Micelles and reverse micelles with a photo and thermo double-responsive block copolymer

Molecular-Gated Drug Delivery Systems Using Light-Triggered Hydrophobic-to-Hydrophilic Switches

A photoresponsive molecular-gated drug delivery system (DDS) based on silicone-hydrogel (poly(HEMA-co-PEGMEA)) interpenetrating polymer networks (IPNs) functionalized with carboxylated spiropyran (SPCOOH) was designed and demonstrated as an on-demand DDS. The triggered-release mechanism relies on controlling the wetting behavior of the surface by light, exploiting different hydrophobicities between the "closed" and "open" isomers of spiropyran as a photoswitchable molecular gate on the surface of IPN (SP-photogated IPN). Light-triggered release of doxycycline (DOX) as a model drug indicated that the spiropyran (SP) molecules provide a hydrophobic layer around the drug carrier and have a good gate-closing efficiency for IPNs with 20-30% hydrogel content. Upon UV light irradiation, SP converts into an open hydrophilic merocyanine state, which triggers the release of DOX. These results were compared with a previously developed SP-bulk modified IPN using the same hydrogel as a control, proving the efficiency of the gated IPN system. The covalent attachment of SPCOOH to the alcohol groups of the hydrogel and the structural change caused by UV light was indicated with FTIR analysis. XPS results also confirm the presence of SP by indicating the atomic percentage of nitrogen with respect to the hydrogel content.

Reversible Photoswitching in Poly(2-oxazoline) Nanoreactors

This contribution reports light responsive catalytic nanoreactors based on poly(2-oxazoline) diblock copolymers. The hydrophobic block of the copolymer is a random copolymer consisting of a spiropyran functionalized 2-oxazoline (SPOx) and 2-(but-3-yn-1-yl)-4,5-dihydrooxazole (ButynOx), while the hydrophilic block is based on 2-methyl-2-oxazoline (MeOx). The block copolymer is terminated with tris(2-aminoethyl) amine (TREN) that serves as catalyst in a Knoevenagel condensation. Four block copolymers with different ButynOx/SPOx and hydrophilic/hydrophobic ratios are synthesized and self-assembled through solvent exchange. Micelles and vesicles of various sizes are observed by TEM, which undergo morphological and size changes in response to irradiation with UV light. We hypothesize that these transformations in the nanostructures are caused by increases in the hydrophilicity of the hydrophobic block when spiropyran (SP) isomerizes to merocyanine (MC) in the presence of UV light. The reversible transition from micellar to vesicular nanoreactors resulted in increased reaction kinetics through improved substrate accessibility to the catalytic site, or termination of the catalytic reaction due to polymer precipitation. These nanoreactors present a promising platform towards photoregulating reaction outcomes based on changes in nanostructure morphology.

CO2/N2-responsive oil-in-water emulsions using a novel switchable surfactant

HYPOTHESIS

Recently, switchable or stimuli-responsive emulsions have attracted much research interest in many industrial fields. In this work, a novel CO₂/N₂-responsive surfactant was designed and developed to facilitate the formation of switchable oil-in-water (O/W) emulsions with fast switching characteristics between a stable emulsion and separate phases upon alternatively bubbling CO₂ and N₂.

EXPERIMENTS

The novel CO₂/N₂-responsive surfactant was facilely prepared by mixing an anionic fatty acid (oleic acid) and a cationic amine (1,3-Bis (aminopropyl) tetramethyldisiloxane) at a 1:1 molecular ratio, which was assembled based on electrostatic interactions. The structure and properties of the novel CO₂/N₂-responsive switchable surfactant were investigated by Fourier-transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H NMR) spectroscopy, and interfacial tensions.

FINDINGS

The developed surfactant shows an excellent interfacial activity at the oil/water interface, which can significantly reduce the dosage of the switchable surfactant compared with previous CO₂/N₂-responsive surfactants. The dynamic interfacial tension of n-decane and aqueous phase decreased from 45 mN m^-1 to 5 mN m^-1 within 100 s with the addition of 0.2 mM surfactant. In this work, a low concentration of the novel switchable surfactant (e.g., 20.0 mM) can realize reversible emulsification and demulsification in an emulsion system as compared with the high dosage (e.g., ~150 mM) in previous reports, which will bring huge economic benefits in industrial applications in the future. Moreover, this work expands the family of ion-pair surfactants to small amino-functionalized molecules beyond Jeffamine D-230, which promotes the development of simple and switchable ion-pair surfactant. It is found that the O/W emulsions stabilized by the switchable surfactant show excellent stability, which can be stored for over 60 days at room temperature without any obvious change. Interestingly, the stable O/W emulsion is completely demulsified upon bubbling CO₂ for 30 s and can be easily re-emulsified to the initial state after purging N₂ at 60 °C within 10 min, which demonstrates a rapid and highly efficient switching behavior. The reversible emulsification and demulsification process is ascribed to the reversible assembly and disassembly of the switchable surfactant, which is induced by the removal and purge of CO₂.

