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With the rapid increase in the demand for lithium as an energy-critical element, the recovery of Li+ ions from seawater is a worldwide challenging issue. Herein, we propose a new facile and fast selective recovery approach of Li+ using an Al3+-crosslinked poly(N-isopropylacrylamide) (PNIPAAm)/alginate (Alg) (PNP/Alg(Al)) adsorbent. The in situ TEM images indicate that Alg–Al3+ coordination is reorganized via the rearrangement of PNIPAAm and Alg networks, as the temperature increases. The reorganization eventually leads to the formation of polycrystalline structure. The in situ FTIR results exhibit that PNP/Alg(Al) composite has peculiar phase transitions, which includes a retrogressive phase change from hydrophobic to hydrophilic. The synergetic effect of the strong repulsion force of Al3+ ions and the attractive force of negatively charged polymeric chains enables the efficient adsorption of Li+ ions with a low affinity from Li-spiked seawater. 7.3% of Li+ ions are recovered from Li-spiked seawater although the concentration of Li-spiked seawater is very high. In addition, Li+ ions can be extracted from PNP/Alg(Al) composite with the use of a small thermal energy. The proposed thermoresponsive IPN gel provides a strong potential in practical applications for Li+ recovery as an innovative energy-material strategy.

In this study, Poly(N-isopropylacrylamide) (PNIPAM) hydrogels were produced from N-isopropylacrylamide (NIPAM), at three different concentrations of crosslinker, N,N´-methylenebisacrylamide (BIS) (0.50%, 0.35%, and 0.25%) using two types of photoinitiator, a hydrophilic photoinitiator (Irgacure 2959) and a hydrophobic photoinitiator (Irgacure 651). When Irgacure 651 was used photopolymerization process was completed in 20 min compared to two hours with Irgacure 2959. However, the resultant hydrogels were opaque suggesting a heterogeneous structure, which in turn led to low compressive strength. Besides, when hydrogel solution was prepared with Irgacure 651 in water/ethanol mixture 0.25% crosslinker ratio was not sufficient to form a hydrogel. Irgacure 2959 produced homogenous transparent hydrogels with a higher degree of swelling. When the crosslinker ratio decreased swelling capacity increased, but hydrogels became weaker. The decrease in compressive strength was particularly high at the 0.25% crosslinker ratio. The crosslinker ratio or photoinitiator type did not have any significant effect on the phase transition temperature. On the other hand, hydrogel samples prepared with Irgacure 651 in water/ethanol mixture showed a quicker response to swelling and deswelling. In conclusion, in terms of morphology, swelling capacity, and compressive strength the best results were obtained with the crosslinker ratio of 0.35% and Irgacure 2959. © 2022, The Polymer Society, Taipei., Türkiye Bilimsel ve Teknolojik Araştırma Kurumu, TÜBİTAK: 119M355, The authors would like to express appreciation for the support of the Scientific and Technological Research Council of Turkey (TÜBİTAK) [Project Number =119M355].

A thermo-sensitive film composed of polycaprolactone and poly(N-isopropylacrylamide) was fabricated via electrospinning, with ketoconazole as the model drug. The morphology, elemental composition, ...

A microscopic understanding of the internal structure and dynamics of poly(N-isopropylacrylamide) (PNIPAM) chains, in microgel colloids, is developed using deuterium NMR (2H NMR) to study deuterate...

We investigate the response speed of thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) brushes by in situ electrical monitoring, which are grafted by surface-initiated activators regenerated b...

Thermoresponsive self-assembled nanogels were conveniently prepared by cholesterol end-capped poly(N-isopropylacrylamide) (PNIPAM) in water. Both cholesterol end-capped PNIPAMs (telelchelic cholesterol PNIPAM, tCH-PNIPAM) formed flower-like nanogels by the self-assembling of four to five polymer chains with multiple domains of cholesterol in water at 20 °C. Meanwhile, one end-group cholesterol-capped PNIPAM (semitelechelic cholesterol PNIPAM, stCH-PNIPAM) was also formed as a nanogel by the self-assembling of 15-20 polymer chains with 3 to 4 cholesterol domains. The hydrophobic cholesterol domains of tCH-PNIPAM nanogels were maintained above the lower critical solution temperature (LCST) of PNIPAM (>32 °C). Differently, the hydrophobic domains of stCH-PNIPAM were disrupted by cholesterol-free PNIPAM chain ends and formed large mesoglobules above the LCST. These transition controls of hydrophilic end-capped smart polymers may open new methodologies to design thermoresponsive nanosystems.

