Mechanically tunable conjugated polymer distributed feedback lasers

Herein we report a low-threshold organic laser device based on semiconducting poly(9, 9′ -dioctylfluoren-2,7-diyl-alt-benzothiadiazole) (F8BT) encapsulated in a mechanically stretchable polydimethylsiloxane (PDMS) matrix. We take advantage of the natural flexibility of PDMS to alter the periodicity of the distributed feedback grating which in turn tunes the gain wavelength at which the resonant feedback is obtained. This way, we demonstrate that low-threshold lasing [6.1 μJ cm-2 (5.3 nJ)] is maintained over a large stretching range of 0%-7% which translates into a tuning range of about 20 nm. © 2010 American Institute of Physics.

A microfluidic device for high density hydrodynamic cell trapping, growth and super-resolution imaging

Super-Resolution imaging techniques such as Fluorescent Photo-Activation Localisation Microscopy (FPALM) have created a powerful new toolkit for investigating living cells, however a simple platform for growing, trapping, holding and controlling the cells is needed before the approach can become truly widespread. We present a microfluidic device formed in polydimethylsiloxane (PDMS) with a fluidic design which traps cells in a high-density array of wells and holds them very still throughout the life cycle, using hydrodynamic forces only. The device meets or exceeds all the necessary criteria for FPALM imaging of Schizosaccharomyces pombe and is designed to remain flexible, robust and easy to use. © 2011 IEEE.

Extracellular-matrix tethering regulates stem-cell fate.

To investigate how substrate properties influence stem-cell fate, we cultured single human epidermal stem cells on polydimethylsiloxane (PDMS) and polyacrylamide (PAAm) hydrogel surfaces, 0.1 kPa-2.3 MPa in stiffness, with a covalently attached collagen coating. Cell spreading and differentiation were unaffected by polydimethylsiloxane stiffness. However, cells on polyacrylamide of low elastic modulus (0.5 kPa) could not form stable focal adhesions and differentiated as a result of decreased activation of the extracellular-signal-related kinase (ERK)/mitogen-activated protein kinase (MAPK) signalling pathway. The differentiation of human mesenchymal stem cells was also unaffected by PDMS stiffness but regulated by the elastic modulus of PAAm. Dextran penetration measurements indicated that polyacrylamide substrates of low elastic modulus were more porous than stiff substrates, suggesting that the collagen anchoring points would be further apart. We then changed collagen crosslink concentration and used hydrogel-nanoparticle substrates to vary anchoring distance at constant substrate stiffness. Lower collagen anchoring density resulted in increased differentiation. We conclude that stem cells exert a mechanical force on collagen fibres and gauge the feedback to make cell-fate decisions.

Transparent nanostructured electrode by centrifuge coating

We employ a new solution-based coating process, centrifuge coating, to fabricate nanostructured conductive layers over large areas. This coating procedure allows fast quenching of the metastable dispersed state of nanomaterials, which minimizes material wastes by mitigate the effects of particle re-aggregation. Using this method, we fabricate SWNT coatings on different substrates such as PET (polyethylene terephthalate), PDMS (polydimethylsiloxane), and an acrylic elastomer. The effects of the choice of solvents on the morphology and subsequent performance of the coating network are studied. © 2012 IEEE.

Centrifuge coating for low-waste solution processing of transparent nanostructured electrodes

Centrifuge coating was implemented to fabricate nanostructured conductive layers through solution processing at room temperature. This coating procedure allows fast evaporation, thereby fixing the nanomaterials in their dispersed state onto a substrate by the centrifuge action. Material wastes were minimized by mitigating the effects of particle reaggregation. Using this method, we fabricate single-wall nanotube coatings on different substrates such as polyethylene terephthalate, polydimethylsiloxane, and an acrylic elastomer with no prior surface modification of the substrate. The effects of the choice of solvents on the morphology and subsequent performance of the coating network are studied. © 2002-2012 IEEE.

Nanoscale-accuracy transfer printing of ultra-thin AlInGaN light-emitting diodes onto mechanically flexible substrates

The transfer printing of 2 μm-thick aluminum indium gallium nitride (AlInGaN) micron-size light-emitting diodes with 150 nm (±14 nm) minimum spacing is reported. The thin AlInGaN structures were assembled onto mechanically flexible polyethyleneterephthalate/polydimethylsiloxane substrates in a representative 16 × 16 array format using a modified dip-pen nano-patterning system. Devices in the array were positioned using a pre-calculated set of coordinates to demonstrate an automated transfer printing process. Individual printed array elements showed blue emission centered at 486 nm with a forward-directed optical output power up to 80 μW (355 mW/cm 2) when operated at a current density of 20 A/cm2. © 2013 AIP Publishing LLC.