NIPAM Monomer Research Articles

Adjustment of temperature sensitivity using hydrophilic materials to develop superabsorbent polymers based on poly(N‐isopropyl acrylamide) as a temperature‐sensitive material

AbstractPoly(N‐isopropyl acrylamide) (PNIPAm) is a temperature‐sensitive material with a fast temperature response and a low critical solubilization temperature (LCST) of approximately 32°C, but it swells only 20–40 times after absorbing water. To enhance its water‐absorption properties, we introduced hydrophilic monomers into the NIPAm monomer to prepare a ternary copolymerized superabsorbent polymer. In addition, we characterized this copolymer using various techniques and analyzed its temperature‐sensitive and water‐absorbing properties. The results showed that the optimal synthesis conditions consisted of m(NIPAm):m(AMPS) = 4, 1.5% initiator, 0.3% cross‐linking agent, and 1.0% quaternized ammonium chitosan, which ensured the significant temperature sensitivity of the water‐absorbent resin. Under these conditions, the swelling ratio of the water‐absorbing resin reached 235.3 times, the LCST value was 44.6°C, the water retention rate was 84.9% at 25°C after 12 h, and the shrinkage ratio reached 81.7% at 60°C after 3 h, and 97.6% after 12 h. The resulting material could be rapidly dehydrated at high temperatures and presented clear temperature‐sensitive characteristics while maintaining excellent water‐absorbing properties.

“Grafting-from” and “Grafting-to” Poly(N-isopropyl acrylamide) Functionalization of Glass for DNA Biosensors with Improved Properties

Surface-based biosensors have proven to be of particular interest in the monitoring of human pathogens by means of their distinct nucleic acid sequences. Genosensors rely on targeted gene/DNA probe hybridization at the surface of a physical transducer and have been exploited for their high specificity and physicochemical stability. Unfortunately, these sensing materials still face limitations impeding their use in current diagnostic techniques. Most of their shortcomings arise from their suboptimal surface properties, including low hybridization density, inadequate probe orientation, and biofouling. Herein, we describe and compare two functionalization methodologies to immobilize DNA probes on a glass substrate via a thermoresponsive polymer in order to produce genosensors with improved properties. The first methodology relies on the use of a silanization step, followed by PET-RAFT of NIPAM monomers on the coated surface, while the second relies on vinyl sulfone modifications of the substrate, to which the pre-synthetized PNIPAM was grafted to. The functionalized substrates were fully characterized by means of X-ray photoelectron spectroscopy for their surface atomic content, fluorescence assay for their DNA hybridization density, and water contact angle measurements for their thermoresponsive behavior. The antifouling properties were evaluated by fluorescence microscopy. Both immobilization methodologies hold the potential to be applied to the engineering of DNA biosensors with a variety of polymers and other metal oxide surfaces.

Water dynamics in solutions of linear poly (N-isopropyl acrylamide) studied by 2H NMR field-cycling relaxometry

We use 2H nuclear magnetic resonance to study the dynamics of deuterated water in a solution of linear poly (N-isopropyl acrylamide) (pNIPAM, 4 wt%) across its coil-to-globule transition at a lower critical solubility temperature (LCST) around 32°C. In agreement with previous studies, we find that the 2H spin-lattice (T1) and, in particular, spin-spin (T2) relaxation times abruptly decrease when heating through the LCST, indicating that the polymer collapse causes an emergence of a water fraction with strongly reduced mobility. To quantify the dynamics of this slow water fraction, we exploit the fact that 2H field-cycling relaxometry allows us to measure the spectral density of the water reorientation in a broad frequency range. We find that the slow water fraction is characterised by a broad logarithmic Gaussian distribution of correlation times (σLG = 2.3), which is centred about τLG ≈ 10–9 s near the LCST. Hence, the common assumption of a Debye spectral density does not apply. We argue that a minor water fraction, which is located inside the pNIPAM globules and shows dynamics governed by the disordered polymer matrix, accompanies a major water fraction with bulk-like dynamics above the LCST. The former fraction amounts to about 0.4 water molecules per NIPAM monomer. Several findings indicate fast exchange between these bound and free water fractions on the T1 and T2 time scales.

