Montmorillonite clay based polyurethane nanocomposite as substrate for retinal pigment epithelial cell growth

The subretinal transplantation of retinal pigment epithelial cells (RPE cells) grown on polymeric supports may have interest in retinal diseases affecting RPE cells. In this study, montmorillonite based polyurethane nanocomposite (PU-NC) was investigated as substrate for human RPE cell growth (ARPE-19 cells). The ARPE-19 cells were seeded on the PU-NC, and cell viability, proliferation and differentiation were investigated. The results indicated that ARPE-19 cells attached, proliferated onto the PU-NC, and expressed occludin. The in vivo ocular biocompatibility of the PU-NC was assessed by using the HET-CAM; and through its implantation under the retina. The direct application of the nanocomposite onto the CAM did not compromise the vascular tissue in the CAM surface, suggesting no ocular irritancy of the PU-NC film. The nanocomposite did not elicit any inflammatory response when implanted into the eye of rats. The PU-NC may have potential application as a substrate for RPE cell transplantation.     

Plasma polymer coatings to aid retinal pigment epithelial growth for transplantation in the treatment of age related macular degeneration

Subretinal transplantation of functioning retinal pigment epithelial (RPE) cells grown on a synthetic substrate is a potential treatment for age-related macular degeneration (AMD), a common cause of irreversible vision loss in developed countries. Plasma polymers give the opportunity to tailor the surface chemistry of the artificial substrate whilst maintaining the bulk properties. In this study, plasma polymers with different functionalities were investigated in terms of their effect on RPE attachment and growth. Plasma polymers of acrylic acid (AC), allyl amine (AM) and allyl alcohol (AL) were fabricated and characterised using X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Octadiene (OD) hydrocarbon films and tissue culture polystyrene were used as controls. Wettability varied from hydrophobic OD to relatively hydrophilic AC. XPS demonstrated four very different surfaces with the expected functionalities. Attachment, proliferation and morphological examination of an RPE cell line and primary RPE cells were investigated. Both cell types grew on all surfaces, with the exception of OD, although the proliferation rate of primary cells was low. Good epithelial morphology was also demonstrated. Plasma polymerised films show potential as cell carrier surfaces for RPE cells in the treatment of AMD.     

Development of a surface to increase retinal pigment epithelial cell (ARPE-19) proliferation under reduced serum conditions

Age related macular degeneration of the eye is brought about by damage to the retinal pigment epithelium (RPE) and is a major cause of adult blindness. One potential treatment method is transplantation of RPE cells grown in vitro. Maintaining RPE cell viability and physiological function in vitro is a challenge, and this must also be achieved using materials that can be subsequently used to deliver an intact cell sheet into the eye. In this paper, plasma polymerisation has been used to develop a chemically modified surface for maintaining RPE cells in vitro. Multiwell plates modified with a plasma copolymer of allylamine and octadiene maintained RPE cell growth at a level similar to that of TCPS. However, the addition of bound glycosaminoglycans (GAGs) to the plasma polymerised surface significantly enhanced RPE proliferation. Simply adding GAG to the culture media had no positive effect. It is shown that a combination of plasma polymer and GAG is a promising method for developing suitable surfaces for cell growth and delivery, that can be applied to any substrate material.     

Electrochemically Activated Glassy Carbons as potential Supercapacitors and substrates for fixed mediators

Glassy carbon electrodes were prepared in various electrolytes by cyclic voltammetry and constant potential methods under various conditions to explore the factors affecting the response of GC after the electrochemical pretreatment (ECP), including the high pseudo-capacitance, the great ability to absorb and strongly hold redox species and the facilitation of kinetics of electron transfer. Deepening the oxidation via increasing the oxidation potential and the oxidation time or the number of cycles and the final potential in cyclic voltammetry were found to increase the amount of redox species loaded onto GC and the pseudocapacitance due to formation of thicker carbon oxide layer. The increase in the rate of electron transfer reactions on deepening the oxidation is, however, attributed to the generation of more cleaner surface and more reactive sites. The order of increasing the efficiency of ECP; NaOH>KCl>HCl>NaClO₄(MeCN), signifies the role of water and pH on the formation and thickness of the oxide layer formed after ECP. The results support the predominance of the faradaic origin of the pseudo-capacitance of GC after ECP.     

