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Poly(N-isopropylacrylamide) (PNIPAM) is an important thermo-responsive polymer that finds applications in many areas. However, the preparation of PNIPAM-based block copolymer nanoparticles with higher-order morphologies at high solids is challenging. Herein, aqueous photoinitiated polymerization-induced self-assembly (photo-PISA) of N-isopropylacrylamide (NIPAM) using an asymmetrical cross-linker is developed for one-step preparation of PNIPAM-based block copolymer nanoparticles with various morphologies (spheres, worms, and vesicles). It is demonstrated that reaction temperature has a great effect on both polymerization kinetics and morphologies of block copolymer nanoparticles. Reversible addition-fragmentation chain transfer (RAFT) reactive groups embedded inside the PNIPAM core provide a landscape for further functionalization. PNIPAM-based block copolymer nanoparticles with different surface properties are prepared by seeded photo-PISA at room temperature. Finally, these block copolymer nanoparticles are also used as additives to tune mechanical properties of hydrogels via covalent cross-linking.

Stimuli-responsive smart materials are a key to the realization of next-generation medical technologies. Among them, the temperature-responsive polymer poly(N-isopropylacrylamide) (PNIPAAm) is attracting particular attention because it is easy to use in physiological conditions. PNIPAAm-grafted surfaces can undergo temperature-modulated cell adhesion and detachment without proteolytic enzymes, and can be used as cell-separating materials through selective cell adhesion/detachment. However, cell detachment at reduced temperatures is problematic because it takes several hours. A novel thermoresponsive crosslinked microfiber system that can greatly reduce the cell detachment time is introduced in this study. The crosslinked fibers provide temperature-dependent volume change, and enable cell detachment within 10 min of reducing the temperature, which is one-sixth of the time required in previous studies. The prompt cell detachment is thought to arise from a completely new mechanism derived from fiber swelling. This system will make a significant contribution as a novel cell manipulating system for next-generation medical technology.

As a kind of temperature-responsive hydrogel, polystyrene-co-poly(N-isopropylacrylamide)/poly(N-isopropylacrylamide) (PS-co-PNIPAM/PNIPAM) core-shell nanoparticles prepared by two-step copolymerization are widely studied and used because of their specific structures and properties. Unlike most reports about the steady stability of PS-co-PNIPAM/PNIPAM core-shell nanoparticle hydrogel emulsion, in this work, the PS-co-PNIPAM/PNIPAM core-shell nanoparticle hydrogel emulsion (symbolized as PS/PNIPAM hydrogel emulsion), which is prepared after the second step of synthesis and without washing out a large number of PNIPAM polymer segments, shows a reversible temperature-dependent sol-gel transition characteristic during the temperature range of 34-80 °C. The PS/PNIPAM hydrogel emulsion is a normal solution at room temperature, and it changes from a sol to a gel statue when the temperature approaches up to low critical solution temperature (LCST). As the temperature continues to increase, the gel (core-shell nanoparticles as the crosslinkers and the linear PNIPAM chain as the 3D gel network) of the PS/PNIPAM hydrogel emulsion gradually shrinks and drains linearly. Compared with most crosslinked hydrogels, the hydrogel here can be arbitrarily changed in shape according to use needs, which is convenient for use, transportation, and storage. Here a new route is provided for the preparation of a PS/PNIPAM core-shell hydrogel nanoparticle system, as well as a new supramolecular crosslinking sol-gel system for application in biomedical materials, sensors, biological separation, drug release, macromolecular adsorption, and purification.

Triggering the release of cargo from a polymer network by ultrasonication as an external, non-invasive stimulus can be an interesting concept for on-demand release. Here, it is shown that, in pH-and thermosensitive microgels, the ultrasound sensitivity of the polymer network depends on the external conditions. Crosslinked poly[(N-isopropylacrylamide)-co-(vinyl imidazole)] microgels showed a volume phase transition temperature (VPTT) of 25-50 degrees C, which increases with decreasing pH. Above the VPTT the polymer chains are collapsed, while below VPTT they are extended. Only in the case of maximum observed swelling, where the polymer chains are expanded, the microgels are mechanically fragmented through ultrasonication. In contrast, when the polymer chains are partially collapsed it is not possible to manipulate the microgels by ultrasound. Additionally, the ultrasound-induced on-demand release of wheat germ lipase from the microgels could be demonstrated successfully. The principle of conditional ultrasound sensitivity is likely to be general and can be used for selection of matrix-cargo combinations.