A novel ZIF-8@IL-MXene/poly (N-isopropylacrylamide) nanocomposite hydrogel toward multifunctional adsorption

Phenols, dyes, and metal ions present in industrial wastewater can adversely affect the environment and leach biological carcinogens. Given that the current research focuses only on the removal of one or two of those categories. Herein, this work reports a novel ZIF-8@IL-MXene/Poly(N-isopropylacrylamide) (NIPAM) nanocomposite hydrogel that can efficiently and conveniently absorb and separate multiple pollutants from industrial wastewater. Ionic liquid (IL) was grafted onto MXene surfaces using a one-step method, and then incorporated into NIPAM monomer solutions to obtain the IL-MXene/PNIPAM composite hydrogel via in-situ polymerization. ZIF-8@IL-MXene/PNIPAM nanocomposite hydrogels were obtained by in-situ growth of ZIF-8 on the pore walls of composite hydrogels. As-prepared nanocomposite hydrogel showed excellent mechanical properties and can withstand ten repeated compressions without any damage, the specific surface area increased by 100 times, and the maximum adsorption capacities for p-nitrophenol (4-NP), crystal violet (CV), and copper ion (Cu2+) were 198.40, 325.03, and 285.65 mg g−1, respectively, at room temperature. The VPTTs of all hydrogels ranged from 33 to 35 °C, so the desorption process can be achieved in deionized water at 35–40 °C, and its adsorption capacities after five adsorption-desorption cycles decreased to 79%, 91%, and 29% for 4-NP, CV, and Cu2+, respectively. The adsorption data fitting results follow pseudo-second-order kinetics and Freundlich models, which is based on multiple interactions between the functional groups contained in hydrogels and adsorbent molecules. The hydrogel is the first to realize the high-efficiency adsorption of phenols, dyes and metal ions in industrial wastewater simultaneously, and the preparation process of hydrogels is environmentally friendly. Also, giving hydrogel multifunctional adsorption is beneficial to promote the development of multifunctional adsorption materials.

Ionic liquid decorated MXene/Poly (N-isopropylacrylamide) composite hydrogel with high strength, chemical stability and strong adsorption

Organic phenolic pollutants in industrial wastewater cause severe environmental pollution and physiological damage. Poly (N-isopropylacrylamide) (PNIPAM) hydrogels generally have poor mechanical strength and are also intrinsically frangible, limiting their widespread applications in wastewater treatment. Combining them with 2-dimensional materials can also only improve the mechanical properties of hydrogels. Here, we report a high-strength, chemical stability and strong adsorption MXene/poly (N-isopropylacrylamide) (PNIPAM) thermosensitive composite hydrogel for efficient removal of phenolic pollutants from industrial wastewater. Ionic liquids (ILs) were grafted onto the surface of MXenes and introduced into NIPAM monomer solution to obtain composite hydrogels by in-situ polymerization for improved mechanical strength and adsorption capacity of the composite hydrogel. Compared with the MXene/PNIPAM composite hydrogel, the introduction of ILs simultaneously improves the mechanical and adsorption properties of the composite hydrogel. The ILs bind to the surface of MXene flakes through electrostatic interactions, which improved the thermal stability and oxidation resistance of MXenes while maintaining its good dispersion. Using 1-Ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) modified MXene (MXene-EMIMBF4) did not change significantly were observed after aging for 45 days. As-prepared composite hydrogels demonstrated excellent mechanical properties, reusability, and high adsorption capacity for p-Nitrophenol (4-NP). The MXene-EMIMBF4/PNIPAM hydrogel could recover after ten 95% strain compression cycles under the synergistic effect of chemical bonding and electrostatic attraction. Its maximum adsorption capacity for 4-NP was 200.29mgg-1 at room temperature, and the adsorption capacity maintained at ∼90% of its initial value after five adsorption cycles, which was related to the introduction of EMIMBF4 to form a denser network structure. The adsorption data followed the pseudo-second-order kinetics and Freundlich models.

Copolymerization Kinetics of Dopamine Methacrylamide during PNIPAM Microgel Synthesis for Increased Adhesive Properties.

