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A new technique is proposed for obtaining thin films of a cross-copolymer of poly-N-isopropylacrylamide and acrylamide on glass and silicon surfaces. The technique is based on polymerization of individual monomers followed by the crosslinking of polymer chains during spin-coating onto a substrate. The effect of temperature on the hydrophobicity of the obtained films is studied. Reversible changes in the contact angle are demonstrated when the substrate temperature is varied above and below 35°C. [ABSTRACT FROM AUTHOR]

Porous silicon 1D photonic crystals, namely rugate filters, are covered with a loosely packed hexagonally ordered array of stimuli‐responsive hydrogel microgels, and the optical properties of the resulting hybrid sensor are thoroughly investigated. For this purpose, both rugate filters with and without hydrogel microgel on top are immersed in ethanol/water mixtures possessing different compositions and NaCl solutions. Reflectance spectra of all samples are taken and analyzed concerning the spectral positions and reflectance intensity of the strong peak related to the photonic crystal rugate peak as well as the side bands resulting from Fabry–Pérot interference at the interfaces bordering the porous silicon. For the latter analysis, a Fourier transform is applied to the side bands for calculating the effective optical thickness (EOT). Thereby it can be shown that the spectral position of both the rugate peak and the EOT peak is best suited for monitoring refractive index changes in the immersion medium whereas the swelling and collapse of the stimuli‐responsive hydrogel microgel can be only detected by variations in the amplitude of the rugate peak and the EOT peak. These results are confirmed by simulations using a simple geometrical model and shall serve as guide for developing tailor‐made optical sensors. [ABSTRACT FROM AUTHOR]

Abstract Porous silicon 1D photonic crystals, namely rugate filters, are covered with a loosely packed hexagonally ordered array of stimuli‐responsive hydrogel microgels, and the optical properties of the resulting hybrid sensor are thoroughly investigated. For this purpose, both rugate filters with and without hydrogel microgel on top are immersed in ethanol/water mixtures possessing different compositions and NaCl solutions. Reflectance spectra of all samples are taken and analyzed concerning the spectral positions and reflectance intensity of the strong peak related to the photonic crystal rugate peak as well as the side bands resulting from Fabry–Pérot interference at the interfaces bordering the porous silicon. For the latter analysis, a Fourier transform is applied to the side bands for calculating the effective optical thickness (EOT). Thereby it can be shown that the spectral position of both the rugate peak and the EOT peak is best suited for monitoring refractive index changes in the immersion medium whereas the swelling and collapse of the stimuli‐responsive hydrogel microgel can be only detected by variations in the amplitude of the rugate peak and the EOT peak. These results are confirmed by simulations using a simple geometrical model and shall serve as guide for developing tailor‐made optical sensors.

Chromotropism in clay-polymer nanocomposite consisted of synthetic saponite, poly-N-isopropylacrylamide (PNIPAAm), and 3,3′,5,5′-tetramethylbenzidine (TMB) was investigated by diffuse reflectance spectroscopy for dry powder specimens and UV-visible absorption spectroscopy for gel specimens. TMB was introduced in the photopolymerized saponite-PNIPAAm via a commonly used cation exchange method. The nanocomposites showed yellow color attributed to TMB radical in dry state but it turned to green by partial formation of blue charge-transfer complex in contacting to water, methanol, and acetonitrile vapor or liquid. The color change was particularly pronounced for acetonitrile and was evident even in a 10% aqueous solution for hydrogels. [ABSTRACT FROM AUTHOR]

