeared to enhance the interfacial adhesion between filler and matrix by chemical and physical bonding. The migration tendency of different components inside silicate layers was also studied where the confinement of host polymer chains occurred between clay platelets, after modification through ionomer.

Bias sputtered NbN and superconducting nanowire devices

Superconducting nanowire single photon detectors (SNSPDs) promise to combine near-unity quantum efficiency with >100 megacounts per second rates, picosecond timing jitter, and sensitivity ranging from x-ray to mid-infrared wavelengths. However, this promise is not yet fulfilled, as superior performance in all metrics is yet to be combined into one device. The highest single-pixel detection efficiency and the widest bias windows for saturated quantum efficiency have been achieved in SNSPDs based on amorphous materials, while the lowest timing jitter and highest counting rates were demonstrated in devices made from polycrystalline materials. Broadly speaking, the amorphous superconductors that have been used to make SNSPDs have higher resistivities and lower critical temperature (Tc) values than typical polycrystalline materials. Here, we demonstrate a method of preparing niobium nitride (NbN) that has lower-than-typical superconducting transition temperature and higher-than-typical resistivity. As we will ...

Cellulose nanofiber assisted deposition of titanium dioxide on fluorine-doped tin oxide glass

Microspores, highly ordered, 300–340 nm thick blocks of titanium dioxide (TiO2) nanoparticles (5–10 nm) were deposited on fluorine-doped tin oxide (FTO) glass by using low concentration of cellulose nanofibers from bacterial origin, through sol–gel process followed by spin coating.