Light-responsive Block Copolymer Research Articles

Light-Responsive Shape- and Color-Changing Block Copolymer Particles with Fast Switching Speed.

Polymer particles capable of dynamic shape changes in response to light have received substantial attention in the development of intelligent multifunctional materials. In this study, we develop a light-responsive block copolymer (BCP) particle system that exhibits fast and reversible shape and color transitions. The key molecular design is the integration of spiropyran photoacid (SPPA) molecules into the BCP particle system, which enables fast and dynamic transformations of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) particles in response to light. The SPPA photoisomerization, induced by 420 nm light irradiation, lowers the pH of the aqueous surroundings from 5.5 to 3.3. The protonated P4VP block substantially increases in domain size from 14 to 39 nm, resulting in significant elongation of the BCP particles (i.e., an increase in the aspect ratio (AR) of the particles from 1.8 to 3.4). Moreover, SPPA adsorbed onto the P4VP surface induces significant changes in the luminescent properties of the BCP particles via photoisomerization of SPPA. Notably, the BCP particles undergo fast, dynamic shape and color transitions within a period of 10 min, maintaining high reversibility over multiple light exposures. Functional dyes are selectively incorporated into different domains of the light-responsive BCP particles to achieve different ranges of color responses. Thus, this study showcases a light-responsive hydrogel display capable of reversible and multicolor photopatterning.

Light-Responsive, Shape-Switchable Block Copolymer Particles.

A robust strategy is developed for preparing light-responsive block copolymer (BCP) particles in which shape and color can be actively controlled with high spatial and temporal resolution. The key to achieving light-responsive shape transitions of BCP particles is the design and synthesis of surfactants containing light-active groups (i.e., nitrobenzyl esters and coumarin esters) that modulate the amphiphilicity and interfacial activity of the surfactants in response to light of a specific wavelength. These light-induced changes in surfactant structure modify the surface and wetting properties of BCP particles, affording both shape and morphological transitions of the particles, for example from spheres with an onion-like inner morphology to prolate or oblate ellipsoids with axially stacked nanostructures. In particular, wavelength-selective shape transformation of the BCP particles can be achieved with a mixture of two light-active surfactants that respond to different wavelengths of light (i.e., 254 and 420 nm). Through the use of light-emitting, photoresponsive surfactants, light-induced changes in both color and shape are further demonstrated. Finally, to demonstrate the potential of the light-triggered shape control of BCP particles in patterning features with microscale resolution, the shape-switchable BCP particles are successfully integrated into a patterned, free-standing hydrogel film, which can be used as a portable, high-resolution display.

Light-responsive block copolymers with a spiropyran located at the block junction

Block copolymers with a functional group between their blocks are relatively little explored even though this molecular architecture can reduce the aggregation of the functional groups, promote the phase separation in nanophase-separated materials, and has other interesting effects. Spiropyrans are well-known for their ability to switch to their polar merocyanine form in response to light, force and other stimuli. The synthesis of stimuli-responsive AB-type block copolymers with spiropyran moieties located at the junction of the blocks is presented here. A homopolymer is synthesized from a trimethylindolenine-based atom transfer radical polymerization (ATRP) initiator, followed by its modification to a spiropyran end-functionalized polymer. The spiropyran functionalized polymer is then used as a macro-initiator for the synthesis of a second polymer block by ring opening polymerization (ROP). Alternatively, spiropyran homopolymers are conjugated to other preformed polymers by esterification. The resulting block copolymers reversibly switch under UV and white light irradiation over multiple cycles, and a block copolymer reduced the tendency of the merocyanine to aggregate during switching. The stimuli-responsive block copolymer could be useful for a range of applications, e.g. for bioinspired polymersome nanoreactors, or in membranes with switchable permeability.

Highly Effective Photocontrollable Drug Delivery Systems Based on Ultrasensitive Light-Responsive Self-Assembled Polymeric Micelles: An in Vitro Therapeutic Evaluation.