Abstract Background Biodistribution of photosensitizer (PS) in photodynamic therapy (PDT) can be assessed by fluorescence imaging that visualizes the accumulation of PS in malignant tissue prior to PDT. At the same time, excitation of the PS during an assessment of its biodistribution results in premature photobleaching and can cause toxicity to healthy tissues. Combination of PS with a separate fluorescent moiety, which can be excited apart from PS activation, provides a possibility for fluorescence imaging (FI) guided delivery of PS to cancer site, followed by PDT. Results In this work, we report nanoformulations (NFs) of core–shell polymeric nanoparticles (NPs) co-loaded with PS [2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a, HPPH] and near infrared fluorescent organic dyes (NIRFDs) that can be excited in the first or second near-infrared windows of tissue optical transparency (NIR-I, ~ 700–950 nm and NIR-II, ~ 1000–1350 nm), where HPPH does not absorb and emit. After addition to nanoparticle suspensions, PS and NIRFDs are entrapped by the nanoparticle shell of co-polymer of N-isopropylacrylamide and acrylamide [poly(NIPAM-co-AA)], while do not bind with the polystyrene (polySt) core alone. Loading of the NIRFD and PS to the NPs shell precludes aggregation of these hydrophobic molecules in water, preventing fluorescence quenching and reduction of singlet oxygen generation. Moreover, shift of the absorption of NIRFD to longer wavelengths was found to strongly reduce an efficiency of the electronic excitation energy transfer between PS and NIRFD, increasing the efficacy of PDT with PS-NIRFD combination. As a result, use of the NFs of PS and NIR-II NIRFD enables fluorescence imaging guided PDT, as it was shown by confocal microscopy and PDT of the cancer cells in vitro. In vivo studies with subcutaneously tumored mice demonstrated a possibility to image biodistribution of tumor targeted NFs both using HPPH fluorescence with conventional imaging camera sensitive in visible and NIR-I ranges (~ 400–750 nm) and imaging camera for short-wave infrared (SWIR) region (~ 1000–1700 nm), which was recently shown to be beneficial for in vivo optical imaging. Conclusions A combination of PS with fluorescence in visible and NIR-I spectral ranges and, NIR-II fluorescent dye allowed us to obtain PS nanoformulation promising for see-and-treat PDT guided with visible-NIR-SWIR fluorescence imaging.

[Display omitted] Polymer stimuli-responsive microgels find their use in various applications. The knowledge of its internal structure is of importance for further improvement and expanding the scope. Interpenetrating network (IPN) microgels may possess a remarkable feature of strongly non-uniform inner architecture, even microphase separation, in conditions of a selective solvent. In this research, we, for the first time, use a combination of static light scattering (SLS) and small-angle X-ray scattering (SAXS) techniques to collect the structure factors of aqueous dispersions of poly(N-isopropylacrylamide)-polyacrylic acid IPN microgels on the broad scale of q values. We study the influence of solvent quality on microgel conformations and show that in a selective solvent, such a system undergoes microphase separation: the sub-network in a poor solvent conditions forms dense small aggregates inside the large swollen sub-network in a good solvent. We propose the microstructured sphere model for the IPN microgel structure factor interpretation and perform additional analysis and verification through coarse-grained molecular dynamics computer simulations. [ABSTRACT FROM AUTHOR]

The advantages of mesoporous hydroxyapatite and the thermo-responsive property of poly-N-isopropylacrylamide make them attractive in drug delivery system, respectively. In this work, mesoporous poly-N-isopropylacrylamide-hydroxyapatite composite microspheres (PNIPAM-m-HAP) were synthesized, characterized and applied as a drug carrier. Doxorubicin was selected as a typical anticancer drug to study the in-vitro release characteristics of drug from PNIPAM-m-HAP in PBS. The release mechanism and release kinetics was also studied. Furthermore, the biocompatibility of the PNIPAM-m-HAP material was evaluated by MTT method. The experimental results depicted that the synthesized PNIPAM-m-HAP material was biocompatible, pH and thermo-responsive, which showed controlled release of doxorubicin. Highlights: PNIPAM-m-HAP microspheres were synthesized, characterized and used as anticancer drug carrier. PNIPAM-m-HAP was pH and thermo-responsive, which showed sustainable release of doxorubicin. The release mechanism was studied and the biocompatibility of PNIPAM-m-HAP was evaluated. [ABSTRACT FROM AUTHOR]