Combining stimuli-responsive properties of gels with adhesive properties of mussels is highly interesting for a large field of applications as, e.g., in life science. Therefore, the present paper focuses on the copolymerization of poly(N-isopropylacrylamide) (PNIPAM) microgels with dopamine methacrylamide (DMA). A detailed understanding of reaction kinetics is crucial to figure out an optimized synthesis strategy for tailoring microgels with adhesive properties. The present study addresses the influence of relevant synthesis parameters as the injection time of DMA during the microgel synthesis and the overall reaction time of the microgel. Reaction kinetics were studied by mass spectrometry of time samples taken during the microgel synthesis. This allowed us to determine the monomer consumption of NIPAM, the cross-linker N,N'-methylenebisacrylamide (BIS), and DMA. A second-order reaction kinetics was found for DMA incorporation. The amount of DMA incorporated in the resulting microgel was successfully determined by a combination of UV-vis and NMR spectroscopy to level off limitations of both methods. The dependence of the hydrodynamic radius on temperature was determined by DLS measurements for the microgels. While an early injection of DMA stops the PNIPAM polymerization due to scavenging, it greatly enhances the reaction speed of DMA. The faster reaction of DMA and the incomplete NIPAM and BIS conversion also compensate for shorter reaction times with respect to the incorporated amount of DMA. On the contrary, a later injection of DMA leads to a full NIPAM monomer and BIS cross-linker consumption. An overall reaction time of 60 min ensures the DMA incorporation. Longer reaction times lead to clumping. First adhesion tests show an increased adhesion of P(NIPAM-co-DMA) microgels compared to pure PNIPAM microgels, when mechanical stress is applied.

Fluorescent and thermoresponsive tetraphenylethene-based cross-linked poly(N-isopropylacrylamide)s: Synthesis, thermal/AIE properties, and cell viability

BackgroundThe synthesis, thermal properties, and aggregation-induced emission (AIE)-responsive properties of a series of tetraphenylethene (TPE)-based cross-linked poly(N-isopropylacrylamide)s (PNIPAms) consisting of a hydrophilic/thermosensitive NIPAm monomer and AIE-responsive/hydrophobic TPE derivative through reversible addition-fragmentation chain transfer polymerization was investigated in this study. MethodsThe AIE effect was investigated in a H2O/THF mixture via photoluminescence intensity measurements, and the polymers showed emission (λem = 485 ± 5 nm). When the water fraction was 90%, the PL intensity was enhanced to the highest value. Significant findingsPolymers P1–P3 showed the low critical solution temperature (LCST) at approximately 33.5, 32.4, and 28.1 °C, respectively, and deformed at P4 and P5. From dynamic light scattering, the hydrodynamic diameters of P0 and P1–P2 at a temperature higher than the LCST decreased from 564.0 to 159.6 nm, 417.4 to 126.7 nm, and 469.4 to 134.5 nm (P0, P1, and P2, respectively), indicating the thermoresponsive property. A MTT assay was used for HepG2 liver cancer cells at a concentration of 2 µg/mL, and all the polymers showed cell viability over 80%. P2 and P3 showed emission in the living HepG2 cells for 96 h of incubation. These findings suggest that the synthesized polymers have potential as drug carriers.

Thermo-induced inversion of water-in-water emulsion stability by bis-hydrophilic microgels

HypothesisStabilization of water-in-water (W/W) emulsions resulting from the separation of polymeric phases such as dextran (DEX) and poly(ethyleneoxide) (PEO) is highly challenging, because of the very low interfacial tensions between the two phases and because of the interface thickness extending over several nanometers. In the present work, we present a new type of stabilizers, based on bis-hydrophilic, thermoresponsive microgels, incorporating in the same structure poly(N-isopropylacrylamide) (pNIPAM) chains having an affinity for the PEO phase and dextran moieties. We hypothesize that these particles allow better control of the stability of the W/W emulsions. ExperimentsThe microgels were synthesized by copolymerizing the NIPAM monomer with a multifunctional methacrylated dextran. They were characterized by dynamic light scattering, zeta potential measurements and nuclear magnetic resonance as a function of temperature. Microgels with different compositions were tested as stabilizers of droplets of the PEO phase dispersed in the DEX phase (P/D) or vice-versa (D/P), at different concentrations and temperatures. FindingsOnly microgels with the highest DEX content revealed excellent stabilizing properties for the emulsions by adsorbing at the droplet surface, thus demonstrating the fundamental role of bis-hydrophilicity. At room temperature, both pNIPAM and DEX chains were swollen by water and stabilized better D/P emulsions. However, above the volume phase transition temperature (VPTT ≈ 32 °C) of pNIPAM the microgels shrunk and stabilized better P/D emulsions. At all temperatures, excess microgels partitioned more to the PEO phase. The change in structure and interparticle interaction induced by heating can be exploited to control the W/W emulsion stability.