Functional Macromolecule-Enabled Colloidal Synthesis: From Nanoparticle Engineering to Multifunctionality

The synthesis of well-defined inorganic colloidal nanostructures using functional macromolecules is an enabling technology that offers the possibility of fine-tuning the physicochemical properties of nanomaterials and has contributed to a broad range of practical applications. The utilization of functional reactive polymers and their colloidal assemblies leads to a high level of control over structural parameters of inorganic nanoparticles that are not easily accessible by conventional methods based on small-molecule ligands. Recent advances in polymerization techniques for synthetic polymers and newly exploited functions of natural biomacromolecules have opened up new avenues to monodisperse and multifunctional nanostructures consisting of integrated components with distinct chemistries but complementary properties. Here, the evolution of colloidal synthesis of inorganic nanoparticles is revisited. Then, the new developments of colloidal synthesis enabled by functional macromolecules and practical applications associated with the resulting optical, catalytic, and structural properties of colloidal nanostructures are summarized. Finally, a perspective on new and promising pathways to novel colloidal nanostructures built upon the continuous development of polymer chemistry, colloidal science, and nanochemistry is provided.

Emerging Trends in Polymerization-Induced Self-Assembly

In this Perspective, we summarize recent progress in polymerization-induced self-assembly (PISA) for the rational synthesis of block copolymer nanoparticles with various morphologies. Much of the PISA literature has been based on thermally initiated reversible addition-fragmentation chain transfer (RAFT) polymerization. Herein, we pay particular attention to alternative PISA protocols, which allow the preparation of nanoparticles with improved control over copolymer morphology and functionality. For example, initiation based on visible light, redox chemistry, or enzymes enables the incorporation of sensitive monomers and fragile biomolecules into block copolymer nanoparticles. Furthermore, PISA syntheses and postfunctionalization of the resulting nanoparticles (e.g., cross-linking) can be conducted sequentially without intermediate purification by using various external stimuli. Finally, PISA formulations have been optimized via high-throughput polymerization and recently evaluated within flow reactors for facile scale-up syntheses.

Photo-Rheological Fluid-Based Colorimetric Ultraviolet Light Intensity Sensor

This study presents an introduction to a new type of ultraviolet (UV) light intensity sensor using photo-rheological (PR) fluids whose properties, such as color, can be changed by UV light. When the PR fluids were irradiated by UV light, colorimetric transitions were observed. Effectively, this means that their color changed gradually from yellow to red. The degree of the color change depended on the UV light intensity and was characterized by the hue value of the images acquired with a compact image sensor. We demonstrated that UV light-responsive capabilities can be readily imparted to PR fluids, and that the colorimetric responses to different UV light intensities can be used to measure the UV light intensities.

Synthesis and solution behaviour of dual light- and temperature-responsive poly(triethylene glycol-co-spiropyran) copolymers and block copolymers

We herein report on the synthesis and characterization of materials featuring a dual-responsive copolymer segment consisting of photo-responsive spiropyran (SPA) and temperature-responsive triethylene glycol acrylate (TEGA).

The light-controlling of temperature-responsivity in stimuli-responsive polymers

Light-controlling of phase separation in temperature-responsive polymer solutions by using light-responsive materials for reversible controlling physical and chemical properties of the media with an out-of-system stimulus with tunable intensity.

