fabrication-gradient-nanopattern-thermal-nanoimprinting-technique

Fabrication of Gradient Nanopattern by Thermal Nanoimprinting Technique and Screening of the Response of Human Endothelial Colony-forming Cells

Nanotopography can be found in various extracellular matrices (ECMs) around the body and is known to have important regulatory actions upon cellular ...

Korea University

Acrylated hyaluronic acid (HA) was used as a scaffold for bone morphogenic protein-2 (BMP-2) and human mesenchymal stem cells (hMSCs) for rat calvarial defect regeneration. HA was acrylated by two-step reactions: (1) introduction of an amine group using adipic acid dihydrazide (ADH); (2) acrylation by N-acryloxysuccinimide. Tetrathiolated poly(ethylene) glycol (PEG-SH(4)) was used as a cross-linker by a Michael-type addition reaction and the hydrogel was formed within 10min under physiological conditions. This hydrogel is degraded completely by 100U/ml hyaluronidase in vitro. hMSCs and/or BMP-2 was added during gelation. Cellular viability in vitro was increased up to 55% in the hydrogels with BMP-2 compared with the control. For in vivo calvarial defect regeneration, five different samples (i.e., control, hydrogel, hydrogel with BMP-2, hydrogel with MSCs, and hydrogel with BMP-2 and MSCs) were implanted for 4 weeks. The histological results demonstrated that the hydrogels with BMP-2 and MSCs had the highest expression of osteocalcin and mature bone formation with vascular markers, such as CD31 and vascular endothelial growth factors, compared with the other samples. This study demonstrated that HA base hydrogel can be used for cell and growth factor carriers for tissue regeneration.

Bone regeneration using hyaluronic acid-based hydrogel with bone morphogenic protein-2 and human mesenchymal stem cells.

In this paper, we introduce a new continuous production technique of calcium alginate fibers with a microfluidic platform similar to a spider in nature. We have used a poly(dimethylsiloxane) (PDMS) microfluidic device embedded capillary glass pipet as the apparatus for fiber generation. As a sample flow, we introduced a sodium alginate solution, and, as a sheath flow, a CaCl2 solution was introduced. The coaxial flows were generated at the intersection of both flows, and the sodium alginate was solidified to calcium alginate by diffusion of the Ca2+ ions during traveling through the outlet pipet. The diameter changes in the sample and sheath flow variations were examined, and the size of alginate fibers was well regulated by changing both flow rates. In addition, we have measured the elasticity of dried fibers. We evaluated the potential use of alginate fibers as a cell carrier by loading human fibroblasts during the "on the fly" fabrication process. From the LIVE/DEAD assay, cells survived well during the fiber fabrication process. In addition, we evaluate the capability of loading the therapeutic materials onto the alginate fibers by immobilized bovine serum albumin-fluorescein isothiocyanate in the fibers.

"On the fly" continuous generation of alginate fibers using a microfluidic device.

A well known fibrous protein, fibronectin was successfully immobilized onto well-fabricated nanopatterns of polystyrene (PS) substrates. The nanopatterns with finely-defined physical dimensions were obtained by nanoimprinting lithography (NIL) using anodized aluminum oxide (AAO) molds of which the pore sizes were controlled in nanometer scale; 45 nm, 250 nm and 410 nm for the widths and 110 nm and 500 nm for the pitches. Discrete changes of the surface images before and after the protein-adsorption on the patterns were demonstrated by scanning electron microscope (SEM), and the effect of the patterned features on the immobilization has been investigated and discussed.

Immobilization of fibronectin onto a large area nanoimprinted polystyrene patterns.

Hyaluronic acid is a natural glycosaminoglycan involved in biological processes. Low-molecular-weight hyaluronic acid (10 and 50 kDa)-based hydrogel was synthesized using derivatized hyaluronic acid. Hyaluronic acid was acrylated by two steps: (1) introduction of an amine group using adipic acid dihydrazide, and (2) acrylation by N-acryloxysuccinimide. Injectable hyaluronic acid-based hydrogel was prepared by using acrylated hyaluronic acid and poly(ethylene glycol) tetra-thiols via Michael-type addition reaction. Mechanical properties of the hydrogel were evaluated by varying the molecular weight of acrylated hyaluronic acid (10 and 50 kDa) and the weight percent of hydrogel. Hydrogel based on 50-kDa hyaluronic acid showed the shortest gelation time and the highest complex modulus. Next, human mesenchymal stem cells were cultured in cell-adhesive RGD peptide-immobilized hydrogels together with bone morphogenic protein-2 (BMP-2). Cells cultured in the RGD/BMP-2-incorporated hydrogels showed proliferation rates higher than that of control or RGD-immobilized hydrogels. Real-time RT-PCR showed that the expression of osteoblast marker genes such as CBFalpha1 and alkaline phosphatase was increased in hyaluronic acid-based hydrogel, and the expression level was dependent on the molecular weight of hyaluronic acid, RGD peptide, and BMP-2. This study indicates that low-molecular-weight hyaluronic acid-based hydrogel can be applied to tissue regeneration as differentiation guidance materials of stem cells.

