Search Results (375)

Despite its widespread application in targeted drug delivery, soft robotics, and smart screens, magnetic hydrogel still faces challenges from lagging mechanical performance to sluggish response times. In this paper, a methodology of in situ generation of magnetic hydrogel based on 3D printing of poly-N-isopropylacrylamide (PNIPAM) is presented. A temperature-responsive PNIPAM hydrogel was prepared by 3D printing, and Fe₂O₃ magnetic particles were generated in situ within the PNIPAM network to generate the magnetic hydrogel. By forming uniformly distributed magnetic particles in situ within the polymer network, 3D printing of customized magnetic hydrogel materials was successfully achieved. The bilayer hydrogel structure was designed according to the different swelling ratios of temperature-sensitive hydrogel and magnetic hydrogel. Combined with the excellent mechanical properties of PNIPAM and printable magnetic hydrogel, 4D-printed remote magnetic field triggered shape morphing of bilayers of five-petal flower-shaped hydrogels was presented, and the deformation process was finished within 300 s. Full article

Understanding the adsorption features of polymer microgels with different chemical compositions and structures is crucial in studying the mechanisms of respective emulsion stabilization. Specifically, the use of stimuli-responsive particles can introduce new properties and broaden the application range of such complex systems. Recently, we demonstrated that emulsions stabilized by microgels composed of interpenetrating networks (IPNs) of poly-N-isopropylacrylamide (PNIPAM) and polyacrylic acid (PAA) exhibit higher colloidal stability upon heating compared to PNIPAM homopolymer and other relevant PNIPAM-based copolymer counterparts. In the present work, using pendant drop tensiometry, we studied the evolution of water–tetradecane interfacial tension during the adsorption of PNIPAM-PAA IPN particles, comparing them with single-network P-(NIPAM-co-AA) and PNIPAM microgels. The results showed that, despite having the same chemical composition, copolymer particles exhibit completely different adsorption behavior in comparison to other microgel architectures. The observed disparity can be attributed to the nonuniform distribution of charged acrylic acid groups within the P-(NIPAM-co-AA) network obtained through precipitation polymerization. Oppositely, the presence of IPN architecture provides a uniform distribution of different monomers inside respective microgels. Additionally, hydrogen bonding between PNIPAM and PAA subchains appears to reduce the electrostatic energy barrier, enhancing the ability of IPN particles to successfully cover the liquid interface. Overall, our findings confirm the efficiency of using PNIPAM-PAA IPN microgels for the preparation of oil-in-water emulsions and their stability, even when the temperature rises above the lower critical solution temperature of PNIPAM. Full article

A two-dimensional array of microfluidic ports with remote-controlled valve actuation is of great interest for applications involving localized chemical stimulation. Herein, a macroporous silicon-based platform where each pore contains an independently controllable valve made from poly(N-isopropylacrylamide) (PNIPAM) brushes is proposed. These valves are coated with silica-encapsulated gold nanorods (GNRs) for NIR-actuated switching capability. The layer-by-layer (LBL) electrostatic deposition technique was used to attach the GNRs to the PNIPAM brushes. The deposition of GNRs was confirmed by dark-field optical microscopy, and the localized surface plasmon resonance (LSPR) of the deposited GNRs was analyzed using UV-Vis spectra. To evaluate the chemical release behaviors, fluorescein dye was employed as a model substance. The chemical release properties, like OFF-state diffusion through the valve, the ratio between ON-state and OFF-state chemical release, and the rapidness of chemical modulation of the valve, were investigated, varying the PNIPAM brush thickness. The results indicate that enhancing the thickness of the PNIPAM brush in our platform improves control over the chemical modulation properties. However, excessive increases in brush length may lead to entanglement, which negatively impacts the chemical modulation efficiency. Full article