Monolithic (non-porous) nanocomposite hydrogels were synthesized, with double and ultra-fast stimuli-responsiveness to temperature (T) and to pH. Such a fast stimulus-response is exceptional in case of bulk gels, and the prepared hydrogels additionally possess extraordinarily high tensile, mechanical, and self–recovery properties. The presented materials might be of interest as actuators, drug- or reagent-release systems. They are based on poly(N-isopropylacrylamide) (PNIPAm) physically crosslinked by clay nanoplatelets. This crosslinking lends the gels their unique mechanical properties, PNIPAm a distinct T responsiveness, and the sodium methacrylate (SMA) co-monomer (just 1.5 mol%) a strong pH-responsiveness. The gels display a quasi-one-way and complex response to T- and pH-stimuli: very fast deswelling and slow re-swelling. Extremely fast, as for monolithic gels, is the T induced deswelling at pH2: ca. 10 min are needed for the whole process. This rapid kinetics is attributed to micro-phase-separation which does not destroy mechanical properties. Re-swelling of the gels is always slow: more than 2 days are needed for 35% completion of the process in case of gels shrunken in the neutral bath. In case of gels shrunken in acidic conditions, simple re-swelling is practically blocked (due to the micro-phase-separation): both cooling and pH reversal is needed for ‘un-blocking’ and re-swelling.

A new type of thermo-responsive polymer film is fabricated by the immobilization of poly(N-isopropylacrylamide) (PNIPAAm) to the pore-selectively carboxyl group functionalized honeycomb-patterned porous polystyrene film. To check the smartness of the film to the temperature change, the thermo-responsive release of rhodamine B (RB) above the lower critical solution temperature (LCST) (~32.5 °C) of the PNIPAAm was studied together with the change in morphology of the pore surface by the scanning electron microscopy (SEM). The thermo-responsive release was monitored by the UV–vis absorbance at a fixed wavelength of λmax of RB ~553 nm. The absorbance of λmax in the equilibrium state significantly increased with the increase in temperature above the LCST of PNIPAAm. The result of the SEM image showed a higher rugged surface morphology with a temperature above the LCST which indicates that the change in the pore surface from the coil to globule state supports the thermo-responsive swell and de-swelling state of PNIPAAm. Temperature-dependent RB release kinetics was performed at 25–40 °C. The result showed pseudo-first-order kinetics by the Korsmeyer-Peppas model. The transport exponent (n) is higher than 1 as ~6.66 above the LCST region which is indicating the temperature responsive release by the change in PNIPAAm morphology.

Using N-isopropylacrylamide (NIPAM) and acrylic acid (AAc) as monomers, N,N′-methylenebisacrylamide (MBA) as a cross-linking agent, and molybdenum disulfide (MoS2) as functional particles, a P(NIPAM-co-AAc)/MoS2 composite hydrogel was prepared by free radical polymerization initiated by ultraviolet light. The results of Fourier transform infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy show that MoS2 has been successfully introduced into the P(NIPAM-co-AAc) system, and the obtained composite hydrogel has a porous network structure. Studies on the swelling property and dye adsorption performance show that the addition of MoS2 can increase the swelling ratio of P(NIPAM-co-AAc) hydrogels to a certain extent and can significantly improve the ability of the P(NIPAM-co-AAc) hydrogel to adsorb methylene blue (MB). The adsorption process of MB by the composite hydrogels conforms to the pseudo-second-order kinetics and the Langmuir isotherm adsorption models. The estimated equilibrium adsorption capacity (Qm) using the Langmuir isotherm model can reach 1258 mg/g, mainly due to the electrostatic interaction between the negatively charged groups −COO– and MoS2 particles on the network structure and the positively charged dye MB. The adsorption of MB by P(NIPAM-co-AAc)/MoS2 composite hydrogels depends on the temperature during adsorption. Compared with room temperature, a high temperature of 40 °C above the poly(N-isopropylacrylamide) (PNIPAM) phase transition temperature (∼32 °C) leads to a decreased adsorption capacity of the P(NIPAM-co-AAc)/MoS2 composite hydrogel for MB due to the enhanced hydrophobic properties of the network structure and the decrease of the swelling ratio. The prepared hydrogel material can be used as a good adsorbent for dyes, which is promising in wastewater treatment.