Light-Induced Aggregation and Disaggregation of Stimuli-Responsive Latex Particles Depending on Spiropyran Concentration: Kinetics of Photochromism and Investigation of Reversible Photopatterning

Light-controlling the physical and chemical properties of smart polymers by using photochromic compounds has been an interesting research subject. Incorporation of spiropyran (SP) on the surface of particles can induce photoswitchable aggregation/disaggregation to stimuli-responsive colloids. Herein, we developed a novel class of stimuli-responsive latex particles bearing SP with different contents (0, 0.5, 1, 3, and 5 wt %) by semicontinuous emulsifier-free emulsion copolymerization, which is able to change the particle size by light-induced aggregation/disaggregation in response to ultraviolet (UV) irradiation and visible light. The scanning electron microscopy images revealed the spherical morphology of the latex particles, with the size in the range of 400-900 nm. Light-induced aggregation and disaggregation of stimuli-responsive latex particles were investigated by dynamic light scattering and also confirmed by variation of transmittance during UV illumination time using ultraviolet-visible spectroscopy. The range of the light-induced shift in the particle size is about 200-600 nm (depending on the concentration of SP), where the reduction of transmittance upon UV irradiation (and conversely upon visible light) confirms the ability of latex particles for displaying reversible photoswitchable aggregation/disaggregation and also light-controlling the particle size. The kinetics of SP to merocyanine (MC) and MC to SP isomerizations were experimentally investigated and fitted by exponential equations. The photochromic latexes displayed remarkable photoswitchability and photofatigue resistant properties under alternating UV and visible light irradiation cycles. Additionally, these stimuli-responsive latexes displayed potential applications such as anticounterfeiting inks in erasable and rewritable writings on cellulosic papers for increasing safety in security documents.

Rewritable Anticounterfeiting Polymer Inks Based on Functionalized Stimuli-Responsive Latex Particles Containing Spiropyran Photoswitches: Reversible Photopatterning and Security Marking

Increase of safety in security documents by using anticounterfeiting inks based on fluorochromic and photochromic compounds has attracted a great deal of attention in the recent years. Herein, we developed novel functionalized stimuli-responsive latex particles containing spiropyran (1 wt %) by semicontinuous emulsifier-free emulsion polymerization, which are usable as anticounterfeiting inks for marking on security documents and also photopatterning on cellulosic papers. The size and morphology of the latex particles were characterized by scanning electron microscopy and dynamic light scattering and their functionality was characterized by Fourier-transform infrared spectroscopy. All the stimuli-responsive latexes are composed of spherical particles with different hydroxyl, epoxy, and carboxylic acid functional groups, and the size of the particles varies in the range of 400-900 nm. Additionally, the latex particles undergo a remarkable light-induced size variation (aggregation-disaggregation) upon UV illumination (365 nm), depending on the functional group type, as a result of π-π stacking interactions and also electrostatic attractions between the different particles. The photochromic behavior, kinetics of the SP ⇌ MC isomerization, photoswitchability, and photofatigue-resistant characteristics of the prepared latexes were extensively investigated. The results display that the photochromic behavior and SP ⇌ MC isomerization can significantly be influenced by the polar interactions between the functional groups and MC molecules. As a novel application, the prepared stimuli-responsive latexes were used as anticounterfeiting inks for writing on cellulosic paper and also security marking on several monies, where the written phrase displayed red fluorescence emission and coloration under and after UV illumination (365 nm), respectively. Additionally, the latexes were sprayed on cellulosic papers to prepare stimuli-responsive papers for investigation of their photopatterning ability under UV irradiation and different masking. The presence of functional groups and large particle sizes are the main effective factors for stabilization of the latex particles on cellulosic papers. This is the first report on application of functionalized stimuli-responsive latex particles containing spiropyran as anticounterfeiting inks for security marking and photopatterning on cellulosic papers, directly and without using further additives.

Dual Stimuli-Responsive P(NIPAAm-co-SPA) Copolymers: Synthesis and Response in Solution and in Films

We present the synthesis and solution properties of dual stimuli-responsive poly(N-isopropylacrylamide-co-spiropyran acrylate) (P(NIPAAm-co-SPA)) copolymers of varying composition prepared via nitroxide-mediated copolymerization. The resulting copolymers feature molar masses from 40,000 to 100,000 g/mol according to static light scattering and an SPA content of up to 5.3%. The latter was determined by ¹H NMR spectroscopy and UV⁻Vis spectroscopy. These materials exhibit reversible response upon irradiation in polymeric films for a minimum of three cycles; their response in solution to both light and temperature was also investigated in an aqueous TRIS buffer (pH 8). Irradiation was carried out using LED setups with wavelengths of 365 and 590 nm. In aqueous solution, a custom-made setup using a fiber-coupled 200 W Hg(Xe) lamp with 340 and 540 nm filters was used and additional heating of the copolymer solutions during irradiation allowed to study influence of the presence of either the spiropyran or merocyanine form on the cloud point temperature. Hereby, it was found that increasing the SPA content leads to a more pronounced difference between both states and decreasing cloud points in general.

