Sung Gap Im

Direct Monolithic Integration of Organic Photovoltaic Circuits on Unmodified Paper

There has been signifi cant recent interest in integrating electronics into low-cost paper substrates, including transistors, storage devices, displays, and circuitry. [ 1–4 ] Paper-based photovoltaics (PVs) could serve as an “on-chip” power source for these paper electronics, and also create attractive new paradigms for solar power distribution, including seamless integration into ubiquitous formats such as window shades, wall coverings, apparel, and documents. Module installation may be as simple as cutting paper to size with scissors or tearing it by hand and then stapling it to roof structures or gluing it onto walls. Moreover, paper is ∼ 1000 times less expensive ( ∼ 0.01

Patterning Nanodomains with Orthogonal Functionalities: Solventless Synthesis of Self-Sorting Surfaces

· m − 2 ) than traditional glass substrates ( ∼ 10

BMP-2 peptide-functionalized nanopatterned substrates for enhanced osteogenic differentiation of human mesenchymal stem cells.

· m − 2 ) [ 5 , 6 ]

Conformal coverage of poly(3,4-ethylenedioxythiophene) films with tunable nanoporosity via oxidative chemical vapor deposition.

Vapor deposited functional polymer thin films can undergo rapid covalent functionalization. Patterning of two functional layers displaying orthogonal reactivity enables sorting of aqueous mixtures of dyes and nanoparticles, such as quantum dots, onto selective areas of nanopatterned surfaces.

Doping level and work function control in oxidative chemical vapor deposited poly (3,4-ethylenedioxythiophene)

A variety of biophysical and biochemical factors control stem cell differentiation. In this study, we developed a nanopatterned substrate platform to surface immobilize osteoinductive bone morphogenetic protein-2 (BMP-2) peptides. Specifically, polyurethane acrylate (PUA) substrates with nanometer-scale groove- and dot-shaped topography were fabricated. The nanopatterned PUA surface was uniformly coated with poly(glycidyl methacrylate) (pGMA) by initiated chemical vapor deposition (iCVD) followed by covalent immobilization of BMP-2 peptides. This approach resulted in much more efficient BMP-2 peptide immobilization than physical adsorption. The combined effects of biochemical signals from BMP-2 peptides and nanotopographical stimulation on osteogenic differentiation of hMSCs were examined in culture with and without soluble osteogenic factors. Results of Alizarin Red S staining, immunostaining, and quantitative real-time polymerase chain reaction revealed that hMSCs cultured on nanopatterned surfaces with immobilized BMP-2 peptides exhibited greater potential for osteogenic differentiation than hMSCs on a flat surface. Furthermore, the nanopatterned substrates with BMP-2 peptides directed osteogenic differentiation of hMSCs even without osteogenesis soluble inducing factors. Substrates with nanotopography and bioactive signals that induce differentiation of stem cells towards specific lineages could be used to develop functional stem cell culture substrates and tissue engineered scaffolds for therapeutic applications.

Chondrogenic Priming Adipose-Mesenchymal Stem Cells for Cartilage Tissue Regeneration

Novel nanoporous poly(3,4-ethylenedioxythiophene) (PEDOT) films with basalt-like surface morphology are successfully obtained via a one-step, vapor phase process of oxidative chemical vapor deposition (oCVD) by introducing a new oxidant, CuCl(2). The substrate temperature of the oCVD process is a crucial process parameter for controlling electrical conductivity and conjugation length. Moreover, the surface morphology is also systemically tunable through variations in substrate temperature, a unique advantage of the oCVD process. By increasing the substrate temperature, the surface morphology becomes more porous, with the textured structure on the nanometer scale. The size of nanopores and fibrils appears uniformly over 25 mm x 25 mm areas on the Si wafer substrates. Conformal coverage of PEDOT films grown with the CuCl(2) oxidant (C-PEDOT) is observed on both standard trench structures with high aspect ratio and fragile surfaces with complex topology, such as paper, results which are extremely difficult to achieve with liquid phase based processes. The tunable nanoporosity and its conformal coverage on various complex geometries are highly desirable for many device applications requiring controlled, high interfacial area, such as supercapacitors, Li ion battery electrodes, and sensors. For example, a highly hydrophilic surface with the static water contact angle down to less than 10 degrees is obtained solely by changing surface morphology. By applying fluorinated polymer film onto the nanoporous C-PEDOT via initiative chemical vapor deposition (iCVD), the C-PEDOT surface also shows the contact angle higher than 150 degrees . The hierarchical porous structure of fluorinated polymer coated C-PEDOT on a paper mat shows superhydrophobicity and oil repellency.