Background: Biodistribution of photosensitizer (PS) in photodynamic therapy (PDT) can be assessed by fluorescence imaging that visualizes the accumulation of PS in malignant tissue prior to PDT. At the same time, excitation of the PS during an assessment of its biodistribution results in premature photobleaching and can cause toxicity to healthy tissues. Combination of PS with a separate fluorescent moiety, which can be excited apart from PS activation, provides a possibility for fluorescence imaging (FI) guided delivery of PS to cancer site, followed by PDT. Results: In this work, we report nanoformulations (NFs) of core–shell polymeric nanoparticles (NPs) co-loaded with PS [2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a, HPPH] and near infrared fluorescent organic dyes (NIRFDs) that can be excited in the first or second near-infrared windows of tissue optical transparency (NIR-I, ~ 700–950 nm and NIR-II, ~ 1000–1350 nm), where HPPH does not absorb and emit. After addition to nanoparticle suspensions, PS and NIRFDs are entrapped by the nanoparticle shell of co-polymer of N-isopropylacrylamide and acrylamide [poly(NIPAM-co-AA)], while do not bind with the polystyrene (polySt) core alone. Loading of the NIRFD and PS to the NPs shell precludes aggregation of these hydrophobic molecules in water, preventing fluorescence quenching and reduction of singlet oxygen generation. Moreover, shift of the absorption of NIRFD to longer wavelengths was found to strongly reduce an efficiency of the electronic excitation energy transfer between PS and NIRFD, increasing the efficacy of PDT with PS-NIRFD combination. As a result, use of the NFs of PS and NIR-II NIRFD enables fluorescence imaging guided PDT, as it was shown by confocal microscopy and PDT of the cancer cells in vitro. In vivo studies with subcutaneously tumored mice demonstrated a possibility to image biodistribution of tumor targeted NFs both using HPPH fluorescence with conventional imaging camera sensitive in visible and NIR-I ranges (~ 400–750 nm) and imaging camera for short-wave infrared (SWIR) region (~ 1000–1700 nm), which was recently shown to be beneficial for in vivo optical imaging. Conclusions: A combination of PS with fluorescence in visible and NIR-I spectral ranges and, NIR-II fluorescent dye allowed us to obtain PS nanoformulation promising for see-and-treat PDT guided with visible-NIR-SWIR fluorescence imaging. [ABSTRACT FROM AUTHOR]

Brillouin spectroscopy is a powerful technique to probe the viscoelastic properties of materials. However, the phenomenon of multiple scattering makes getting information from opaque liquids quite difficult, thus limiting the use of this spectroscopy. In this paper we present a new method that greatly simplifies the problem of analyzing Brillouin spectra affected by multiple scattering from samples of moderate opacity. Our approach is based on the observation that multiple-scattered contributions broaden the spectrum acquired in external backscattering geometry, while preserving in the external side the information related to internally backscattered light. The new strategy avoids unnecessary approximations and requires minimum numerical effort to extract physical information. Here, we show the results of two Brillouin light scattering experiments performed on prototypical hard and soft colloidal systems. First, measurements on latex suspensions as a function of depth are used to validate the method and to derive new relations between the back-scattered and multiple-scattered components of the Brillouin spectrum. Second, measurements on poly-N-isopropylacrylamide (PNIPAM) microgels in water as a function of temperature are used as a testing ground to demonstrate the method's capabilities. Our analysis confirms that sound waves are extremely sensitive to the volume-phase transition of thermoresponsive particles. The presented approach, however, shows that a marked increase of attenuation is accompanied by only a moderate decrease of sound velocity. The study revises the viscoelastic properties of PNIPAM suspensions; more generally, it provides a new guideline in the characterization of moderately opaque media and fosters new theoretical investigations. [ABSTRACT FROM AUTHOR]

A second-order scattering (SOS) method is presented for the characterization of aqueous particle suspensions undergoing aggregation. Scattering intensities are measured at 90° by a standard fluorimeter and referenced against dynamic light scattering (DLS) measurements to determine particle size increase in a metal-promoted aggregation process for 0.05 mg/mL aqueous poly-N-isopropylacrylamide (PNIPAm), MW ∼10 k g/mol. Particle size increases monotonically from 30 nm to 210 nm at temperature 308 K. A further validation of the SOS method was performed using monodisperse polystyrene reference particles sized at 52 nm, 101 nm, 151 nm, and 206 nm, which demonstrated the technique’s accuracy to within 6% and its versatility with respect to sample composition. The technique is ideal for monitoring colloidal stability and macromolecular assembly and it can be performed at lower concentrations than are typically used in DLS. [ABSTRACT FROM AUTHOR]