Micellization of Photo-Responsive Block Copolymers

This review focuses on block copolymers featuring different photo-responsive building blocks and self-assembly of such materials in different selective solvents. We have subdivided the specific examples we selected: (1) according to the wavelength at which the irradiation has to be carried out to achieve photo-response; and (2) according to whether irradiation with light of a suitable wavelength leads to reversible or irreversible changes in material properties (e.g., solubility, charge, or polarity). Exemplarily, an irreversible change could be the photo-cleavage of a nitrobenzyl, pyrenyl or coumarinyl ester, whereas the photo-mediated transition between spiropyran and merocyanin form as well as the isomerization of azobenzenes would represent reversible response to light. The examples presented cover applications including drug delivery (controllable release rates), controlled aggregation/disaggregation, sensing, and the preparation of photochromic hybrid materials.

Field responsive materials: photo-, electro-, magnetic- and ultrasound-sensitive polymers

Recent advances in field-responsive polymers, which have emerged as highly promising materials for numerous applications, are highlighted.

RAFT synthesis and micellization of a photo-, temperature- and pH-responsive diblock copolymer based on spiropyran

A photo-, temperature- and pH-responsive diblock copolymer containing a rigid spiropyran moiety was synthesized and its micellization was investigated.

Schizophrenic poly(ε-caprolactone)s: synthesis, self-assembly and fluorescent decoration

Double hydrophilic copolymers PCCL-b-PPIL and their pyrene-modified copolymers showed pH-responsive “schizophrenic” aggregation behaviors.

Multiresponsive Behavior of Functional Poly(p-phenylene vinylene)s in Water

The multiresponsive behavior of functionalized water-soluble conjugated polymers (CPs) is presented with potential applications for sensors. In this study, we investigated the aqueous solubility behavior of water-soluble CPs with high photoluminescence and with a particular focus on their pH and temperature responsiveness. For this purpose, two poly(phenylene vinylene)s (PPVs)-namely 2,5-substituted PPVs bearing both carboxylic acid and methoxyoligoethylene glycol units-were investigated, with different amount of carboxylic acid units. Changes in the pH and temperature of polymer solutions led to a response in the fluorescence intensity in a pH range from 3 to 10 and for temperatures ranging from 10 to 85 °C. Additionally, it is demonstrated that the polymer with the largest number of carboxylic acid groups displays upper critical solution temperature (UCST)-like thermoresponsive behavior in the presence of a divalent ion like Ca2+. The sensing capability of these water-soluble PPVs could be utilized to design smart materials with multiresponsive behavior in biomedicine and soft materials.

Photo, pH, and thermo triple-responsive spiropyran-based copolymer nanoparticles for controlled release

A spiropyran-based amphiphilic random copolymer was synthesized and self-assembled into photo-, pH-, and thermo-responsive micellar nanoparticles. The triple-stimuli triggered morphological changes of the nanoparticles were revealed by TEM and DLS. Highly efficient controlled release of encapsulated molecules, coumarin 102, from the nanoparticles under stimulation of UV light, acid and the combined stimuli could be realized.

Synthesis and micellization of a multi-stimuli responsive block copolymer based on spiropyran

A pH-, light-, LCST- and UCST-responsive block copolymer based on spiropyran is synthesized and the modulated micellization is demonstrated.

A physical operation of hydrodynamic orientation of an azobenzene supramolecular assembly with light and sound

Photoisomerizations of a newly designed azobenzene derivative reversibly change its self-assembly in a solution to form twisted supramolecular nanofibers and amorphous aggregates, respectively. When irradiating the sample solution with audible sound, the former assembly exhibits a LD response due to its hydrodynamic orientation, but the latter one is LD silent, in the sound-induced fluid flows.

Micellar assembly of a photo- and temperature-responsive amphiphilic block copolymer for controlled release

Block copolymeric micellar nanoparticles in response to light and temperature change have been constructed for the controlled release of encapsulated molecules under stimulation with light and temperature change.

Self-assembly of photoswitchable diblock copolymers: salt-induced micellization and the influence of UV irradiation

Inorganic salts are able to induce micellization of PEG-b-PSPMA in a 10 : 1 DMF/water mixture upon UV irradiation. The complex formation between inorganic ions and MC isomers plays a key role in the self-assembly process.

