Thermoresponsive Core Research Articles

A synthetic optimization study on thermoresponsive core cross-linked starpolymers (CCSs)

The well-defined starpolymers can offer a precise stimuli-responsive drug delivery system (SDDS). For this, core cross-linked starpolymers (CCSs) using the poly(N-isopropylacrylamide)-b-poly(n-butyl acrylate) (PNB) linear arm chain and ethylene glycol diacrylate (EGDA) cross-linker were designed and synthesized by the reversible addition-fragmentation chain transfer (RAFT) system. The important synthetic parameters, including reaction time, radical concentration, and cross-linker concentration, were varied to optimize the reaction conditions for highly uniform PNiPAM-based amphiphilic starpolymers (PNBA). The reaction was monitored by GPC, resulting in the sharp monomodal PNBA GPC curve with an almost degraded original curve corresponding to the PNB linear chain. The PNBA revealed a dramatic size increase from 150 nm to 15,000 nm when the temperature increased up to 40 °C. Notably, the uniform CCS structure gives rise to a particular phase transformation system, which can be helpful in biomedical and catalytic applications with enhanced performance.

In situ characterization of crystallization and melting of soft, thermoresponsive microgels by small-angle X-ray scattering.

Depending on the volume fraction and interparticle interactions, colloidal suspensions can form different phases, ranging from fluids, crystals, and glasses to gels. For soft microgels that are made from thermoresponsive polymers, the volume fraction can be tuned by temperature, making them excellent systems to experimentally study phase transitions in dense colloidal suspensions. However, investigations of phase transitions at high particle concentration and across the volume phase transition temperature in particular, are challenging due to the deformability and possibility for interpenetration between microgels. Here, we investigate the dense phases of composite core–shell microgels that have a small gold core and a thermoresponsive microgel shell. Employing Ultra Small-Angle X-ray Scattering, we make use of the strong scattering signal from the gold cores with respect to the almost negligible signal from the shells. By changing the temperature we study the freezing and melting transitions of the system in situ. Using Bragg peak analysis and the Williamson–Hall method, we characterize the phase transitions in detail. We show that the system crystallizes into an rhcp structure with different degrees of in-plane and out-of-plane stacking disorder that increase upon particle swelling. We further find that the melting process is distinctly different, where the system separates into two different crystal phases with different melting temperatures and interparticle interactions.

Thermoresponsive SERS Nanocapsules Constructed by Linear-Dendritic Poly(urea/malonamide) for Tunable Biomolecule Detection

In this work, thermoresponsive core–shell micelle-embedded silver nanoparticles (AgNPs) were prepared from a series of monodisperse linear-dendritic poly(urea/malonamide). Through efficient iterative synthesis, well-defined dendritic amphiphiles bearing dual functionality provide nucleation sites as excellent templates for immobilizing AgNPs on one end, while oligoethers anchor water to stabilize these micelles in water as polymer dispersions. During the heating process, linear-dendritic poly(urea/malonamide) with various ratios of hydrophilic/hydrophobic segments resulted in the size-dependent lowest critical solution temperature (LCST), ranging from 72 to 54 °C in aqueous media. As a result, the gap distances between AgNPs could be manipulated, resulting in a stronger hot spot effect using thermoresponsive nanocapsules for surface-enhanced Raman scattering (SERS) analysis. Consequently, the signal was enhanced at temperatures over the LCST. For AgNPs@TD-G1.5 thermoresponsive SERS nanocapsules, an ∼33 times enhancement during the LCST transition was obtained. The high sensitivity and stability of the intelligent AgNPs@thermoresponsive SERS nanocapsules endow them with great potential in the rapid SERS detection of small-molecule analytes by adsorbing analytes at room temperature (below the LCST) and encapsulating the analytes into micelles at high temperatures (above the LCST) in the application of monitoring trace-level and diverse analytes.

How a family of nanostructured amphiphilic block copolymers synthesized by RAFT-PISA take advantage of thiol groups to direct the in situ assembly of high luminescent CuNCs within their thermo-responsive core