The solubility transition at the lower critical solution temperature (LCST, 32 °C) of poly(N-isopropylacrylamide) (PNIPAM) is widely used as a thermal switch to rapidly and reversibly capture and release proteins and cells. It is generally assumed that proteins adsorbed to PNIPAM above the LCST are unaffected by polymer interactions. Here we show that the folding stability of the enzyme phosphoglycerate kinase (PGK) is increased by interactions with end-grafted PNIPAM films above the LCST. We systematically compare two protein mutants with different stabilities. The stabilization mirrors the degree of protein adsorption under grafting conditions studied previously. Maximum stabilization occurs when proteins adsorb to low density, collapsed polymer "mushrooms". In the denser polymer "brush" regime, protein stabilization decreases back to a value indistinguishable from the bulk solution, consistent with low protein adsorption on dense, collapsed brushes. The temperature-dependent kinetics measured by Fast Relaxation Imaging reveals that PNIPAM does not affect the overall folding/unfolding mechanism. Based on the different stabilizations of two mutants and the relaxation kinetics, we hypothesize that the polymer acts mainly by increasing the conformational entropy of the folded protein by interacting with the protein surface and less by crowding the unfolded state of PGK.

It is meaningful and challenging to design and develop a fluorescent probe for living cell temperature sensors since it should have good cell compatibility and high-resolution features. In this work, the temperature-sensitive polymer of PA-loaded cysteine (Cys) modified chitosan (Cs) grafted PNIPAM (Cs-Cys-PN/PA) with aggregation-induced emission enhancement (AIEE) properties that reversible hydrogel in an aqueous solution is synthesized. Here, we interpret the temperature stimulus as a monochromatic signal through the AIEE active reversible hydrogel of Cs-Cys-PN. In addition, the cytotoxicity test shown that Cs-Cys-PN has good biocompatibility. Cs-Cys-PN can be used to build antibacterial drugs carrier, thereby providing a new platform of self-released drugs for the treatment of bacterial infections.

열방성 고분자를 이용한 스마트 윈도우는 수용액 내에서의 상전이에 따른 광산란을 통해 태양광의 투광도를 조절할 수 있다. 주로 활용되었던 폴리(N-이소프로필아크릴아미드) 계열의 열방성 고분자는 고정된 상전이 온도(32 ℃)로 인해, 다양한 기후에 적용할 수 없다는 한계가 있다. 본 연구에서는 N-이소프로필 아크릴아마이드와 친수성 혹은 소수성 단량체와의 공중합을 통해 고분자의 화학적 조성과 상전이 온도와의 상관관계가 규명되었다. 소수성인 N,N"-디에틸아크릴아미드와의 공중합은 고분자와 용매인 물과의 상호작용을 약화시켜 상전이 온도를 낮추는 결과를 보였다. 반대로 친수성의 N-바이닐피롤리돈과의 공중합을 통해 강화된 고분자-용매의 상호작용은 상전이 온도를 상승시켰다. 상전이 온도는 공중합체의 조성에 따라 24-48 ℃ 구간 내에서 조절할 수 있었다. 합성된 공중합체를 이용하여 제작된 스마트 윈도우는 다양한 지역의 기후에 따라 맞춤형 작동이 가능함을 확인하였다.

Poly(N-isopropylacrylamide) (PNIPAM) nanogels were prepared by emulsion polymerization using sodium dodecyl sulfate (SDS) and employed as a capping agent in platinum nanoparticle (Pt NP) synthesis by liquid-phase reduction with hydrogen gas. When the PNIPAM nanogels were used without removing SDS, that is, a slight amount of SDS was included in the reaction solution, Pt nanocubes (NCs) were predominantly produced (>80%). The proportion of the resultant Pt NCs was much higher than that obtained using the PNIPAM linear polymer (∼60%). To clarify the effects of the three-dimensional polymer network and SDS, we synthesized Pt NPs using the PNIPAM nanogel without SDS (SDS-free PNIPAM nanogel) and found that Pt NCs are rarely formed, and most NPs obtained have an irregular shape. When only SDS was used as a capping agent, NCs were hardly obtained, but other polyhedral NPs were formed. Furthermore, the use of SDS together with the PNIPAM polymer led to the decrease in the proportion of the Pt NCs compared with that obtained using only the linear polymer. These results indicate that the enhancement of the Pt NC proportion using the PNIPAM nanogel with SDS is attributable to not only the three-dimensional polymer network of the PNIPAM nanogel but also the assist of SDS as a capping agent.

We have investigated the colloidal phase-separating dilute solution of aqueous poly(N-isopropylacrylamide) (PNIPAM) with a molecular weight of 1.24 × 105 by small-angle X-ray scattering (SAXS) as well as static and dynamic light scattering (SLS and DLS). Those scattering experiments provide us with the average size and size distribution of concentrated-phase droplets and the concentration cconc of the coexisting concentrated phase. While the average droplet size is almost constant above 35 °C in the temperature-scan experiments, it is a decreasing function of temperature above 35 °C in the temperature-jump experiments. This heating rate dependence of the average droplet size arises from the fact that concentrated-phase droplets in the aqueous PNIPAM solution grow only in a limited temperature range (31.5-35 °C). The scattering results on the temperature dependence of cconc are combined with previously reported results of turbidity and DSC, giving the phase diagram of the Type II phase behavior with the off-zero critical point at high molecular weight.