Poly-N-isopropylacrylamide (PNIPAA) is a biocompatible thermosensitive polymer that is promising for using in nanobiotechnologies since this polymer has a phase transition temperature (LCST) in the physiological temperature range. LCST can be regulated by changing the hydrophilic-hydrophobic balance of the PNIPAA-containing macromolecule or by changing its structure. The incorporation of gold nanoparticles into PNIPAA polymer-nanocarrier is one of the modern approaches for the creation of new generation of drugs for photodynamic and photothermal antitumor therapy. The gold nanoparticles were synthesized in situ into polymeric matrix of branched star-shaped thermosensitive copolymer with dextran core and grafted poly-N-isopropylacrylamide chains (D-PNIPAA). Transmission electron microscopy has shown that gold nanoparticles had a spherical shape and a size of 5-10 nm. Dynamic light scattering was used for study D-PNIPAA/Au nanosystem in the region of the conformational transition of a polymer matrix. It was established that nanosystem D-PNIPAA/Au contained free nanoparticles of metals, as well as aggregates of polymer macromolecules with incorporated Au nanoparticles. The size of gold nanoparticles did not change in the studied temperature region. [ABSTRACT FROM AUTHOR]

In this paper, we report an easy route for preparing new metal nanorod-polymer composites consisting of gold nanorods, Au NRs, and temperature responsive copolymer "microgel" particles. The microgel particles of ~200 nm in size, which contain carboxylic acid groups, were prepared by surfactant-free emulsion polymerization of a selected mixture made of N-isopropylacylamide and acrylic acid in the presence of a cross-linker N,N0-methylenebisacrylamide. The electrostatic interactions between the cationic cetyltrimethylammonium bromide (CTAB) stabilized Au NRs and anionic microgel particles were expected to occur in order to prepare stable Au NRs-microgel composite particles. The optical and structural characterization of the composite was achieved using UV-Vis spectroscopy, Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and dynamic light scattering (DLS). TEM image shows that Au NRs are attached on the surface of the microgel particles. Dynamic light scattering measurements prove that the composite particles are temperature responsive, which means the particles undergo a decrease in size as the temperature increases above its phase transition temperature. In vitro cytotoxicity of the composite materials were tested by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), Lactate dehydrogenase (LDH), and hemolysis assay, which showed non-toxicity (biocompatibility). [ABSTRACT FROM AUTHOR]

Radical copolymerization method was used for the synthesis of the star-like copolymers with dextran core of various molecular weights and with various amount of grafted poly-N-isopropylacrylamide chains (D-PNIPAM). These polymers have been characterized self-exclusion chromatography and NMR-spectroscopy. It was shown by Dynamic Light Scattering method that LCST as well as conformational transition characteristics affect the molecular structure of the branched macromolecule D-PNIPAM, namely, the distance between grafts. It was found that the inflexibility of the macromolecules of copolymers D-PNIPAM determined by the distance between grafts. By reducing the distance between the chain grafts PNIPAM change conformation from mushroomlike to wormlike. Hydrodynamic size of D-PNIPAM macromolecule deceases more significally at conformational "coil-globule" transition for copolymers with mushroom conformation of grafted chains. [ABSTRACT FROM AUTHOR]

In this study, A green nano-emulsifier (Fe 3 O 4 @SiO 2 @PNIPAM) showing magnetic and thermal responsiveness have been successfully prepared by single-electron-transfer living radical polymerization (SET-LRP). Fe 3 O 4 @SiO 2 @PNIPAM can be easily separated by external magnets, the grafting of PNIPAM increases the heat recovery efficiency of nanoparticles, which is convenient for recycling. The Pickering emulsion prepared by Fe 3 O 4 @SiO 2 @PNIPAM could convert arbitrarily in emulsified state and demulsified state at the external temperature and magnetic field. [Display omitted] • An intelligent green nano-emulsifier was prepared by single-electron-transfer living radical polymerization (SET-LRP). • By adjusting the external temperature and magnetic field, Pickering emulsions can be converted between emulsified state and demulsified state. • Above LCST, grafting of PNIPAM improves the thermal separation recovery efficiency of nanoparticles. In recent years, intelligent nano-emulsifiers have received extensive attention in various fields. In this study, core–shell–shell nanoparticles (Fe 3 O 4 @SiO 2 @PNIPAM) showing magnetic and thermal responsiveness have been successfully prepared as a green nano-emulsifier by single-electron-transfer living radical polymerization (SET-LRP). The emulsifying properties of Fe 3 O 4 @SiO 2 @PNIPAM with different PNIPAM contents in toluene/water systems and the magnetic and thermal responsiveness of Pickering emulsions have been mainly investigated. The research shows that when the content of PNIPAM is higher, Fe 3 O 4 @SiO 2 @PNIPAM has the strongest emulsifying power and the Pickering emulsion is the most stable. After applying a magnet field outside the emulsion, Fe 3 O 4 @SiO 2 @PNIPAM nanoparticles can be separated rapidly, which leads to emulsion demulsification. When the temperature is above the low critical solution temperature (LCST), the PNIPAM chain shrinks and the Pickering emulsion is demulsified. When the temperature returns below the LCST, the emulsion is emulsified again, and a stable emulsion can still be formed. Therefore, the Pickering emulsion made by Fe 3 O 4 @SiO 2 @PNIPAM as an intelligent and efficient green nano-emulsifier can be converted between emulsified state and demulsified state by the control of magnetic field and temperature. These provide a wide range of ideas for Pickering emulsion recycling, industrial oil-containing wastewater separation and enhanced oil recovery. [ABSTRACT FROM AUTHOR]