A doubly cross-linked nano-adhesive for the reliable sealing of flexible microfluidic devices

Control over doping level and work function is achieved for poly(3,4-ethylenedioxythiophene) (PEDOT) films deposited by oxidative chemical vapor deposition (oCVD). Surface analysis reveals the equivalence of the surface and bulk compositions for the oCVD films. The oCVD PEDOT polymer chains doped solely with Cl− ions. By increasing the substrate temperature used for deposition, the doping level was monotonically increased from 17to33at.%, resulting in a corresponding ability to tune the work function from 5.1to5.4eV. The controllability of doping level and work function of oCVD PEDOT offers great potential advantages for organic devices.

Oxidative chemical vapor deposition (oCVD) of patterned and functional grafted conducting polymer nanostructures

ABSTRACTPurposeChondrocytes lose their ability to produce cartilaginous matrix during multiplication in culture through repeated passages, resulting in inferior tissue phenotype. To overcome the limited amount of primary chondrocytes, we aimed to determine the optimal culture condition for in vitro/in vivo cartilage regeneration using human adipose-derived mesenchymal stem cells (AMSCs).MethodsTo evaluate the effects exerted by the chondrocytic culture condition on AMSC, we utilized chondrocyte conditioned medium (CM) and/or co-culture methods to prime and differentiate AMSCs. We evaluated ultimate in vivo engineered cartilage with primed AMSCs with that of chondrocytes. To examine the link between conditioned factors and proliferation/differentiation, cell cycle progression of AMSCs were examined using 5-ethynyl-2′-deoxyuridine (EdU), and gene expression was monitored.ResultsWe report that AMSCs can be stimulated to become chondrogenic cells when expanded with chondrocyte CM. Polymeric scaffolds co-seeded with CM- expanded AMSCs and primary chondrocytes resulted in in vivo cartilaginous tissues with similar biochemical content to constructs seeded with chondrocytes alone.ConclusionThese results indicate that chondrocyte CM consists of suitable morphogenetic factors that induce the chondrogenic priming of AMSCs for cartilage tissue engineering.

Initiated chemical vapor deposition of thermoresponsive poly (N-vinylcaprolactam) thin films for cell sheet engineering

Along with the expansion of microfluidics into many areas of applications such as sensors, microreactors and analytical tools, many other materials besides poly(dimethylsiloxane) (PDMS) have been suggested such as poly(imide) (PI) or poly(ethylene terephthalate) (PET). However, the sealing methods for these materials are not reliable in that many of the methods are specific to the substrate materials. Here, we report a novel robust doubly cross-linked nano-adhesive (DCNA) for bonding of various heterogeneous substrates. By depositing 200 nm of epoxy-containing polymer, poly(glycidyl methacrylate), via initiated chemical vapour deposition (iCVD) onto various substrates and cross-linking them with ethylenediamine, a strong adhesion was obtained between the substrates. This adhesive system was not only able to bond various difficult-to-bond substrates, such as PET or PI, but it could also preserve the complicated morphology of the surfaces owing to the thin nature of the DCNA system. The DCNA allowed fabrication of microfluidic devices using both rigid substrates, such as silicon wafer and glass, and flexible substrates, such as PDMS, PET and PI. The burst pressure of the devices sealed with DCNA exceeded 2.5 MPa, with a maximum burst pressure of 11.7 MPa. Furthermore, the adhesive system demonstrated an exceptional chemical and thermal resistance. The adhesion strength of the adhesive sandwiched between glass substrates remained the same even after a 10 day exposure to strong organic solvents such as toluene, acetone, and tetrahydrofuran (THF). Also, exposure to 200 °C for 15 h was not able to damage the adhesion strength. Using the high adhesive strength and flexibility of DCNA, flexible microfluidic devices that can be completely folded or rolled without any delamination during the operation were fabricated. The DCNA bonding is highly versatile in the sealing of microfluidic systems, and is compatible with a wide selection of materials, including flexible and foldable substrates, even upon sealing few-μm-sized channels.

Synthesis of single-walled carbon nanotube-incorporated polymer hydrogels via click chemistry

We present a simple one-step process to simultaneously create patterned and amine functionalized biocompatible conducting polymer nanostructures, using grafting reactions between oxidative chemical vapor deposition (oCVD) PEDOT conducting polymers and amine functionalized polystyrene (PS) colloidal templates. The functionality of the colloidal template is directly transferred to the surface of the grafted PEDOT, which is patterned as nanobowls, while preserving the advantageous electrical properties of the bulk conducting polymer. This surface functionality affords the ability to couple bioactive molecules or sensing elements for various applications, which we demonstrate by immobilizing fluorescent ligands onto the PEDOT nanopatterns. Nanoscale substructure is introduced into the patterned oCVD layer by replacing the FeCl3 oxidizing agent with CuCl2.