Jun Hyup Lee

Mussel-Inspired Cell-Adhesion Peptide Modification for Enhanced Endothelialization of Decellularized Blood Vessels

Enhanced endothelialization of tissue-engineered blood vessels is essential for vascular regeneration and function of engineered vessels. In this study, mussel-inspired surface chemistry of polydopamine (pDA) coatings are applied to functionalize decellularized vein matrix (DVM) with extracellular matrix-derived cell adhesion peptides (RGD and YIGSR). DVMs engineered with pDA-peptides enhance focal adhesion, metabolic activity, and endothelial differentiation of human endothelial progenitor cells (EPCs) derived from cord blood and embryonic stem cells compared with EPCs on non-coated or pDA-coated DVMs. These results indicate that pDA-peptide functionalization may contribute to enhanced, rapid endothelialization of DVM surfaces by promoting adhesion, proliferation, and differentiation of circulating EPCs. Ultimately, this approach may be useful for improving in vivo patency and function of decellularized matrix-based blood vessels.

Nonlinearity from FT-rheology for liquid crystal 8CB under large amplitude oscillatory shear (LAOS) flow

This study systematically investigated the nonlinear stress behavior of liquid crystal (8CB, 4-4′-n-octyl-cyanobiphenyl) in lamellar smectic A phase under large amplitude oscillatory shear (LAOS) flow. To investigate the nonlinear stress response under LAOS flow, the nonlinearity (I3/1) from Fourier transform-rheology as a function of applied shear time (3600 s) was calculated according to changes in both strain amplitude γ0 and frequency ω. The storage modulus G′(t) and loss modulus G″(t) from the conventional rheometer program under various LAOS flow conditions decreased and reached equilibrium as a function of time. This could be attributed to shear alignment of the lamellar smectic A structure. On the contrary, with G′(t) and G″(t), the nonlinearity I3/1(t) showed three different behaviors depending on the magnitude of strain amplitude: (1) Region I: Increased (increased and reached equilibrium), (2) region II: Increased and decreased (showed maximum value; decreased and reached equilibrium), and (3) ...

Implantable microfluidic device for the formation of three-dimensional vasculature by human endothelial progenitor cells

Vasculogenesis is an important morphogenetic event for vascular tissue engineering and ischemic disease treatment. Stem and progenitor cells can contribute to vasculogenesis via endothelial differentiation and direct participation in blood vessel formation. In this study, we developed an implantable microfluidic device to facilitate formation of three-dimensional (3D) vascular structures by human endothelial progenitor cells (hEPCs). The microfluidic device was made of biodegradable poly(lactic-co-glycolic acid) (PLGA) using a microchannel patterned silicon wafer made by soft lithography. A collagen type I (Col I) hydrogel containing hEPCs filled the microfluidic channels to reconstitute a 3D microenvironment for facilitating vascular structure formation by hEPCs. The device seeded with hEPCs was implanted into the subcutaneous space of athymic mice and retrieved one and four weeks after implantation. Histology and immunohistochemistry revealed that hEPCs formed a 3D capillary network expressing endothelial cell-specific proteins in the channel of the PLGA microfluidic device. This result indicates that a 3D microscale extracellular matrix reconstituted in the microchannel can promote the endothelial differentiation of hEPCs and in turn hEPC-mediated vasculogenesis. The PLGA microfluidic device reported herein may be useful as an implantable tissue-engineering scaffold for vascularized tissue reconstruction and therapeutic angiogenesis.

In situ self-assembled homeotropic alignment layer for fast-switching liquid crystal devices

ABSTRACT We propose a novel method for homeotropic alignment of liquid crystals (LCs) utilising in situ self-assembly of a low concentration of 4-(4-heptylphenyl)benzoic acids that form hydrogen bond with the indium tin oxide (ITO) substrates. Stable homeotropic alignment in the LC device is achieved with a simple mixing process of benzoic acid derivative in LC media, and it yields electro-optical performance similar to that achieved with the conventional alignment method using polyimides. It is experimentally confirmed that an ultrathin self-assembled molecular layer of 4-(4-heptylphenyl)benzoic acid formed by hydrogen bonding on ITO substrate makes it possible to attain a reliable homeotropic alignment of LCs. Furthermore, this simple approach provides a cost-effective and stable LC alignment layer with fast response time and thermal stability. GRAPHICAL ABSTRACT

Vertical alignment of liquid crystal using an in situ self-assembled molecular layer on hydrophilic ITO electrodes

ABSTRACT Vertical alignment of liquid crystals (LCs) was implemented by forming an in situ self-assembled molecular layer on hydrophilic indium tin oxide (ITO) electrodes. Improvement in hydrophilicity of the ITO electrode according to ultraviolet (UV) irradiation time was confirmed. The self-assembled molecular layer offered stable vertical alignment of nematic LCs via hydrogen bonding between 4´-heptylbiphenyl-4-carboxylic acid and the hydroxyl groups on the ITO surface. Further, the electro-optical property of the LC cell irradiated by UV light was investigated to confirm the improved performance of the LC device.