Characterization of low-molecular-weight hyaluronic acid-based hydrogel and differential stem cell responses in the hydrogel microenvironments.

Hyaluronic acid is a naturally derived glycosaminoglycan (GAG) involved in biological processes. A low molecular weight hyaluronic acid (50 kDa)-based hydrogel was synthesized using acrylated hyaluronic acid. Matrix metalloproteinase (MMP) sensitive hyaluronic acid-based hydrogels were prepared by conjugation with two different peptides: cell adhesion peptides containing integrin binding domains (Arg-Gly-Asp: RGD) and a cross-linker with MMP degradable peptides to mimic the remodeling characteristics of natural extracellular matrices (ECMs) by cell-derived MMPs. Mechanical properties of these hydrogels were evaluated with different molecular weights of acrylated hyaluronic acid (10 kDa and 50 kDa) cross-linked by MMP sensitive peptides by measuring elastic modulus, viscous modulus, swelling ratio and degradation rate. The MMP sensitive hydrogel based on the 50 kDa hyaluronic acid showed a 31.5-fold shorter gelation time, 4.7-fold higher storage modulus and 0.51-fold smaller swelling ratio than those of the hydrogel based on the 10 kDa. Degradation rate was dependent on MMP sensitivity of the peptide cross-linker. MMP sensitive hyaluronic acid based hydrogels were degraded faster than MMP insensitive-hyaluronic acid-based hydrogels. Human mesenchymal stem cells (MSCs) were cultured in MMP-sensitive or insensitive hyaluronic acid-based hydrogels (50 kDa hyaluronic acid) and/or immobilized cell adhesive RGD peptides. Cells cultured in the MMP-sensitive hydrogel with RGD peptides showed dramatic cell spreading compared with that of the control, which remained round. This MMP-sensitive low molecular weight hyaluronic acid-based hydrogel could be useful in tissue engineering by improving tissue defect regeneration and tissue remodeling.

Synthesis and characterization of matrix metalloprotease sensitive-low molecular weight hyaluronic acid based hydrogels.

Water-droplet adhesiveness was freely controlled on a single platform of superhydrophobic anodized aluminum oxide (AAO) within the range from highly adhesive to self-cleanable. Changing the structure from nanopore to nanopillar arrays at the surface caused a dramatic increase in the receding angle and a decrease in the hysteresis of water contact angles. The presence of dead-end nanopores but not through nanoholes was recognized as one of the main causes of the adhesiveness of superhydrophobic surfaces. The adhesiveness-controllable superhydrophobic AAO can be an excellent platform on which to elucidate the physical nature of the wetting phenomenon related to the nanostructure and has promising potential in technological applications.

Nanostructure-dependent water-droplet adhesiveness change in superhydrophobic anodic aluminum oxide surfaces: from highly adhesive to self-cleanable.

The utility of electro-responsive smart materials has been limited by bubble generation (hydrolysis) during application of electrical fields and by biocompatibility issues. Here we describe the design of a device that overcomes these limitations by combining material properties, new design concepts, and microtechnology. 4-hydroxybutyl acrylate (4-HBA) was used as a backbone hydrogel material, and its actuating behavior, bending force, and elasticity were extensively characterized as a function of size and acrylic acid concentration. To prevent bubble generation, the system was designed such that the hydrogel actuator could be operated at low driving voltages (<1.2 V). A microfluidic channel with an integrated electroactive hydrogel actuator was developed for sorting particles. This device could be operated in cell culture media, and the sorting capabilities were initially assessed by sorting droplets in an oil droplet emulsion. Biocompatibility was subsequently tested by sorting mouse embryoid bodies (mEBs) according to size. The sorted and collected mEBs maintained pluripotency, and selected mEBs successfully differentiated into three germ layers: endoderm, mesoderm, and ectoderm. The electroactive hydrogel device, integrated into a microfluidic system, successfully demonstrated the practical application of smart materials for use in cell biology.

Electrically-driven hydrogel actuators in microfluidic channels: fabrication, characterization, and biological application.