ZnO nanowire arrays as substrates for cell proliferation and differentiation

In the latest years, the use of zinc oxide (ZnO) nanostructures has been proposed in different biomedical applications, however, to date, only a few contrasting results concerning their biocompatibility can be found in the literature. In particular, the application of the extraordinary piezoelectric properties of ZnO nanostructures has poorly been explored for the culture of electrically excitable cells, and, for this reason, systematic investigations of their interactions with these living systems appear to be necessary. In this paper, we report about adhesion, proliferation and differentiation of two mammalian cell lines (PC12, as model of neuronal cells, and H9c2, as model of muscle cells) over ZnO nanowire arrays. We demonstrate suitability of these arrays in sustaining cellular functions, and their potential in applications that range from tissue engineering to minimally invasive sensing and/or stimulation.     

Polyurethanes as self adhesive matrix for the transdermal drug delivery of testosterone

The new technology to manufacture transdermal active patches without solvents or increased temperatures described here is based on polyol and isocyanate reacting to polyurethane (PU) in the presence of the drug. The technology was proven using testosterone (T) as the drug and N,N-Diethyl-m-toluamide (DEET) and Limonene (L) as enhancers for skin permeation. The experimental patches varied in drug content and enhancer concentration. The patches were evaluated regarding adhesion to stainless steel or leather, in vitro drug release and T permeation across human cadaver skin using Franz cell. Comparing the results with those of a parallel investigation of the commercial product, Testopatch(?), adhesion to leather and in vitro drug release of the experimental patches were found to be higher. The steady-state flux (J(SS)) of T from the experimental patches was found lower than Testopatch(?). The flux of the experimental patch P3, which had the highest concentration of DEET and a low concentration of L was comparable to J(SS) of the commercial product, Testopatch(?).     

Mesoscopic patterning of cell adhesive substrates as novel biofunctional interfaces

In this report, cell adhesion to honeycomb-patterned films is described with respect to the dimensions of the honeycomb structure. The honeycomb-patterned films can be fabricated by casting a dilute solution of amphiphilic polymers on solid substrates. The honeycomb structure is not homogeneous in all dimensions. Analysis of distribution of the honeycomb hole sizes demonstrates a gradual decrease in honeycomb hole diameter along the radius of the cast area. The largest holes were located near geometric center of the cast area. The diameter of the largest honeycomb holes in the cast area could be controlled by varying the cast volume of the polymer solution. Cell cultures on the honeycomb films demonstrated that cell adhesion could be inhibited at the outer region of the cast area. The extent of the inhibition of cell adhesion was influenced by the chemical properties of the polymers constituting the honeycomb films.     

Nanotextured metal copper substrates as powerful and long-lasting fuel cell anodes

Fuel cells (FCs) are promising electrochemical devices that convert chemical energy of fuels directly into electrical energy. We present a new anode material based on nanotextured metal copper for fuel cell applications. We have demonstrated that low-cost copper catalyst anodes act as highly efficient and ultra-long-lasting materials for the direct electro-oxidation of ammonia-borane and additional amine derivatives. High power densities of ca. 1W·cm(-2) (ca. -1 V vs Ag/AgCl at 1 A) are readily achieved at room temperature. We fabricate fuel cell devices based on our nanotextured Cu anodes in combination with commercial air cathodes.     

Phospholipid membranes as substrates for polymer adsorption

A largely unsolved problem in soft materials is how surface reconstruction competes with the rate of adsorption. Here, supported phospholipid bilayers of DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) were employed as substrates for the adsorption of a weak polyelectrolyte, polymethacrylic acid, whose time-dependent ratio of charged to uncharged functional groups served to probe the local dielectric environment. Chains that encountered sparsely covered surfaces spread to maximize the number of segment-surface contacts at rates independent of the molar mass (which was varied by a factor of 30), but dependent on the phase of the lipid bilayer, gel or liquid crystal. Surface reconstruction rather than molar mass of the adsorbing molecules seemed to determine the rate of spreading. The significance of these findings is the stark contrast with well-known views of polymer adsorption onto surfaces having structures that are 'frozen' and unresponsive, and is relevant not just from biological and biophysical standpoints, but also in the formulation of many cosmetics and pharmaceutical products.     

