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.
Summary: 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.
Schematic representation of the preparation of Ag nanoparticles in hydrogel networks. 相似文献
Two kinds of representative polymers, poly(N‐isopropylacrylamide) (PNIPAAm) and β‐cyclodextrin (β‐CD) were selected and modified with azide and alkyne fucntional groups, respectively. When the solutions of these two modified polymers were mixed together, a cross‐linking reaction, a type of Huisgen's 1,3‐dipolar azide‐alkyne cycloaddition, occurred in the presence of Cu(I) catalyst. The strategy described here provides several advantages for the hydrogel formation including mild reaction conditions and controllable gelation rate. The resulted hydrogels were studied in terms of scanning electric microscopy (SEM), equilibrium swelling ratio and swelling/shrinking kinetics. The data obtained demonstrated the hydrogels had a porous structure as well as favorable thermosensitivity.
A dextran‐based dual‐sensitive polymer is employed to endow gold nanoparticles with stability and pH‐ and temperature‐sensitivity. The dual‐sensitive polymer is prepared by RAFT polymerization of N‐isopropylacrylamide from trithiocarbonate groups linked to dextran and succinoylation of dextran after polymerization. The functionalized nanoparticles show excellent stability under various conditions and can be stored in powder‐form. UV and DLS measurements confirm that the temperature‐induced optical changes and aggregation behaviors of the particles are strongly dependent on pH.
A novel amphiphilic diblock copolymer composed of a hydrophilic poly(ethylene oxide) block and a hydrophobic block copolymerized by azobenzene‐containing methacrylate and N‐isopropylacrylamide was synthesized using ATRP. The polymer micelles showed dual responsiveness to heat and light. The size of the micelles was dependent on temperature and the encapsulated substance in the hydrophobic cores was released during heating and cooling processes. The hydrophobicity of the micellar cores appeared as a reversible change in response to light with neither disruption of the micelles nor leakage of the encapsulated substance while H‐aggregation of the azobenzene moieties was detected.
In this paper, self‐assembled polymeric toroids formed by a temperature‐driven process are reported. Rhodamine B (RhB) end‐capped poly(N‐isopropylacrylamide) (PNIPAAm) demonstrating a lower critical solution temperature (LCST) is prepared. In a two‐phase system, the polymer in the aqueous phase could move to the chloroform phase on raising the temperature above its LCST. This temperature‐driven process results in the formation of polymeric toroids in the chloroform phase, and the strategy affords a new pathway to toroidal self‐assembly of polymers. Moreover, the photoluminescent behavior of the RhB end‐capped PNIPAAm species formed by the process is also studied and discussed.
Distinct differences between the thermodynamics of open and closed cavities are observed in confinement free energy of macromolecules as a function of chain length and cavity radius and can be of special importance in the case of processes in spatially heterogeneous confinements encountered in various nano‐ and biostructures. In treatments of the confinement free energy, special attention is given to the equilibrium conditions (a full equilibrium for free exchange of macromolecules between cavity and bulk solution or a restricted equilibrium with number of chains in cavity constant) and associated polymer concentration changes. Increased chain stiffness brings about additional effects and complexity, for which the first results are presented here.
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. 相似文献
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.
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.
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.
Stimuli‐sensitive polymer materials have limited device functionality, design and manufacturing flexibility although they are pushed to enable smart device applications. Here we demonstrate the capability of integrating thermoresponsive poly(N‐isopropylacrylamide) (PNIPAAm) hydrogels with silicon nanoribbons, and enable the stiff silicon ribbons to become adaptive and drivable by the soft environmentally sensitive substrate, such as becoming mechanically stretched and compressed on temperature change. These and related soft/hard smart devices and systems may open new opportunities in biomedical applications.
Summary: The D ‐glucose imprinted core‐shell nanosphere with an average size of ≈60 to 80 nm showed a significant preference for the binding of D ‐glucose than the non‐imprinted core‐shell nanosphere. Depending on temperature, the binding site in the shell with N‐isopropylacrylamide oligomer underwent a significant change in binding affinity. In addition, the D ‐glucose imprinted core‐shell nanosphere showed a two times higher affinity for D ‐glucose than L ‐glucose, suggesting chiral recognition of the binding site. The core‐shell nanosphere reported here is a good biomimetic model system with a well‐defined morphology, high surface area, and variable binding affinity through a change in temperature.
