Light-Induced Living Polymer Networks with Adaptive Functional Properties.

The advent of covalent adaptable networks (CANs) through the incorporation of dynamic covalent bonds has led to unprecedented properties of macromolecular systems, which can be engineered at the molecular level. Among the various types of stimuli that can be used to trigger chemical changes within polymer networks, light stands out for its remote and spatiotemporal control under ambient conditions. However, most examples of photoactive CANs need to be transparent and they exhibit slow response, side reactions, and limited light penetration. In this vein, it is interesting to understand how molecular engineering of optically active dynamic linkages that offer fast response to visible light can impart "living" characteristics to CANs, especially in opaque systems. Here, the use of carbazole-based thiuram disulfides (CTDs) that offer dual reactivity as photoactivated reshuffling linkages and iniferters under visible light irradiation is reported. The fast response to visible light activation of the CTDs leads to temporal control of shape manipulation, healing, and chain extension in the polymer networks, despite the lack of optical transparency. This strategy charts a promising avenue for manipulating multifunctional photoactivated CANs in a controlled manner.

An Electron Spin Resonance Study Comparing Nanometer-Nanosecond Dynamics in Diblock Copolymers and Their Poly(methyl Methacrylate) Binary Blends.

Block copolymers are a class of materials that are particularly interesting with respect to their capability to self-assemble in ordered structures. In this context, the coupling between environment and dynamics is particularly relevant given that movements at the molecular level influence various properties of macromolecules. Mixing the polymer with a second macromolecule appears to be an easy method for studying these relationships. In this work, we studied blends of poly(methyl methacrylate) (PMMA) and a block copolymer composed of PMMA as the first block and poly(3-methyl-4-[6-(methylacryloyloxy)-hexyloxy]-4'-pentyloxy azobenzene) as the second block. The relaxational properties of these blends were investigated via electron spin resonance (ESR) spectroscopy, which is sensitive to nanometric length scales. The results of the investigations on the blends were related to the dynamic behavior of the copolymers. At the nanoscale, the study revealed the presence of heterogeneities, with slow and fast dynamics available for molecular reorientation, which are further modulated by the ability of the block copolymers to form supramolecular structures. For blends, the heterogeneities at the nanoscale were still detected. However, it was observed that the presence of the PMMA as a major component of the blends modified their dynamic behavior.

A Red-Light-Responsive DASA-Polymer with High Water Stability for Controlled Release.

Photoresponsive polymers hold vast potential in the realm of drug delivery. Currently, most photoresponsive polymers use ultraviolet (UV) light as the excitation source. However, the limited penetration ability of UV light within biological tissues serves as a significant hindrance to their practical applications. Given the strong penetration ability of red light in biological tissues, the design and preparation of a novel red-light-responsive polymer with high water stability, incorporating the reversible photoswitching compound and donor-acceptor Stenhouse adducts (DASA) for controlled drug release is demonstrated. In aqueous solutions, this polymer exhibits self-assembly into micellar nanovectors (~33 nm hydrodynamic diameter), facilitating the encapsulation of the hydrophobic model drug Nile red (NR) within the micellar core. Upon irradiation by a 660 nm LED light source, photons are absorbed by DASA, leading to the disruption of the hydrophilic-hydrophobic balance of the nanovector and thereby resulting in the release of NR. This newly designed nanovector incorporates red light as a responsive switch, successfully avoiding the problems of photodamage and limited penetration of UV light within biological tissues, thereby further promoting the practical applications of photoresponsive polymer nanomedicines.

The Role of Crosslinker Molecular Structure on Mechanical and Light-Actuation Properties in Liquid Crystalline Networks.

Phase behavior modulation of liquid crystalline molecules can be addressed by structural modification at molecular level. Starting from a rigid rod-like core reduction of the symmetry or increase of the steric hindrance by different substituents generally reduces the clearing temperature. Similar approaches can be explored to modulate the properties of liquid crystalline networks (LCNs)-shape-changing materials employed as actuators in many fields. Depending on the application, the polymer properties have to be adjusted in terms of force developed under stimuli, kinetics of actuation, elasticity, and resistance to specific loads. In this work, the crosslinker modification at molecular level is explored towards the optimization of LCN properties as light-responsive artificial muscles. The synthesis and characterization of photopolymerizable crosslinkers, bearing different lateral groups on the aromatic core is reported. Such molecules are able to strongly modulate the material mechanical properties, such as kinetics and maximum tension under light actuation, opening up to interesting materials for biomedical applications.

