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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 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.

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.

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.

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

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.

Ion specific effects are ubiquitous in solutions and govern a large number of colloidal phenomena. To date, a substantial and sustained effort has been directed at understanding the underlying molecular interactions. As a new approach, we address this issue by sensitive 1H NMR methods that measure the electrophoretic mobility and the self-diffusion coefficient of poly(N-isopropylacrylamide) (PNIPAM) chains in bulk aqueous solution in the presence of salts with the anion component varied from kosmotropes to chaotropes along the Hofmeister series. The accuracy of the applied electrophoretic NMR experiments is exceptionally high, on the order of 10–10 m2/(V s), corresponding to roughly 10–4 elementary charges per monomer effectively associated with the neutral polymer. We find that chaotropic anions associate to PNIPAM with an apparent Langmuir-type saturation behavior. The polymer chains remain extended upon ion association, and momentum transfer from anion to polymer is only partial which indicates weak attractive short-range forces between anion and polymer and, thereby and in contrast to some other ion–polymer systems, the lack of well-defined binding sites. QC 20210607

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.

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.

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.

Salt effects on the solubility of uncharged polymers in aqueous solutions are usually dominated by anions, while the role of the cation with which they are paired is often ignored. In this study, we examine the influence of three aqueous metal iodide salt solutions (LiI, NaI, and CsI) on the phase transition temperature of poly(N-isopropylacrylamide) (PNIPAM) by measuring the turbidity change of the solutions. Weakly hydrated anions, such as iodide, are known to interact with the polymer and thereby lead to salting-in behavior at low salt concentration followed by salting-out behavior at higher salt concentration. When varying the cation type, an unexpected salting-out trend is observed at higher salt concentrations, Cs+ > Na+ > Li+. Using molecular dynamics simulations, it is demonstrated that this originates from contact ion pair formation in the bulk solution, which introduces a competition for iodide ions between the polymer and cations. The weakly hydrated cation, Cs+, forms contact ion pairs with I- in the bulk solution, leading to depletion of CsI from the polymer-water interface. Microscopically, this is correlated with the repulsion of iodide ions from the amide moiety.

Per- and polyfluoroalkyl substances (PFAS) have rapidly accumulated in the environment due to their widespread use prior to commercial discussion in the early 21st century, and their slow degradation has magnified concerns of their potential toxicity. Monitoring their distribution is, therefore, necessary to evaluate and control their impact on the health of exposed populations. This investigation evaluates the capability of a simple polymeric detection scheme for PFAS based on crosslinked, thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) hydrogels. Surveying swelling perturbations induced by several hydrotropes and comparable hydrocarbon analogs, tetraethylammonium perfluorooctane sulfonate (TPFOS) showed a significantly higher swelling ratio on a mass basis (65.5 ± 8.8 at 15°C) than any of the other analytes tested. Combining swelling with the fluorimetric response of a solvachromatic dye, nile red, revealed the fluorosurfactant to initiate observable aggregation (i.e., its critical aggregation concentration) at 0.05 mM and reach saturation (i.e., its charge neutralization concentration) at 0.5 mM. The fluorosurfactant was found to homogeneously distribute throughout the polymer matrix with energy dispersive X-ray spectroscopy, marking the swelling response as a peculiar nexus of fluorinated interfacial positioning and delocalized electrostatic repulsion. Results from the current study hold promise for exploiting the physiochemical response of PNIPAM to assess TPFOS's concentration.

The low stability of InP-based quantum dots (QDs) under high temperature and humidity is a major obstacle to their practical applications and commercialization. Herein, we report on the stability enhancement of InP QD/poly(methyl methacrylate) (PMMA) nanocomposites against heat and moisture by grafting poly(N-isopropylacrylamide) (PNIPAM) on the QDs. PNIPAM-grafted QDs were prepared via ligand exchange and dispersed in a PMMA solution to fabricate the nanocomposites. For comparison, nanocomposites containing bare QDs and PMMA-grafted QDs were also fabricated, and their optical properties and light-emitting diode (LED) applications were investigated. The quantum efficiency, luminous efficacy, and color-conversion efficiency of the nanocomposites containing polymer-grafted QDs were significantly higher than those of the nanocomposites with bare QDs because of the affinity between the polymeric ligands (PMMA and PNIPAM) and the PMMA matrix. In addition, the stability of the nanocomposites was estimated at 85 °C/85% relative humidity for 30 days. The results indicate that the nanocomposites containing polymer-grafted QDs were more stable against heat and moisture than the nanocomposites containing bare QDs. Furthermore, the nanocomposites containing PNIPAM-grafted QDs exhibited superior stability to that of the nanocomposites containing PMMA-grafted QDs. The excellent stability of the nanocomposites containing PNIPAM-grafted QDs was attributed to the thermoresponsive characteristics of PNIPAM, which effectively hindered the penetration of water molecules to the QD surface, thereby preventing oxidation at a temperature above the lower critical solution temperature.

