Jiheun Ryu

Processable high internal phase Pickering emulsions using depletion attraction

High internal phase emulsions have been widely used as templates for various porous materials, but special strategies are required to form, in particular, particle-covered ones that have been more difficult to obtain. Here, we report a versatile strategy to produce a stable high internal phase Pickering emulsion by exploiting a depletion interaction between an emulsion droplet and a particle using water-soluble polymers as a depletant. This attractive interaction facilitating the adsorption of particles onto the droplet interface and simultaneously suppressing desorption once adsorbed. This technique can be universally applied to nearly any kind of particle to stabilize an interface with the help of various non- or weakly adsorbing polymers as a depletant, which can be solidified to provide porous materials for many applications.

Intravascular optical imaging of high-risk plaques in vivo by targeting macrophage mannose receptors.

Macrophages mediate atheroma expansion and disruption, and denote high-risk arterial plaques. Therefore, they are substantially gaining importance as a diagnostic imaging target for the detection of rupture-prone plaques. Here, we developed an injectable near-infrared fluorescence (NIRF) probe by chemically conjugating thiolated glycol chitosan with cholesteryl chloroformate, NIRF dye (cyanine 5.5 or 7), and maleimide-polyethylene glycol-mannose as mannose receptor binding ligands to specifically target a subset of macrophages abundant in high-risk plaques. This probe showed high affinity to mannose receptors, low toxicity, and allowed the direct visualization of plaque macrophages in murine carotid atheroma. After the scale-up of the MMR-NIRF probe, the administration of the probe facilitated in vivo intravascular imaging of plaque inflammation in coronary-sized vessels of atheromatous rabbits using a custom-built dual-modal optical coherence tomography (OCT)-NIRF catheter-based imaging system. This novel imaging approach represents a potential imaging strategy enabling the identification of high-risk plaques in vivo and holds promise for future clinical implications.

High-speed time-resolved laser-scanning microscopy using the line-to-pixel referencing method.

Fluorescence lifetime imaging microscopy (FLIM) is a powerful technique to visualize photophysical characteristics of biological targets. However, conventional FLIM methods have some limitations that restrict obtaining high-precision images in real time. Here, we propose a high-speed time-resolved laser-scanning microscopy by incorporating a novel line-to-pixel referencing method into the previously suggested analog mean-delay (AMD) method. The AMD method dramatically enhances the photon accumulation speed for achieving the certain precision compared to the time-correlated single-photon counting (TCSPC) method while maintaining high photon efficiency. However, its imaging pixel rate can still be restricted by the rearm time of the digitizer when it is triggered by laser pulses. With our line-to-pixel referencing method, the pulse train repeats faster than the trigger rearm time can be utilized by generating a line trigger, which is phase-locked with only the first pulse in each horizontal line composing an image. Our proposed method has been tested with a pulsed laser with 40 MHz repetition rate and a commercial digitizer with a 500 ns trigger rearm time, and a frame rate of 3.73 fps with a pixel rate of 3.91 MHz was accomplished while maintaining the measurement precision under 20 ps.

Real-time Fluorescence Lifetime Imaging Microscopy Implementation by Analog Mean-Delay Method through Parallel Data Processing

Fluorescence lifetime imaging microscopy (FLIM), especially based on the most accurate and frequently used technique called time-correlated single photon counting (TCSPC), has been widely employed for it gives not only morphological information but also chemical information. Chemical properties such as pH value (Hanson et al., 2002), ion or oxygen concentration (Gilbert et al., 2007), molecular dynamics and even the disease progression (Park et al., 2012) can be investigated and studied by TCSPC-FLIM. This powerful traits of FLIM has led many researchers and developers to include FLIM into their imaging system. Even though TCSPC-FLIM technique gives precise and accurate measurement of fl uorescence decay curves, its core technology, called single photon counting (SPC), inherently limits the system from high speed imaging. In the case of the state-of-art single channel TCSPC-FLIM, more than one minute is required to produce an image of 512 by 512 pixels with 10% accuracy. The acquisition time could be lengthened up to five minutes for 3% accuracy (Kollner & Wolfrum, 1992). To overcome such drawback of the long acquisition time of TCSPC-FLIM, analog mean-delay FLIM (AMD-FLIM) was recently developed (Moon et al., 2009; Won et al., 2009). Rather than using the stochastic reconstruction used in SPC techniques, AMD method extracts a decay constant directly by subtracting the mean-delay time (or mean-arrival time) of reflected photon flux from that of fluorescence photon fl ux. The total amount of alterations in the mean-delay time

Therapeutic Effects of Targeted PPARɣ Activation on Inflamed High-Risk Plaques Assessed by Serial Optical Imaging In Vivo

Rationale: Atherosclerotic plaque is a chronic inflammatory disorder involving lipid accumulation within arterial walls. In particular, macrophages mediate plaque progression and rupture. While PPARγ agonist is known to have favorable pleiotropic effects on atherogenesis, its clinical application has been very limited due to undesirable systemic effects. We hypothesized that the specific delivery of a PPARγ agonist to inflamed plaques could reduce plaque burden and inflammation without systemic adverse effects. Methods: Herein, we newly developed a macrophage mannose receptor (MMR)-targeted biocompatible nanocarrier loaded with lobeglitazone (MMR-Lobe), which is able to specifically activate PPARγ pathways within inflamed high-risk plaques, and investigated its anti-atherogenic and anti-inflammatory effects both in in vitro and in vivo experiments. Results: MMR-Lobe had a high affinity to macrophage foam cells, and it could efficiently promote cholesterol efflux via LXRα-, ABCA1, and ABCG1 dependent pathways, and inhibit plaque protease expression. Using in vivo serial optical imaging of carotid artery, MMR-Lobe markedly reduced both plaque burden and inflammation in atherogenic mice without undesirable systemic effects. Comprehensive analysis of en face aorta by ex vivo imaging and immunostaining well corroborated the in vivo findings. Conclusion: MMR-Lobe was able to activate PPARγ pathways within high-risk plaques and effectively reduce both plaque burden and inflammation. This novel targetable PPARγ activation in macrophages could be a promising therapeutic strategy for high-risk plaques.

Feedforward reference compensation using bilinear interpolation for long range motion of six degrees-of-freedom magnetic levitation planar motor

Magnetic levitation planar motor was researched and developed for vacuum compatibility. Laser interferometers are used in order for high precision measurement. However, the magnetic levitations cannot experience full working range due to the high sensitivity of the laser interferometers. Especially, angular alignment is important for laser interferometer to measure the motions. In this paper, a cause of the lower angular alignment along the long range motion is investigated and feedforward reference compensation using bilinear interpolation is utilized to improve the angular alignment. In order for verifying the compensation, experimental work was performed and the result showed that the angular alignment was improved. Finally, the magnetic levitation planar motor can have full working range motions including 2-dimensional motions by suggested compensation.