Conducting cryogel scaffold as a potential biomaterial for cell stimulation and proliferation

The aim of the study was to demonstrate the potential of the cryogelation technique for the synthesis of the conducting cryogel scaffolds which would encompass the advantages of the cryogel matrix, like the mechanical strength and interconnected porous network as well as the conductive properties of the incorporated conducting polymeric material, polypyrrole. The cryogels were synthesized using different combinations of oxidizing agents and surfactants like, sodium dodecyl sulfate (SDS)/ammonium persulfate (APS), SDS/iron chloride (FeCl₃), cetyl trimethyl ammonium bromide (CTAB)/APS, and CTAB/FeCl₃. The synthesized gels were characterized by scanning electron microscopic analysis for morphology, Fourier transform infrared spectroscopy for analyzing the presence of the polypyrrole (0.5–4 %) as nano-fillers in the gel. It was observed that the presence of these nano-fillers increased the swelling ratio by approximately 50 %. The synthesized conducting cryogels displayed high stress bearing capacity without being deformed as analysed by rheological measurements. The degradation studies showed 12–15 % degradation in 4 weeks time. In vitro studies with conducting and non-conducting cryogel scaffold were carried out to optimize the stimulation conditions for the two cell lines, neuro2a and cardiac muscle C2C12. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed approximately 25 and 15 % increase in the cell proliferation rate for neuro2a and C2C12 cell line, respectively. This was observed at a specific voltage of 100 mV and 2 V, for a specified duration of 2 h and 1 min, respectively for the conducting scaffold as compared to the control. This can play an important role in tissue engineering applications for cell lines where acquiring a high cell number and functionality is desired.     

Polymer films with surfaces unmodified and modified by non-thermal plasma as new substrates for cell adhesion

The surface properties of biomaterials, such as wettability, polar group distribution, and topography, play important roles in the behavior of cell adhesion and proliferation. Gaseous plasma discharges are among the most common means to modify the surface of a polymer without affecting its properties. Herein, we describe the surface modification of poly(styrene) (PS) and poly(methyl methacrylate) (PMMA) films using atmospheric pressure plasma processing through exposure to a dielectric barrier discharge (DBD). After treatment the film surface showed significant changes from hydrophobic to hydrophilic as the water contact angle decreasing from 95° to 37°. All plasma-treated films developed more hydrophilic surfaces compared to untreated films, although the reasons for the change in the surface properties of PS and PMMA differed, that is, the PS showed chemical changes and in the case of PMMA they were topographical. Excellent adhesion and cell proliferation were observed in all films. In vitro studies employing flow cytometry showed that the proliferation of L929 cells was higher in the film formed by a 1:1 mixture of PS/PMMA, which is consistent with the results of a previous study. These findings suggest better adhesion of L929 onto the 1:1 PS/PMMA modified film, indicating that this system is a new candidate biomaterial for tissue engineering.     

Multifunctional substrates of thin porous alumina for cell biosensors

We have fabricated anodic porous alumina from thin films (100/500 nm) of aluminium deposited on technological substrates of silicon/glass, and investigated the feasibility of this material as a surface for the development of analytical biosensors aiming to assess the status of living cells. To this goal, porous alumina surfaces with fixed pitch and variable pore size were analyzed for various functionalities. Gold coated (about 25 nm) alumina revealed surface enhanced Raman scattering increasing with the decrease in wall thickness, with factor up to values of approximately 10⁴ with respect to the flat gold surface. Bare porous alumina was employed for micro-patterning and observation via fluorescence images of dye molecules, which demonstrated the surface capability for a drug-loading device. NIH-3T3 fibroblast cells were cultured in vitro and examined after 2 days since seeding, and no significant (P > 0.05) differences in their proliferation were observed on porous and non-porous materials. The effect on cell cultures of pore size in the range of 50–130 nm—with pore pitch of about 250 nm—showed no significant differences in cell viability and similar levels in all cases as on a control substrate. Future work will address combination of all above capabilities into a single device.     