Thermo-responsive fluorescent materials are promising candidates for the development of fluorescent thermometers, biological sensors and biomedicine. Since the interesting phenomenon of aggregation...

The phase transitions of poly(N-isopropylacrylamide) (PNIPAM) in water–methanol mixed solutions were studied in detail by high-sensitivity differential scanning calorimetry. From this study, the de...

Poly(N-isopropylacrylamide) (PNIPAM) is a representative thermoresponsive polymer, and its aqueous solution becomes phase-separated at a temperature higher than the cloud point (Tcₚ) at ∼304 K, which plays an important role in various biomedical applications. Thus, to further promote the use of PNIPAM as a functional material, it is necessary to gain a better understanding of its phase behavior especially at a temperature just below Tcₚ. To this end, we examined the local rheological properties of atactic PNIPAM solutions with a concentration of 10 wt % by a particle tracking technique, in which the thermal motion of probe particles in the solution was tracked, in conjunction with Fourier-transform infrared spectroscopy, small-angle X-ray scattering measurements, fluorescence spectroscopy, and confocal laser scanning microscopy. At temperatures far below Tcₚ, the solution exhibited one-phase homogeneous characteristics. After the PNIPAM aqueous solution was left undisturbed at a temperature just below Tcₚ (302 K), it formed a physical gel. Changing the size of probe particles for the tracking measurements, we found that the resultant gel was spatially heterogeneous in terms of its rheological properties at a length scale of approximately 50–100 nm. The gelation of the solution promoted by the formation of hydrophobic pearls in PNIPAM chains led to the formation of network junctions with heterogeneity. The knowledge obtained here should be useful for understanding and controlling the phase behavior of the PNIPAM solution, thereby leading to the further development of thermoresponsive functional materials.

Thermoresponsive microgels composed of poly(N-isopropylacrylamide) (PNIPAM) and chitosan (CS) were synthesized by soap-free emulsion polymerization of N-isopropylacrylamide monomer in the presence ...

Double hydrophilic ABA-type amphiphilic polyurethane (PU)-based poly(N-vinylpyrrolidone) (PNVP)-b-PU-b-PNVP and poly(N-isopropylacrylamide) (PNIPAM)-b-PU-b-PNIPAM triblock copolymers have successfu...

Thermoresponsive phase separation mechanisms of aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions were investigated using an optical tweezer combined with a Raman microspectroscope. A near-inf...

A thermal-responsive Y-shaped amphiphilic block copolymer, namely poly(N-isopropylacrylamide-block-[poly(e-caprolactone)]2 (PNIPAAm-b-PCL2), was synthesized through the combination of atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP) techniques, and its potential as smart anti-cancer drug delivery system was investigated preliminary. The fabricated polymers were characterized using FTIR and 1H NMR spectroscopy, and GPC analysis. The self-assembly behavior of the fabricated PNIPAAm-b-PCL2 copolymer under thermal stimuli was investigated using dynamic light scattering and UV–Vis spectroscopy. The lower critical solution temperature of the synthesized PNIPAAm-b-PCL2 was found to be 39–41°C. The doxorubicin hydrochloride loading and encapsulation capacities of the fabricated PNIPAAm-b-PCL2 were calculated to be 62 ± 3%, and 75 ± 4%, respectively; the drug release value was up to 46.5% during 40 h at 37°C and up to 88% at 40°C.

Poly(N-isopropylacrylamide) (PNIPAAm)-based thermally responsive micelles are of great importance as smart materials for a number of applications such as drug delivery and biosensing, owing to thei...

This paper presents a light-switchable phase separation of poly(N-isopropylacrylamide) (PNIPAm) in aqueous solutions using an azobenzene-based ionic liquid as a molecular trigger. A different UV re...