• Multithiolated block copolymer nanoparticles (P-NPs) were synthesized by RAFT-PISA. • Monodisperse P-NPs with tunable size are formed under uncontrolled RAFT polymerization. • P-NPs with thermo-responsive core and hydrophilic shell exhibit high water stability. • Thiolated P-NPs serve as template for in situ assembly of luminescent CuNCs in water. • Fluorescent nanohybrids exhibit pH/thermo-response, photostability and oxidation resistance. The development of fluorescent water stable copper nanoclusters (CuNCs) deserves the scientific interest due to their outstanding properties and low-cost. These fluorescent CuNCs can be synthesized using natural or synthetic polymers with thiol groups. Herein, for the first time, we propose the use of novel amphiphilic block copolymer nano-objects, synthesized by polymerization induced self-assembly (PISA) via reversible-addition fragmentation chain transfer (RAFT), as templates for the synthesis and water stabilization of CuNCs. The polymeric NPs provide water-stability due to the poly(hydroxyethyl acrylate) corona and the thermos-responsive core, based on 2-(2-methoxyethoxy) ethyl methacrylate (MEO 2 MA) and 2-(acetylthio) ethyl methacrylate (AcSEMA) decorated with protected thiol groups, drive the “ in situ ” reduction of copper ions into copper nanocrystals and their assembling in high luminescent nanohybrids in water. In order to optimize the fluorescence properties a methodical study was carried out varying polymers composition and architecture, thiol content and nanoparticle size. All the polymeric nanoparticles synthesized by PISA and decorated with thiol groups induce the formation of luminescent CuNCs in their hydrophobic core. The sizes of the hydrophilic/hydrophobic block, as well as, thiol content are key factors in the emission properties of the CuNC nanohybrids that offer high colloidal stability in water, pH- and thermo-response, significance photostability and strong resistance to oxidation.

Self-Assembled Thermoresponsive Molecular Brushes as Nanoreactors for Asymmetric Aldol Addition in Water

The manipulation and tunability of self-assembled block copolymers through external stimuli present an attractive strategy to develop smart polymer-based nanoreactors as supports for non-orthogonal tandem catalysis. We report on thermoresponsive core–shell micelles based on poly[norbornene-poly(2-methyl-2-oxazoline-block-2-propyl-2-oxazoline)]-graft-poly[norbornene l-proline] (P[NB-P(MeOx-b-PropOx)]-graft-P[NB-l-proline]) as catalyst supports for l-proline. These molecular brushes exhibit large differences in lower critical solution temperature behavior and nanostructure size in water, depending on chain lengths and proline connectivity. l-Proline-mediated aldol reactions expose the efficiency by which the molecular brushes self-assemble into micelles. Molecular brushes with an extended backbone show higher activity and selectivity, suggesting better core–shell segregation of the micelles and exclusion of water from the catalytic site. Catalytic efficiencies are not improved above the cloud point temperature, and the catalytic behavior is rather sensitive to conformational changes of the polymer chains.

Kinetics of the Reduction of 4-Nitrophenol by Silver Nanoparticles Immobilized in Thermoresponsive Core–Shell Nanoreactors

We present a kinetic study on the reduction of 4-nitrophenol (NO2) with borohydride, catalyzed by silver nanoparticles. The latter are immobilized inside the hydrogel shell of core–shell nanoreactors, comprising a polystyrene core and surrounded by a thermoresponsive poly-N-isopropylacrylamide (PNIPAM) hydrogel shell. Cryogenic transmission electron microscopy shows that silver nanoparticles with an average diameter of 5.6 ± 2.4 nm are located deep inside the PNIPAM shell. The Levenberg–Marquardt algorithm is applied for the decomposition of the UV–vis spectra recorded during the reduction of NO2, and its potential use in the assessment and evaluation of model reactions is demonstrated. The decomposition of the UV–vis spectra, obtained in a wavelength range of 240–500 nm, shows that the reactant NO2 is directly transferred to the product 4-aminophenol (NH2) without accumulation of intermediates. Hence, a stationary state for the intermediate 4-hydroxylaminophenol is present from the beginning of the reaction onwards. Based on this, a kinetic model is presented, which is related to a model previously derived for the kinetic analysis of the reaction catalyzed by gold. The kinetic data, obtained at room temperature at nine different combinations of NO2 and borohydride concentrations, are globally fitted by a genetic approach. The results are in good accordance with previous results obtained on gold and, furthermore, show that the adsorption of NH2 to the catalyst surface has a substantial influence on the kinetics of silver. The measurements between T = 10 and 50 °C reveal a non-Arrhenius dependency of the reaction rate, caused by the thermoresponsive PNIPAM hydrogel. We show how a systematic decomposition of kinetic, adsorption, and partitioning effects provides useful qualitative insights into the partitioning coefficients of reactants and products, i.e., the ratio of the concentration inside/outside the hydrogel network, which play a significant role in the kinetics of PNIPAM-based catalysts. Furthermore, it is found that small ions like chloride and borohydride show a similar partitioning behavior in PNIPAM.