Thermoresponsive polymers, with special emphasis on poly(N-isopropylacrylamide) (PNIPAAM) have been the focus of several investigations due to its potential applications in many fields of physical and polymer chemistry. PNIPAAM has a “lower critical solution temperature” at 32°C. The LCST can be finely tuned by copolymerization with hydrophobic or hydrophilic comonomers, and with a change of physical chemical parameters, such as ionic strength of the solution. We investigated the effect of polymer concentration on the LCST in two different solution environment, in pure water and in 50 mM NaCl solution with small-angle X-ray scattering (SAXS) of relatively low molecular mass polymers. We showed that the radius of gyration of the pNIPAAM chains increases with the addition of NaCl to the system due to the low level of specific adsorption of chloride ions on the polymer, whilst increasing the temperature causes a shrinkage of the polymer chains. Furthermore, by increasing the temperature the attractive interaction between the individual polymer chains is enhanced which turns into aggregation at the LCST.

Conjugation of nanoparticles with organic compounds are performed to enhance the activity and to increase their stability. This property would aid in developing different life saving biomedical products. Based on this objective, silver nanoparticle – poly (N-isopropylacrylamide) conjugate was developed with the aim of investigating its wound healing ability and biocompatibility in the present study. Chemical characterization of developed silver nanoparticles was also studied using FESEM and UV spectroscopic analysis.

For the improvement of poly (N-isopropylacrylamide) properties, new series of poly (N-isopropylacrylamide-Co-acrylic acid-Co-vanillin acrylate) terpolymer was fabricated with molar concentrations 5, 10, and 15 mol% of acrylic acid (AA) with 10 mol% of vanillin acrylate (VA). Monomer and polymers were chemically evaluated using (1H NMR, 13C, FT-IR, and UV); all structures emphasized logical results. The post-polymerization has been done for terpolymer with tryptophan and threonine; they were chemically investigated. Polymers and post-polymers have been physically characterized using SEM, X-ray, DSC, TGA, and SEM. Lower critical solution temperature was measured using turbidity by UV–VIS spectroscopy and by micro-DSC. These polymers will be used in the post-polymerization of many biomolecules for biomedical applications

Hypothesis Relative to the bulk systems, the near-wall ( Experiments The combination of active microrheometry (multipole magnetic tweezers) and total internal reflection microscopy (TIRM) was employed to probe the structure–rheology relationships of microgel dispersions near a substrate surface. The ω, T, and ϕeff-dependences of the storage modulus (G′), loss modulus (G"), and softness (J) were analyzed by power-law and Arrhenius-like scaling theories. The fluctuation of J was further analyzed to give a quantitative description of the inhomogeneity in the near-wall regions. Findings (1) Remarkable differences in the rheological behaviors between the bulk and near-wall cases are revealed, where the latter shows a segmented overlap behavior in ϕeff; (2) Five regimes of ϕeff that correspond to distinct physical states of the microgel dispersions are determined; (3) The near-wall local structures exhibit more heterogeneity in the glass and colloidal gel regimes as compared to the liquid regime.

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 ofqvalues. 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.

In this paper, we report a microcapsule embedded PNIPAN in P (TPC-EDA) shell and it can be regarded as an interpenetrating polymer network (IPN) structure, which can accelerate the penetration of oily substances at a certain temperature, and the microcapsules are highly monodisperse and dimensionally reproducible. The proposed microcapsules were fabricated in a three-step process. The first step was the optimization of the conditions for preparing oil in water emulsions by microfluidic device. In the second step, monodisperse polyethylene terephthaloyl-ethylenediamine (P(TPC-EDA)) microcapsules were prepared by interfacial polymerization. In the third step, the final microcapsules with poly(N-isopropylacrylamide) (PNIPAM)-based interpenetrating polymer network (IPN) structure in P(TPC-EDA) shells were finished by free radical polymerization. We conducted careful data analysis on the size of the emulsion prepared by microfluidic technology and used a very intuitive functional relationship to show the production characteristics of microfluidics, which is rarely seen in other literatures. The results show that when the IPN-structured system swelled for 6 h, the adsorption capacity of kerosene was the largest, which was promising for water–oil separation or extraction and separation of hydrophobic drugs. Because we used microfluidic technology, the products obtained have good monodispersity and are expected to be produced in large quantities in industry.

pH-/temperature-sensitive ampholytic poly(N-isopropylacrylamide) (PNIPAAm) hydrogels containing N-[3-(dimethylamino)propyl]methacrylamide-itaconic acid (DMAPMAAm-IA) and DMAPMAAm-AMPS (2-acrylamido...