The cononsolvency effect of poly(N-isopropylacrylamide) (PNIPAM) in a mixture of water and methanol is investigated at variable temperatures (∼20–50 °C) and pressures (0.1–265 MPa) using small-angl...

Cononsolvency occurs if a mixture of two good solvents causes the collapse or demixing of polymers into a polymer-rich phase in a certain range of compositions of these two solvents. The better sol...

Trapping biomolecules in nanosized gaps is of great interest in novel systems for single molecule analysis and membranes, which filter biomolecules. Current platforms are lacking in full functionality to facilitate biomolecule trapping and transport in their native environment and without covalent tethering to surfaces. Thus, we propose a system of thermo-responsive polymer poly(N-isopropylacrylamide) (PNIPAM) coated nanostructures, which are suited to controllably trap and release proteins, and overcome such challenges. PNIPAM polymer brushes (i.e. the barrier for proteins) on nanostructures were prepared via Activators Regenerated by Electron Transfer Atom Transfer Radical Polymerization (ARGET-ATRP) by employing a self-assembled monolayer of initiator molecules for the reaction. Variation of PNIPAM reaction time and/or solvent constituency during the polymerization results in different swollen/collapsed polymer brush thicknesses, indicated by the plasmonic shifts in extinction spectroscopy and surface plasmon resonance experiments. By having sufficient polymer film thickness and grafting density for nanowells, e.g. 120 nm, polymer conformational change below and above LCST allowed for controlled gating of these nanostructures. This feature was used to allow or block proteins from entering the interior of the nanostructures (small molecules diffuse freely in both states) as investigated by nanostructure plasmonic activity (extinction spectroscopy) and fluorescence microscopy below and above PNIPAM lower critical solution temperature (32 °C in water). In addition, with fluorescence microscopy experiments we showed that it is possible to trap and release many proteins with single nanowell resolution.

Natural alkaloid galantamine is widely used for the treatment of Alzheimer’s disease and various other memory impairments. Galantamine hydrobromide (GH) is available as fast-release tablets, extended-release capsules, and oral solution. However, oral delivery of GH can cause side effects, such as nausea, vomiting, and gastrointestinal disturbance. Transdermal delivery is one possible way to avoid such unwanted effects and is also patient friendly, especially for unconscious patients, patients with swallowing difficulties, and patients with mental disturbances. In this work, thermoresponsive copolymer networks based on poly(N-isopropylacrylamide) were studied as new platforms for potential transdermal GH delivery. Series of networks of varied structure and composition were synthesized and investigated by applying swelling kinetics and different spectroscopic and thermal methods. The network films were drug loaded in GH aqueous solution and main characteristics of the obtained GH delivery systems were evaluated. The GH release kinetic profiles in BS at 37 °C were established and discussed.

Smart temperature- and pH-responsive nanocarriers could be considered as potent vehicle in drug delivery systems. By this means, a thermo-responsive polymeric nanocarrier based on a random copolymer of poly(N-isopropylacrylamide-co-acrylamide) was prepared using controlled polymerization technique known as reversible addition fragmentation chain transfer (RAFT) polymerization. The presence of hydrophilic group in the chain, acrylamide, enhanced the lower critical solution temperature (LCST) to 37 °C in agreement with body normal temperature and made the structure suitable for drug delivery purposes. To reach this goal, the as-prepared structure was modified with hydrazine and then the anti-cancer drug, doxorubicin, was conjugated to hydrazine-modified chains through a Schiff-base linkage (acid-cleavable bond) to provide nanodrug carrier capable of responding to heat and pH. The product of each step was characterized with defined techniques. 1HNMR spectroscopy provided data for molecular weight determination. The hydrodynamic size was figured out by dynamic light scattering to be less than 300 nm. A comprehensive study on the topology of nanodrug carrier was performed by scanning electron microscopy, and the structural changes below and above the LCST were followed by transmission electron microscopy and atomic force microscopy which showed coil-like composition to globule assembly at temperature above the LCST. Furthermore, the release pattern of nanodrug carrier was assessed in the simulated medium of healthy organs or cancer tissue with pH 7.4 and 5 (37 and 42 °C). Finally, the cytotoxicity assay was performed on breast cancer/MCF-7 cell line which showed high potential of nanodrug carrier as a highly intelligent anti-cancer agent.

Here, we report the observation of an unusual thermoresponsive volume phase transition behavior of cubic poly(N-isopropylacrylamide) (PNIPAM) microgels. Cubic PNIPAM microgels with a mean edge size...