One‐Step Generation of Core–Gap–Shell Microcapsules for Stimuli‐Responsive Biomolecular Sensing

AbstractThe versatile design of stimuli‐responsive microparticles embedding valuable biomolecules has great potential in a variety of engineering fields, such as sensors, actuators, drug delivery, and catalysis. Here, results are reported on thermoresponsive core–gap–shell (TCGS) microcapsules made of poly(N‐isopropylacrylamide) (PNIPAm), which encapsulate hydrophilic payloads in a simple and stable manner. These are realized by a one‐step microfluidic approach using the phase separation of a supersaturated aqueous solution of NIPAm. Various designs of the microcapsules are achieved by individual control of the swelling or by incorporating pH‐responsive comonomers of the inner core and outer shell. The gap, i.e., the space between the inner core and outer shell, can be loaded with cargo‐like nanoparticles. The outer shell can serve as a stimuli‐responsive gateway for the transport of smaller molecules from the external solution. It is shown that the TCGS microcapsules are suitable as temperature controllable glucose sensors and hold promise in the design of controllable enzymatic reactions. The proposed platform provides an avenue for developing a new‐generation of microparticles for diverse and efficient engineering applications.

Tuneable liquid crystal asymmetric dual-core photonic crystal fiber mode converter

In this work, a novel and compact mode selective coupler based on an asymmetric dual core photonic crystal fiber with a thermo-responsive core is proposed and numerically studied. Simulation results show that high conversion efficiencies are achieved between LP01 and LP11 modes in the O-band with a wide bandwidth of 24.55 nm and a mode conversion efficiency over 60% when it has a total length of 3.15 mm and the operating wavelength is 1310 nm. In addition, the thermally tuneability was evaluated when this device was submitted to thermal changes from 15°C to 35°C. The results evidence that thermal effect allows to control the operating wavelength and the mode coupling efficiency of the mode converter when it is used to couple energy from the LP01 mode to the LP11 mode. Therefore, the proposed device could be useful in high-bandwidth mode division multiplexed communication systems.

The Belousov-Zhabotinsky Reaction in Thermoresponsive Core-Shell Hydrogel Microspheres with a Tris(2,2'-bipyridyl)ruthenium Catalyst in the Core.

The Belousov-Zhabotinsky (BZ) reaction shows temporal or spatiotemporal structures such as redox oscillation of the catalyst, [ruthenium(II)tris(2,2'-bipyridine)][PF6]2 ([Ru(bpy)3][PF6]2). In this study, autonomously oscillating hydrogel microspheres (microgels) were investigated, which show swelling/deswelling oscillation induced by the redox oscillation of the BZ reaction inside the gel. Despite the periodically and autonomously induced oscillation that does not require an external stimulus, it has not been possible to perform any manipulation of the oscillatory behavior over time. The results of the present study show that it is possible to reversibly switch the microgel oscillations from an "on" active state of the BZ reaction to an "off" inactive state by changing the temperature in combination with thermoresponsive microgels. To realize on-demand switching, the construction of double-shell structures is crucial; the thermoresponsive first shell allows the microgels to modulate the diffusion of the substrates or intermediates in the BZ reaction, while the second shell maintains colloidal stability under high temperatures and high ion concentrations. The functionalized double-shell microgels were prepared via multistep seeded precipitation polymerization. The oscillatory switching behavior of the BZ reaction was observed directly and evaluated by ultraviolet-visible (UV-vis) spectroscopy. The central concept of this study, i.e., "on-off switching" can be expected to benefit the development of advanced bioinspired materials.

Switchable Wettability of Thermoresponsive Core–Shell Nanofibers for Water Capture and Release

The capture and release of water from atmospheric humidity is a recognized green technology for efficient water harvesting. A key issue limiting this technology is the lack of water sorbents capabl...

Thermoresponsive core cross-linked star-shaped poly(N-isopropylacrylamide) for reversible and controlled aggregation of nanoscale molecular units

Core cross-linked star-shaped poly(N-isopropylacrylamide) (PNIPAAm), which was prepared via an arm-first method by reversible addition-fragmentation chain-transfer polymerization, was shown to exhibit unique thermoresponsive behavior in water. Star polymers with ~20–35 arms with narrow molecular weight distributions apparently had a more hydrophilic nature compared with that of linear PNIPAAm, judging from their thermoresponsive behavior. Most importantly, an aqueous solution of the star PNIPAAm with carboxy ends remained transparent even at 70 °C.

