Exposures to humidifier disinfectant and various health conditions in Korean based on personal exposure assessment data of claimants for compensation.

BACKGROUND: Humidifier disinfectants (HDs) were commonly used household chemicals to prevent microbial growth in a humidifier water tank in South Korea. A growing body of evidence has indicated that its airborne exposure can induce severe lung injury. However, there has been low awareness of other health outcomes in HD users. This study aimed to evaluate health conditions appealed by claimants for compensation in relation with an increased exposure to HD. METHODS: From survey data of personal HD exposure assessment of claimants for compensation in Korea, we included a total of 4,179 subjects [cases in each dataset were defined by nine reported health conditions, i.e., pneumonia, asthma, cardiovascular disease, respiratory disease, otorhinolaryngologic disease, brain disease (including cerebrovascular disease), dermatological disease, lung cancer, and all cancers]. HD exposures was considered as the following exposure criteria: exposure duration, exposure proximity, exposure direction, chemical type, cumulative exposure time, indoor air concentration, and cumulative exposure level. Logistic regression models were used to evaluate the associations between HD exposure and health conditions. RESULTS: After adjusting for sociodemographic and health behavioral factors and other chemical exposures (households, environmental, and occupational exposures), an increase in cumulative HD exposure time was significantly associated with risks of all nine diseases (all p-trends < 0.05). An increase in HD exposure duration was associated with asthma, respiratory disease, otorhinolaryngologic disease, dermatological disease, all cancers, and lung cancer (p-trends < 0.05). Indoor HD concentration was associated with only pneumonia (p-trend = 0.015). CONCLUSIONS: Our findings suggest that cumulative exposures to airborne HD might potentially increase the risk of various reported health outcomes.

New-Onset and Exacerbation of Lung Diseases after Short-Term Exposures to Humidifier Disinfectant during Hospitalization.

(1) Background: Humidifier disinfectant (HD) is a biocidal chemical to keep the water tank inside a humidifier clean. Thousands of Koreans have experienced HD-related lung injuries. Of them, 6.9% were exposed to HD in hospitals. (2) Methods: This study investigated changes of diseases in patients (or caregivers) who experienced HD exposures during hospitalization and also investigated characteristics of hospital exposure using data from all HD-related lung injury enrollment in Korea. (3) Results: Of a total of 162 subjects, 139 subjects were hospitalized for non-lung diseases, and 23 people were hospitalized for lung diseases at the time of hospitalization. During hospital exposure, 99 (71.2%) of those hospitalized with non-lung disease experienced a new-onset of lung disease, and 15 (65.2%) of those hospitalized with lung diseases experienced exacerbation of their existing lung diseases. When we compared their exposure characteristics, those exposed in hospitals (vs. non-hospital, mostly home) were exposed for shorter periods, at closer distances, at higher HD indoor concentrations, constantly all day, and directly in the facial direction. (4) Conclusion: In conclusion, HD exposures in hospital with a high intensity even for a short term were associated with new-onset or exacerbation of lung diseases. Our findings suggest that acute exposures to HD can cause lung diseases.

Misclassification and characterization of exposure to humidifier disinfectants using a questionnaire.

BACKGROUND: Lung disease caused by exposure to chemical substances such as polyhexamethylene guanidine (PHMG) used in humidifier disinfectants (HDs) has been identified in Korea. Several researchers reported that exposure classification using a questionnaire might not correlate with the clinical severity classes determined through clinical diagnosis. It was asserted that the lack of correlation was due to misclassification in the exposure assessment due to recall bias. We identified the cause of uncertainty to recognize the limitations of differences between exposure assessment and clinical outcomes assumed to be true value. Therefore, it was intended to check the availability of survey using questionnaires and required to reduce misclassification error/bias in exposure assessment. METHODS: HDs exposure assessment was conducted as a face-to-face interview, using a questionnaire. A total of 5245 applicants participated in the exposure assessment survey. The questionnaire included information on sociodemographic and exposure characteristics such as the period, frequency, and daily usage amount of HDs. Based on clinical diagnosis, a 4 × 4 cross-tabulation of exposure and clinical classification was constructed. When the values of the exposure rating minus the clinical class were ≥ 2 and ≤ - 2, we assigned the cases to the overestimation and underestimation groups, respectively. RESULTS: The sex ratio was similar in the overestimation and underestimation groups. In terms of age, in the overestimation group, 90 subjects (24.7%) were under the age of 10, followed by 52 subjects (14.2%) in their 50s. In the underestimation group, 195 subjects (56.7%) were under the age of 10, followed by 80 subjects (23.3%) in their 30s. The overestimation group may have already recovered and responded excessively due to psychological anxiety or to receive compensation. However, relatively high mortality rates and surrogate responses observed among those under 10 years of age may have resulted in inaccurate exposure in the underestimation group. CONCLUSIONS: HDs exposure assessment using a questionnaire might not correlate with adverse health effects due to recall bias and various other causes such as recovery of injury and psychological anxiety. This study revealed exposure misclassification and characteristics affected by HDs and proposed a questionnaire-based exposure assessment methodology to overcome the limitations of past exposure assessment.

Neuronal differentiation of human mesenchymal stem cells in response to the domain size of graphene substrates.