Control of the temperature responsiveness of poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) copolymer using ultrasonic irradiation

Poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) (poly(NIPAM-co-HEMA)) is a temperature-responsive copolymer that is expected to be applicable as an advanced functional polymeric material in various fields. In this study, a novel method was developed to control the responsive temperature of poly(NIPAM-co-HEMA) using an ultrasonic polymerization technique. Initially, the behavior of the reaction was investigated using NIPAM and HEMA monomers under ultrasonic irradiation. A high ultrasonic power was found to produce a high reaction rate and low number average molecular weight of the copolymer. The polydispersity of the synthesized copolymer was approximately 1.5 for all ultrasonic powers examined. In the early stage of the reaction, the molar fraction of NIPAM in the copolymer was lower than the initial molar fraction of the monomers. It was concluded that ultrasonic irradiation affected the initiation reaction and polymer degradation, but did not affect the propagation reaction. Furthermore, the effect of the ultrasonic irradiation conditions on the temperature responsiveness of the copolymer was investigated. The lower critical solution temperature (LCST) of the copolymer was found to increase with increasing ultrasonic irradiation time. In addition, in the early stages of the reaction, the measured values of the LCST were higher than the estimated values using copolymer composition. This can be attributed to some parts of the copolymer chain possessing a higher NIPAM fraction than the overall fraction due to different reactivities of the monomers and terminated radicals. This hypothesis was indirectly verified by the synthesis of a block copolymer from the PNIPAM homopolymer and HEMA monomer.

Solid-liquid-solid conversion microextraction combined with high-performance liquid chromatography for determination of bisphenols

A novel solid-liquid-solid conversion microextraction combined with high-performance liquid chromatography method (SLSC-ME-HPLC-UV) has been developed to preconcentrate trace bisphenols (BPs) in environmental water, in which poly (isopropyl acrylamide-co-methyl methacrylate) P(MMA-co-NIPAM) was used as the extractant. The hydrogen bond and hydrophobic interaction play an important role between the P(MMA-co-NIPAM) and BPs. The ratio of copolymer MMA to NIPAM monomers, type and concentration of salt, extraction time and acetonitrile volume, as variables affecting the efficiency of extraction process, were investigated with the aid of single-variable optimization. Under optimal conditions, the coefficient of determination (R2) of calibration curves was greater than 0.999. Enrichment factors (EFs) ranged from 74 to 128. Extraction recoveries (ERs) ranged from 44 to 77%. The limits of detection (LODs) and limits of quantification (LOQs) were in the ranges of 0.20–0.90 and 0.68–3.01 μg L−1, respectively. The values for intra-day and inter-day precisions were lower than 3.6% and 3.3%, respectively.

Polymer gel containing N,N′-methylene-bis-acrylamide (BIS) as a single monomer for radiotherapy dosimetry

In this study, the first polymer gel that contains N,N′-methylene-bis-acrylamide (BIS) crosslinker without the need of adding another radiosensitive monomer has been introduced as a new low toxic polymer gel dosimeter. Various concentrations (0–0.9 M) of magnesium chloride (MgCl2) were added to BIS gel to improve the dose-response of the gel dosimeter. The gel samples were irradiated in a water phantom to different doses using 6 MV Linac X-ray beams with 200 cGy/min dose rate. The samples were read out using nuclear magnetic resonance (NMR) spectroscopy to measure the relaxation rates (R2) of the scanned samples by a standard Multi-Spin-Echo sequence. The optimum formulation gels were irradiated to different dose-rates (200 and 500 cGy/min) with a fixed radiation-energy of 6 MV, while other samples were irradiated to different radiation-energy (6 and15 MV) with a fixed dose rate of 200 cGy/min to investigate the influence of these important parameters on the performance of gel dosimeters. The dose sensitivity of the composition containing BIS, gelatin and antioxidant agent (BISGAT) polymer gel was very small (0.07 Gy−1s−1) compared to the available normoxic polymer gels such as NIMPAGAT. A significant increase in dose sensitivity (0.33 Gy−1s−1) of BISGAT dosimeter was achieved after adding 0.9 M MgCl2 to the gel which is greater than the standard composition of NIPAMGAT (i.e. BIS and NIPAM monomer) polymer gel with dose sensitivity of 0.16 Gy−1 s−1.The temporal stability of irradiated samples to different doses changed insignificantly (0.07%) in the period up to 6 days. The BISGAT gel with MgCl2 was independent of dose-rate (200 and 500 cGy/min) as well as radiation energy (6 and 15 MV). Additionally, the gel is water equivalent and has theoretical energy-independent response from 0.1 to 20 MeV for the optimum composition. The gel dosimetry accuracy was evaluated in this study by calculating the overall uncertainty and found to be 7.04% (2σ, 95% confidence level).