Polymer-based aqueous redox flow batteries (RFBs) are attracting increasing attention as a promising next-generation energy storage technology due to their potential for low cost and environmental friendliness. The search for new redox-active organic compounds for incorporation into polymer materials is ongoing, with anolyte-type compounds in high demand. In response to this need, we have synthesized and tested a range of new water-soluble redox-active s-tetrazine derivatives, including both low molecular weight compounds and polymers with different architectures. S-tetrazines are some of the smallest organic molecules that can undergo a reversible two-electron reduction in protic media, making them a promising candidate for anolyte applications. We have successfully modified linear polyacrylic acid and poly(N-isopropylacrylamide-co-acrylic acid) microgels with pendent 1,2,4,5-tetrazine groups. Electrochemical testing has shown that the new tetrazine-containing monomers and, importantly, the water-soluble redox polymers, both linear and microgel, demonstrate the chemical reversibility of the reduction process in an aqueous solution containing acetate buffer. This expands the range of water-soluble anodic materials suitable for water-based organic RFBs. The reduction potential value can be adjusted by changing the substituents in the tetrazine core. It is also worth noting that the choice of electrode material plays an important role in the kinetics of the tetrazine reaction: the use of carbon electrodes is particularly beneficial. Full article

The synthesis of poly(N-isopropyl acrylamide) (pNIPA)-based polymers via the surfactant-free precipitation polymerization (SFPP) method produced thermosensitive nanospheres with a range of distinctive physicochemical properties. Nano- and microparticles were generated using various initiators, significantly influencing particle characteristics, including the hydrodynamic diameter (D_H), which varied from 87.7 nm to 1618.1 nm. Initiators, such as potassium persulfate and 2,2′-azobis(2-methylpropionamidine) dihydrochloride, conferred anionic and cationic functionalities, respectively, impacting the electrokinetic potential (EP) of the particles. Notably, certain particles with cationic initiators exhibited negative EP values at 18 °C, attributed to residual initiator components that affected the surface charge distribution. The presence of hydrophilic N-(2-hydroxyethyl)acrylamide (HEAA) segments also influenced solubility and phase transition behaviors, with critical dependencies on the HEAA/NIPA (N-isopropyl acrylamide) molar ratios. EP measurements taken at 18 °C and 42 °C revealed substantial differences, primarily governed by the initiator type and polymer composition. Observed variations in particle stability and size were associated with the choice of crosslinking agents and comonomer content, which affected both D_H and EP in distinct ways. This study provides insights into key factors influencing colloidal stability and electrostatic interactions within thermosensitive polymer systems, underscoring their potential applications in biomedical and industrial fields. Full article

An imbalance in the body’s pH or temperature may modify the immune response and result in ailments such as autoimmune disorders, infectious diseases, cancer, or diabetes. Dual pH- and thermo-responsive carriers are being evaluated as advanced drug delivery microdevices designed to release pharmaceuticals in response to external or internal stimuli. A novel drug delivery system formulated as hydrogel was developed by combining a pH-sensitive polymer (the “biosensor”) with a thermosensitive polymer (the delivery component). Thus, the hydrogel was created by cross-linking, using a solvent-free thermal approach, of poly(N-isopropylacrylamide-co-N-hydroyethyl acrylamide), P(NIPAAm-co-HEAAm), and poly(methylvinylether-alt-maleic acid), P(MVE/MA). The chemical structure of the polymers and hydrogels was analyzed using Fourier-transform infrared (FTIR) and proton nuclear magnetic resonance (¹H NMR) spectroscopies. The pH/thermosensitive hydrogel loses its thermosensitivity under physiological conditions but, remarkably, can recover the thermosensitive capabilities when certain physiologically active biomolecules, acting as triggering agents, electrostatically interact with pH-sensitive units. Our research aimed to develop a drug delivery system that could identify the disturbance of normal physiological parameters and instantaneously send a signal to thermosensitive units, which would collapse and modulate the release profiles of the drug. Full article

Currently, polymer actuators capable of photothermal response are being developed to be more sensitive and repeatable. In this work, a three-layered structured soft film actuator (NA/PET/NI-3) was designed by combining poly(N-isopropylacrylamide) (PNIPAM), poly(N-(2-aminoethyl)-acrylamide) (PANGA) and poly(ethylene glycol-co-terephthalate) (PET) film. Coconut water and PEI were used to synthesize a new kind of carbon nanosheet (PEI-CCS), which, when triggered by near-infrared light, will enable photothermal bending behavior in the micrometer-scale NA/PET/NI-n film, while PET served as the supporting and heat conducting layer. This three-layered actuator utilized the synergistic effects of two kind of polymers, PNIPAM and PNAGA, on either side of PET, with the upper critical solution temperatures and lower critical solution temperatures when subjected to temperature changes. This bilateral polymer design exhibited a rapid response under near-infrared light stimulation, bending to 180° within 4 s and recovering to its original shape within 30 s. When the bending process was set to 90° as in the standard experiment, NA/PET/NI-3 responded within 2 s and recovered within 8 s. NA/PET/NI-3 also demonstrated good reversibility and repeatability, capable of undergoing reversible driving over 120 times. The design and preparation of this actuator provided new ideas for the development of polymer soft actuators. Full article