Quantification of the stimuli-responsive phase transition in polymers is topical and important for the understanding and development of novel stimuli-responsive materials. The temperature-induced phase transition of poly(N-isopropylacrylamide) (PNIPAm) with one thiol end group depends on the confinement—free polymer or polymer brush—on the molecular weight and on the nature of the second end. This paper describes the synthesis of heterotelechelic PNIPAm of different molecular weights with a thiol end group—that specifically binds to gold nanorods and a hydrophilic NIPAm end group by reversible addition-fragmentation chain-transfer polymerization. Proton high-resolution magic angle sample spinning NMR spectra are used as an indicator of the polymer chain conformations. The characteristics of phase transition given by the transition temperature, entropy, and width of transition are obtained by a two-state model. The dependence of thermodynamic parameters on molecular weight is compared for hydrophilic and hydrophobic end functional-free polymers and brushes.

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The photo- and thermoresponse of poly(N-isopropylacrylamide) (pNIPAAm) functionalized with spiropyran chromophore is examined with respect to the influence of molecular recognition by cyclodextrin (CD). Characterization in aqueous solutions of spiropyran-functionalized poly(N,N-dimethylacrylamide) under coexistence of α-, β-, or γ-CD reveals that β-CD selectively includes the ring-closing isomer of the chromophore, which is dominant under light irradiation, while no inclusion is observed for the protonated ring-opening isomer, which is dominant in the dark before irradiation. As a result, it is shown that the selective inclusion of the chromophore at a polymer side chain is switched by light irradiation. Further, drastic photoresponsive dehydration of spiropyran-functionalized pNIPAAm is inhibited only by β-CD out of three examined CDs, demonstrating that the molecular recognition regulates the dehydration of the whole polymer triggered by the photoswitching of the chromophore introduced at only 1 mol% functionalization.

At the basis of smart self-assembled materials are lying small building blocks that can hierarchically assemble in response to stimuli, e.g., temperature or chemical species. In this context, the synthesis of terpyridine end-capped poly(2-(dimethylamino)ethyl methacrylate)-block-poly(N-isopropylacrylamide) diblock copolymers via controlled radical copolymerization is reported here. The self-assembly of those copolymers is investigated in dilute aqueous solutions while varying temperature or adding transition metal ions, respectively, leading to the formation of micellar nanostructures or metallosupramolecular triblock copolymers.

Ruthenium-functionalized poly(N-isopropyl acrylamide)-based chemically oscillating microgels with diameters between 1 and 6 µm are synthesized by a modified precipitation polymerization approach. It is found that the initial amount of N-isopropyl acrylamide (NIPAAm) can significantly affect the final sizes of the microgels. 2.5 g of initial NIPAAm results in microgels with maximum average diameter of ≈6 ± 0.5 µm. Making use of their fluorescence due to their ruthenium contents and their larger sizes compared to microgels prepared using other traditional methods, the impact of changes in the NaBrO3 concentrations on their microscopic behavior is studied using a combination of fluorescence microscopy and dynamic light scattering techniques. When increasing the concentration of NaBrO3 in a solution, the microgels first experience a decrease in size followed by aggregation that leads to the loss of colloidal stability. Finally, the redox potential behavior and optical performance of the Belousov-Zhabotinsky reaction catalyzed by these microgels are studied by electrochemical and spectroscopic means.

Homocysteine (Hcy) and cysteine (Cys) are two important kinds of amino acids in human bodies. Herein, we synthesized an iridium(III) complex-functionalized poly(N-isopropylacrylamide) and its hydrogel, which could be used as the excellent phosphorescent bioprobe for sensing Hcy and Cys. Their detection can be realized in aqueous system through the variations in absorption and photoluminescence spectra. Furthermore, living cell imaging experiments demonstrate that the phosphorescent bioprobe is membrane permeable and can monitor the changes of Hcy and Cys within living cells. In addition, the probe is also thermoresponsive, and its photoluminescence intensified with increasing temperature. These results suggests that this bioprobe has promising application in biomedical fields.