Reactivity Control of Polymer Functional Groups by Altering the Structure of Thermoresponsive Triblock Copolymers.

A thermoresponsive ABA triblock copolymer bearing an aldehyde group on the thermoresponsive A segments was synthesized. The polymer formed a micellar assembly due to the hydrophobic interactions of the thermoresponsive segment above the lower critical solution temperature (LCST). In contrast, the ABA polymer assembly decomposed upon lowering the temperature below the LCST. Using this structural change, the reactivity of the aldehyde group toward primary amines of albumin and poly(allylamine) was investigated. When the ABA polymer assembly and reactant were mixed above the LCST, Schiff base formation was suppressed because of the aldehyde group being protected by the hydrophobic thermoresponsive core. In contrast, Schiff base formation between the ABA triblock copolymer and the primary amine moiety on the molecules was confirmed below the LCST. The reactivity of the aldehyde functional group can therefore be controlled by altering the structure of the thermoresponsive ABA polymer.

Precise Self-Assembly and Controlled Catalysis of Thermoresponsive Core–Satellite Multicomponent Hybrid Nanoparticles

The construction of multicomponent hybrid nanomaterials with well-controlled architecture, especially bearing an ordered homogeneity and distribution of the subunits with tunable functions, is a key challenge in chemistry and material science. Herein, we reported a versatile and novel strategy to fabricate core-satellite multicomponent nanostructures with tunable interparticle distances and catalysis properties by the combination of surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization and self-assembly. The arrangement and interparticle distance of gold satellites could be precisely tuned by the SI-RAFT polymerization process and the feeding ratio of gold nanoparticles (AuNPs) and the core nanoparticle. It is worthto note that multilayered core-satellite nanostructures have been fabricated by a high-feeding ratio of AuNPs and magnetite NP (MNP)@SiO2-PNIPAm. Notably, the core-satellite MNP@SiO2-PNIPAm-Au nanoparticles exhibited excellent thermoresponsive behaviors with the change of temperature. Furthermore, the catalytic efficiency of MNP@SiO2-PNIPAm-Au nanoparticles via the reduction of 4-nitrophenol to 4-aminophenol can be well modulated by the nanoparticle size, temperature, and polymer feed ratio. This strategy for precise construction of core-satellite nanostructures would open a new pathway to construct multicomponent functionalnanostructures.

Comparison of Skin Penetration, Pathological and Clinical Effects of Novel Drug Transporters – Thermoresponsive Nanogels and Core Multishell Nanocarriers – in a Murine Model of Atopic Dermatitis

Comparison of Skin Penetration, Pathological and Clinical Effects of Novel Drug Transporters – Thermoresponsive Nanogels and Core Multishell Nanocarriers – in a Murine Model of Atopic Dermatitis

Inkjet printing based assembly of thermoresponsive core-shell polymer microcapsules for controlled drug release.

A controlled drug delivery system (DDS) was designed by integrating the thermoresponsive copolymer poly(N-isopropylacrylamide-co-methacrylic acid) (poly(NIPAAm-co-MAA)) with core-shell 1,6-hexanediol diacrylate (HDDA) microparticles. The monodisperse HDDA particles with a hollow core and a nanoporous shell were fabricated in a continuous manner by an initially proposed inkjet printing process combined with UV polymerization. The thermoresponsive poly(NIPAAm-co-MAA) copolymer was grafted onto the surface of HDDA microcapsules by free radical initiated polymerization. Particularly, the lower critical solution temperature (LCST) of the copolymer was adjusted to human physiological temperature by the optimal comonomer ratio of MAA. With temperature changes at around the LCST, the copolymer, which was modified on the internal nanopore, served as a "retractable gate" by virtue of its changes in conformation between swollen and collapsed structures. Thus, controlled drug release was achieved by the reversible "open-close" transition characteristics of the nanopores. Fluorescein as a hypothetical drug molecule was loaded in the microcapsules and used to investigate the controlled release of the material. The results confirmed that this system represents a promising candidate for use in preparing controlled DDSs.

Fast and facile one-step synthesis of monodisperse thermo-responsive core–shell microspheres and applications

Highly monodisperse PMMA microspheres covered with a thermo-responsive shell were synthesized in a single step by means of photoinitiated RAFT dispersion polymerization at room temperature.