Understanding the nature of adjuvants and the immune priming events in autoimmune diseases, such as rheumatoid arthritis, is a key challenge to identify their aetiology. Adjuvants are, however, complex structures with inflammatory and immune priming properties. Synthetic polymers provide a possibility to separate these functions and allow studies of the priming mechanisms in vivo. A well-balanced polymer, poly-N-isopropyl acrylamide (PNiPAAm) mixed with collagen type II (CII) induced relatively stronger autoimmunity and arthritis compared with more hydrophilic (polyacrylamide) or hydrophobic (poly-N-isopropylacrylamide-co-poly-N-tertbutylacrylamide and poly-N-tertbutylacrylamide) polymers. Clearly, all the synthesized polymers except the more hydrophobic poly-N-tertbutylacrylamide induced arthritis, especially in Ncf1-deficient mice, which are deficient in reactive oxygen species (ROS) production. We identified macrophages as the major infiltrating cells present at PNiPAAm-CII injection sites and demonstrate that ROS produced by the macrophages attenuated the immune response and the development of arthritis. Our results reveal that thermo-responsive polymers with high immune priming capacity could trigger an autoimmune response to CII and the subsequent arthritis development, in particular in the absence of NOX2 derived ROS. Importantly, ROS from macrophages protected against the autoimmune priming, demonstrating a critical regulatory role of macrophages in immune priming events. [ABSTRACT FROM AUTHOR]

The present research reports the synthesis of poly-N-isopropylacrylamide / mesoporous carbon composites, prepared by radical polymerization of N-isopropylacrylamide inside mesoporous carbon pores functionalized with carboxylic groups. The deposition of poly-N-isopropylacrylamide on mesoporous carbon was confirmed by FT-IR spectroscopy, TEM, N2e-sorption measurements. The mesoporous carbon material was found to adsorb vitamin B2 from aqueous solution at room temperature. The obtained composite, poly-N-isopropylacrylamide / mesoporous carbon, exhibited a higher adsorption capacity for vitamin B2 as compared to un-functionalized mesoporous carbon sample, due to hydrogen bonding between carbonyl groups of poly-Nisopropylacrylamide immobilized on the mesoporous carbon surface and amino groups of vitamin B2 molecules. [ABSTRACT FROM AUTHOR]

Highlights: [•] Thermo-responsive poly-N-isopropylacrylamide-β-galactosidase was synthesized. [•] PNIPAAm-β-galactosidase had lower LCST than PNIPAAm polymer. [•] PNIPAAm-β-galactosidase showed higher stability than native enzyme. [•] Activity of PNIPAAm bioconjugate improved in the presence of ethylene glycol. [•] Galacto-oligosaccharides were synthesized with PNIPAAm-β-galactosidase. [ABSTRACT FROM AUTHOR]

Two types of poly-N-isopropylacrylamide (p-NIPAM)/Cloisite 30B clay nanocomposite (NC) hydrogels were synthesized where the first one contained Cloisite 30B without modification. However, the second one contained Cloisite 30B with glycopolymer units attached onto its surface by surface-initiated atom transfer radical polymerization. The main purpose of this article was to study the effect of surface grafting of glycopolymer onto Cloisite 30B clay surface on the physical properties of the resulting NC hydrogels such as swelling ratio, deswelling behavior and thermal behavior. It was found that NC hydrogels containing glyco-units had better properties than the first one. [ABSTRACT FROM PUBLISHER]