The present study synthesized silver nanoparticles supported on a thermosensitive polymer with a core–shell structure, formed by a polystyrene (PS) core and a poly(N-isopropylacrylamide) (PNIPAM)/Poly(N, N-methylenebisacrylamide) (MBA) shell. The PS core was synthesized via semicontinuous heterophase polymerization at a flow of 0.073 g/min, enabling polystyrene nanoparticles with an average size (Dz) of 35.2 nm to be obtained. In the next stage, the conditions required for polymerization synthesis were established in seeded microemulsion using PS nanoparticles as seed and semicontinuously adding the thermosensitive shell monomer (PNIPAM/MBA) under monomer-flooded conditions to favor shell formation. The non-homopolymerization of PNIPAM/MBA was demonstrated by obtaining nanoparticles with a core–shell structure, with average particle sizes of 41 nm and extremely low and narrow polydispersity index (PDI) values (1.1). The thermosensitive behavior was analyzed by QLS, revealing an average shrinkage of 4.03 nm and a percentage of shrinkage of 23.7%. Finally, silver nanoparticles were synthesized on the core–shell heat-sensitive nanoparticles in a colloidal solution containing the latices, while silver nanoparticles were anchored onto the cross-linked heat-sensitive network via the formation of complexes between the Ag+ ions and the nitrogen contained in the PNIPAM/MBA network, favoring anchorage around the network and maintaining a size of 5 nm. Full article

This study aims to design microgels that are thermo- and pH-sensitive for controlled doxorubicin (Dox) release in response to tumor microenvironment changes. N-isopropylacrylamide (NIPAAm) is widely used for thermoresponsive tumor-targeted drug delivery systems for the release of therapeutic payloads in response to temperature changes. Herein, a NIPAAm microgel (MP) that is responsive to temperature and pH was designed for the smart delivery of Dox. MP was made from NIPAAm, and polyethylene glycol methyl ether methacrylate (PEGMA) was copolymerized with 5%, 10%, or 15% mol of methacryloylamido hexanoic acid, (CAM5) an amphiphilic acid. We characterized the microgels using FTIR-ATR, DLS, and FESEM. The MP 10% CAM5 exhibited a particle size of 268 nm, with a transition temperature of 44 °C. MP had a drug loading capacity of 13% and entrapment efficiency of 87%. Nearly 100% of the Dox was released at pH 5 and 42 °C, compared to 30% at pH 7.4 and 37 °C. MP 10% CAM5 showed cytocompatibility in HeLa cells using the MTT assay. However, the cell viability assay showed that dox-MP was twice as effective as free Dox. Specifically, 3 μg/mL of free Dox resulted in 74% cell viability, while the same doses of Dox in NP reduced it to 35%. These results are promising for the future tumor-targeted delivery of antineoplastic-drugs, as they may reduce the side effects of Dox. Full article