Stimulus-responsive nanoparticles stand out in studies for cancer treatment since these systems can promote a selective release of the drug in tumor tissues and cells, minimizing the effects caused by conventional chemotherapy. Dextran-graft-poly (N-isopropylacrylamide) copolymers were synthesized via Schiff base formation. The synthesis of copolymers was confirmed by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (NMR) and the analyses of dynamic light scattering (DLS) showed that the copolymers were thermal and pH dual-responsive. The chemotherapy drug doxorubicin (DOX) was conjugated to the copolymers via Schiff base formation, obtaining nanoparticles by self-assembling with size smaller than 130 nm. A higher percentage of doxorubicin was released at pH 5.0 (59.1 ± 2.1%) compared to physiological pH (34.9 ± 4.8%), confirming a pH-sensitive release profile. The in vitro cytotoxicity assay demonstrated that DOX-loaded nanoparticles can inhibit cancer cell proliferation and promote reduced cytotoxicity in non-tumor cells. The D45kP30k-DOX nanoparticles induced morphological changes in HCT-116 cells suggesting cell death and the cell uptake assay indicated that the nanoparticles can be internalized by endocytosis. Therefore, DOX-loaded nanoparticles exhibited potential as smart systems for cancer treatment.

An investigation on the application of thermosensitive core-shell Fe3O4@PNIPAM nanogels in enhanced oil recovery was successfully performed. Here, the unique core-shell architecture was fabricated by conducting the polymerization at the surface of 3-butenoic acid-functionalized Fe3O4 nanoparticles and characterized using X-ray diffraction (XRD), 1H NMR, vibration sample magnetometer (VSM), and high-resolution transmission electron microscopy (HR-TEM). According to the results, this core-shell structure was beneficial for achieving the desired high viscosity and low nanofluid mobility ratio at high temperatures, which is essential for enhanced oil recovery (EOR) application. The results demonstrated that the nanogels exhibited a unique temperature-dependent flow behavior due to the PNIPAM shell's ability to transform from a hydrated to a dehydrated state above its low critical solution temperature (LCST). At such conditions, the nanogels exhibited a significantly low mobility ratio (M = 0.86), resulting in an even displacement front during EOR and leads to higher oil production. Based on the result obtained from sand pack flooding, about 25.75% of an additional secondary oil recovery could be produced when the nanofluid was injected at a temperature of 45 °C. However, a further increase in the flooding temperature could result in a slight reduction in oil recovery due to the precipitation of some of the severely aggregated nanogels at high temperatures.

The self-assembly of thermoresponsive amphiphilic diblock copolymer PMMA21-b-PNIPAM283 is studied in different water/methanol mixtures. It consists of a short hydrophobic poly(methyl methacrylate) block and a long thermoreponsive poly(N-isopropylacrylamide) block. Adding methanol as a cosolvent causes the PNIPAM block, which is soluble in both pure water and pure methanol, to collapse due to so-called co-nonsolvency effect. Meanwhile, the addition of methanol reduces the incompatibility of the PMMA block with water. By means of turbidimetry and differential scanning calorimetry, the solvent-composition-dependent phase diagram is constructed. Dynamic light scattering and synchrotron radiation based small-angle X-ray scattering (SAXS) provide structural information at 20 °C in dependence on the solvent composition. In water-rich solvent mixtures, self-assembled spherical core-shell micelles are formed. The internal structure of the micelles is adjusted by the solvent compositions in two ways: methanol softens the PMMA micellar core, while it causes the shrinkage of the PNIPAM micellar shell. In methanol-rich solvent mixtures beyond the miscibility gap, the copolymers are molecularly dissolved chains. They are collapsed near the coexistence line, while they become random coils as the methanol content increases. We propose that the internal morphology of the micelles and the conformation of the dissolved chains depend strongly on the solvent composition, as a consequence of the superposed co-nonsolvency effect of PNIPAM and the overall enhanced solvation of PMMA when adding m ethanol.