Silver-embedded zeolite crystals as substrates for surface-enhanced Raman scattering

This paper reports the preparation of a type of Ag-embedded zeolite crystals as surface-enhanced Raman spectroscopy (SERS) substrates by chemical reduction of Ag⁺-exchanged ZSM-5. Ag⁺ ions were loaded into the zeolite framework by ion exchange. Then the exchanged-Ag⁺ ions were reduced and metallic silver clusters formed inside the zeolite channel. The resulting Ag-embedded zeolite crystals are characterized by using a number of techniques including X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy to confirm silver formed inside the crystal channel. The fabricated Ag-embedded ZSM-5 zeolite substrates displayed strong and reproducible SERS activity for different Raman probe molecules such as Tris(2,2′-bipyridyl) ruthenium(II) chloride (RuBpy) and rhodamine 6G (R6G). Since silver embedded into the zeolite channel without changing the crystal surface property, the Ag–ZSM-5 zeolite crystal can be used to prepare different SERS-active substrate (SERS-tags), in which different probe molecules may be detected. Such Ag-embedded zeolite substrate would be useful in chemical and biological sensing and in the development of SERS-based analytical devices.     

Silver nanowire layer-by-layer films as substrates for surface-enhanced Raman scattering

In this paper, the fabrication of highly stable, surface-enhanced Raman scattering (SERS) active dendrimer/silver nanowire layer-by-layer (LBL) films is reported. Ag nanowires, approximately 100 nm in diameter, were produced in solution and transferred, using the LBL technique, onto a single fifth-generation DAB-Am dendrimer layer on a glass substrate. The Ag nanowires, and the resulting LBL films were characterized using UV-visible surface plasmon absorbance, while the LBL films were further characterized by atomic force microscopy measurements and surface-enhanced Raman and resonance Raman scattering of several analytes. The dendrimer was found to effectively immobilize the Ag nanowires with increased control over spacing and aggregation of the particles. These films are shown to be excellent substrates for SERS/SERRS measurements, demonstrating significant enhancement, and trace detection capability. Several trial analytes were tested using a variety of excitation energies, and results confirmed effective enhancement of Raman signals throughout the visible range (442-785 nm) with different molecules. Analytes were deposited onto the enhancing Ag nanowire LBL films surface using both casting and Langmuir-Blodgett monolayer transferring techniques.     

Use of near-infrared as a screening technique for CdZnTe substrates

Epitaxial layers of Cd _x Hg_1–xTe (CMT) are grown onto Cd_1–yZn _y Te (CZT) substrates in order to minimize misfit dislocations at the growth interface. For long wavelength focal plane array infrared detector requirements x = 0.22 CMT is nominally lattice matched to CZT alloys with y ~ 0.04. However, the rate of change of lattice parameter, as a function of y, means that the uniformity and definition of the required Zn concentration is important. We report here a non-contact, non-destructive technique for screening/mapping CZT substrates using the near infrared (NIR) band edge cut-on, defined by the wavelength corresponding to an absorption coefficient () = 10cm^–1, which automatically corrects for thickness or transmission variations. Details of the experimental set-up and a novel holder for vertical mounting of substrates are given. A comparison of results from this technique and X-ray diffraction (XRD) lattice parameter data is also presented.     

Movable Au microplates as fluorescence enhancing substrates for live cells

Hexagonal and triangular Au microplates extending over an area of ?12,000 ?m² with thickness in the range 30–1000 nm have been synthesized using a single step thermolysis of (AuCl4)^?-tetraoctylammonium bromide complex in air. The microplates are self-supporting and can be easily manipulated using a sharp pin, a property which enables them to serve as substrates for living cells. The microplate surface is non-toxic to living cells and can enhance the fluorescence signal from fluorophores residing within the cell by an order of magnitude. In addition, the microplates are smooth and single-crystalline, and ideal as microscopy substrates and molecular electrodes. The growth of the microplates in the initial stages is interesting in that they seem to grow perpendicular to the substrate, as evidenced by in situ microscopy. Open image in new window     

Stem cell differentiation on electrospun nanofibrous substrates for vascular tissue engineering

