Nano-Second Laser Interference Photoembossed Microstructures for Enhanced Cell Alignment.

Photoembossing is a powerful photolithographic technique to prepare surface relief structures relying on polymerization-induced diffusion in a solventless development step. Conveniently, surface patterns are formed by two or more interfering laser beams without the need for a lithographic mask. The use of nanosecond pulsed light-based interference lithography strengthens the pattern resolution through the absence of vibrational line pattern distortions.

Enhanced Thermal Conductivity in Oriented Polyvinyl Alcohol/Graphene Oxide Composites.

Polymer composites have attracted increasing interest as thermal management materials for use in devices owing to their ease of processing and potential lower costs. However, most polymer composites have only modest thermal conductivities, even at high concentrations of additives, resulting in high costs and reduced mechanical properties, which limit their applications. To achieve high thermally conductive polymer materials with a low concentration of additives, anisotropic, solid-state drawn composite films were prepared using water-soluble polyvinyl alcohol (PVA) and dispersible graphene oxide (GO).

NIR-vis-UV Light-Responsive High Stress-Generating Polymer Actuators with a Reduced Creep Rate.

Untethered, light-responsive, high-stress-generating actuators based on widely-used commercial polymers are appealing for applications in soft robotics. However, the construction of actuators that are stable and reversibly responsive to low-intensity ultraviolet, visible, and infrared lights remains challenging. Here, transparent, stress-generating actuators are reported based on ultradrawn, ultrahigh molecular weight polyethylene films.

The Role of Polyethylene Wax on the Thermal Conductivity of Transparent Ultradrawn Polyethylene Films.

Transparency and thermal conductivity of ultradrawn, ultrahigh-molecular-weight polyethylene films containing different contents of low-molecular-weight polyethylene wax (PE) are explored from experimental and theoretical viewpoints. It is shown that the addition of PE decreases light scattering in all directions, resulting from a reduction of defects while having little effect on crystallinity or chain orientation of ultradrawn films. In general, upon the addition of PE, the thermal conductivity of ultradrawn films increases with the highest conductivity being 47 (W m K) and subsequently decreases at higher concentrations.

Ultra-High Actuation Stress Polymer Actuators as Light-Driven Artificial Muscles.

Remotely addressable actuators are of great interest in fields like microrobotics and smart textiles because of their simplicity, integrity, flexibility, and lightweight. However, most of the existing actuator systems are composed of complex assemblies and/or offer a low response rate. Here, the actuation performance of a light-driven, highly oriented film based on ultra-high molecular weight polyethylene (UHMW-PE), containing a photo-responsive additive, 2-(2-benzotriazol-2-yl)-4,6-ditertpentylphenol (BZT), is reported.

Direct Laser Writing of Four-Dimensional Structural Color Microactuators Using a Photonic Photoresist.

With the advent of direct laser writing using two-photon polymerization, the generation of high-resolution three-dimensional microstructures has increased dramatically. However, the development of stimuli-responsive photoresists to create four-dimensional (4D) microstructures remains a challenge. Herein, we present a supramolecular cholesteric liquid crystalline photonic photoresist for the fabrication of 4D photonic microactuators, such as pillars, flowers, and butterflies, with submicron resolution.

Thermoplastic, rubber-like marine antifouling coatings with micro-structures mechanical embossing.

New processing routes and materials for non-biocidal, antifouling (AF) coatings with an improved performance are currently much sought after for a range of marine applications. Here, the processing, physical properties and marine AF performance of a fluorinated coating based on a thermoplastic (non-crosslinked) fluorinated polymer are reported. It was found that the addition of lubricating oil and hydrodynamic drag reducing microstructures improved the AF properties substantially, i.

An Optical Steam Sterilization Sensor Based On a Dual-Responsive Supramolecular Cross-Linked Photonic Polymer.

An optical time-temperature steam sensor is presented based on the loss of structural color in a supramolecularly cross-linked cholesteric liquid crystal photonic coating. A gradual decrease in the selective reflection band is observed upon exposure to temperatures above 105 °C related to the cholesteric to isotropic transition temperature. The linear polymers with carboxylic acid side chains provide physical cross-linking through hydrogen bonding that allows a time-temperature-dependent order loss through the dynamic equilibrium between supramolecular dimer and free monomer states.