Polymer-matrix stabilized metal nanoparticles: Synthesis, characterizations and insight into molecular interactions between metal ions, atoms and polymer moieties

Handling nanoparticles on a mesoscale order enhances the functionality of nanoparticles for high-end technological applications such as photonics, catalysis, biomedical applications, etc. In this context, polymer-metal hybrids have shown very popularity among material scientists in recent years where a suitable polymer matrix can be effectively used to stabilize nanoparticles through different mechanisms. The current paper deals with the synthesis of different types of hybrid particles of gold (Au), silver (Ag) and iron (Fe) using micron size carboxylic group functionalized Poly(N-isopropyl acrylamide) (PNIPAM) stimuli-responsive cross-linked microgels as micro-reactor in an in-situ approach. Transmission electron microscope (TEM) directly confirms the successful loading of metal nanoparticles within microgels and all the hybrid microgels have a narrow size distribution. Dynamic light scattering (DLS) measurement in the solution state shows that the swollen size of microgel-metal hybrid is comparatively smaller than that of pure microgels. UV-VIS spectroscopy strongly reveals the presence of plasmon peaks at 520 and 405 nm in case of gold and silver microgel hybrids respectively. In case of microgel-iron hybrids, the particles nicely respond to the applied magnetic field exerted by an external magnet and the effect is also reversible when the magnet is removed. Finally, to understand the type of molecular interaction that is responsible in holding the nanoparticles within the polymer matrices of microgels, we have carried out molecular docking between different metal ions (Au3+, Ag+, Fe2+) and atoms of gold, silver and iron (Au0, Ag0, Fe0) with the functional moieties (NIPAM monomer and carboxylate ion, COO−) of the polymer. Molecular docking studies with different types of interaction potentials (Van der Waals, hydrophobic, solvation, torsional and electrostatic) suggest that the electrostatic attraction dominates over all other potentials between positive metal ions and negative carboxylate ion (COO−) giving rise to the net binding energy of −9.28, −5.7, −1.46 kcal/mol for Fe2+, Au3+, and Ag+ respectively.

Thermoresponsive polymer gated and superparamagnetic nanoparticle embedded hollow mesoporous silica nanoparticles as smart multifunctional nanocarrier for targeted and controlled delivery of doxorubicin

