Youngkyu Song

Sunlight-induced self-healing of a microcapsule-type protective coating.

Photopolymerization behavior of a methacryloxypropyl-terminated polydimethylsiloxane (MAT-PDMS) healing agent was investigated in the presence of benzoin isobutyl ether (BIE) photoinitiator by Fourier transform infrared (FT-IR) spectroscopy. MAT-PDMS and BIE were microencapsulated with urea-formaldehyde polymer. The surface and shell morphology of the microcapsules was investigated by scanning electron microscopy (SEM). Mean diameter and size distribution of the microcapsules could be controlled by agitation rate. A coating matrix formulation was prepared by sol-gel reaction of tetraethyl orthosilicate (TEOS) in the presence of a polysiloxane and by subsequent addition of an adhesion promoter. The formulation and microcapsules were mixed to give a self-healing coating formulation, which was then sprayed to surface of cellulose-fiber-reinforced-cement (CRC) board or mortar. Contact angle measurements showed that both the polymerized MAT-PDMS and the prepared coating matrix are hydrophobic, and the coating matrix has good wettability with MAT-PDMS. It was confirmed by optical microscopy and SEM that, when the self-healing coating is damaged, the healing agent is released from ruptured microcapsules and fills the damaged region. The self-healing coating was evaluated as protective coating for mortar, and it was demonstrated by water permeability and chloride ion penetration tests that our system has sunlight-induced self-healing capability. Our self-healing coating is the first example of capsule-type photoinduced self-healing system, and offers the advantages of catalyst-free, environmentally friendly, inexpensive, practical healing.

Fluorescence sensing of microcracks based on cycloreversion of a dimeric anthracene moiety

Novel fluorescent crack sensors have been developed based on dimeric anthracene moiety-containing polymers. Two anthracene derivatives, 9-anthraldehyde (AA) and 9-anthracenecarboxylic acid (AC), were photodimerized to obtain cyclooctane-type dimers. Crack-sensing polymers (Poly-AA and Poly-AC) were prepared by crosslinking of poly(vinyl alcohol) by using the dimers as crosslinkers. The polymers afforded transparent, hard coatings. Upon cracking, the polymers exhibited strong optical absorption and fluorescence emission while the uncracked original polymers did not. This was explained by regeneration of the anthracene moiety by mechanochemical cycloreversion of the cyclooctane dimer structure. It was found that the crack planes emitted fluorescence having emission maxima in the range of 500–600 nm when excited with 330–385 nm UV light. Absolute fluorescence quantum yield measurements indicated that the polymers could have good capability of fluorescence crack sensing. Preliminary evaluation of the crack-sensing ability of Poly-AA and Poly-AC was performed with the polymer films, and fluorescence emission was clearly observed along the crack planes upon excitation with 330–385 nm UV light. Poly-AA and Poly-AC are promising as fluorescent crack sensors because the anthracene moiety regenerated upon cracking has relatively long excitation and emission wavelengths as well as strong fluorescence.

Repeatable self-healing of a microcapsule-type protective coating

Cinnamide moiety-containing polydimethylsiloxane (CA-PDMS) was prepared and used as a healing agent. The photo-cross-linking behavior of CA-PDMS was investigated by UV-vis and Fourier transform infrared (FT-IR) spectroscopy. Upon photo-irradiation, CA-PDMS generates viscoelastic substances which have intrinsic recoating (or self-healing) capability when scribed with a cutter blade. CA-PDMS was microencapsulated with a urea-formaldehyde polymer, and the mean diameter and size distribution of the microcapsules could be controlled by the agitation rate. The prepared microcapsules were integrated into a commercial enamel paint to create a self-healing coating. It was confirmed by optical microscopy and scanning electron microscopy (SEM) that, when the self-healing coating is scribed, the healing agent is released from ruptured microcapsules and fills the scribed region. The scribed self-healing coating was photo-irradiated to induce photo-cross-linking of the released CA-PDMS. SEM imaging provided visual evidence that, when the scribed and healed region is re-scribed, repeated self-healing is accomplished. It was successfully demonstrated by anticorrosion and electrochemical tests that the CA-PDMS-based self-healing coating system has repeatable self-healing capability. Our self-healing coating is the first example of microcapsule-type repeatable self-healing system, and offers the advantages of simple, inexpensive, practical healing.