This review details the challenges with the canonical polymer swelling theory in its ability to accurately estimate realistic polymer swelling behavior. It is important to quantify this behavior si...

In the past few years, laser-assisted methods have greatly influenced biomedical studies due to less invasive ways of treatment and higher precision. New stimuli-responsive drug carriers are still explored by scientists to achieve a better spatiotemporal control of drug carriers by using visible to NIR light instead of phototoxic ultra-violet irradiation. Due to their biocompatibility and high loading capacity of hydrophilic drugs, hydrogels have been used extensively in this area. However, poor cellular uptake and restricted loading of hydrophobic drugs are challenges that should be addressed. In this study, a previously known nanogel system based on chitosan and poly(N-isopropylacrylamide) was synthesized and optimized to reach a light-responsive drug carrier. Gold nanoparticles (GNPs) were formed in situ on the surface of chitosan to act as photothermal transducers. The chemical structure optimization led to spherical and uniform nanogels with high photothermal conversion ability. The effects of the loading of Fe3O4 nanoparticles on the drug release profiles were also examined. This comprehensive study revealed the considerable potential of the achieved intelligent nanogel as a visible light-sensitive drug carrier.

Nanothermometry became a very active research field, particularly in the biomedical area, given the interrelationship between abnormal temperatures and pathological conditions, as well as the development of heating-mediated therapies. In order to provide an accurate assessment of temperature in the submicron range, several thermosensitive optical materials have been developed. In this work, a new water-soluble, optical ratiometric nanothermometer, composed of pNIPAM nanoparticles grafted to lanthanide complexes, was designed and synthesized. A chelator monomer derivative of dipicolinic acid was successfully synthesized and incorporated into the pNIPAM network through free radical emulsion polymerization. The further coordination of trivalent lanthanide ions (LnIII = Tb and/or Eu) to the obtained nanoparticles yielded luminescent thermosensitive polymers with a tunable temperature-responsive range, depending on the adopted synthesis conditions. A synergy between the pNIPAM thermosensitive response and the susceptibility of the lanthanide ion emission to be suppressed through multiphonon relaxation was explored, giving rise to optical temperature probes with reversible response, high relative thermal sensitivity, low temperature uncertainties, and excellent repeatability in aqueous solution. The obtained results indicate that the system has great potential for temperature probing in aqueous media, showing one of the highest relative thermal sensitivities so far described in the literature for water-soluble, lanthanide-based systems with ratiometric response within the biological temperature range.

Poly(N-isopropylacrylamide-co-N-vinylpyrrolidone) (poly(NIPAAm-co-NVP)) with a co-monomer molar ratio in copolymer of 91.5/8.5 (NIPAAm/NVP) was synthesized as an interesting thermosensitive material possessing a sharp phase transition at 36 °C under simulated physiological conditions. The effect of the co-monomer molar ratio as well as of the ionic strength and nature of ions on the lower critical solution temperature (LCST) was investigated. Cross-linked poly(NIPAAm-co-NVP) thermoresponsive microspheres were synthesized by the suspension polymerization technique respecting the same NIPAAm/NVP molar ratio as for linear polymer. The microspheres were loaded with the model drug diclofenac (DF) by the solvent evaporation method; differential scanning calorimetry (DSC) demonstrates a dispersion of drug crystals within the polymeric matrix. The DF release rate is deeply influenced by the drug loading degree. Only microspheres with low DF loading are able to release the bioactive compound through a pulsatile mechanism.

Through the cooperation of atom transfer radical polymerization (ATRP) and the click reaction, star-shaped poly(N-isopropylacrylamide), namely, (ZnTHPP-(PNIPAM-ZnTPP)4) with 5,10,15,20-tetra(4-(2-bromoisobutoxy)phenyl)-21H,23H-zincporphyrin (ZnTHPP-4Br) as the core group and 5-(4-propargyloxyphenyl)-10,15,20-triphenylzinc-21H,23H-porphyrin (ZnTPP-Py) as the end group was prepared, and it was used as a photocatalyst for the degradation of Rhodamine B under visible light irradiation. The structure of the star-shaped polymer was characterized by FT-NIR, 1H NMR, UV-Vis and GPC analyses. The photocatalytic property study indicated that ZnTHPP-(PNIPAM-ZnTPP)4 had higher photocatalytic activity than the polymer ZnTHPP-(PNIPAM-Br)4 before the click reaction and could be recycled by warming.