An ultrasensitive light-responsive block copolymer, a combination of a multiarmed poly(ethylene glycol)-b-poly(caprolactone) polymer as a water-soluble element and maleimide-anthracene linkers as a photosensitive group, was successfully synthesized and rapidly self-assembled to form spherical micellar nanoparticles in aqueous media and phosphate-buffered saline. Their unique characteristics, such as extremely low critical micelle concentration, desirable micellar stability, well-controlled light-responsiveness, tailorable drug-loading content, and ultrasensitive light-induced drug release, make these micelles potential candidates for development of a more effective, safer drug delivery platform for cancer treatment. In vitro studies revealed that the drug-loaded micelles exhibited high structural stability in serum-containing media and very low toxicity toward normal and cancer cells under physiological conditions. Irradiation of cancer cells incubated with the drug-loaded micelles with ultraviolet light at 254 nm for only 10 s triggered rapid and complete release of the drug in the intracellular environment and induced strong antiproliferative/cytotoxic activity. Importantly, real-time cytotoxic assays and fluorescence imaging analysis further demonstrated that the drug-loaded micelles were rapidly taken up into the cytosol or nuclei of the cells, and subsequent ultraviolet exposure induced drug release and apoptotic cell death. Given their simplicity of design, high reliability, and performance, this new light-sensitive micelle may provide a promising route for developing a multifunctional therapeutic nanocarrier system.

Polymeric Micelles Based on Light-Responsive Block Copolymers for the Phototunable Detection of Mercury(II) Ions Modulated by Morphological Changes.

Polymeric micelles based on light-responsive block copolymers were prepared and used for the phototunable detection of mercury(II) ions. 2-Nitrobenzyl acrylate (NBA) and ( E)-2-((4-((4-formylphenyl)diazenyl)phenyl)(methyl)amino) ethyl acrylate (FPDEA) were copolymerized from a poly(ethylene oxide) (PEO) macroinitiator via atom transfer radical polymerization (ATRP), leading to a well-defined block copolymer of PEO113- b-[p(NBA10- co-FPDEA3)] with a low polydispersity index (PDI = 1.16). After polymerization, the aldehyde groups of PEO- b-[p(NBA- co-FPDEA)] were converted to aldoxime groups by reacting with hydroxylamine, leading to the formation of a final oxime-containing polymeric probe, PEO- b-[p(NBA- co-HPDEA)], P1. The resulting block copolymer, P1, was self-assembled in water to yield spherical micelles that consist of a PEO block forming a hydrophilic shell and a copolymer of light-responsive NBA and a mercury(II) ion-detecting HPDEA block forming a hydrophobic core. Upon the addition of mercury(II) ions to this micellar solution, no detection was observed since water-soluble mercury(II) ions have limited accessability to the oxime units of P1, which are located in the hydrophobic core. After UV light irradiation, however, the photolabile 2-nitrobenzyl moieties were cleaved, and hydrophobic PNBA was transformed to hydrophilic poly(acrylic acid) (PAA), leading to the photoinduced dissociation of micelles to unimers. As a result, the oxime units of P1 were exposed to a hydrophilic environment and could react with mercury(II) ions to form nitrile groups, resulting in the turn-on detection of mercury(II) ions by UV light irradiation.

Effect of the polymer architecture on the photoinduction of stable chiral organizations

The paper presents a series of light responsive block copolymers that have been prepared by sequential polymerization of propargyl methacrylate and methyl methacrylate by atom transfer radical polymerization (ATRP). The pendant alkyne groups of the poly (propargyl methacrylate) block have been subsequently modified with azides from 2,2-bis(hydroxymethyl)propanoic acid decorated with two motifs, either two azobenzenes or one azobenzene and one biphenyl. This general and versatile synthetic approach simplifies the rational inclusion of structural modifications onto these polymers and, thus, establishing structure-properties relationships as a way to tailor the final properties of the material. By polymerizing the poly(propargyl methacrylate) firstly and poly(methyl methacrylate) secondly, block copolymers with low mass fractions, i.e. highly diluted contents, of the photoresponsive block have been achieved where the effect of the polymeric architecture on the induction of chirality using circularly polarized light (CPL) and its temporal stability has been evaluated. The relevance of the liquid crystallinity on the photoinduction of chirality in the block copolymers has also been investigated mainly in relation to thick films of good optical quality.