Fabrication of photoluminescent liquid crystal device using an in situ self-assembled molecular layer of a pyrene derivative

An in situ self-assembled molecular layer of 1-pyrenesulfonic acid sodium salt as an alignment agent was formed on indium tin oxide substrates for vertically aligning liquid crystals (LCs). The thus-aligned LCs exhibited uniform vertical alignment under crossed polarisers. The electro-optical characteristic of the LC cell fabricated using this method exhibited better performance than those of conventional LC cells with a polyimide alignment layer. Because the proposed alignment method is a simple one and involves low concentrations of the alignment agent (0.05 wt%), it is highly cost-effective. Further, the pyrene derivative, when mixed with LCs, exhibited photoluminescence (PL) under ultraviolet light. Given that the proposed method resulted in highly vertically aligned LCs and the alignment agent exhibited PL, the method should find wide use in the fabrication of colour-filter-free LC displays.

Novel tweezers using acoustically oscillating twin bubbles

This paper describes a novel tweezing system using cavitational microstreaming flows generated by acoustically oscillating twin bubbles for non-contact micromanipulation. A tweezing system with a single acoustically oscillating bubble attached on the tip of a rod integrated with a three-dimensional traverse system is firstly tested to manipulate a fish egg (1 mm diameter) in an aqueous medium. Although the flow generated from the single oscillating bubble is strong enough to push and move the fish egg, the moving direction of the fish egg is not controllable. To improve the control of the manipulation, identical twin bubbles, which have the same size and resonant frequency, are applied. To obtain the identical bubbles, an electrolysis chip consisting of sharp tip-shaped electrodes is microfabricated, and each bubble is generated from the chip by controlling the applied voltage and time and then transported to the tips of a U-shaped rod. Manipulation of a fish egg (1 mm diameter) and glass beads (100 µm diameter) is experimentally demonstrated using acoustically oscillating twin bubbles. Using a high speed camera, the force generated by the acoustically oscillating bubbles and its direction are analyzed in various acoustic excitation conditions. The results show that the generated force is proportional to the bubble oscillation amplitude, and the direction of the force depends on the distance between a bubble and object. A steel ball (500 µm diameter) is used for the investigation of the force direction. When a bubble (600 µm diameter) is acoustically excited, the steel ball is pulled into the oscillating bubble in the short distance (<3 mm); however, the steel ball is pushed from the oscillating bubble in the long distance.

Fabrication of a new homeotropic alignment layer for nematic liquid crystals using an in situ self-assembly of alkylated benzoic acid derivative

ABSTRACT We have presented a novel vertical alignment method simultaneously enhancing the alignment ability and electro-optical performances of nematic liquid crystals (LCs). The method relies on the self-assembly of 4-(4-heptylphenyl)benzoic acid and 2-carboxyethyl acrylate through hydrogen bonding with conventional polyimide and the generation of pre-tilting in the LC molecules using ultraviolet irradiation under applied voltage. The electro-optical measurements of a LC device fabricated by using this self-assembled polyimide layer exhibited strong homeotropic alignment and fast response time. The proposed alignment method may be valuable in providing new functional alignment materials for high-performance LC devices.

Simple vertical alignment of liquid crystals using photo-polymerization of alkyl acrylate monomer

ABSTRACT A new method for vertical alignment of liquid crystals (LCs) via in situ photo-polymerization of alkyl acrylate monomer on indium tin oxide, without the use of conventional polyimide layer is presented. The UV irradiation of the LC mixture doped with acrylate monomer containing long alkyl group in the confined LC cell provides uniform and stable homeotropic alignment of the LC molecules. The electro-optical characteristic of the fabricated LC cell using this method exhibits similar performance to that of the LC device prepared by using the conventional polyimide alignment layer.

Fabrication of a fast-switching liquid crystal device using reactive self-assembled polyimide alignment layer

ABSTRACT We proposed a new vertical alignment method for simultaneously improving the alignment force and electro-optical properties. The key point of the new method is the self-assembly of the reactive monomer via hydrogen bonding with the polyimide alignment layer and the formation of pre-tilt using the reactive monomer on an alignment layer. Through the self-assembly of the reactive monomer and the generation of the pre-tilt, it is possible to obtain a higher alignment force and a fast response time. As a result, through a simple additional step, we can fabricate a fast-switching liquid crystal device using a reactive self-assembled alignment layer.