Statistical copolymers of N-isopropylacrylamide containing 2.2 – 2.7 mol % D,L-allylglycine were synthesized. The sample with 2.2 mol % allylglycine and molar mass 320000 g/mol was studied ...

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

N-isopropylacrylamide was successfully polymerized on silicon disc surfaces at room temperature by interface-mediated dissociative electron transfer reversible addition–fragmentation chain transfer (IMDET-RAFT) polymerization. The IMDET-RAFT technique was used for the first time to synthesize polymer brushes with a new mechanism using inorganic sulfides without using metal at room temperature. The polymerization was well controlled and the PNIPAAm brushes were successfully grown on silicon disc surfaces. The presence of sulfur atoms at the chain end was demonstrated by XPS experiments to demonstrate the controlled nature of the polymerization. Polymer brushes synthesized by IMDET-RAFT technique have high grafting density and grafting density was found to be 0.76 chain/nm2. This study is thought to be an important alternative to the new generation controlled/living polymerization, especially for RAFT polymerization techniques used in polymer brush synthesis. PNIPAAm brushes synthesized with IMDET-RAFT technique are an important starting point for future studies in terms of the synthesis of polymer brushes with IMDET-RAFT technique using a wide range of monomers both at ambient temperature and metal free. It is believed that this technique has the potential to be used in the future, especially in the preparation of temperature sensitive surfaces, bio-application studies and many surface modifications. In this study, application of silicon disc surfaces IMDET-RAFT polymerization was used for the first time to afford preparation of well-defined poly (NIPAAm) brushes at ambient temperature.

Thermosensitive polymers such as poly(N-isopropylacrylamide) (PNIPAM) undergo a phase transition in aqueous solution from a random-coil structural ensemble to a globule structural ensemble at the lower critical solution temperature (LCST). Above this temperature, PNIPAM agglomerates and becomes insoluble, whereas it is soluble below the temperature. Thus, thermosensitive polymers represent essential targets for several applications, e.g., in drug delivery. Although their ability to change structure in response to a temperature alteration is highly relevant for industrial processes, their thermodynamic properties are mostly qualitatively understood, and the quantitative thermodynamic picture is still elusive. In this study, we used a combined atomistic molecular dynamics and well-tempered metadynamics simulation approach to estimate coil-globule transition thermodynamics. An isotactic 30-mer of PNIPAM was investigated over a broad temperature range between 200 and 360 K. The transition from the globule to the random-coil structure was observed with well-tempered metadynamics. For the first time, the free energy surface of PNIPAM was estimated and it is shown that the simulation results are in line with the experimentally observed thermosensitive behavior. Below the LCST, the random-coil ensemble represents the global energy minimum and is thermodynamically favored by 21 ± 9 kJ/mol compared to the globule ensemble; both are separated by a barrier of 49 ± 14 kJ/mol. In contrast, above the LCST, the globule ensemble is thermodynamically favored by 21 ± 8 kJ/mol over the random-coil ensemble. The barrier from random-coil to globule is 17 ± 10 kJ/mol.

Poly(ethylene oxide) (PEO)-poly(N-isopropylacrylamide) (PNiPAm) alternating multiblock (AMB) copolymers have been prepared by means of the stereospecific reversible-addition–fragmentation chain transfer polymerization of α,ω-dicarboxy PNiPAm, followed by the amide condensation with α,ω-diamino PEO. The meso diad (m) contents of PNiPAm blocks for the AMB copolymers (AMBm45, AMBm50, and AMBm58) are 45, 50, and 58%, respectively. Dynamic light scattering and small-angle X-ray scattering (SAXS) techniques have revealed that the unimer of AMBm45 in water behaves as an extended coil near room temperature, whereas those of AMBm50 and AMBm58 shrink slightly. As the temperature goes up, a uniform aggregate appears above a certain temperature. The fluorescent probe method has indicated that the hydrophobic core is formed as the temperature increases. According to SAXS and static light scattering measurements, the aggregate possesses a spherical core–shell structure with 10–15 nm radius and consists of 9–14 unimers....