It is a great challenge to refine precious metals from e-wastes under mild conditions without hazardous reagents. Herein, black phosphorus (BP) was covalently functionalized with poly(N-isopropylacrylamide) (PNIPAM) to obtain thermo/near-infrared (NIR)-responsive BP-P for precious metal recovery. Precious metals (Au, Ag, and Pd) with higher redox potentials than BP-P could be efficiently recovered by reduction-driven enrichment. Taking Au as an example, the recovery process presented fast kinetics (

Responsive hydrogels have found widespread applications in biomedical science and engineering fields, especially for drug delivery. Despite the superior performance of responsive hydrogels, challenges still exist in drug-delivery efficiency when environmental stimuli are weak. Recently, the demand in the design of hydrogel-based drug delivery systems has stimulated considerable interest in the search for new strategies, for instance, the application of nanocomposite hydrogels for reinforcing the versatility and flexibility in controlled drug delivery. In this study, a novel and effective nanocomposite hydrogel microcapsule drug delivery system, which is composed of poly(N-isopropylacrylamide) (PNIPAM) and alginate interpenetrating polymer and GO-Fe3O4 nanomaterials, is developed to achieve NIR light-, magneto-, and pH-responsive drug release. The GO-Fe3O4 nanomaterials embedded in the interpenetrating polymer enable the PNIPAM hydrogel deswelling by raising temperature above the lower critical solution temperature under NIR light and alternating magnetic field, thus accelerating the release of doxorubicin. In addition, the introduction of alginate into PNIPAM hydrogels endows nanocomposite hydrogels (NCHs) with quick gelation property, enhanced mechanical property, and pH-responsive performance. The in vitro cytotoxicity assay confirmed that the NCH platform can effectively kill the cancer cells. This novel multiresponsive drug delivery system holds great promise for the treatment of diseases.

The characteristics of cultured cell attachment onto poly-l-lysine (PLL), collagen, and the thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPAM) were studied using a quartz crystal microbalance (QCM). A QCM with microscope cameras enclosed in a Peltier chamber was developed to enable QCM measurements and microphotographic imaging to be conducted in a temperature-controlled CO(2) incubator. Human hepatoma cell line HepG2 cells were cultured on the quartz crystals coated with PLL, collagen, and PNIPAM. Response curves of the resonant frequency of the quartz crystals during the cell attachment process were analyzed on the basis of the parameters of modeling curves fit to the experimentally obtained curves. Analysis of the fitting curves showed that the time constants of the first-lag response were 11 h for PLL, 16 h for collagen, and 38 h for PNIPAM and that the frequency change for the PNIPAM films was six times smaller than those for the PLL and collagen films. These findings were supported by photographic images showing wider cell spread on PLL and collagen than on PNIPAM. The response of cells on PNIPAM was measured during a thermal cycle from 37 to 20 °C to 37 °C. In the resonance frequency–resonance resistance (F–R) diagram, the slopes of ΔR/ΔF corresponding to the cell attachment process and those corresponding to the thermal cycling process differed; the positions in the F–R diagram also shifted to higher resonant frequencies after the thermal cycle. These results suggested that the mass effect decreased as a result of the weakening of the cell attachment strength by the thermal cycle because the molecular brushes of PNIPAM were disarranged. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10867-021-09568-7.

Hollow gold nanoparticles (HAuNPs) have received significant attention for photothermal applications owing to their strong absorbance in the near-field region, resulting in high photothermal conver...

In this study, one of the thermoresponsive polymers, block copolymer consisting of poly(ethylene glycol) and poly( N-isopropylacylamide), was investigated using Fourier transform infrared (FT-IR) spectroscopy, principal component analysis (PCA), and two-dimensional correlation spectroscopy (2D-COS). The apparent trend of the spectral changes in the temperature-dependent FT-IR spectra of poly(ethylene glycol)- block-poly( N-isopropylacylamide) (PEG- b-PNiPAAm) hydrogel during the heating process looks similar to that during the cooling process. The results of the PCA and 2D-COS, however, clearly indicate an irreversible phase transition mechanism of PEG- b-PNiPAAm hydrogel during the heating and cooling processes. It has been also shown that PEG affects the phase transition mechanism of PEG- b-PNiPAAm hydrogel, especially during the heating process. Consequently, we can successfully determine the phase transition temperature and the mechanism of PEG- b-PNiPAAm hydrogel during the heating and cooling processes using PCA and 2D-COS, respectively.

The temperature-sensitive inverse macroporous membranes containing thermo-responsive poly (N-isopropylacrylamide) (PNIPAM) were prepared by a template of silica microspheres. The inverse membranes ...

Several fluorescence patterns derived from the excimer states of perylene have been reported, but most of these have been obtained from rigid forms such as crystals or for perylene embedded in hard polymers. We observed perylene excimer emission on absorption of water by a poly-N-isopropylacrylamide gel containing perylene molecules, which were not fixed to the gel framework by chemical bonding. We propose that this emission arises because the hydrophobic perylene molecules cannot dissolve in water and form aggregates. The perylene aggregation was quickly lost on dehydration of the gel, and the luminescence reverted to that of the monomer. In a dehydrated environment, perylene was rapidly dispersed in the gel network. In other words, solid-liquid phase separation of perylene was induced by uptake of water into the gel, and perylene dissolved in the gel on dehydration. Because the outside of the gel is always in an aqueous environment, perylene will remain semipermanently in the gel. Therefore, monomer emission and excimer emission can be switched reversibly and repeatedly.

