Smart Coatings Prepared via MAPLE Deposition of Polymer Nanocapsules for Light-Induced Release.

Herein, smart coatings based on photo-responsive polymer nanocapsules (NC) and deposited by laser evaporation are presented. These systems combine remotely controllable release and high encapsulation efficiency of nanoparticles with the easy handling and safety of macroscopic substrates. In particular, azobenzene-based NC loaded with active molecules (thyme oil and coumarin 6) were deposited through Matrix-Assisted Pulsed Laser Evaporation (MAPLE) on flat inorganic (KBr) and organic (polyethylene, PE) and 3D (acrylate-based micro-needle array) substrates. SEM analyses highlighted the versatility and performance of MAPLE in the fabrication of the designed smart coatings. DLS analyses, performed on both MAPLE- and drop casting-deposited NC, demonstrated the remarkable adhesion achieved with MAPLE. Finally, thyme oil and coumarin 6 release experiments further demonstrated that MAPLE is a promising technique for the realization of photo-responsive coatings on various substrates.

Light-responsive and self-healing behavior of azobenzene-based supramolecular hydrogels.

HYPOTHESIS: Multi-component supramolecular hydrogels are gaining increasing interest as stimuli-responsive materials. To fully understand and possibly exploit the potential of such complex systems, the hierarchical structure of the gel network needs in-depth investigations across multiple length scales. We show that a thorough structural and rheological study represents a crucial pillar for the exploitation of this class of functional materials. EXPERIMENTS: Supramolecular hydrogels are prepared by self-assembly of hexadecyltrimethylammonium bromide (CTAB) and azobenzene-4,4'-dicarboxylic acid (AZO) in alkaline aqueous solution. The CTAB/AZO concentration was varied from ϕ = 0.25 to 4 wt% keeping the CTAB:AZO molar ratio fixed at 2:1. The systems were thoroughly studied through a combination of X-ray scattering, microscopy, rheological and spectroscopic analyses. FINDINGS: The CTAB/AZO solutions form a self-supporting gel with nanofibrillar structure below ~30 °C. The critical gelation concentration is ϕc = 0.45 wt%. Above this threshold, the gel elasticity and strength increase with CTAB/AZO content as ~(ϕ-ϕc)1. The hydrogels exhibit self-healing ability when left at rest after a stress-induced damage. Moreover, the light-induced isomerization of the AZO moieties provides the gel with light-responsiveness. Overall, the multi-stimuli responsiveness of the studied CTAB/AZO hydrogels makes them a solid starting point for the development of sensors for mechanical vibrations and UV/visible light exposure.

Molecular Design of Microcapsule Shells for Visible Light-Triggered Release.

The development of photo-responsive capsules to tune and control the sustained-release of encapsulated actives is a fascinating and challenging route to improve the performances and effectiveness of a wide range of delivery applications. In this work, we report the preparation of visible light-responsive capsules obtained via oil-in-water interfacial polycondensation between modified diacyl-chloride azobenzene moiety and diamine flexible spacer in the presence of cross-linkers with different structures and functionalities. The effect on the release profile of the encapsulated perfume oil was investigated using three flexible spacers with different lengths (1,8-diaminooctane; 1,6-diaminohexane and 1,4-diaminobutane) and two types of cross-linkers (1,3,5-benzenetricarbonyl trichloride and melamine). We analyzed how the properties of microcapsules can be tailored changing the design of the shell structure. Fine tuning of the perfume release profiles was obtained. The changes in capsules size and morphology due to visible light irradiation were monitored via light scattering, optical microscopy and atomic force microscopy. Perfume release was 50% faster in the systems prepared with melamine as the cross-linker. Modelling studies were carried out to support the discussion of the experimental results.

Light-Responsive Nanocapsule-Coated Polymer Films for Antimicrobial Active Packaging.

The development of antimicrobial active packaging constitutes a powerful tool to reduce waste and increase quality standards of perishable goods. Among numerous available antimicrobial agents, essential oils stand out for their renowned efficiency, and their use is beneficial due to their sustainability compared to other oil-based antimicrobials. In this work, we report on the use of photo-responsive nanocapsules containing thyme essential oil as functional coatings for polyethylene and polylactic acid films to obtain antimicrobial active packaging. Polymer surface activation treatment enhanced compatibility with nanocapsules solution. The films were analyzed to assess the structural and functional properties of the coating, evaluate morphological changes due to their photo-responsive behavior, and monitor the light-induced release of volatile thyme oil. It was found that 24 h after a 15-min UV exposure of the coated films, the concentration of thyme oil in the headspace was eight times higher with respect to un-irradiated films, thus confirming the efficiency of the light-triggered release system. Therefore, the manufactured films are proposed as on-demand release devices for application in non-contact antimicrobial active packaging.

Recent Advances in Nanoparticle-Mediated Delivery of Anti-Inflammatory Phytocompounds.

Phytocompounds have been used in medicine for decades owing to their potential in anti-inflammatory applications. However, major difficulties in achieving sustained delivery of phyto-based drugs are related to their low solubility and cell penetration, and high instability. To overcome these disadvantages, nanosized delivery technologies are currently in use for sustained and enhanced delivery of phyto-derived bioactive compounds in the pharmaceutical sector. This review focuses on the recent advances in nanocarrier-mediated drug delivery of bioactive molecules of plant origin in the field of anti-inflammatory research. In particular, special attention is paid to the relationship between structure and properties of the nanocarrier and phytodrug release behavior.

Light-Responsive Polymer Micro- and Nano-Capsules.

A significant amount of academic and industrial research efforts are devoted to the encapsulation of active substances within micro- or nanocarriers. The ultimate goal of core⁻shell systems is the protection of the encapsulated substance from the environment, and its controlled and targeted release. This can be accomplished by employing "stimuli-responsive" materials as constituents of the capsule shell. Among a wide range of factors that induce the release of the core material, we focus herein on the light stimulus. In polymers, this feature can be achieved introducing a photo-sensitive segment, whose activation leads to either rupture or modification of the diffusive properties of the capsule shell, allowing the delivery of the encapsulated material. Micro- and nano-encapsulation techniques are constantly spreading towards wider application fields, and many different active molecules have been encapsulated, such as additives for food-packaging, pesticides, dyes, pharmaceutics, fragrances and flavors or cosmetics. Herein, a review on the latest and most challenging polymer-based micro- and nano-sized hollow carriers exhibiting a light-responsive release behavior is presented. A special focus is put on systems activated by wavelengths less harmful for living organisms (mainly in the ultraviolet, visible and infrared range), as well as on different preparation techniques, namely liposomes, self-assembly, layer-by-layer, and interfacial polymerization.