The design and development of drug-delivery nanocarriers with high loading capacity, excellent biocompatibility, targeting ability and controllability have been the ultimate goal of the biomedical research community. In this work, we have reported the synthesis and characterization of novel and smart thermoresponsive polymer coated and Fe3O4 embedded hollow mesoporous silica (HmSiO2) based multifunctional superparamagnetic nanocarriers for the delivery of doxorubicin (Dox) for cancer treatment. P(NIPAM-MAm) coated and Fe3O4 nanoparticle (NP) embedded hollow mesoporous silica nanocomposite (HmSiO2-F-P(NIPAM-MAm)) was prepared by the in situ polymerization of NIPAM and MAm monomers on the surface of hollow mesoporous silica NPs (HmSiO2) in the presence of Fe3O4 NPs, oxidizer and crosslinker. TEM analysis showed nearly spherical morphology of HmSiO2-F-P(NIPAM-MAm) nanocarrier with a diameter in the range of 100–300 nm. The coating of P(NIPAM-MAm) layer and embedding of Fe3O4 NPs on the surface of the HmSiO2 NPs was revealed by HRTEM analysis. XRD and FTIR analysis also confirmed the presence of P(NIPAM-MAm) shells and Fe3O4 NPs on hollow mesoporous silica NPs. VSM analysis suggested the superparamagnetic nature of HmSiO2-F-P(NIPAM-MAm) nanocarrier. DSC analysis of HmSiO2-F-P(NIPAM-MAm) nanocarrier showed a phase transition at the temperature of ∼38 °C. The prepared HmSiO2-F-P(NIPAM-MAm) nanocarrier was investigated for its suitability for drug-delivery application using doxorubicin as the model drug by an in vitro method. The encapsulation efficiency and encapsulation capacity were found to be 95% and 6.8%, respectively. HmSiO2-F-P(NIPAM-MAm)-Dox has shown a pH and temperature-dependent Dox release profile. A relatively faster release of Dox from the nanocarrier was observed at temperature above the lower critical solution temperature (LCST) than below the LCST. HmSiO2-F-P(NIPAM-MAm) nanocarrier was found to be biocompatible in nature. In vitro cytotoxicity studies against Hela cells suggested that the HmSiO2-F-P(NIPAM-MAm)-Dox nanocomposite nanocarrier has good anticancer activity. In vitro cellular uptake study of HmSiO2-F-P(NIPAM-MAm)-Dox nanocomposite nanocarrier demonstrated its good internalisation ability into Hela cells. Thus, the prepared nanocomposites show potential as nanocarrier for targeted and controlled drug delivery for cancer treatment.

The Properties of Thermosensitive Zwitterionic Sulfobetaine NIPAM-<i>co</i>-DMAAPS Polymer and the Hydrogels: The Effects of Monomer Concentration on the Transition Temperature and Its Correlation with the Adsorption Behavior

The properties of N-isopropylacrylamide copolymerized with N,N-dimethyl(acrylamidopropyl)ammonium propane sulfonate [poly(NIPAM-co-DMAAPS)] prepared with various monomer ratios such as transition temperature, molecular structure, viscosity were systematically investigated in water and Zn(NO3)2 solution. Poly(NIPAM-co-DMAAPS) in water and Zn(NO3)2 solution exhibited a phase transition with a lower critical solution temperature (LCST). The higher ratio of NIPAM monomer in poly(NIPAM-co-DMAAPS), the lower the LCST of the polymer. Furthermore, the transition temperature of poly(NIPAM-co-DMAAPS) with a lower NIPAM concentration were not confirmed both in water nor Zn(NO3)2 solution. The more increase the NIPAM concentration used in the preparation, the more increase the polymer viscosity. Moreover, the more increase the adsorption amount of ions onto the gel, the more increase the polymer transmittance as well.

Amphiphilic Copolymer Inhibition of PNIPAM-PS Aggregation is HLB Dependent

Injury due to physical trauma is mediated by alteration in biomolecular structure and intra- and inter-molecular bonding. When primary molecular structure of proteins survives trauma, we postulate that disaggregation may be catalyzed using certain amphiphilic block copolymers (ABCs). The ABC's ability to disaggregate is highly affected by structure, molecular weight, and hydrophobicity (HLB). A range of engineered polystyrene- poly(N-isopropylacrylamide)-polystyrene (PS-PNIPAm-PS) protein mimics (PMs) with different hydrophobic domains were engineered to study effectiveness of PEO-PPO ABCs to disaggregate thermally denatured PMs. PMs were synthesized by reverse-addition-fragmentation-transfer (RAFT) polymerization. The chain transfer agent, 3,5-Bis(2-dodecylthiocarbonothioylthio-1-oxopropoxy)benzoic acid, NIPAm monomer, and azobisisobutylnitrile (AIBN) initiator were mixed in dichloromethane under nitrogen (70 °C, 24 h), purified by precipitation in hexanes, and filtered. The resulting macroCTA was mixed with AIBN and styrene under nitrogen (70 °C, 6 h). Conversion to final PM structure was confirmed by size exclusion chromatography (SEC) and 1HNMR analysis in CDCl3. Cloud point at 400 nm was measured by thermal ramping (Shimadzu UV-3600 Plus Spectrophotometer). Differential scanning calorimetry (DSC) (TA Instruments Discovery 2500) was used to measure heat flow. Dynamic Light Scattering (DLS) (637 nm, 35mW laser, Brookhaven BI-APD autocorrelator) was used to measure hydrodynamic radii (Rh). SEC analysis revealed complete conversion of monomers to PMs. NMR confirmed PM structure: 7.2-5.8ppm (aromatic PS), 4.0ppm (-CONHCH(CH3)), 2.7-0.9 ppm (PS/PNIPAM backbone, -CONHCH(CH3)2). DSC and UV-VIS indicated that PMs have transitions in the expected temperature range (30-33 °C) and are fully reversible. DLS showed the heated PMs (50 °C) had higher Rh (∼500-800nm) compared to 20 °C PMs (10 ± 0.5 nm). The addition of ABCs reduced the Rh 59-95%. With all PMs, the larger the Mw of the chaperone, the greater the effect in reducing aggregate size.