Zwitterionic light-responsive polymeric micelles for controlled drug delivery

Novel amphiphilic light-responsive block copolymer spiropyran-poly(2-methacryloyloxyethyl phosphorylcholine) (SP-PMPC) was reported and used as smart drug nanocarriers. SP-PMPC was easily synthesized via atom transfer radical polymerization (ATRP) of 2-methacryloyloxyethyl phosphorylcholine (MPC) using 2-bromo-2-methylpropanoate-ethyl-3′,3′-dimethyl-6-nitrospiro (2H-1-benzopyran-2,2′-indoline) (SP-Br) as initiator. SP-PMPC can self-assemble to micelles with relatively low critical micelle concentration (CMC) value (0.037 mg mL−1). Because of the reversible photochemical isomerization of hydrophobic spiropyran (SP) to hydrophilic merocyanine (MC), the self-assembly and disassembly of SP-PMPC micelles can be well controlled by an external light source, which was proved by ultraviolet-visible light (UV–vis) spectrometry, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The hydrophobic anticancer drug doxorubicin (DOX) can be encapsulated into micelles. In vitro drug release studies showed that the release of DOX was accelerated in the presence of UV irradiation (λ = 365 nm) when compared to similar systems without UV irradiation treatment. The SP-PMPC micelles exhibited superior biocompatibility as measured by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay owing to the stealth phosphorylcholine outer shell. Moreover, the DOX-loaded SP-PMPC micelles under UV irradiation exhibited better anticancer activity than that of the nonirradiated ones.

Crystallization-driven solution self-assembly of block copolymers with a photocleavable junction.

Light-responsive block copolymers have been prepared with a crystallizable core-forming poly(ferrocenyldimethylsilane) (PFS) block, a corona-forming segment of poly(2-vinylpyridine) (P2VP), and a photocleavable o-nitrobenzyl (ONB) junction. These PFS-ONB-P2VP materials form monodisperse cylindrical micelles by living crystallization-driven self-assembly in a selective solvent for P2VP. The P2VP coronas were readily removed by photocleavage at the ONB linker, leading to PFS cylinders with a residual percentage of corona chains dependent on the photoirradiation time. Addition of PFS block copolymer unimers to a solution of the cylinders with ca. 10% residual coronal chains led to the formation of branched rather than linear micelles. The synthetic utility of the PFS-ONB-P2VP materials was further demonstrated by the preparation of nearly monodisperse P2VP nanotubes of tunable length using a strategy that also involved corona cross-linking.

Fabrication of Upconverting Hybrid Nanoparticles for Near-Infrared Light Triggered Drug Release

Low tissue penetration and harmful effects of (ultraviolet) UV or visible light on normal tissue limit exploiting nanocarriers for the application of light-controlled drug release. Two strategies may solve the problem: one is to improve the sensitivity of the nanocarriers to light to decrease the radiation time; the other one is using more friendly light as the trigger. In this work, we fabricated a core-shell hybrid nanoparticle with an upconverting nanoparticle (UCNP) as the core and thermo- and light-responsive block copolymers as the shell to combine the two strategies together. The results indicated that the sensitivity of the block copolymer to light could be enhanced by decreasing the photolabile moieties in the polymer, and the UCNP could transfer near-infrared (NIR) light, which is more friendly to tissue and cell, to UV light to trigger the phase conversion of the block polymersin situ. Using Nile Red (NR) as the model drug, the hybrid nanoparticles were further proved to be able to act as carriers with the character of NIR triggered drug release.

Coumarin-containing photo-responsive nanocomposites for NIR light-triggered controlled drug release via a two-photon process.

A new multifunctional nanovehicle for tumor therapy and cell imaging was fabricated by coating NIR light-responsive polymers (HAMAFA-b-DDACMM) onto the surface of octadecyltrimethoxysilane (C18)-modified hollow mesoporous silica nanoparticles (HMS@C18) via self-assembly. First, the targeting NIR light-responsive block copolymer was synthesized by the RAFT living polymerization of [7-(didodecylamino) coumarin-4-yl] methyl methacrylate with hydroxyethylacrylate and N-(3-aminopropyl) methacrylamide hydrochloride and then grafted with folic acid (FA). The copolymers could be disrupted by excitation by a femtosecond NIR light laser (800 nm) via a two-photon absorption process due to the high two-photon absorption cross-section of the coumarin moiety. In order to enhance the drug loading capacity and biological stability of the nanovehicle, HMS nanoparticles modified by hydrophobic octadecyl chains were selected as the "core", which had a considerable drug loading efficiency of more than 70%. Then the core-shell nanocomposites (HMS@C18@HAMAFA-b-DDACMM) were obtained by coating the amphiphilic copolymers onto the core via self-assembly. Under excitation by NIR light at 800 nm, the pre-loaded drugs could be released from the nanocomposites due to the degradation of the light-responsive copolymers and the release efficiency was correlated with the irradiation time and light power. The in vitro experiments indicated that the nanocomposites were easily targeted into the tumor cells that over-expressed folic acid receptor (FR(+)) such as KB cells by endocytosis. Furthermore, the copolymer itself had strong fluorescence, which could be used to track the process of drug delivery.