Thermoresponsive core–shell nanoparticles with cross-linked π-conjugate core based on amphiphilic block copolymers by RAFT polymerization and palladium-catalyzed coupling reactions

Well-defined amphiphilic block copolymers composed of S-vinyl sulfides and N-isopropyl acrylamide (NIPAM) were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. Thermoresponsive core–shell nanoparticles with cross-linked π-conjugate cores were obtained by in situ cross-linking reactions between 4-bromophenyl moieties in the block copolymers and diboronic acids or a diamine compound in the presence of a palladium catalyst following micelle formation in ethanol/H2O or ethanol. We initially investigated RAFT polymerization of two S-vinyl sulfide derivatives, namely phenyl vinyl sulfide (PVS) and 4-bromophenyl vinyl sulfide (BPVS), using a dithiocarbamate-type chain transfer agent (CTA). Then, RAFT polymerization of NIPAM using poly(S-vinyl sulfide) macro-CTAs was conducted to synthesize the amphiphilic block copolymers. Suzuki and Buchwald-Hartwig coupling reactions were found to be effective in the preparation of core–shell nanoparticles with thermoresponsive shells and cross-linked optoelectronic cores. The resulting nanoparticles showed characteristic thermoresponsive properties, as confirmed by turbidity and dynamic light scattering measurements. Stable and uniform core cross-linked nanoparticles were successfully prepared by the in situ palladium-catalyzed coupling reactions, and the optoelectronic and thermoresponsive properties of the nanoparticles could be tuned depending on the nature of the difunctional coupling agents, reaction conditions, and comonomer composition of the block copolymers.

Controllable Optical Properties of Polystyrene/PNIPAM-Gold Composite Nanoparticles

The optical properties of polystyrene-gold nanoparticles are simulated to understand the role of surface coverage, particle spacing, and plasmonic coupling on the optical properties. The particles are based on recent work in synthesizing composite particles via one-step Pickering emulsion techniques. These techniques can be used to develop particles with variable gold particle surface coverage on the surface of the thermoresponsive polymer core. With careful control of the surface coverage, it can be shown through simulation that a thermoresponsive particle can dynamically control the absorption peak from that of a single gold sphere (∼520 nm) to the red-shifted absorption peak of a uniform core-shell nanoparticle of similar geometry. The optical properties are shown to reside with the bounding limits of simple gold nanoparticles and core-shell nanoparticles of similar geometry but are highly dependent on the surface coverage. Furthermore, it is demonstrated how the overall extinction of asymmetric particles can be dominated by either the core particle or the attached surface particles, depending upon the temperature state of the particle.

Thermoresponsive submicron-sized core–shell hydrogel particles with encapsulated olive oil

Thermoresponsive submicron-sized core–shell hydrogel particles with incorporated olive oil were synthesised and studied. The microspheres having poly(N-isopropylacrylamide-co-methyl methacrylate) core and poly(N-isopropylacrylamide) shell were synthesised by emulsifier-free seed polymerisation method. The morphology, particle size and distribution characteristics of the core microspheres were studied with different amount of initiator, monomer–solvent ratio and polymerisation time using scanning electron microscopy and dynamic light scattering particle size analysis. The prepared core and core–shell microspheres were regularly spherical with average size of around 190.0 and 320.0 nm respectively and nearly monodispersed size distribution. Transmission electron microscopy study revealed the core–shell structure of the microspheres. The thermoresponsive transition temperature (T t) of the core–shell microspheres was determined as 33 °C by optical absorbance measurement, dynamic light scattering particle size analysis and differential scanning calorimetry. The release rate of olive oil from core–shell microspheres was accelerated by squeezing out the entrapped olive oil as the temperature was increased above T t. Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy study indicated the formation of copolymer.

Cell viability study of thermo-responsive core–shell superparamagnetic nanoparticles for multimodal cancer therapy

This is a vital extension of our previously published work. Thermo-responsive copolymer coated superparamagnetic MnFe2O4 nanoparticles are tested for cell viability and affinity on HeLa carcinoma cells under different conditions. Nanoparticles were loaded with anticancer drug doxorubicin. Composite nanoparticles of average diameter 45 nm were of core–shell structure having magnetic core of about 18 nm. Magnetic hyperthermia effects on cell viability and drug delivery were studied by exposing the cell suspension to high frequency magnetic field, and living cells were quantified using MTT method. There was almost absence of drug release at 37 °C. Drug was released at temperatures above lower critical solution temperature (LCST) by magnetic heating. LCST of the thermo-responsive copolymer was observed to be around 39 °C. Below this temperature, copolymer was hydrophilic and swelled. But above LCST, copolymer could become hydrophobic, expel water and drug and shrink in volume. Combination of hyperthermia and drug delivery effectively treated cancer cells.