The present study pertains to the study of ferroin-catalyzed Belousov–Zhabotinsky (BZ) oscillatory chemical reaction having catechol as an organic substrate in aqueous acid media at 30 ± 0.1 °C under stirred batch conditions. The above system shows oscillations within narrow range of concentration of initial reagents which was monitored potentiometrically in oxidation reduction mode. The system shows a long induction time and a good number of oscillations at 30 ± 0.1 °C. The temperature dependence of the above system was studied. Activation parameters have been calculated, and the results showed good agreement with Arrhenius equation. Thermosensitive polymer, Poly(N-isopropylacrylamide) (PNIPAA), was synthesized by conventional method, and the polymer was characterized by different techniques. The catechol-based BZ system with ferroin as a catalyst was perturbed with N-isopropylacrylamide (NIPAA) monomer and the PNIPAA. Both NIPAA and PNIPAA affected mostly the induction time and number of oscillations. Comparative studies of catechol systems based on Ce(IV) and Mn(II) as metal catalysts were also carried out both in the presence and absence of NIPAA and PNIPAA to explore its oscillatory behavior.

A route for the facile and modular assembly of a plasmonic/photonic structure was developed based on the covalent attachment of a thermoresponsive polymer film with a few nanometers thickness betwe...

To optimize the phase separation temperature of poly (N-isopropylacrylamide) two monomers have been used to fabricate a series of three functional and thermo-pH terpolymers. N-(2-(dimethylamino)ethyl)acrylamide (DMAEAm) acts as a hydrophilic and pH-responsive monomer and 4-formyl-2-methoxyphenylacrylate or vanillin acrylate (VA) as hydrophobic and functional monomer both monomers have been synthesized in a one-step reaction. They were investigated by 1H, 13C NMR, and FTIR and demonstrated good agreement with their chemical structures. Dual responsive functional terpolymers have been fabricated in different molar ratios of (DMAEAm) (10, 15, and 20 mol%) with 10 mol% of VA; they have been investigated by chemical methods such as 1H, and FTIR as well. The physical characterization has also been achieved using GPC for molecular weight and molecular weight distributions, DSC for glass transition temperature. The vital point is studying the phase separation temperature or the lower critical solution temperature of the polymer solution, and the relative influence of DMAEAm and VA on transition temperature Tc of terpolymer solution; it has been recorded by turbidity test using UV–Vis-spectroscopy as the change of transmittance with temperature, on the other hand using micro-DSC of the polymer solution was tested. This optimization in the poly (NIPAAm) characterization encourages the application of the new terpolymer as a biosensor.

Hypothesis Grafting nanoparticles surfaces with water-soluble polymers modify interparticle interactions that are pivotal for assembling them into ordered phases. By manipulating salt concentrations of gold nanoparticles (AuNPs) that are grafted with poly(N-isopropylacrylamide) (PNIPAM-AuNPs), we hypothesize that various aggregated phases form at the suspension/vapor interface or in the bulk that depend on the molecular weight (MW) of PNIPAM and on salt concentrations. Experiments AuNPs are grafted with thiolated PNIPAM of molecular weights of 3 or 6 kDa, and grafting is confirmed by dynamic light scattering. Liquid-surfaces X-ray reflectivity and grazing incidence small-angle X-ray scattering are used to determine the density profiles of the suspension/vapor interface and their inplane structure as salt is added to the suspensions. Findings We find that surface enrichment is induced by adding NaCl to the suspensions, and that at low salt concentrations, the monoparticle layer formed is dispersed, and above a threshold salt concentration, depending on MW of PNIPAM, the PNIPAM-AuNPs order in a hexagonal structure. We show that the lattice constant of the two-dimensional hexagonal structure varies with salt concentration, and more significantly with MW of PNIPAM.

We report on the dynamic response of aqueous solution containing poly(N-isopropylacrylamide)-capped gold (pNIPAM-capped Au) nanoparticles to the introduction of NaCl. The addition of NaCl increases...