Light-Responsive Block Copolymer Micelles

The association state of light-responsive block copolymer (BCP) micelles in aqueous solution can be altered, often reversibly, by light. Driven by the potential application in controlled drug delivery, this type of stimuli-responsive polymer micelles has received increasing attention. This Perspective highlights the progress achieved in recent years. On the one hand, we discuss the different approaches of rational BCP design, making use of various photochromic moieties and photochemical reactions, and the underlying mechanisms leading to photoinduced disruption of BCP micelles. On the other hand, we suggest possible future directions in this area, including exploration of new mechanisms and chemistry and solutions to the excitation wavelength problem crucial for biomedical applications.

Light-responsive block copolymer vesicles based on a photo-softening effect

We report the synthesis and study of two series of amphiphilic block copolymers (BCPs) of which the hydrophilic block is either poly(acrylic acid) (PAA) or poly(N,N-dimethylacrylamide) (PDMA) and the hydrophobic block is a side-chain liquid crystalline polymer (SCLCP) bearing biphenyl mesogens in majority and azobenzene mesogens in minority, namely, a random copolymer of 6-[4-(4-cyanophenyl)phenoxyl]hexyl acrylate with 6-[4-(4-methoxyphenylazo)phenoxyl]hexyl acrylate (P(BiPA-co-Azo)). Samples of both BCPs, PDMA-b-P(BiPA-co-Azo) and PAA-b-P(BiPA-co-Azo), could form large vesicles in aqueous solution with a SCLCP membrane. The BCPs were designed for investigating photoinduced order-disorder transition of the mesogens confined inside the vesicle membrane as a result of the trans–cisphotoisomerization of azobenzene and the LC cooperative effect. From photo-optical measurements on a BCP vesicle solution, we found evidence that a photoinduced LC order–disorder transition could occur inside the vesicle membrane in aqueous solution. Moreover, using a pH-sensitive fluorescent probe, we studied the photo-softening effect on the proton transfer across the vesicle membrane. Similar to plasticization of the vesicle membrane upon addition of a good solvent in aqueous solution, photo-induced softening could increase the rate of proton diffusion from inside to outside of the vesicle through the SCLCP membrane.

Macromol. Rapid Commun. 18/2010

Back Cover: The picture presents stimuli-responsive polymers, which are able to show responses to various environmental changes. Among those stimuli, light has attracted much attention since it can be localized in time and space, and it can also be triggered from outside the system. In the related feature article, light-responsive block copolymers are reviewed. Further details can be found in the article by J.-M. Schumers, C.-A. Fustin,* and J.-F. Gohy* on page 1588.

Light‐Responsive Block Copolymers

Stimuli-responsive polymers are the subject of intense research because they are able to show responses to various environmental changes. Among those stimuli, light has attracted much attention since it can be localized in time and space and it can also be triggered from outside of the system. In this paper, we review light-responsive block copolymers (LRBCs) that combine characteristic features of block copolymers, e.g., self-assembly behavior, and light-responsive systems. The different photo-responsive moieties that have been incorporated so far in block copolymers as well as the proposed applications are discussed.

Thermo- and light responsive micellation of azobenzene containing block copolymers

In this communication, the synthesis and characterization of thermo- and light responsive block copolymers is reported. PEO-b-PNIPAM polymers with azobenzene moieties were prepared and analyzed by turbidimetry, fluorescence, NMR and DLS measurements. A temperature controlled reversible formation as well as a light induced disruption and reformation of micellar structures in water was found.