Photoreconfigurable polymers for biomedical applications: chemistry and macromolecular engineering

Stimuli-responsive polymers play an important role in many biomedical technologies. Light responsive polymers are particularly desirable because the parameters of irradiated light and diverse photoactive chemistries produce a large number of combinations between functional materials and associated stimuli. This Review summarizes recent advances in utilizing photoactive chemistries in macromolecules for prospective use in biomedical applications. Special focus is granted to selection criterion when choosing photofunctional groups. Synthetic strategies to incorporate these functionalities into polymers and networks with different topologies are also highlighted herein. Prospective applications of these materials are discussed including programmable matrices for controlled release, dynamic scaffolds for tissue engineering, and functional coatings for medical devices. The article concludes by summarizing the state of the art in photoresponsive polymers for biomedical applications including current challenges and future opportunities.

Photo-responsive polymeric micelles

Photo-responsive polymeric micelles have received increasing attention in both academic and industrial fields due to their efficient photo-sensitive nature and unique nanostructure. In view of the photo-reaction mechanism, photo-responsive polymeric micelles can be divided into five major types: (1) photoisomerization polymeric micelles, (2) photo-induced rearrangement polymeric micelles, (3) photocleavage polymeric micelles, (4) photo-induced crosslinkable polymeric micelles, and (5) photo-induced energy conversion polymeric micelles. This review highlights the recent advances of photo-responsive polymeric micelles, including the design, synthesis and applications in various biomedical fields. Especially, the influence of different photo-reaction mechanisms on the morphology, structure and properties of the polymeric micelles is emphasized. Finally, the possible future directions and perspectives in this emerging area are briefly discussed.

Photoresponsive phase separation of a poly(NIPAAm-co-SPO-co-fluorophore) random copolymer in W/O droplet

The photoresponsive phase separation of a poly(N-isopropylacrylamide-co-spironaphthoxazine methacryloyl-co-allyl-2-(2,6-bis((E)-4-(diphenylamino)styryl)-4H-pyran-4-ylidene)-2-cyanoacetate) random copolymer, i.e., poly(NIPAAm-co-SPO-co-fluorophore), in water-in-oil (W/O) droplets is described. The photoresponsive aqueous droplets were generated in the coflow regime of a simple tubular microfluidic device. The phase separation of the copolymer in the W/O droplets was induced by UV light at 365 nm and was affected significantly by the presence of 2,2-diethoxyacetophenone (DEAP) and sorbitan monooleate (Span 80). When the droplets were subjected to UV irradiation for more than 2 min, the phase-separated copolymer was transferred completely from the aqueous droplet to the continuous phase of hexadecane. The phase separation arises from the photoisomerization shifting the spiro to the merocyanine form of the SPO pendant group in the copolymer, which in turn reduces the hydrophilicity of the copolymer via attractive hydrogen-bonding interactions between the merocyanine group and hydrophobic additives, i.e., Span 80, DEAP, and some stable fragments derived from the photocleavage of DEAP under UV irradiation. These interactions cause the copolymer to associate with the additives and then accelerate the phase separation of the copolymer and subsequent phase transfer of copolymer aggregates. The separate effects of DEAP and Span 80 were also investigated by UV spectrophotometric analysis of the rate coefficient of the reverse transformation (merocyanine to spiro) of the photochromic monomer. We propose a mechanism of phase separation of the copolymer in the W/O droplet based on the NMR and GC-MASS analyses of DEAP.

A light and pH dual-stimuli-responsive block copolymer synthesized by copper(0)-mediated living radical polymerization: solvatochromic, isomerization, and "schizophrenic" behaviors

A "schizophrenic" block copolymer (poly[1'-(2-methacryloxyethyl)-3',3'-dimethyl-6-nitrospiro-(2H-1-benzopyran-2,2'-indoline)]-b-poly(acrylic acid) (PSPMA-b-PAA)) was synthesized by sequential copper(0)-mediated living radical polymerization (Cu(0)-mediated LRP) at 30 °C in an oxygen-tolerant system followed by hydrolysis of the resulting polymer. The solvatechromic behaviors of the PSPMA10-b-poly(t-butyl acrylate)40 (PSPMA10-b-PtBA40) and PSPMA10-b-PAA40 block copolymers in organic solvents were investigated by UV-vis spectroscopy. The PSPMA10-b-PtBA40 stabilizes the nonpolar photoisomer and is not sensitive to the polarity of the solvent, while the PSPMA10-b-PAA40 stabilizes the planar zwitterionic form without irradiation. Furthermore, light-induced isomerization of spiropyran (Sp) moieties from Sp to merocyanine (Mc) was demonstrated. Finally, the "schizophrenic" micellization behavior of as-prepared copolymer in aqueous solution regulated by light and pH stimuli was vividly demonstrated, and the reversibility of micellization processes performed in this study was also examined. The large compound micelles can bring out a gradually extended and even transformed conformation with increasing deprotonation degree at pH > pKa.