To illuminate the impacts of sugar concentration and stereochemistry on protein protection we used attenuated-total-reflectance Fourier-transform infrared-spectroscopy (ATR-FTIR) to study the effects of four aldohexoses on poly-N-isopropylacrylamide (PNIPA) phase transition. Protein stability in aqueous solutions is essential in numerous fields, predominantly biotechnology and food science. Saccharides protect proteins against thermal denaturation, but the mechanisms are still debatable. We therefore studied the effect of sugar concentration and stereochemistry on the LCST phase transition of PNIPA as a model for protein cold renaturation, using ATR-FTIR. The transition temperature of PNIPA, as observed by both the shift in amide II peak and its area, revealed the following order: galactose > glucose > mannose > talose, i.e., galactose is the most kosmotropic of the four isomers and talose is the least. We concluded that the soluting-out effect exerted on the polymer by these sugars positively correlates with the sugar hydration number governed by sugar stereochemistry. [ABSTRACT FROM AUTHOR]

Abstract: Novel temperature-responsive copolymers of N-isopropylacrylamide and monoaza-tetrathioether derivative, were synthesized for the selective extraction of soft metal ions such as silver(I), copper(I), gold(III) and palladium(II) ion. The ratio between N-isopropylacrylamide group and monoaza-tetrathioether group in the copolymer was determined. The ratio between N-isopropylacrylamide group and monoaza-tetrathioether group varied in the range of 66:1–187:1. Each lower critical solution temperature (LCST) of the polymer solution was determined spectrophotometrically by the relative absorbance change at 750nm via temperature of the polymer solution. Metal ion extraction using the copolymer with appropriate counter anions such as picrate ion, nitrate or perchlorate ion was examined. Soft metal ions such as silver(I), copper(I), gold(III) and palladium(II) ion were extracted selectively into the solid polymer phase. The extraction efficiency of a metal ion such as silver ion increased as the increase of the ratio of the monoaza-tetrathioether group to N-isopropylacrylamide group in the polymer. The quantitative extraction of class b metal ions as well as the liquid–liquid extraction of metal ions with monoaza-tetrathioether molecule was performed. [ABSTRACT FROM AUTHOR]

We have fabricated a simple Si-MEMS device consisting of a microcantilever and a base to measure active tension generated by skeletal muscle myotubes derived from murine myoblast cell line C2C12. We have developed a fabrication process for integration of myotubes onto the device. To position myotubes over the gap between the cantilever and the base without damage due to mechanical peeling or the use of an enzymatic reaction, we cultured myotubes on poly-N-isopropylacrylamide (PNIPAAm) as a sacrifice layer. By means of immune staining of α-actinin, it was confirmed that a myotube micropatterned onto the device bridged the gap between the cantilever and the base. After 7d differentiation, the myotube was actuated by electrical stimulation. The active tension generated by the myotube was evaluated by measuring the bending of the cantilever using image processing. On twitch stimulation, the myotube on the device contracted and generated active tension in response to the electrical signals. On tetanus tension measurement, approximately 1.0 μN per single myotube was obtained. The device developed here can be used in wide area of in vitro skeletal muscle studies, such as drug screening, physiology, regenerative medicine, etc. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, non-ionic poly-N-isopropylacrylamide (PNIPAM) minigels and ionic imidazolium based minigels are synthesized to study the swelling after the addition of solvent. The kinetics of swelling is described using Tanaka''s model and the diffusion coefficients are calculated. They are of the same order of magnitude of those reported for macro- and microgels and far from that of water self-diffusion. The presence of charge for ionic minigels allows swelling control through the ions present in the surrounding solvent. [Copyright &y& Elsevier]

Abstract: Effects of poly-N-isopropylacrylamide (polyNIPAM) on the fluorescence properties of core/shell type CdS/Cd(OH)2 nanoparticles (NPs) have been studied in water. The NPs show strong fluorescence at low temperature, but the intensity decreases at >32°C, allowing an on–off fluorescence switching by temperature. The heat-induced fluorescence quenching is due to the phase transition of polyNIPAM from coil to globule state. The NPs in solution associate with polyNIPAM via a hydrogen bonding interaction. Upon heating the solution, the NPs are confined within the polymer matrices during polymer aggregation. The aggregated polymer suppresses the incident absorption of inner NPs, resulting in fluorescence quenching. A notable feature obtained by the polyNIPAM addition is the enhanced thermal stability of NPs. The NPs confined within the polymer matrices are separated from each other. This therefore suppresses the coalescence of NPs, resulting in high stability even at high temperature. [Copyright &y& Elsevier]