Soft temperature-responsive microgels of complex shape in stop-flow lithography.

Stop-flow lithography (SFL) has emerged as a facile high-throughput fabrication method for μm-sized anisometric particles; yet, the fabrication of soft, anisometric microgels has not frequently been addressed in the literature. Furthermore, and to the best of the authors' knowledge, no soft, complex-shaped microgels with temperature-responsive behavior have been fabricated with this technology before. However, such microgels have tremendous potential as building blocks and actuating elements in rapidly developing fields, such as tissue engineering and additive manufacturing of soft polymeric building blocks, bio-hybrid materials, or soft micro-robotics. Given their great potential, we prove in this work that SFL is a viable method for the fabrication of soft, temperature-responsive, and complex-shaped microgels. The microgels, fabricated in this work, consist of poly(N-isopropylacrylamide) (pNIPAm), which is crosslinked with N,N'-methylenebis(acrylamide). The results confirm that the shape of the pNIPAm microgels is determined by the transparency mask, used in SFL. Furthermore, it is shown that, in order to realize stable microgels, a minimum threshold of crosslinker concentration of 2 wt% is required. Above this threshold, the stiffness of pNIPAm microgels can be deliberately altered by adjusting the concentration of the crosslinker. The fabricated pNIPAm microgels show the targeted temperature-responsive behavior. Within this context, temperature-dependent reversible swelling is confirmed, even for fractal-like geometries, such as micro snowflakes. Thus, these microgels provide the targeted unique combination of softness, shape complexity, and temperature responsiveness and increase the freedom of design for actuated building blocks.

Fabrication of Photothermally Responsive Nanocomposite Hydrogel through 3D Printing

AbstractThe responsive hydrogels have received great attention in many fields. However, the molding method and response mode of such hydrogels are criticized when it comes to real applications. In this work, a novel class of poly(N‐isopropyl acrylamide)/graphene oxide (PNIPAm/GO) nanocomposite hydrogel through self‐assembly three‐dimensional (3D) printing via ultraviolet light polymerization. The precursor is ordinarily constituted by NIPAm monomer, crosslinker, and water mixed with a photoinitiator, besides the introduction of nanoclay adjusts the shear thinning properties to an optimal level, which is important for the 3D printing precision. Then, the graphite oxide as infrared light absorber endows the hydrogel fast photothermal excited responsivity instead of conventional temperature response. The shrinkage and swelling of the composite hydrogel can be controlled by turning the near‐infrared light on or off. Meanwhile, the reversible behavior of as‐prepared hydrogel is easily regulated by altering the content of GO and illumination time of near‐infrared light. Additionally, a round tube is obtained based on the as‐prepared hydrogel, which can be driven to get a pencil, indicating their potential applications in actuator and other functional program.