The monomers 2-methyl-2-oxazine (MeOZI), 2-ethyl-2-oxazine (EtOZI), and 2-n-propyl-2-oxazine (nPropOZI) were synthesized and polymerized via the living cationic ring-opening polymerization (CROP) under microwave-assisted conditions. pEtOZI and pnPropOZI were found to be thermoresponsive, exhibiting LCST behavior in water and their cloud point temperatures (T(CP)) are lower than for poly(2-oxazoline)s with similar side chains. However, comparison of poly(2-oxazine) and poly(2-oxazoline)s isomers reveals that poly(2-oxazine)s are more water soluble, indicating that the side chain has a stronger impact on polymer solubility than the main chain. In conclusion, variations of both the side chains and the main chains of the poly(cyclic imino ether)s resulted in a series of distinct homopolymers with tunable T(CP).

Poly(N-isopropylacrylamide) (PNIPAAm) grafted dextran nanogels with dodecyl and thiol end groups have been synthesized by RAFT process. Dodecyl-terminated polymers (DexPNI) can be readily dissolved in water and further self assemble into ordered stable nanostructures through direct noncovalent interactions at room temperature. SEM, AFM and DLS measurements confirm the formation of spherical nanogels at hundred-nanometer scales. The elevation of environment temperature will indirectly result in the formation of collapsed nanostructures due to the LCST phase transition of PNIPAAm side chains. Turbidimetry results show that the phase transition behaviors of DexPNI are greatly dependent on PNIPAAm chain length and polymer concentration: increasing PNIPAAm chain length and polymer concentration both lead to lower LCSTs and sharper phase transitions. Moreover, the dodecyl-terminated polymers can transform into thiol-terminated versions by aminolysis of trithiocarbonate groups, and further into chemical (disulfide) cross-linked versions (SS-DexPNI) by oxidation. SS-DexPNI nanogels have "doubled" chain length of PNIPAAm, and hence sharper phase transitions. In situ DLS measurements of the evolution of hydrodynamic radius attest that the self assembly of SS-DexPNI nanogels can be selectively directed by the change in either external temperature or redox potential. These nanogels thus are promising candidates for triggered intracellular delivery of encapsulated cargo. We can also expect that the polymer can be noncovalently (by dodecyl end groups) or covalently (by thiol end groups) coated on a series of nanomaterials (e.g., carbon nanotubes, graphene, gold nanomaterials) to build a variety of novel smart, and robust nanomaterials.

The thermal-response and mechanical properties of poly(N-isopropylacrylamide) (PNIPAm) are improved by controlling the polymer nanostructure through photopolymerization in a bicontinuous cubic lyotropic liquid crystal (LLC) template. The bicontinuous cubic nanostructure increases the rate and amount of water expelled from PNIPAm for heating above the lower critical solution temperature (LCST) relative to an isotropic PNIPAm hydrogel while maintaining the mechanical integrity of the polymer. These results could allow development of PNIPAm hydrogels with proper water uptake, deswelling kinetics, volume transition, and mechanical properties required for successful performance in a growing number of advanced biological and industrial applications.

Herein, we report an effective and rapid method to purify glutathione S-transferase (GST) using glutathione (GSH)-modified poly(N-isopropylacrylamide) (pNIPAAm) and mild, thermal conditions. A chain transfer agent modified with pyridyl disulfide was employed in the reversible addition-fragmentation chain transfer (RAFT) polymerization of NIPAAm. The resulting polymer had a narrow molecular weight distribution (polydispersity index = 1.21). Conjugation of GSH to the pyridyl disulfide-pNIPAAm reached 95% within 30 min as determined by UV-Vis monitoring of the release of pyridine-2-thione. GST was successfully thermoprecipitated upon heating the GSH-pNIPAAm above the lower critical solution temperature (LCST). The pull down assay was repeated with bovine serum albumin (BSA) and T4 lysozyme (T4L), which demonstrated the specificity of the polymer for GST. Due to its simplicity and high efficiency, this method holds great potential for large-scale purification of GST-tagged proteins.

A macroporous material composed of closely aggregated particles was prepared by cryostructuration of N-isopropylacrylamide-co-N-hydroxymethylacrylamide (NIPA-co-HMAm) particle suspensions. The formed structure was maintained by the formation of covalent bonds through self-crosslinking between the particles while the system was in a semi-frozen state thus avoiding the need to freeze-dry the sample. This resulted in macroporous structure composed of closely aggregated thermoresponsive particles which exhibit an ultrafast temperature response. The response rate can be attributed both to the macroporous structure as well as the fast responsive properties of the individual particles.