Abstract: Thermo-sensitive poly-N-isopropylacrylamide (poly-NIPAAm) was grafted onto lyocell fibres using cerium ammonium nitrate (CAN) as initiator. The effects of initiation time, initiator concentration, monomer concentration and grafting time on the degree of grafting were investigated. A 15–60min exposure time, 7.5mM CAN solution concentration and a 0.5–1mM NIPAAm monomer concentration were optimal for obtaining a maximum degree of grafting (60–70% at 24h grafting time) of poly-NIPAAm on lyocell fibres. Higher degree of grafting was obtained increasing the grafting time, such as 120% at 72h. The properties of the obtained poly-NIPAAm/lyocell copolymer were also investigated. Specifically, the effects of temperature and degree of grafting of poly-NIPAAm on the swelling behaviour of the copolymer were experimentally determined. Moreover, structural characterization, thermal behaviour and morphology of the poly-NIPAAm/lyocell copolymers were examined by Fourier Transform Infrared Spectroscopy (FTIR), Differencial Scanning Calorimetry (DSC) and Scanning electron microscopy (SEM) techniques, respectively. [Copyright &y& Elsevier]

Abstract: A thermoresponsive polymer, N-isopropylacrylamide-co-acrylamide (Mn 6kDa) with a lower critical solution temperature (LCST) of 37°C, was activated and conjugated to avidin to yield a derivative with 200kDa molecular weight. Gel permeation analysis demonstrated that the new bioconjugate possessed an apparent size corresponding to a 220kDa globular protein. Photon correlation spectroscopy and turbidometric studies showed that the bioconjugate underwent temperature dependent phase transitions. The protein–co-polymer bioconjugate displayed the same onset phase transition temperature (LCST) as the original synthetic co-polymer. Nevertheless, the aggregation profile of the bioconjugate shifted at higher temperature as compared to the original polymer. This indicated that the aggregation behaviour coil-to-globule transition of the co-polymer was modified by anchoring to the protein surface. Circular dichroism analysis showed that the co-polymer conjugation did not alter the protein tertiary structure tertiary the aromatic amino acid environment. The bioconjugate maintained 85±3% of native avidin affinity for biotin and biotin-Mab, and high affinity was maintained after three heating cycles. Pharmacokinetic studies demonstrated that the co-polymer bioconjugation increased the avidin residence time in the bloodstream. The distribution phase of avidin-co-polymer was longer than the native protein by a factor of 20. The co-polymer conjugation decreased by three-fold the distribution extent of avidin and reduced significantly its up-take to the liver. [Copyright &y& Elsevier]

A buffer consisting of tris(hydroxymethyl)aminomethane, 2-( N-moropholino)ethanesulfonic acid (Mes) and EDTA with constant ion strength was used to investigate the effect of buffer pH on the dynamic coating behavior of poly( N-isopropylacrylamide) (PNIPAM) for DNA separation. The atomic force microscopy (AFM) image illustrated that PNIPAM in lower-pH buffer was much more efficient in covering a silica wafer than that in higher-pH buffer. The coating performance of PNIPAM was also quantitatively analyzed by Fourier transform IR attenuated total reflectance spectroscopy and by measuring the electroosmotic flow (EOF). These results indicated that the stability of the dynamic coating was dependent on the pH of the sieving matrix and was improved by reducing the pH to the weak-acid range. The lower pH of the sieving buffer may induce the polymer more efficiently to adsorb on the capillary wall to suppress EOF and DNA–capillary wall interaction for DNA separation. The enhanced dynamic coating capacity of PNIPAM in lower-pH buffer may be attributed to the hydrogen bonds between the hydroxyl groups of the silica surface and the oxygen atom of the carbonyl groups of PNIPAM. [ABSTRACT FROM AUTHOR]