Unravelling humidity-gated, temperature responsive bilayer actuators.

By spraying liquid crystal mixtures onto stretched polyamide 6 (PA6) substrates, dual-responsive heat/humidity bilayer actuators are generated. The oriented PA6 guides the self-organization of the liquid crystal monomers into well-aligned, anisotropic liquid crystal networks. The bilayer responds to changes in the environmental relative humidity, resulting in bending of the actuator with the liquid crystal network inside the curvature.

Transparent, High-Thermal-Conductivity Ultradrawn Polyethylene/Graphene Nanocomposite Films.

Transparent, ultradrawn, ultrahigh molecular weight polyethylene (UHMWPE)/graphene nanocomposite films with a high thermal conductivity are successfully fabricated by solution-casting and solid-state drawing. It is found that the low optical transmittance (<75%) of the ultradrawn UHMWPE/graphene composite films is drastically improved (>90%) by adding 2-(2H-benzontriazol-2-yl)-4,6-ditertpentylphenol (BZT) as a second additive. This high transmission is interpreted in terms of a reduced void content in the composite films and the improved dispersion of graphene both of which decrease light scattering.

Rewritable Optical Patterns in Light-Responsive Ultrahigh Molecular Weight Polyethylene.

Spiropyran is used as a photochromic dye to create colored patterns in highly drawn ultrahigh molecular weight polyethylene (UHMW PE) films. The dye is incorporated in highly crystalline, drawn UHMW PE tapes and fibers and isomerizes to its merocyanine state upon UV light irradiation, resulting in a color change from transparent to purple. The isomerization from merocyanine to spiropyran to erase the color can be simply induced by using heat or a green LED light.

Optical Patterns on Drawn Polyethylene by Direct Laser Writing.

Optical patterns are produced on the surface of drawn linear polyethylene containing 2-(2H-benzotriazol-2-yl)-4,6-ditertpentylphenol (BZT), a photothermal dye, by direct laser writing. The photothermal dye absorbs the UV light and dissipates heat in the polyethylene film. This heat locally results in the melting, shrinking, and recrystallization of PE and the loss of the fibrillar crystalline morphology which is typical for these materials.

Surface Micropatterning of Uniaxially Oriented Polyethylene Films Using Interference Holography for Strain Sensors.

A new procedure is presented for direct generation of surface micropatterns on uniaxially oriented polyethylene (PE) films using interference holography with a nanosecond pulsed laser. An ultraviolet absorber, 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (BZT) is incorporated into PE prior to stretching to generate absorption at the wavelength of the laser. Illumination with an interference pattern in the absorption band of BZT leads to an obvious height variation in the exposed regions and consequently relief gratings are generated.

Photonic Shape Memory Polymer with Stable Multiple Colors.

A photonic shape memory polymer film that shows large color response (∼155 nm) in a wide temperature range has been fabricated from a semi-interpenetrating network of a cholesteric polymer and poly(benzyl acrylate). The large color response is achieved by mechanical embossing of the photonic film above its broad glass transition temperature. The embossed film, as it recovers to its original shape on heating through the broad thermal transition, exhibits multiple structural colors ranging from blue to orange.

Responses of Vascular Endothelial Cells to Photoembossed Topographies on Poly(Methyl Methacrylate) Films.

Failures of vascular grafts are normally caused by the lack of a durable and adherent endothelium covering the graft which leads to thrombus and neointima formation. A promising approach to overcome these issues is to create a functional, quiescent monolayer of endothelial cells on the surface of implants. The present study reports for the first time on the use of photoembossing as a technique to create polymer films with different topographical features for improved cell interaction in biomedical applications.

Degradation and biocompatibility of photoembossed PLGA-acrylate blend for improved cell adhesion.

We have shown previously that PMMA-acrylate photopolymers are biocomopatible and can exhibit improved cell adhesion compared to PMMA, due to an increase in negative surface charge caused by UV radiation PLGA has been used widely in soft tissue regeneration due to its high biocompatibility and cell adhesion. This polymer is also biodegradable and can be utilised in the field of vascular regeneration. In this study, PLGA is blended with a triacrylate monomer (TPETA) to create a degradable photopolymer blend.