Graphene is a noncytotoxic monolayer platform with unique physical, chemical, and biological properties. It has been demonstrated that graphene substrate may provide a promising biocompatible scaffold for stem cell therapy. Because chemical vapor deposited graphene has a two dimensional polycrystalline structure, it is important to control the individual domain size to obtain desirable properties for nano-material. However, the biological effects mediated by differences in domain size of graphene have not yet been reported. On the basis of the control of graphene domain achieved by one-step growth (1step-G, small domain) and two-step growth (2step-G, large domain) process, we found that the neuronal differentiation of bone marrow-derived human mesenchymal stem cells (hMSCs) highly depended on the graphene domain size. The defects at the domain boundaries in 1step-G graphene was higher (×8.5) and had a relatively low (13% lower) contact angle of water droplet than 2step-G graphene, leading to enhanced cell-substrate adhesion and upregulated neuronal differentiation of hMSCs. We confirmed that the strong interactions between cells and defects at the domain boundaries in 1step-G graphene can be obtained due to their relatively high surface energy, which is stronger than interactions between cells and graphene surfaces. Our results may provide valuable information on the development of graphene-based scaffold by understanding which properties of graphene domain influence cell adhesion efficacy and stem cell differentiation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 43-51, 2018.

The role of graphene formed on silver nanowire transparent conductive electrode in ultra-violet light emitting diodes.

This paper reports a highly reliable transparent conductive electrode (TCE) that integrates silver nanowires (AgNWs) and high-quality graphene as a protecting layer. Graphene with minimized defects and large graphene domains has been successfully obtained through a facile two-step growth approach. Ultraviolet light emitting diodes (UV-LEDs) were fabricated with AgNWs or hybrid electrodes where AgNWs were combined with two-step grown graphene (A-2GE) or conventional one-step grown graphene (A-1GE). The device performance and reliability of the UV-LEDs with three different electrodes were compared. The A-2GE offered high figure of merit owing to the excellent UV transmittance and reduced sheet resistance. As a consequence, the UV-LEDs made with A-2GE demonstrated reduced forward voltage, enhanced electroluminescence (EL) intensity, and alleviated efficiency droop. The effects of joule heating and UV light illumination on the electrode stability were also studied. The present findings prove superior performance of the A-2GE under high current injection and continuous operation of UV LED, compared to other electrodes. From our observation, the A-2GE would be a reliable TCE for high power UV-LEDs.

Tailored CVD graphene coating as a transparent and flexible gas barrier.

The chemical vapor deposition (CVD) method to obtain tailored graphene as a transparent and flexible gas barrier has been developed. By separating nucleation step from growth, we could reduce early graphene nucleation density and thus induce better stitching between domain boundaries in the second growth step. Furthermore, two step growth in conjunction with electrochemical polishing of Cu foils achieved large graphene domains and improved graphene quality with minimized defects. The performance of resulting graphene as a gas barrier was superior to the graphene obtained by one-step growth on polished or unpolished Cu foils. The CVD graphene reported here could open up the possibility for exploring graphene-based gas barrier due to the minimized density of defect area.

Efficient stress-relaxation in InGaN/GaN light-emitting diodes using carbon nanotubes.

A facile method to facilitate epitaxial lateral overgrowth (ELO) of gallium nitride (GaN) was developed by using single-walled carbon nanotubes (SWCNTs). High-quality GaN was achieved on sapphire by simply coating the SWCNTs as an intermediate layer for stress and defect mitigation. SWCNTs maintained their integrity at high reaction temperature and led to suppression of edge dislocations and biaxial stress relaxation by up to 0.32 GPa in a GaN template layer. InGaN/GaN multi-quantum-well light-emitting diodes (LEDs) on this high-quality GaN template offered enhanced internal quantum efficiency and light output power with reduced efficiency droop. The method developed here has high potential to replace current ELO methods such as patterned sapphire substrates or buffer layers like SiO2 and SiNx.

Investigation of Thickness Dependence of Metal Layer in Al/Mo/4H-SiC Schottky Barrier Diodes.

In this paper, we present the preparation and characterization of Schottky barrier diodes based on silicon carbide with various Schottky metal layer thickness values. In this structure, molybdenum and aluminum were employed as the Schottky barrier metal and top electrode, respectively. Schottky metal layers were deposited with thicknesses ranging from 1000 to 3000 Å, and top electrodes were deposited with thickness as much as 3000 Å. The deposition of both metal layers was performed using the facing target sputtering (FTS) method, and the fabricated samples were annealed with the tubular furnace at 300 degrees C under argon ambient for 10 min. The Schottky barrier height, series resistance, and ideality factor was calculated from the forward I-V characteristic curve using the methods proposed by Cheung and Cheung, and by Norde. For as-deposited Schottky diodes, we observed an increase of the threshold voltage (V(T)) as the thickness of the Schottky metal layer increased. After the annealing, the Schottky barrier heights (SBHs) of the diodes, including Schottky metal layers of over 2000 Å, increased. In the case of the Schottky metal layer deposited to 1000 Å, the barrier heights decreased due to the annealing process. This may have been caused by the interfacial penetration phenomenon through the Schottky metal layer. For variations of V(T), the SBH changed with a similar tendency. The ideality factor and series resistance showed no significant changes before or after annealing. This indicates that this annealing condition is appropriate for Mo SiC structures. Our results confirm that it is possible to control V(T) by adjusting the thickness of the Schottky metal layer.