A new route to synthesize stimuli-responsive poly(N-vinylcaprolactam) (PNVCL) microgels decorated with zwitterionic poly(sulfobetaine) (PSB) chains was developed, using reversible addition-fragmentation chain transfer (RAFT) precipitation polymerization. The polyzwitterionic PSB macro-RAFTS of controlled molecular weight were synthesized by RAFT polymerization of sulfobetaine (SB). Using this method, macro-RAFTs with good control over the molecular weight could be achieved. The PSB macro-RAFTs, having different molecular weights (1000, 5000, 10,000 g/mol) and concentrations (1, 2, 2.5 mol%), were used along with different amount of the cross-linker N,N'-methylenebisacrylamide (BIS) (1.5 and 2.5 mol%) in the precipitation polymerization of PNVCL microgels to obtain varying amounts of surface-grafted polyzwitterionic chains of controlled length and variable cross-linking degrees. The successful incorporation of PSB macro-RAFTS into PNVCL microgels was characterized by FTIR and H-1 NMR studies. Increasing the PSB concentration and BIS content in the PNVCL microgels resulted in a linear increase in electrophoretic mobility (mu(e)) and volume phase transition temperature (VPTT). However, increasing the molecular chain length of the zwitterionic macro-RAFT resulted in a shift of VPTT towards lower temperatures. This kind of stimuli-responsive, polyzwitterion decorated PNVCL microgels can be a potential material for biomedical applications.

In order to develop a smart Cu(II) ion adsorption and removal system for water purification, poly(N-isopropylacrylamide) (PNIPAAm) was grafted to alginate to give a thermoresponsive Alg-g-PNIPAAm graft copolymer. With low or high initial Cu(II) concentrations, the thermoresponsive Alg-g-PNIPAAm graft copolymer could precipitate at 50 °C, with which Cu(II) was efficiently adsorbed and removed from solutions. Alg gel beads crosslinked by calcium ion Ca(II) could adsorb and remove Cu(II), but the beads released significant amount of Ca(II). The adsorption isotherm study showed that thermoresponsive Alg-g-PNIPAAm and Alg gel beads followed the same Langmuir isotherm model for Cu(II) adsorption and removal, but Alg-g-PNIPAAm demonstrated much higher adsorption capacity than Alg gel beads, because the carboxyl groups in Alg-g-PNIPAAm were free, whereas those in Alg gel beads were complexed with Ca(II). In conclusion, the Alg-g-PNIPAAm copolymer formed a smart Cu(II) adsorption and removal system with superior performance.

Co-nonsolvency occurs if a mixture of two good solvents causes the collapse or demixing of polymers into a polymer-rich phase in a certain range of compositions of these two solvents. In this work, we systematically study the co-nonsolvency behavior of poly(N-isopropylacrylamide) brushes of different grafting densities in a series of alcohol–water binary mixtures with increasing hydrophobic parts ranging from methanol to 1-butanol by using ellipsometry. We report a strong collapse transition by increasing the alcohol concentration in the water-rich phase, which is enhanced for longer-chain alcohols. The analysis of the thermodynamic properties of the alcohol–water series displays that an increasing demixing tendency between alcohol and water is correlated with an enhancement of the collapse transition of the brush. The increase of grafting density weakens the transition behavior but does not shift the solvent composition point of maximum brush collapse, which is in agreement with the predictions of a rece...

Stimulus-responsive nanoparticles have been widely used for many applications in biotechnology and medicine. In this study, dual thermo- and pH-responsive P(NIPAM-co-DMAEMA)-g-PEG nanoparticles has been synthesized by emulsion polymerization. The obtained nanoparticles were characterized by TEM, DLS, UV–Vis, 1HNMR and GPC analytical methods. The P(NIPAM-co-DMAEMA)-g-PEG nanoparticles showed higher LCST than poly(N-isopropylacrylamide) nanoparticles at 45 °C. Swelling and drug release measurements were taken under different conditions. The released amount of methotrexate (MTX) at normal physiological pH and temperature was limited (24%), while an accumulation drug release of about 70% was obtained after 48 h at pH = 5.5 under hyperthermia conditions (45 °C). MTX release data from the prepared nanoparticles were applied to the various conventional kinetic equations. The model with the highest R2 was considered as the best one. MCF-7 cell line was used to evaluate the cytotoxicity of the unloaded and MTX-loaded nanoparticles alone or in combination with hyperthermia. The results showed that the MTX-loaded nanoparticles in combination with hyperthermia suppressed tumor growth efficiently. According to the results, it can be concluded that the prepared nanoparticles might be regarded as promising agents in controlled drug delivery and multimodal cancer therapy to achieve a more effective treatment.