Nanotechnology has enabled the engineering of a variety of materials to meet the current challenges and requirements in vascular tissue regeneration. In our study, poly-l-lactide (PLLA) and hybrid PLLA/collagen (PLLA/Coll) nanofibers (3:1 and 1:1) with fiber diameters of 210 to 430 nm were fabricated by electrospinning. Their morphological, chemical and mechanical characterizations were carried out using scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared (ATR-FTIR), and tensile instrument, respectively. Bone marrow derived mesenchymal stem cells (MSCs) seeded on electrospun nanofibers that are capable of differentiating into vascular cells have great potential for repair of the vascular system. We investigated the potential of MSCs for vascular cell differentiation in vitro on electrospun PLLA/Coll nanofibrous scaffolds using endothelial differentiation media. After 20 days of culture, MSC proliferation on PLLA/Coll(1:1) scaffolds was found 256% higher than the cell proliferation on PLLA scaffolds. SEM images showed that the MSC differentiated endothelial cells on PLLA/Coll scaffolds showed cobblestone morphology in comparison to the fibroblastic type of undifferentiated MSCs. The functionality of the cells in the presence of ‘endothelial induction media’, was further demonstrated from the immunocytochemical analysis, where the MSCs on PLLA/Coll (1:1) scaffolds differentiated to endothelial cells and expressed the endothelial cell specific proteins such as platelet endothelial cell adhesion molecule-1 (PECAM-1 or CD31) and Von Willebrand factor (vWF). From the results of the SEM analysis and protein expression studies, we concluded that the electrospun PLLA/Coll nanofibers could mimic the native vascular ECM environment and might be promising substrates for potential application towards vascular regeneration.     

Aligned silver nanorod arrays as substrates for surface-enhanced infrared absorption spectroscopy

Preferentially aligned silver nanorod arrays prepared by oblique angle vapor deposition were evaluated as substrates for surface-enhanced infrared absorption (SEIRA) spectroscopy. These nanorod arrays have an irregular surface lattice and are composed of tilted, cylindrically shaped nanorods that have an average length of 868 nm +/- 95 nm and an average diameter of 99 nm +/- 29 nm. The overall enhancement factor for chemisorbed organic films of para-nitrobenzoic acid (PNBA) deposited onto the Ag nanorod arrays analyzed by external reflection SEIRA was calculated to be 31 +/- 9 compared to infrared reflection-absorption spectroscopy (IRRAS) obtained from a 500 nm Ag film substrate. This enhancement is attributed to the unique optical properties of the nanorod arrays as well as the increased surface area provided by the nanorod substrate. SEIRA reflection-absorbance intensity was observed with both p- and s-polarized incident radiation with angles of incidence ranging from 25 degrees to 80 degrees . The largest intensity was achieved with p-polarization and incident angles larger than 75 degrees . Polarization-dependent ultraviolet/visible/near-infrared (UV/Vis/NIR) spectra of the nanorod arrays demonstrate that the red-shifted surface plasmon peaks of the elongated nanorods may be partially responsible for the observed SEIRA response. The SEIRA detection limit for the Ag nanorod arrays was estimated to be 0.08 ng/cm(2). Surface-enhanced Raman scattering (SERS) and SEIRA analysis of chemisorbed PNBA utilizing the same nanorod substrate is demonstrated.     

Strip gratings on dielectric substrates as output couplers for submillimeter lasers

This paper describes the use and advantages of metallic strip gratings on dielectric substrates as output couplers for both optically pumped and discharge-excited submillimeter lasers. Formulas are presented for the calculation of transmittance and loss of such couplers, taking account of loss in the strip grating as well as loss and multiple reflections in the substrate. Included are expressions for the phase shifts on reflection and transmission by an arbitrary lossy grid on a plane boundary between two dielectrics according to a transmission-line model that is applicable for wavelengths in both dielectrics longer than the grid period. In relation to these phase shifts attention is drawn to an important sign convention. The theory is shown to agree well with measured transmittance of a typical device between 500 and 1600 GHz as well as spot measurements at 891 (337-microm HCN laser), 1540, and 1578 GHz (195- and 190-microm DCN laser). Finally, the theory is used to design a low-loss coupler for the low-gain 119-microm line of discharge excited H2O.