A novel approach of controlled drug delivery using thermosensitive polymers is developed in this paper. The drug release occurs at physiological temperature, at which the polymer is normally not soluble, and no medium temperature changes are required to bring about the delivery. For this purpose benefit is taken from the specific binding properties of some anionic surfactants and poly(N-isopropylacrylamide) (PNIPAAm) in order to modify the dissolution properties of PNIPAAm and of a copolymer with N-vinyl-acetamide (NVA), and so to induce the release of a drug contained in compression coated tablets. The influence of surfactant type and amount on the drug release rates and lag times from tablets coated with PNIPAAm or with the copolymer are discussed. It was found that the lag time is influenced by the surfactant species and amount. When use is made of a copolymer as coating agent, it is possible to bring about the release of the drug by incorporating only a very small amount (as low as 2%) of sodium dodecyl sulfate (SDS) in the coating. [Copyright &y& Elsevier]

In this study, controlled release ophthalmic agents for glaucoma therapy were developed based on the thermosensitivity of poly-N-isopropylacrylamide (PNIPAAm). The clear solution of PNIPAAm was known to undergo phase transition when the temperature was raised from the room temperature to about 32°C. The drug was entrapped in the tangled polymer chains or encapsulated within the crosslinked polymer hydrogel at room temperature, and released progressively after topical application (i.e., at a higher temperature). Linear PNIPAAm and crosslinked PNIAAm nanoparticles containing epinephrine were prepared. The drug release rate and cytotoxicity were investigated in vitro. Ophthalmic formulations based on either linear PNIPAAm or the mixture of linear PNIPAAm and crosslinked PNIPAAm nanoparticles were administered to rabbits and the intraocular pressure (IOP)-lowering effect was evaluated. The decreased pressure response of the formulation based on linear PNIPAAm lasted six-fold longer than that of the conventional eye drop. Furthermore, for formulation based on the mixture of linear PNIPAAm and crosslinked nanoparticles, the pressure-lowering effect lasted eight times longer. These results suggest the use of thermosensitive polymer solutions or hydrogels is potential in controlled release antiglaucoma ophthalmic drugs. [Copyright &y& Elsevier]

Hydrogel actuators belong to a type of smart soft materials which can take place anisotropic thrust and/or displacement under various environmental stimuli including thermal, light, pH, humidity etc. Robust strength and rapid response are of critical importance to high-performance hydrogel actuators. Here we report the syntheses and investigations of mechanical properties for series novel organic-inorganic hydrogels by using vinyl functionalized silicon nanoparticles (SiNPs) as the cross-linker. The doped SiNPs significantly enhance the mechanical strength of polyacrylamide (PAAm) hydrogels. Furthermore, the SiNPs composite poly- N -isopropylacrylamide (PNIPAm) hydrogels exhibit rapid response in deswelling and swelling behaviours. The excellent mechanical and responsive properties are attributed to the enhanced rigidity via SiNPs doping into the hydrogel network and the improved water diffusion through mPEG branch chains on the surface of nanoparticles, respectively. As a proof of concept, a bilayer PNIPAm@PAAm hydrogel actuator is facilely synthesized via an in-situ polymerization process. This composite hydrogel actuator shows extremely fast response rate of directional bending in hot water, about 6 times faster than the control without doping of SiNPs. This work demonstrates that these SiNPs composite hydrogels provide enhanced mechanical and responsive performances and may expand the future applications in smart hydrogel materials. [Display omitted] ∙ The functionalized silicon nanoparticles doped in SiNPs/PNIPAm@PAAm bilayer hydrogel actuator significantly improve its mechanical strength and thermal response rate. [ABSTRACT FROM AUTHOR]

This study investigates the formation of microstructured macromaterials from thermo- and pH-sensitive microgels based on interpenetrating networks of poly-N-isopropylacrylamide (PNIPAM) and polyacrylic acid (PAA). Macromaterials are produced as a result of the deposition of microgel particles and subsequent crosslinking of polyacrylic acid subnetworks to each other due to the formation of the anhydride bonds during annealing. Since both PNIPAM and PAA are environment-sensitive polymers, one can expect that their conformational state during material development will affect its resulting properties. Thus, the influence of conditions of preparation for annealing (pH of the solution, the temperature of preliminary drying) on the swelling behavior, pH- and thermosensitivity, and macromaterial inner structure was investigated. In parallel, the study of the effect of the relative conformations of the IPN microgel subnetworks on the formation of macromaterials was carried out by the computer simulations method. It was shown that the properties of the prepared macromaterials strongly depend both on the temperature and pH of the PNIPAM-PAA IPN microgel dispersions. This opens up new opportunities to obtain materials with pre-chosen characteristics and environmental sensitivity. [ABSTRACT FROM AUTHOR]