Lumazine Synthase Protein Nanoparticle-Gd(III)-DOTA Conjugate as a T1 contrast agent for high-field MRI

With the applications of magnetic resonance imaging (MRI) at higher magnetic fields increasing, there is demand for MRI contrast agents with improved relaxivity at higher magnetic fields. Macromolecule-based contrast agents, such as protein-based ones, are known to yield significantly higher r1 relaxivity at low fields, but tend to lose this merit when used as T1 contrast agents (r1/r2 = 0.5 ~ 1), with their r1 decreasing and r2 increasing as magnetic field strength increases. Here, we developed and characterized an in vivo applicable magnetic resonance (MR) positive contrast agent by conjugating Gd(III)-chelating agent complexes to lumazine synthase isolated from Aquifex aeolicus (AaLS). The r1 relaxivity of Gd(III)-DOTA-AaLS-R108C was 16.49 mM−1s−1 and its r1/r2 ratio was 0.52 at the magnetic field strength of 7 T. The results of 3D MR angiography demonstrated the feasibility of vasculature imaging within 2 h of intravenous injection of the agent and a significant reduction in T1 values were observed in the tumor region 7 h post-injection in the SCC-7 flank tumor model. Our findings suggest that Gd(III)-DOTA-AaLS-R108C could serve as a potential theranostic nanoplatform at high magnetic field strength.

The Neuromelanin-related T2* Contrast in Postmortem Human Substantia Nigra with 7T MRI

High field magnetic resonance imaging (MRI)-based delineation of the substantia nigra (SN) and visualization of its inner cellular organization are promising methods for the evaluation of morphological changes associated with neurodegenerative diseases; however, corresponding MR contrasts must be matched and validated with quantitative histological information. Slices from two postmortem SN samples were imaged with a 7 Tesla (7T) MRI with T1 and T2* imaging protocols and then stained with Perl’s Prussian blue, Kluver-Barrera, tyrosine hydroxylase, and calbindin immunohistochemistry in a serial manner. The association between T2* values and quantitative histology was investigated with a co-registration method that accounts for histology slice preparation. The ventral T2* hypointense layers between the SNr and the crus cerebri extended anteriorly to the posterior part of the crus cerebri, which demonstrates the difficulty with an MRI-based delineation of the SN. We found that the paramagnetic hypointense areas within the dorsolateral SN corresponded to clusters of neuromelanin (NM). These NM-rich zones were distinct from the hypointense ventromedial regions with high iron pigments. Nigral T2* imaging at 7T can reflect the density of NM-containing neurons as the metal-bound NM macromolecules may decrease T2* values and cause hypointense signalling in T2* imaging at 7T.

Is apparent diffusion coefficient reliable and accurate for monitoring effects of antiangiogenic treatment in a longitudinal study

To evaluate the reliability and accuracy of the apparent diffusion coefficient (ADC) for monitoring antiangiogenic treatment in a longitudinal study.