A mask-free, cost-effective dry-etching method for the fabrication of height- and spacing-controlled, pillar-like nanostructures was established in order to detect DNA molecules. The height and spacing of the quartz nanostructure were regulated by successive O(2) and CF(4) reactive ion etching times. The height and spacing of the nanostructures were tuned between 118 and 269 nm and between 107 and 161 nm, respectively. Probe DNA was immobilized on the structure and hybridized with fluorescently-labeled target DNA. Increases in the height and spacing of the nanopillar structure positively correlated with the fluorescence intensity of bound DNA. Usage of the nanostructure increased the DNA detection limit by up to 100-fold.

Size-controllable quartz nanostructure for signal enhancement of DNA chip.

 Both self-cleanability and antireflectivity were achieved on quartz surfaces by forming heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane self-assembled monolayer after fabrication of nanostructures with a mask-free method. By exposing polymethylmethacrylate spin-coated quartz plates to O2 reactive ion etching (RIE) and CF4 RIE successively, three well-defined types of nanopillar arrays were generated: A2, A8, and A11 patterns with average pillar widths of 33 ± 4 nm, 55 ± 5 nm, and 73 ± 14 nm, respectively, were formed. All the fabrication processes including the final cleaning can be finished within 4 h. All nanostructured quartz surfaces exhibited contact angles higher than 155° with minimal water droplet adhesiveness and enhanced transparency (due to antireflectivity) over a broad spectral range from 350 to 900 nm. Furthermore, A2 pattern showed an enhanced antireflective effect that extends to the deep-UV range near 190 nm, which is a drawback region in conventional thin-film-coating approaches as a result of thermal damage. Because, by changing the conditions of successive RIE, the geometrical configurations of nanostructure arrays can be easily modified to meet specific needs, the newly developed fabrication method is expected to be applied in various optic and opto-electrical areas.PACS codes: 06.60.Ei; 81.65.Cf; 81.40.Vw.

A simple and fast fabrication of a both self-cleanable and deep-UV antireflective quartz nanostructured surface.

The topographical environment, which mimics the stem cell niche, provides mechanical cues to regulate the differentiation of mesenchymal stem cells (MSC). Diverse topographical variations have been engineered to investigate cellular responses; however, the types of mechanical parameters that affect cells, and their underlying mechanisms remain largely unknown. In this study, we screened nanotopological pillars with size gradient to activate transcriptional coactivator with PDZ binding motif (TAZ), which stimulates osteogenesis of MSC. We observed that a nanotopological plate, 70 nm in diameter, significantly induces osteogenic differentiation with the activation of TAZ. TAZ activation via the nanotopological plate was mediated by actin polymerization and Rho signaling, as evidenced by the cytosolic localization of TAZ under F-actin or Rho kinase inhibitor. The FAK and MAPK pathways also play a role in TAZ activation by the nanotopological plate because the inhibitor of ERK and JNK blocked nanopattern plate induced osteogenic differentiation. Taken together, these results indicate that nanotopology regulates cell differentiation through TAZ activation.

Nanotopological plate stimulates osteogenic differentiation through TAZ activation.

Nanotopography plays a pivotal role in the regulation of cellular responses. Nonetheless, little is known about how the gradient size of nanostructural stimuli alters the responses of endothelial progenitor cells without chemical factors. Herein, the fabrication of gradient nanopattern plates intended to mimic microenvironment nanotopography is described. The gradient nanopattern plates consist of nanopillars of increasing diameter ranges [120-200 nm (GP 120/200), 200-280 nm (GP 200/280), and 280-360 nm (GP 280/360)] that were used to screen the responses of human endothelial colony-forming cells (hECFCs). Nanopillars with a smaller nanopillar diameter caused the cell area and perimeter of hECFCs to decrease and their filopodial outgrowth to increase. The structure of vinculin (a focal adhesion marker in hECFCs) was also modulated by nanostructural stimuli of the gradient nanopattern plates. Moreover, Rho-associated protein kinase (ROCK) gene expression was significantly higher in hECFCs cultured on GP 120/200 than in those on flat plates (no nanopillars), and ROCK suppression impaired the nanostructural-stimuli-induced vinculin assembly. These results suggest that the gradient nanopattern plates generate size-specific nanostructural stimuli suitable for manipulation of the response of hECFCs, in a process dependent on ROCK signaling. This is the first evidence of size-specific nanostructure-sensing behavior of hECFCs.

Kyu Back Lee

School of Biomedical Engineering

Korea University

Fabrication of Gradient Nanopattern by Thermal Nanoimprinting Technique and Screening of the Response of Human Endothelial Colony-forming Cells

Kyu Back Lee

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}School of Biomedical Engineering

Korea University

Fabrication of Gradient Nanopattern by Thermal Nanoimprinting Technique and Screening of the Response of Human Endothelial Colony-forming Cells

School of Biomedical Engineering