The extraordinary mechanical and swelling/deswelling properties of nanocomposite (NC) gels are attributed to their unique organic (polymer)/inorganic (clay) network structure. In this study, poly(N-isopropylacrylamide) (PNIPA) was successfully separated from an NC gel network by decomposing the clay (hectorite) using hydrofluoric acid (HF). A very low HF concentration (0.2 wt.-%) was adequate for the decomposition of the clay without causing any damage to PNIPA. The separated PNIPA had a high $\overline M _{\rm w}$ (=5.5 × 10(6) g · mol(-1) ). Also, $\overline M _{\rm w}$ was almost constant regardless of the clay concentration (C(clay) = 1-25 × 10(-2) mol · l(-1) ), even though the properties of the NC gel varied widely over this C(clay) range. Comparisons of NC gels, PNIPA, and SiO(2) -NC gels indicated that the clay platelets specifically play an important role in NC gels.

A novel semi-interpenetrating polymer network based on alginate and poly(N-isopropylacrylamide) (PNiPAAm) has been synthesized that shows response to temperature and magnetic fields. Highly homogeneous porous hydrogels are obtained by copolymerizing N-isopropylacrylamide and bis-acrylamide in the presence of an aqueous alginate solution. The synthesis of magnetic iron oxides by in-situ oxidation of iron cations coordinated to the alginate network results in a hydrogel with an enhanced deswelling rate with respect to pure PNiPAAm.

The 2-chloropropionamide derivative featuring an azido group is used as the initiator for the ATRP of N-isopropylacrylamide (NIPAM) with copper(i) chloride (CuCl) and tris[2-(dimethyl-amino)ethyl]amine (Me 6 TREN) to produce the PNIPAM end-functionalized with an azido group. Subsequently, the 'click' reaction between the azido end-group and acetylene derivatives is demonstrated to produce PNIPAM in which the end-groups are modified by the phenyl, 4-phenoxyphenyl, butyl, octyl, carboxylic acid, and hydroxymethyl groups. The resulting PNIPAM derivatives show a LCST that ranges from 34.8 to 44.6 °C depending on the introduced end-group.

Surfactant-grafted hydrogels with a fast response to temperature were prepared. In order to clarify the mechanism of rapid shrinking, the effects of the grafted surfactant and the homogeneity of the main chain were investigated. Poly(NIPAAm-co-S180A) gels prepared using a chemical cross-linker (bis-PNS gels) exhibited rapid shrinking, as did PNS gels prepared by γ-ray irradiation (y-PNS gels). This suggested that the rapid shrinking of the PNS gel did not depend on the homogeneity of the main-chain structure. The shrinking kinetics of the bis-PNS gels depended on the amount of the introduced surfactant, which means that shrinking is enhanced by micelle formation as a dynamic driving force. From the analysis by dynamic light scattering (DLS) and scanning microscopic light scattering (SMILS), it was suggested that the micelle structure, which induced rapid shrinking, existed in the bis-PNS gel.

In this study, the hydrophobic liquid template method was firstly used to prepare temperature sensitive, porous poly(N -isopropylacrylamide) (PNIPAAm) hydrogel. During the radical polymerization, hydrophobic polydimethylsiloxane (PDMS) and surfactant sodium dodecyl sulfate (SDS) were used as liquid templates and stabilizer, respectively. After removal of the liquid templates, porous PNIPAAm hydrogel was obtained. This gel exhibited superfast shrinking properties when being transferred from below to above the lower critical solution temperature (LCST), which was ascribed to the interconnected porous structures.

A series of novel pH- and temperature-responsive diblock copolymers composed of poly(N-isopropylacrylamide) (PNIPAM) and poly[(L-glutamic acid)-co-(gamma-benzyl L-glutamate)] [P(GA-co-BLG)] were prepared. The influence of hydrophobic benzyl groups on the phase transition of the copolymers was studied for the first time. With increasing BLG content in P(GA-co-BLG) block, the thermal phase transition of the diblock copolymer became sharper at a designated pH and the critical curve of phase diagram of the diblock copolymer shifted to a higher pH region.

Metallo-supramolecular polymers offer attractive possibilities to combine the properties of polymers with the characteristics offered by the metal-ligand coordination. Here we present for the first time the combination of metal-bis(terpyridine) complexes and lower critical solution temperature (LCST) polymers that can be switched by addressing either the thermosensitive polymer or the metal complex. We describe a new strategy for the synthesis of poly(N-isopropylacrylamide) (PNIPAM) end functionalized with a terpyridine moiety, which is further used for the preparation of Fe II and Zn II -bis(terpyridine PNIPAM). The comparison of the LCST behavior of the uncomplexed ligands and their metal complexes that bear different counter ions is included. Furthermore, the switchability of the synthesized Fe II system is demonstrated by a decomplexation reaction followed by the characterization of the uncomplexed ligand.