The phase transition behavior of differently crosslinked poly(N-isopropylacrylamide)/N,N’-methylenebisacrylamide (PNiPAM/BIS) microgels with varying crosslinker content is investigated in presence of aromatic additives. The influence of meta-hydroxybenzaldehyde (m-HBA) and 2,4-dihydroxybenzaldehyde (2,4-DHBA), chosen as model drugs, on the volume phase transition temperature (VPTT) is analyzed by dynamic light scattering (DLS), differential scanning calorimetry (DSC), and 1H-NMR, monitoring and comparing the structural, calorimetric, and dynamic phase transition, respectively. Generally, the VPTT is found to increase with crosslinker content, accompanied by a drastic decrease of transition enthalpy. The presence of an additive generally decreases the VPTT, but with distinct differences concerning the crosslinker content. While the structural transition is most affected at lowest crosslinker content, the calorimetric and dynamic transitions are most affected for an intermediate crosslinker content. Additive uptake of the collapsed gel is largest for low crosslinked microgels and in case of large additive-induced temperature shifts. Furthermore, as temperature is successively raised, 1H NMR data, aided by spin relaxation rates, reveal an interesting uptake behavior, as the microgels act in a sponge-like fashion including a large initial uptake and a squeeze-out phase above VPTT.

Storage and transportation of protein therapeutics using refrigeration is a costly process; a reliable electrical supply is vital, expensive equipment is needed, and unique transportation is requir...

We report photothermal phase separation of aqueous poly(N-isopropylacrylamide) (PNIPAM)/1-butanol (BuOH) solutions by focused 1064 nm laser irradiation and subsequent single microparticle formation in the solution. The single microparticle [diameter = ∼10 μm and volume = ∼picoliter (pL)] produced by laser irradiation was optically trapped by the incident 1064 nm laser beam, and this enabled us in situ Raman/fluorescence microspectroscopies of the particle. Raman spectroscopy demonstrated that the particle produced by laser irradiation was composed of PNIPAM and BuOH. In the presence of rhodamine B (RhB) in the solution, RhB was distributed from the water phase to the PNIPAM/BuOH microparticle produced by laser irradiation, as confirmed by fluorescence microspectroscopy. Laser-induced distribution/extraction of RhB to a single PNIPAM/BuOH microparticle was shown to be possible at the RhB concentration as low as 10-14 mol/dm3, where the RhB fluorescence intensity from the particle showed a step-by-step increase by every ∼3 min laser irradiation. This is the first demonstration of laser-induced simultaneous extraction and detection of single RhB molecules in solution.

Thermo-responsive polymers can experience the coil-to-globule transition with the temperature increases through the lower critical solution temperature (LCST). In this work, the coarse-grained molecular dynamics and Metadynamics (MetaD) are employed to investigate the dynamics and thermodynamics of structural change of a pair of poly(N-isopropylacrylamide) (PNIPAM) chains in aqueous solution. The results reveal that the PNIPAM molecules can move freely in aqueous solution below LCST, resulting in many extended conformations moving among several free energy basins on the free energy surface (FES); and these structures are dominated by the interaction force between PNIPAM and the water molecules. However, the PNIPAM molecules aggregate above LCST with collapsed conformations, leading to a deep basin on the FES; and these structures are dominated by the force between neighbouring PNIPAM chains. Each of the dominant mechanisms, namely, PNIPAM-water interaction force and intermolecular interaction force between PNIPAM chains, has an extreme tendency and corresponds to the extended and collapsed structures, respectively. However, the compromise in competition between these two mechanisms inevitably results in different characteristic structures including the extended and collapsed ones. In addition, the evolution of the trajectories at different temperatures are also analysed to examine the pathway of structural change.

Many applications of responsive microgels rely on the fast adaptation of the polymer network. However, the underlying dynamics of the de-/swelling process of the gels have not been fully understood. In the present work, we focus on the collapse kinetics of poly-N-isopropylacrylamide (pNIPAM) microgels due to cononsolvency. Cononsolvency means that either of the pure solvents, e.g., pure water or pure methanol, act as a so-called good solvent, leading to a swollen state of the polymer network. However, in mixtures of water and methanol, the previously swollen network undergoes a drastic volume loss. To further elucidate the cononsolvency transition, pNIPAM microgels with diameters between 20 and 110 μm were synthesized by microfluidics. To follow the dynamics, pure water was suddenly exchanged with an unfavorable mixture of 20 mol% methanol (solvent-jump) within a microfluidic channel. The dynamic response of the microgels was investigated by optical and fluorescence microscopy and Raman microspectroscopy. The experimental data provide unique and detailed insight into the size-dependent kinetics of the volume phase transition due to cononsolvency. The change in the microgel's diameter over time points to a two-step process of the microgel collapse with a biexponential behavior. Furthermore, the dependence between the two time constants from this biexponential behavior and the microgel's diameter in the collapsed state deviates from the square-power law proposed by Tanaka and Fillmore [ J. Chem. Phys. 1979, 70, 1214-1218]. The deviation is discussed considering the adhesion-induced deformation of the gels and the physical processes underlying the collapse.

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.