Diffractive flat panel solar concentrators of a novel design.

A novel design for a flat panel solar concentrator is presented which is based on a light guide with a grating applied on top that diffracts light into total internal reflection. By combining geometrical and diffractive optics the geometrical concentration ratio is optimized according to the principles of nonimaging optics, while the thickness of the device is minimized due to the use of total internal reflection.

Improving the Transparency of Ultra-Drawn Melt-Crystallized Polyethylenes: Toward High-Modulus/High-Strength Window Application.

Highly transparent, ultradrawn high-density polyethylene (HDPE) films were successfully prepared using compression molding and solid-state drawing techniques. The low optical transmittance (<50%) of the pure drawn HDPE films can be drastically improved (>90%) by incorporating a small amount (>1 wt %/wt) of specific additives to HDPE materials prior to drawing. It is shown that additives with relatively high refractive index result in an increased optical transmittance in the visible light wavelength which illustrates that the improvement in optical characteristics probably originates from refractive index matching between the crystalline and noncrystalline regions in the drawn films.

Thermoresponsive scattering coating for smart white LEDs.

White light emitting diode (LED) systems, capable of lowering the color temperature of emitted light on dimming, have been reported in the literature. These systems all use multiple color LEDs and complex control circuitry. Here we present a novel responsive lighting system based on a single white light emitting LED and a thermoresponsive scattering coating.

Humidity-responsive liquid crystalline polymer actuators with an asymmetry in the molecular trigger that bend, fold, and curl.

We show a versatile method for the preparation of a variety of humidity-responsive actuators based on a single sheet of a hydrogen-bonded, uniaxially aligned liquid crystal polymer network. In this approach, the asymmetry in the molecular trigger in the anisotropic polymer film plays a dominant role leading to programmed deformation events. The material is locally treated with a potassium hydroxide solution to create the asymmetry in the responsiveness toward humidity, which allows to prepare actuators that bend, fold, or curl.

Photoembossing of surface relief structures in polymer films for biomedical applications.

Photoembossing is a technique used to create relief structures using a patterned contact photo-mask exposure and a thermal development step. Typically, the photopolymer consists of a polymer binder and a monomer in a 1/1 ratio together with a photo-initiator, which results in a solid and non-tacky material at room temperature. Here, new mixtures for photoembossing are presented which are potentially biocompatible.

Patterned silver nanoparticles embedded in a nanoporous smectic liquid crystalline polymer network.

A nanoporous smectic liquid crystalline polymer network has been exploited to fabricate photo patternable organic-inorganic hybrid materials, wherein, the nanoporous channels control the diameter and orientational order of the silver nanoparticles.

New approach toward reflective films and fibers using cholesteric liquid-crystal coatings.

A new approach for the production of oriented films and fibers with angular-dependent reflective colors is presented. The process consists of spray coating a solution of cholesteric liquid-crystalline monomers onto a melt-processed and oriented polyamide-6 substrate followed by UV curing. Reflectivity measurements and optical microscopy show that a well-defined liquid-crystalline and planar alignment is obtained.

Humidity-responsive bilayer actuators based on a liquid-crystalline polymer network.

A humidity-responsive bilayer actuator has been developed that consists of an oriented polyamide-6 substrate and a liquid-crystalline polymer coating. The oriented substrate acts as an alignment layer for the liquid crystal. The liquid-crystalline polymer consists of a supramolecular network having hydrogen-bonded entities that, after activation with an alkaline solution, exhibit deformation in response to a change in humidity.

(Photo-)thermally induced formation of dynamic surface topographies in polymer hydrogel networks.

In this Article, we report on our approaches to creating responsive hydrogel coatings with surfaces that can be switched between a close to flat state and a state with a predesigned topographic pattern. The trigger is either temperature or, indirectly, light. The hydrogel coatings are based on the known thermal responsive poly(N-isopropylacrylamide) utilizing its solubility change at its lower critical solution temperature (LCST) at around 32 °C.