A functional coil-rod-coil triblock copolymer containing a terfluorene unit as the rigid segment and poly(N-isopropylacrylamide) (PNIPAAm) as the flexible block was successfully synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization using terfluorene-based dithioester as the RAFT agent. The temperature-responsive optical properties were investigated with the aid of dynamic light scattering and fluorescence techniques. Additionally, the relationship between the optical properties and the reversible phase transition of the doping system formed by blending the copolymer with tetraphenylporphine tetrasulfonic acid was studied. Above the lower critical solution temperature, the energy transfer efficiency decreased as a result of the globule-to-coil transition from PNIPAAm segments. The result indicates that these copolymers have a potential to be used as responsive fluorescent probes in facile detection of dye-labeled biopolymers.

We report a novel multifunctional material, poly(N-isopropylacrylamide) (PNIPAAm) containing 2-(2-hydroxyphenyl)benzoxazole (HPBO), for sensing pH, zinc ion concentration, or temperature. By titration with zinc ions, a clear blue-shifted emission with a high quantum efficiency was detected since the zinc complex prevented the nonradiative decay pathways of the HPBO moiety. The fluorescence characteristics of the copolymer were similar at various acidic or neutral conditions. However, a large blue shift on the emission maximum was exhibited under the basic condition, due to the disruption of the ESIPT process by the phenolate anion. The LCST affected the fluorescence properties significantly at the basic condition because the incompatibility between the PNIPAAm chain and phenolated HPBO moieties resulted in aggregation formation. The present study demonstrates that the new benzoxazole-containing PINPAAm copolymer could be potentially used as multifunctional sensing material.

Adopting inorganic clay (hectorite) and MBA as physical and chemical cross-linking agents, respectively, PNIPAM microgels were synthesized by SFEP. The chemical structure and morphology of the microgels were confirmed by FTIR, WXRD, and SEM. The temperature-sensitivity of the microgels was investigated by DLS and UV spectrophotometers. The results inferred that clay platelets dispersed in an aqueous medium were fully exfoliated and could act as a kind of multifunctional cross-linking agent and significantly reduced the hydrodynamic diameters of the microgels. In fact, the hydrodynamic diameters of the PNIPAM microgels with clay as cross-linker ranged from 154 to 322 nm which was much smaller than that using MBA as chemical cross-linker, the later was in the range of 284–808 nm on heating from 5 to 50 °C.

This paper describes a simple and facile approach to fabricate well dispersed silver nanoparticles (AgNPs) in poly[N-isopropylacrylamide-co-(sodium acrylate)] hydrogels. The silver nanoparticles formed are spherical in shape with a narrow size distribution in the hydrogel networks in which the nanoparticles are stabilized by the polymer network. Uniformly dispersed silver nanoparticles were obtained with poly[N-isopropylacrylamide-co-[sodium acrylate)] hydrogels, whereas a poly(N-isopropylacrylamide)/poly(sodium acrylate) IPN gel showed aggregated nanoparticles. It is demonstrated that the hydrogel network structure determines the size and shape of the nanoparticles. These particles are more stable in the gel networks compared to other reduction methods. The hydrogel/silver nanohybrids were well characterized by XRD, UV-vis spectrometry, scanning electron microscopy and transmission electron microscopy.

Monodisperse thermosensitive PS-NIPA core-shell particles composed of a PS core and a cross-linked PNIPA shell can be successfully synthesized by a novel method: photoemulsion polymerization. Cryo-TEM images indicate clearly the core-shell morphology of the PS-NIPA particles: A homogeneous regular PNIPA shell has been affixed on the spherical PS core. DLS measurements indicate that the obtained PS-NIPA latex particles are thermosensitive. The shell of PNIPA networks with different cross-linking densities can shrink and re-swell with temperature and the volume transition temperature is around 32 °C in all cases.