Green Light-Triggerable Chemo-Photothermal Activity of Cytarabine-Loaded Polymer Carbon Dots: Mechanism and Preliminary In Vitro Evaluation.

Carbon-based nanostructures are attracting a lot of attention because of their very low toxicity, excellent visible light-triggered optical and photothermal properties, and intriguing applications. Currently, the development of multifunctional carbon-based nanostructures for a synergistic chemo-photothermal approach is a challenging topic for the advancement of cancer treatment. Here, we report an unprecedented example of photoresponsive carbon-based polymer dots (CPDs-PNM) obtained by a one-pot thermal process from poly(N-isopropylacrylamide) (PNIPAM) without using organic solvent and additional reagents. The CPDs-PNM nanostructures were characterized by spectroscopic techniques, transmission electron microscopy, and atomic force microscopy. The CPDs-PNM exhibited high photothermal conversion efficiency, lower critical solution temperature (LCST) behavior, and good cytarabine (arabinosyl cytosine, AraC) loading capacity (62.3%). The formation of a CPDs-PNM/AraC adduct and photothermal-controlled drug release, triggered by green light excitation, were demonstrated by spectroscopic techniques, and the drug-polymer interaction and drug release mechanism were well supported by modeling simulation calculations. The cellular uptake of empty and AraC-loaded CPDs-PNM was imaged by confocal laser scanning microscopy. In vitro experiments evidenced that CPDs-PNM did not affect the viability of neuroblastoma cells, while the CPDs-PNM/AraC adduct under light irradiation exhibited significantly higher toxicity than AraC alone by a combined chemo-photothermal effect.

Designing Rewritable Dual-Mode Patterns using a Stretchable Photoresponsive Polymer via Orthogonal Photopatterning.

The fabrication of dual-mode patterns in the same region of a material is a promising approach for high-density information storage, new anti-counterfeiting technologies, and highly secure encryption. However, dual-mode patterns are difficult to achieve because the two patterns in one material may interfere with each other during fabrication and usage. The development of noninterfering dual-mode patterns requires new materials and patterning techniques. Herein, a novel orthogonal photopatterning technique is reported for the fabrication of noninterfering dual-mode patterns on an azopolymer P1. P1 is a unique material that exhibits both photoinduced reversible solid-to-liquid transitions and good stretchability. In the first step of orthogonal photopatterning, patterned photonic structures are fabricated on a P1 film via masked nanoimprinting controlled by photoinduced reversible solid-to-liquid transitions. In the second step, the P1 film is stretched and irradiated with polarized light through a photomask, which generates a chromatic polarization pattern. In particular, the photonic structures and chromatic polarization in the dual-mode pattern are noninterfering. Another feature of dual-mode patterns is that they are rewritable via photo-, thermal, or solution reprocessing, which are useful for recycling and reprogramming. This study opens an avenue for the development of novel materials and techniques for photopatterning.

Opposite Self-Folding Behavior of Polymeric Photoresponsive Actuators Enabled by a Molecular Approach.

The ability to obtain 3D polymeric objects by a 2D-to-3D shape-shifting method is very appealing for polymer integration with different materials, from metals in electronic devices to cells in biological studies. Such functional reshaping can be achieved through self-folding driven by a strain pattern designed into the molecular network. Among polymeric materials, liquid crystalline networks (LCNs) present an anisotropic molecular structure that can be exploited to tailor internal strain, resulting in a natural non-planar geometry when prepared in the form of flat films. In this article, we analyze the influence of different molecular parameters of the monomers on the spontaneous shape of the polymeric films and their deformation under different stimuli, such as heating or light irradiation. Modifying the alkilic chains of the crosslinkers is a simple and highly effective way to increase the temperature sensitivity of the final actuator, while modifying ester orientation on the aromatic core interestingly acts on the bending direction. Combining such effects, we have demonstrated that LCN stripes made of different monomeric mixtures originate complex non-symmetric deformation under light activation, thus opening up new applications in photonic and robotics.

Ultrasensitive separation of methylprednisolone acetate using a photoresponsive molecularly imprinted polymer incorporated polyester dendrimer based on magnetic nanoparticles.