Synthesis of a doubly thermo-responsive schizophrenic diblock copolymer based on poly[N-(4-vinylbenzyl)-N,N-diethylamine] and its temperature-sensitive flip-flop micellization

A doubly thermo-responsive schizophrenic diblock copolymer, poly(tert-butyl methacrylate)-block-poly[N-(4-vinylbenzyl)-N,N-diethylamine], was synthesized and its flip-flop micellization was demonstrated.

Nanomedicine as an innovative therapeutic strategy for pediatric lung diseases

Nanomedicine is a rapidly emerging technology and represents an innovative field for therapy. Nanomaterials have intrinsically defined features for biomedical applications due to the high specific surface area, the amazing diversity, versatility in structure and function and the possibility of surface charge. In particular, the functionalization of targeting or stimuli-responsive unit on the surface of these materials gives them specific targeted therapeutic properties. There are many pediatric lung diseases that could potentially benefit from nanomedicine. Herein, we aim to review various drug carrier systems and release systems specifically targeting pediatric lung diseases. The injection of nanomedicine into in vivo models and their elimination will also be discussed. Finally, the potential toxicity of nanomaterials will be addressed.

Spiropyran-based dynamic materials

In the past few years, spiropyran has emerged as the molecule-of-choice for the construction of novel dynamic materials. This unique molecular switch undergoes structural isomerisation in response to a variety of orthogonal stimuli, e.g. light, temperature, metal ions, redox potential, and mechanical stress. Incorporation of this switch onto macromolecular supports or inorganic scaffolds allows for the creation of robust dynamic materials. This review discusses the synthesis, switching conditions, and use of dynamic materials in which spiropyran has been attached to the surfaces of polymers, biomacromolecules, inorganic nanoparticles, as well as solid surfaces. The resulting materials show fascinating properties whereby the state of the switch intimately affects a multitude of useful properties of the support. The utility of the spiropyran switch will undoubtedly endow these materials with far-reaching applications in the near future.

Multidentate zwitterionic chitosan oligosaccharide modified gold nanoparticles: stability, biocompatibility and cell interactions

Surface engineering of nanoparticles plays an essential role in their colloidal stability, biocompatibility and interaction with biosystems. In this study, a novel multidentate zwitterionic biopolymer derivative is obtained from conjugating dithiolane lipoic acid and zwitterionic acryloyloxyethyl phosphorylcholine to the chitosan oligosaccharide backbone. Gold nanoparticles (AuNPs) modified by this polymer exhibit remarkable colloidal stabilities under extreme conditions including high salt conditions, wide pH range and serum or plasma containing media. The AuNPs also show strong resistance to competition from dithiothreitol (as high as 1.5 M). Moreover, the modified AuNPs demonstrate low cytotoxicity investigated by both MTT and LDH assays, and good hemocompatibility evaluated by hemolysis of human red blood cells. In addition, the intracellular fate of AuNPs was investigated by ICP-MS and TEM. It showed that the AuNPs are uptaken by cells in a concentration dependent manner, and they can escape from endosomes/lysosomes to cytosol and tend to accumulate around the nucleus after 24 h incubation but few of them are excreted out of the cells. Gold nanorods are also stabilized by this ligand, which demonstrates robust dispersion stability and excellent hemocompatibility. This kind of multidentate zwitterionic chitosan derivative could be widely used for stabilizing other inorganic nanoparticles, which will greatly improve their performance in a variety of bio-related applications.

New directions in thermoresponsive polymers

Interest in thermoresponsive polymers has steadily grown over many decades, and a great deal of work has been dedicated to developing temperature sensitive macromolecules that can be crafted into new smart materials. However, the overwhelming majority of previously reported temperature-responsive polymers are based on poly(N-isopropylacrylamide) (PNIPAM), despite the fact that a wide range of other thermoresponsive polymers have demonstrated similar promise for the preparation of adaptive materials. Herein, we aim to highlight recent results that involve thermoresponsive systems that have not yet been as fully considered. Many of these (co)polymers represent clear opportunities for advancements in emerging biomedical and materials fields due to their increased biocompatibility and tuneable response. By highlighting recent examples of newly developed thermoresponsive polymer systems, we hope to promote the development of new generations of smart materials.