Solutions of poly(N-isopropylacrylamide) (PNIPA) with added sodium dodecyl sulfate (SDS) were investigated by light scattering methods at temperatures of 15-40°C. The formation of well-defined nanoparticles of PNIPA was observed on heating at low SDS additions. The effects of PNIPA and SDS concentrations and the molecular weight of PNIPA on nanoparticle parameters were investigated. An interpretation based on stabilization of PNIPA nuclei by SDS was suggested.

This paper demonstrates a new, reliable, and simple method for fabricating micropattemed nanoparticle arrays that can serve as templates for the surface-initiated polymerization of polymer brushes. As a proof of concept, we micropatterned gold nanoparticles (Au-NPs, ≈10 nm) onto glass, silicon, polystyrene, and gold surfaces by a simple three-step process: (1) microcontact printing of soluble polymer, (2) incubation with a solution of Au-NPs, and (3) lift-off of the template in a mixture of ethanol and deionized water. 40 μm wide features were successfully fabricated without any significant defects or nonspecific adsorption on the background. To demonstrate the utility of these Au-NP templates, we subsequently polymerized N-isopropylacry-lamide by surface-initiated polymerization, using a surface-bound initiator.

Here we show a new design concept of functional polymer gel for rapid deswelling by utilizing micelle-forming ability of surfactant. A thermosensitive polymer bearing a surfactant was synthesized by using N-isopropylacrylamide and a reactive surfactant. Above lower critical solution temperature, the grafted surfactant acts to form micelle structure. In the shrinking process, the inside water is rapidly squeezed out through hydrophilic channel between the formed micelles and consequently the gel shrinks quickly.

Robust thermosensitive PAH-g-PNIPAAm/PSS particles were prepared by addition of a poly(allylamine)-graft-poly(N-isopropylacrylamide) particle suspension into poly(styrene sulfonate) solution above the LCST of PAH-g-PNIPAAm. Scanning force microscopy revealed stable and well-separated particles in water at room temperature. The zeta-potential showed a negative surface charge of the particles. Their thermosensitive behavior was demonstrated by dynamic light scattering. The release of rhodamine 6G loaded particles could respond to the incubation temperature.

Summary: Novel temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm) nanoparticle-containing PNIPAAm hydrogels were prepared by radical polymerization. In comparison with conventional PNIPAAm hydrogels, the PNIPAAm gels thus prepared exhibit much faster response rates as the temperature is raised above the lower critical solution temperature. The improved properties are a result of the incorporation of PNIPAAm particles, which first shrink and then generate pores for water molecules to be quickly squeezed out of the bulky PNIPAAm gels. Schematic illustration of the shrinking process: (I) First PNIPAAm particles shrink and generate pores; (II) the bulky gels then shrink further at a rapid rate.

Summary: Self-oscillating polymers and nano-gel particles consisting of N-isopropylacrylamide and the ruthenium catalyst of the Belousov-Zhabotinsky reaction have been prepared. In order to clarify the crosslinking effect on the self-oscillating behavior, the phase transition behaviors were investigated by measuring the transmittance and the fluorescence intensity of the polymer solution and the gel bead suspension. Cooperative effects due to crosslinking will play an important role for the design of nanoactuators. Chemical structure of poly(NIPAAm-co-Ru(bpy)3).

A novel thermosensitive amphiphilic copolymer of PNIPAm grafted polyphosphazene (PNIPAm-g-PPP) has been synthesized through a co-substitution reaction of poly(dichlorophosphazene) with amino terminated NIPAm oligomer and glycine ethyl ester (GlyEt). The polymer obtained had a molar ratio of 1:5.25 PNIPAm to GlyEt and had a lower critical solution temperature (LCST) near 30 °C. The formation of polymeric micelles was confirmed by fluorescence, dynamic light scattering and transmission electron microscopy measurements.

Specific temperature-responsive biodegradable hydrogels were synthesized and characterized in terms of their regulation of enzymatic accessibility based on the physical properties of the temperature-responsive polymers. The hydrogels consist of glycidyl methacrylate-modified dextran grafted with the poly(N-isopropylacrylamide) (PNIPAAm) homopolymer, and cross-linked by co-polymerization with NIPAAn and N,N-dimethylacrylamide (DMAAm). The coil-globule change in the grafted poly(NIPAAm) chains and only a slight dehydration of the poly(NIPAAm-co-DMAAm) cross-linkers are effective in controlling the enzymatic degradation over a specific temperature range. The thermo-responses of the graft chains (steric hindrance) and the crosslinkers (slight deswelling of the hydrogel networks) control the enzymatic degradation of the hydrogel.