We developed an approach for the use of polyester dendrimer during the imprinting process to raise the number of recognized sites in the polymer matrix and improve its identification ability. Photoresponsive molecularly imprinted polymers were synthesized on modified magnetic nanoparticles involving polyester dendrimer which uses the reactivity between allyl glycidyl ether and acrylic acid for the high-yielding assembly by surface polymerization. The photoresponsive molecularly imprinted polymers were constructed using methylprednisoloneacetate as the template, water-soluble azobenzene involving 5-[(4, 3-(methacryloyloxy) phenyl) diazenyl] dihydroxy aniline as the novel functional monomer, and ethylene glycol dimethacrylate as the cross-linker. Through the evaluation of a series of features of spectroscopic and nano-structural, this sorbent showed excellent selective adsorption, recognition for the template, and provided a highly selective and sensitive strategy for determining the methylprednisoloneacetate in real and pharmaceutical samples. In addition, this sorbent according to good photo-responsive features and specific affinity to methylprednisoloneacetate with high recognition ability, represented higher binding capacity, a more extensive specific area, and faster mass transfer rate than its corresponding surface molecularly imprinted polymer.

Optically Responsive, Smart Anti-Bacterial Coatings via the Photofluidization of Azobenzenes.

Antibacterial strategies sans antibiotic drugs have recently garnered much interest as a mechanism by which to inhibit biofilm formation and growth on surfaces due to the rise of antibiotic-resistant bacteria. Based on the photofluidization of azobenzenes, we demonstrate for the first time the ability achieve up to a 4 log reduction in bacterial biofilms by opto-mechanically activating the disruption and dispersion of biofilms. This unique strategy with which to enable biofilm removal offers a novel paradigm with which to combat antibiotic resistance.

Photocontrol in Complex Polymeric Materials: Fact or Illusion?

Photoswitches: Exciting recent progress realized in the field of light-controlled polymeric materials is highlighted. It is discussed how the rational choice of azobenzene molecules and their incorporation into complex materials by making use of physical interactions can lead to genuine photocontrollable polymeric systems.

Light-enabled reversible self-assembly and tunable optical properties of stable hairy nanoparticles.

The ability to dynamically organize functional nanoparticles (NPs) via the use of environmental triggers (temperature, pH, light, or solvent polarity) opens up important perspectives for rapid and convenient construction of a rich variety of complex assemblies and materials with new structures and functionalities. Here, we report an unconventional strategy for crafting stable hairy NPs with light-enabled reversible and reliable self-assembly and tunable optical properties. Central to our strategy is to judiciously design amphiphilic star-like diblock copolymers comprising inner hydrophilic blocks and outer hydrophobic photoresponsive blocks as nanoreactors to direct the synthesis of monodisperse plasmonic NPs intimately and permanently capped with photoresponsive polymers. The size and shape of hairy NPs can be precisely tailored by modulating the length of inner hydrophilic block of star-like diblock copolymers. The perpetual anchoring of photoresponsive polymers on the NP surface renders the attractive feature of self-assembly and disassembly of NPs on demand using light of different wavelengths, as revealed by tunable surface plasmon resonance absorption of NPs and the reversible transformation of NPs between their dispersed and aggregated states. The dye encapsulation/release studies manifested that such photoresponsive NPs may be exploited as smart guest molecule nanocarriers. By extension, the star-like block copolymer strategy enables the crafting of a family of stable stimuli-responsive NPs (e.g., temperature- or pH-sensitive polymer-capped magnetic, ferroelectric, upconversion, or semiconducting NPs) and their assemblies for fundamental research in self-assembly and crystallization kinetics of NPs as well as potential applications in optics, optoelectronics, magnetic technologies, sensory materials and devices, catalysis, nanotechnology, and biotechnology.

Novel Photoresponsive Linear, Graft, and Comb-Like Copolymers with Azobenzene Chromophores in the Main-Chain and/or Side-Chain: Facile One-Pot Synthesis and Photoresponse Properties.

Novel photoresponsive linear, graft, and comb-like copolymers with azobenzene chromophores in the main-chain and/or side-chain are prepared via a sequential ring-opening metathesis polymerization (ROMP) and head-to-tail acyclic diene metathesis (ADMET) polymerization in a one-pot procedure using Grubbs ruthenium-based catalysts. The diluted solutions of these as-prepared copolymers containing azobenzene chromophores exhibit photochemical trans-cis isomerization under the irradiation of UV light, followed by their cis-trans back-isomerization in visible light. The rates of photoisomerization are found to be slower than those of back-isomerization, and the rate for the comb-like copolymer is found to be from 3 to 7 times slower than that obtained for the linear or graft copolymer. This is ascribed to the differences in structure of the copolymers and the specific location of azobenzene chromophores in the copolymer, which favor a side-chain graft structure.