Investigation of dosimetric characteristic of NIPAM polymer gel using x-ray CT

Introduction: Polymer gel dosimeters contain chemical materials sensitive to the radiation which are polymerized by the radiation as a function of absorbed dose. So information of spatial dose distribution can be extracted by imaging from irradiated gel. Among imaging techniques, computed tomography (CT) poses as an attractive method because of practical advantages such as accessibility, easy and speed of image acquisition and dose-response is stable and relatively insensitive to environmental factors. The most major limitation that prevents this method from clinical application is high noise in images that obtained from this system. In this study, imaging parameters in purpose of noise reduction of CT image and then concentration impact of each component of NIPAM gel on dose-response have been investigated. Finally, imaging appropriate parameter for read-out gel and NIPAM gel composition with maximum dose sensitivity for X-ray CT imaging of gel are introduced which would be an attempt to facilitate the application of this method in clinical applications. Materials and Methods: NIPAM gel was made according to the method described by Chain et al.; after the preparation, they were poured inside the vials and retained in refrigerator at 4° C for 24 hours. After this stage, gel-contained vials were subject to irradiation with a cobalt- 60 machine in dose ranging 0-50 Gy. After this, the irradiated gels were imaged with the CT scan. Ultimately, resultant DICOM images were processed in MATLAB and CT mean value of the vials as well as corresponding standard deviation were taken. Results: In this study, the imaging protocol for the Siemens SOMATOS PLUSE 4 CT scanner was investigated to reduce image noise. Parameters of 140 kV, 206 mAs, 5 mm slice thickness and 10AH kernel-based reconstruction are suitable options to evaluate polymer gel using aforementioned device. A number of 25 images for averaging could reduce the noise to an acceptable level. NIPAM polymer gel with 5% gelatin, 10 mM THPC, 17% NIPAM monomer and 3% BIS indicates the biggest changes in the CT value at 0-50 Gy ranging dose for CT imaging method. Conclusion: high-percentage monomer NIPAM polymer gel shows high sensitivity to CT imaging method and has good reproducibility and linear response range; as well as since appropriately choosing imaging protocols and thus achieved image processing reduce the noise to an acceptable level, standing these factors along with applicable advantages of CT method such as accessibility in radiotherapy centers, ease and speed of the image provision, as well as being low-cost exhibits that NIPAM polymer gel dosimeter with CT imaging method has a good potential to become a three-dimensional dosimeter in radiation therapy clinical applications.

Plasmon‐Polariton Induced, “from Surface” RAFT Polymerization, as a Way toward Creation of Grafted Polymer Films with Thickness Precisely Controlled by Self‐Limiting Mechanism

AbstractPlasmon‐induced “from surface” reversible addition‐fragmentation chain‐transfer (RAFT) polymerization is reported for the first time. The gold grating surface, supporting the surface plasmon polariton excitation and propagation, is grafted with RAFT agent, immersed in the solution, containing the NIPAm monomer and AIBN and subsequently illuminated at a wavelength corresponding to plasmon absorption. The grafting of the polymer layer, its thickness, and morphology are characterized by several techniques (including the surface‐enhanced Raman spectroscopy (SERS), scanning electron microscopy and energy‐dispersive X‐ray spectroscopy (SEM‐EDX), X‐ray photoelectron spectroscopy (XPS), nanomechanical atomic force microscopy (AFM) mapping, and goniometry). It is shown that the polymerization efficiently starts only under the surface plasmon‐polariton excitation. The time‐dependent SERS and XPS measurements indicate rather self‐limiting nature of plasmon‐induced “from the surface” PNIPAm growth, namely the reaction takes place up to a certain polymer thickness and is stopped despite a significant excess of polymerization initiator and monomer in the reaction solution. The present results provide the basis for designing further experiments on plasmonic catalysis in general and offer a new way of producing ultrathin polymer films with a defined structural dimension.

Highly sensitive multiresponsive photonic hydrogels based on a crosslinked Acrylamide- N-isopropylacrylamide (AM-NIPAM) co-polymer containing Fe3O4@C crystalline colloidal arrays

Multiresponsive photonic hydrogels (MRPHs) were prepared by magnetically controlled self-assembly of Fe3O4@C nanoparticles and these are sensitive to temperature, humidity, compression, tension and ethanol. This exhibits brilliant structural color thanks to the combination of AM and NIPAM monomers. Along with the increase of compression and tension on the MRPHs, the reflection peak of the samples blue shifts. When exposed MRPHs in environments with different humidity, its structure color red shifts as the humidity increases from 33% RH to 95% RH. Besides, the reflection peak redshift was observed when the MRPHs was immersed in absolute ethyl alcohol. This work may provide a new way to prepare smart photonic hydrogel with integrated functions of mechano-, humidity-, temperature- and solvent- responses.