D ‐glucose imprinted core‐shell nanospheres showed excellent binding over the non‐imprinted core‐shell nanosphere. 相似文献
Summary: A well‐dispersed gold nanoparticle/poly(N‐isopropylacrylamide) (PNIPAm) hydrogel nanocomposite with thermoswitchable electrical properties is prepared by the copolymerization of functional Au nanoparticles with N‐isopropylacrylamide. It is found that the electrical conductivity of the nanocomposite changes by two orders of magnitude at moderate temperature (Ttran) upon temperature stimuli. The change of electrical properties is reversible during a heating and cooling cycle.
Schematic illustration of the mechanism of the thermo‐switchable electronic properties of the Au nanoparticle/PNIPAm composite. 相似文献
We report a new type of step‐growth radical addition‐coupling polymerization (RACP) involving consecutive addition of carbon‐centered radical derived from α,α′‐dibromo dibasic ester to NO double bond of C‐nitroso compound followed by cross‐coupling of carbon‐centered radical and in situ formed nitroxyl radical, which produces alternating copolymers with high molecular weight and unimodal molecular weight distribution from saturated and unsaturated monomers.
An optimum nanoprecipitation technique for gelatin nanoparticles is established, based on aqueous gelatin solution and ethanolic solution containing stabilizer. Crosslinking with glutaraldehyde results in stable gelatine nanoparticles. Several factors such as the surfactant concentration, type of surfactant, type of nonsolvent and gelatin concentration are evaluated. Gelatin nanoparticles with 200–300 nm can be produced using 20–30 mg mL?1 of gelatin and a minimum of 7% w/v stabilizer (Poloxamer 407 or 188). Furthermore, methanol and ethanol are good nonsolvents, whereas other nonsolvents such as acetone, isopropyl alcohol, and acetonitrile, result in phase separation and visible precipitates. The entrapment efficiency of fluorescein‐isothiocyanate (FITC)‐dextran as model drug was determined to 50% with no substantial effect on particle size. 80% of the drug is only released after enzymatic digestion.
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.
Novel antigen responsive hydrogels were prepared by using polymerizable antibody Fab′ fragment from monoclonal anti‐fluorescein BDC1 antibody (IgG2a). To form Fab′ containing hydrogels, the polymerizable Fab′ fragment was copolymerized with N‐isopropylacrylamide (NIPAAm) and N,N′‐methylenebis(acrylamide) (MBAAm; crosslinker) using redox initiators. The thermosensitivity of the hydrogels decreased with increasing Fab′ fragment content. The antigen responsiveness of the hydrogels depended on the Fab′ content, pH, and temperature. When the hydrogels were alternately exposed to antigens fluorescein (FL) and polyamidoamine dendrimer (PAMAM)‐fluorescein (FD), significant reversible volume changes were observed for the hydrogel containing 50% (w/w) Fab′ fragment at 33.7 and 36.8 °C in acetate buffer (10 mM , pH 5.0), respectively, but not at 27.7 °C or in PBS buffer (10 mM , pH 7.4). No noticeable reversible volume changes were observed with pure PNIPAAm hydrogel and the gel containing 10% (w/w) Fab′ fragment.
Two chondrogenic factors, Dex and TGF‐β1, were incorporated into PLGA scaffolds and their chondrogenic potential was evaluated. The Dex‐loaded PLGA scaffold was grafted with AA and heparin, the heparin‐immobilized one was then reacted with TGF‐β1, yielding a PLGA/Dex‐TGF (PLGA/D/T) scaffold. The scaffolds were seeded with rabbit MSCs and cultured for 4 weeks. The results show that the scaffolds including chondrogenic factors strongly upregulated the expression of cartilage‐specific genes and clearly displayed type‐II collagen immunofluorescence. The functionalized PLGA scaffolds could provide an appropriate niche for chondrogenic differentiation of MSC without a constant medium supply of Dex and TGF‐β1.
