Optical Performance and Moisture Stability Enhancement of Flexible Luminescent Films Based on Quantum-Dot/Epoxy Composite Particles

Quantum dots (QDs) have been widely applied in luminescent sources due to their strong optical characteristics. However, a moisture environment causes their quenching, leading to an inferior optical performance in commercial applications. In this study, based on the high moisture resistance of epoxy resin, a novel epoxy/QDs composite particle structure was proposed to solve this issue. Flexible luminescent films could be obtained by packaging composite particles in silicone resin, combining the hydrophobicity of epoxy resin and the flexibility of PDMS simultaneously. The photoluminescence and light extraction were improved due to the scattering properties of the structure of composite particles, which was caused by the refractive index mismatch between the epoxy and silicone resin. Compared to the QD/silicone film under similar lighting conditions, the proposed flexible film demonstrated increased light efficiency as well as high moisture stability. The results revealed that a light-emitting diode (LED) device using the composite particle flexible (CPF) structure obtained a 34.2% performance enhancement in luminous efficiency as well as a 32% improvement in color conversion efficiency compared to those of devices with QD/silicone film (QSF) structure. Furthermore, the CPF structure exhibited strong thermal and moisture stability against extreme ambient conditions of 85 °C and 85% relative humidity simultaneously. The normalized luminous flux degradation of devices embedded in CPF and QSF structures after aging for 118 h were ~20.2% and ~43.8%, respectively. The satisfactory performance of the CPF structure in terms of optical and moisture stability shows its great potential value in flexible commercial QD-based LED displays and lighting applications.

Design, Manufacturing, and Characterization of Thin, Core-Free, Rolled Dielectric Elastomer Actuators

In this work, we develop a coreless rolled dielectric elastomer actuator (CORDEA) to be used as artificial muscles in soft robotic structures. The new CORDEA concept is based on a 50 µm silicone film with screen-printed electrodes made of carbon black suspended in polydimethylsiloxane. Two printed silicone films are stacked together and then tightly rolled in a spiral-like structure. Readily available off-the-shelf components are used to implement both electrical and mechanical contacts. A novel manufacturing process is developed to enable the production of rolled actuators without a hollow core, with a focus on simplicity and reliability. In this way, actuator systems with high energy density can be effectively achieved. After presenting the design, an experimental evaluation of the CORDEA electromechanical behavior is performed. Finally, actuator experiments in which the CORDEA is pre-loaded with a mass load and subsequently subject to cycling voltage are illustrated, and the resulting performance is discussed.

Gemcitabine-incorporated polyurethane films for controlled release of an anticancer drug

Background Local delivery of anti-cancer drugs through a stent is a very promising and anticipated treatment modality for patients who have obstructions in their gastrointestinal tract with malignant tumors. Anticancer drug release via stents, however, needs to be optimized with respect to drug delivery behavior for the stents to be effective for prolonged containment of tumor proliferation and stent re-obstruction. Local stent-based drug delivery has been tested using an effective anti-cancer drug, gemcitabine, but the release from the stent-coated polyurethane films is often too fast and the drug is depleted from the coated film virtually in a day. Methods To moderate the drug release from a polyurethane film, a gemcitabine-incorporated polyurethane film was enveloped with a pure polyurethane film, with no drug loading, and with a silicone film by solution casting after activation of the silicone film surface with plasma treatment. Results The pure polyurethane barrier film was effective; the interface of the two were indistinguishable on scanning electron microscopy, and the initial burst, i.e., the cumulative release in a day, decreased from 90 to 26%. The silicone film barrier, on the other hand, was defective as voids were seen using a scanning electron microscope, and micro-separation of the two layers was observed after the film was immersed in phosphate-buffered saline for 1 day during the in vitro drug release study. Conclusions Enveloping a gemcitabine-releasing polyurethane film with a homo-polymer barrier film was quite effective for moderating the initial burst of gemcitabine, thus, prolonging the release time of the drug. Enveloping the polyurethane film with a silicone film was also possible after plasma treatment of the silicone film surface, but the two films eventually separated in the aqueous environment. More studies are needed to tune the drug release behavior of gemcitabine from the stent covering film before attempting a clinical application of an anti-cancer drug releasing stent.

Plasma Deposition and UV Light Induced Surface Grafting Polymerization of NIPAAm on Stainless Steel for Enhancing Corrosion Resistance and Its Drug Delivery Property

When stainless steel is implanted in human bodies, the corrosion resistance and biocompatibility must be considered. In this study, first, a protective organic silicone film was coated on the surface of stainless steel by a plasma deposition technique with a precursor of hexamethyldisilazane (HMDSZ). Then, ultraviolet (UV) light-induced graft polymerization of N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) in different molar ratios were applied onto the organic silicone film in order to immobilize thermos-/pH-sensitive composite hydrogels on the surface. The thermo-/pH-sensitive composite hydrogels were tested at pH values of 4, 7.4 and 10 of a phosphate buffer saline (PBS) solution at a fixed temperature of 37 °C to observe the swelling ratio and drug delivery properties of caffeine which served as a drug delivery substance. According to the results of Fourier Transformation Infrared (FTIR) spectra and a potential polarization dynamic test, the silicone thin film formed by plasma deposition not only improved the adhesion ability between the substrate and hydrogels but also exhibited a high corrosion resistance. Furthermore, the composite hydrogels have an excellent release ratio of up to 90% of the absorbed amount after 8h at a pH of 10. In addition, the results of potential polarization dynamic tests showed that the corrosion resistance of stainless steel could be improved by the HMDSZ plasma deposition.

Wide gamut white light emitting diodes using quantum dot-silicone film protected by an atomic layer deposited TiO2 barrier

Wide gamut LEDs using QD-silicone film protected by ALD TiO2 film. The QDs with multimodal size distribution are synthesised by a one-pot method.