Response of the Primary Auditory and Non-Auditory Cortices to Acoustic Stimulation: A Manganese-Enhanced MRI Study

Structural and functional features of various cerebral cortices have been extensively explored in neuroscience research. We used manganese-enhanced MRI, a non-invasive method for examining stimulus-dependent activity in the whole brain, to investigate the activity in the layers of primary cortices and sensory, such as auditory and olfactory, pathways under acoustic stimulation. Male Sprague-Dawley rats, either with or without exposure to auditory stimulation, were scanned before and 24–29 hour after systemic MnCl2 injection. Cortex linearization and layer-dependent signal extraction were subsequently performed for detecting layer-specific cortical activity. We found stimulus-dependent activity in the deep layers of the primary auditory cortex and the auditory pathways. The primary sensory and visual cortices also showed the enhanced activity, whereas the olfactory pathways did not. Further, we performed correlation analysis of the signal intensity ratios among different layers of each cortex, and compared the strength of correlations between with and without the auditory stimulation. In the primary auditory cortex, the correlation strength between left and right hemisphere showed a slight but not significant increase with the acoustic simulation, whereas, in the primary sensory and visual cortex, the correlation coefficients were significantly smaller. These results suggest the possibility that even though the primary auditory, sensory, and visual cortices showed enhanced activity to the auditory stimulation, these cortices had different associations for auditory processing in the brain network.

Dynamic contrast-enhanced MRI for monitoring antiangiogenic treatment: determination of accurate and reliable perfusion parameters in a longitudinal study of a mouse xenograft model.

Objective To determine the reliable perfusion parameters in dynamic contrast-enhanced MRI (DCE-MRI) for the monitoring antiangiogenic treatment in mice. Materials and Methods Mice, with U-118 MG tumor, were treated with either saline (n = 3) or antiangiogenic agent (sunitinib, n = 8). Before (day 0) and after (days 2, 8, 15, 25) treatment, DCE examinations using correlations of perfusion parameters (Kep, Kel, and AH from two compartment model; time to peak, initial slope and % enhancement from time-intensity curve analysis) were evaluated. Results Tumor growth rate was found to be 129% ± 28 in control group, -33% ± 11 in four mice with sunitinib-treatment (tumor regression) and 47% ± 15 in four with sunitinib-treatment (growth retardation). Kep (r = 0.80) and initial slope (r = 0.84) showed strong positive correlation to the initial tumor volume (p < 0.05). In control mice, tumor regression group and growth retardation group animals, Kep (r : 0.75, 0.78, 0.81, 0.69) and initial slope (r : 0.79, 0.65, 0.67, 0.84) showed significant correlation with tumor volume (p < 0.01). In four mice with tumor re-growth, Kep and initial slope increased 20% or greater at earlier (n = 2) than or same periods (n = 2) to when the tumor started to re-grow with 20% or greater growth rate. Conclusion Kep and initial slope may a reliable parameters for monitoring the response of antiangiogenic treatment.

Effects of Electrical Characteristics on the Non-Rectangular Gate Structure Variations for the Multifinger MOSFETs

In this paper, modeling methodology of electrical characteristics for non-rectangular gate structured multifinger metal-oxide-semiconductor field-effect transistors based on minimum channel length is proposed. The test structures are fabricated and the parasitic model parameters are extracted using the measured data for the proposed model. The proposed model can support better physical explanation than the previously presented integrated length model. The proposed model can precisely explain the electrical characteristics and is supported by theoretical equations for non-rectangular gates, such as the threshold voltage, the saturation voltage, the saturation current, and the leakage current. However, the previous integrated length model cannot sufficiently explain the electrical characteristics for non-rectangular gates although it is sustained by theoretical equations. Furthermore, this paper shows the relationship between gate poly area and the electrical characteristics. As a result, the electrical characteristics are dependent on the variation of the minimum of the gate length, rather than the profile of gate length variation.

Effects of laser drilling through silicon substrate on MOSFET device characteristics

The effects of laser drilling through silicon substrate formed by femtosecond laser on n-type MOSFET device characteristics are investigated. The tested MOSFET device structures are fabricated using the commercial 130-nm process. Through via holes and laser scanning line affect the device characteristics, such as drain current and threshold voltage, depending on the distance between the location of the drilling. The device degradation and variation along with a distance from the holes or the line are examined and the device characteristic variation is analyzed to determine the reliability of MOSFET devices against laser drilling damage.