A novel approach to load a hydrophilic bovine serum albumin into drug carriers was proposed in terms of temperature-programmed shell-in-shell structures, which were fabricated with poly(N-isopropyl ...

Macroporous temperature-sensitive poly(N-isopropylacrylamide) (PNIPA) hydrogels were prepared by a novel phase-separation technique to improve the response properties. In comparison with a conventional PNIPA hydrogel prepared in water, these macroporous hydrogels, prepared by polymerization in aqueous sucrose solutions, have higher swelling ratios at temperatures below the lower critical solution temperature and exhibit much faster response rates to temperature changes. Scanning electron microscopy image of the surface of a PNIPA hydrogel, prepared in 1.50 M aqueous sucrose solution.

Thermoresponsive poly(N-isopropylacrylamide)/dextran hybrid particles were formed by surface-initiated, aqueous atom transfer radical polymerization via the attachment of a polymerization initiator onto dextran microspheres and polymerization of N-isopropylacrylamide. The resulting hybrid particles were about 250 μm in diameter, and showed thermoresponsiveness: the average diameter changed from 273 μm to 214 μm when the temperature was increased from 25°C to 40°C (22% decrease).

Temperature-triggered switchable nanofibrous membranes are successfully fabricated from a mixture of cellulose acetate (CA) and poly(N-isopropylacrylamide) (PNIPAM) by employing a single-step direct electrospinning process. These hybrid CA-PNIPAM membranes demonstrate the ability to switch between two wetting states viz. superhydrophilic to highly hydrophobic states upon increasing the temperature. At room temperature (23 °C) CA-PNIPAM nanofibrous membranes exhibit superhydrophilicity, while at elevated temperature (40 °C) the membranes demonstrate hydrophobicity with a static water contact angle greater than 130°. Furthermore, the results here demonstrate that the degree of hydrophobicity of the membranes can be controlled by adjusting the ratio of PNIPAM in the CA-PNIPAM mixture.

Spherical single-chain-particles of poly-(N-isopropylacrylamide) were prepared in aqueous solution above the lower critical solution temperature upon the addition of sodium dodecyl sulfate. The size of the single chain-particles was investigated by means of transmission electron microscopy and viscosity measurements of the corresponding solutions, indicating the absence of interchain entanglements among the single-chain-particles.

A series of CB[6]-based macroinitiators with "n" bromo-initiation sites on the "equator" of CB[6] is developed for the synthesis of CB[6]-star poly(N-isopropylacrylamide) (CB[6]-star PNIPAM) by atom transfer radical polymerization. By taking advantage of the exceptional binding affinity of the CB[6] core, CB[6]-star PNIPAM is used as a host macromolecule to construct large compound vesicles in the presence of protonated n-butylamine at pH 5.63. The deprotonated n-butylamine is detached from the CB[6] core at pH 11.1, which destructs the vesicular structures. For CB[6]-star PNIPAM, the thermoresponsive properties can be adjusted by simply changing the formation and destruction of the inclusion complexes of the CB[6] core with n-butylamine. These results suggest that the prepared CB[6]-star PNIPAM shows pH and temperature responsiveness, which has great potential for the design of a dual response smart material.

Poly-(N-isopropylacrylamide) (PNIPA) hydrogel films doped with uniaxially aligned liquid crystalline (LC) nanosheets adsorbed with a dye are synthesized and its anomalous photothermal deformation is demonstrated. The alignment of the nanosheet LC at the cm-scale is easily achieved by the application of an in-plane or out-of-plane AC electric field during photo-polymerization. A photoresponsive pattern is printable onto the gel with μm-scale resolution by adsorption of the dye through a pattern-holed silicone rubber. When the gel is irradiated with light, only the colored part is photothermally deformed. Interestingly, the photo-irradiated gel shows temporal expansion along one direction followed by anisotropic shrinkage, which is an anomalous behavior for a conventional PNIPA gel.

A diblock copolymer of poly(N-isopropylacrylamide) and poly(ethylene oxide) (PiPA-b-PEO) has been prepared by radical polymerization with a ceric ion initiation system. Its thermosensitive micellization has been investigated by means of IR and fluorescence spectroscopy. The PiPA segments are critically dehydrated above 33.5°C (5 wt.-%) and associate through hydrophobic interaction to form the hydrophobic core of the micelle. In contrast, the change in the hydration state of the PEO segments upon micellization is small.