Hydrogel nanocomposites that respond to external stimuli and possess switchable electrical properties are considered as emerging materials with potential uses in electrical, electrochemical, and biological devices. This work reports the synthesis and characterization of thermo-responsive and electroconductive hydrogel nanocomposites based on poly(N-isopropylacrylamide) (PNiPAAm) and gold nanoparticles (nanospheres—AuNPs and nanorods—AuNRs) using two different synthetic techniques. Method I involved γ-irradiation-induced crosslinking of a polymer matrix (hydrogel), followed by radiolytic in situ formation of gold nanoparticles, while Method II included the chemical synthesis of nanoparticles, followed by radiolytic formation of a polymer matrix around the gold nanoparticles. UV–Vis spectral studies revealed the presence of local surface plasmon resonance (LSPR) bands characteristic of nanoparticles of different shapes, confirming their formation and stability inside the polymer matrix. Morphological, structural, and physicochemical analyses indicated the existence of a stable porous polymer matrix, the formation of nanoparticles with a face-centered cubic structure, increased swelling capacity, and a slightly higher volume phase transition temperature (VPTT) for the hydrogel nanocomposites. Comparative electrochemical impedance spectroscopy (EIS) showed an increase in conductivity for the nano Au-PNiPAAm hydrogel nanocomposites compared to the PNiPAAm hydrogel, with a considerable rise detected above the VPTT. By reverting to room temperature, the conductivity decreased, indicating that the investigated hydrogel nanocomposites exhibited a remarkable reversible “on–off” thermo-switchable mechanism. The highest conductivity was observed for the sample with rod-shaped gold nanoparticles. The research findings, which include optical, structural, morphological, and physicochemical characterization, evaluation of the efficiency of the chosen synthesis methods, and conductivity testing, provide a starting point for future research on the given nanocomposite materials with integrated multifunctionality. Full article

A series of copolymers containing a thermo-responsive biocompatible first block of poly[di(ethylene glycol) methyl ether methacrylate)-co-(oligo(ethylene glycol) methyl ether methacrylate], P(DEGMA-co-OEGMA) were chain-extended to incorporate either poly(N-isopropylacrylamide), PNIPAAm or poly(N-isopropylacrylamide-co-butyl acrylate), P(NIPAAm-co-BA) as second thermo-responsive block using reversible addition–fragmentation chain transfer (RAFT) polymerization. P(DEGMA-co-OEGMA)-b-PNIPAAm copolymers showed two response temperatures at 33 and 43 °C in an aqueous solution forming stable aggregates at 37 °C. In contrast, P(DEGMA-co-OEGMA)-b-P(NIPAAm-co-BA) copolymers showed aggregation below room temperature due to the shift in response temperature provoked by the presence of hydrophobic butyl acrylate (BA) units, and shrinkage upon heating up to body temperature, while maintaining the second response temperature above 40 °C. The terminal trithiocarbonate group of the block copolymers was modified to a thiol functionality and used to stabilize gold nanorods (GNRDs) via the “grafting to” approach. The Localized Surface Plasmon Resonance (LSPR) absorption band of GNRDs with an aspect ratio of 3.9 (length/diameter) was located at 820 nm after surface grafting with block copolymers showing a hydrodynamic diameter of 160 nm at 37 °C. On the other hand, the stability of the P(DEGMA-co-OEGMA)-b-PNIPAAm@GNRDs and P(DEGMA-co-OEGMA)-b-P(NIPAAm-co-BA)@GNRDs nanohybrids was monitored for 8 days; where the LSPR absorption band did not shift or show any broadening. Aqueous dispersed nanohybrids were irradiated with a near-infrared laser (300 mW), where the temperature of the surroundings increased 16 °C after 16 min, where conditions for no precipitation were determined. These tailored temperature-responsive nanohybrids represent interesting candidates to develop drug nanocarriers for photo-thermal therapies. Full article

Today, hydrogel dressings that can protect injury sites and effectively promote healing have become highly desirable in wound management. Therefore, multifunctional silver-poli(N-isopropylacrylamide/itaconic acid) (Ag-P(NiPAAm/IA)) hydrogel nanocomposites were developed for potential application as topical treatment dressings. The radiolytic method, used for the crosslinking of the polymer matrix as well as for the in situ incorporation of silver nanoparticles (AgNPs) into the polymer matrix, enables the preparation of hydrogel nanocomposites without introducing harmful and toxic agents. Moreover, materials produced using γ-irradiation are simultaneously sterilized, thus fulfilling one of the basic requirements regarding their potential biomedical applications. The NiPAAm/IA ratio and the presence of AgNPs influenced the microstructural parameters of the investigated systems. Increasing the IA content leads to the formation of a more porous polymer matrix with larger pores, while the incorporated AgNPs act as additional junction points, decreasing the porosity and pore size of the resulting nanocomposite hydrogels. Swelling studies showed that most investigated systems uptake the fluids from their surroundings by non-Fick diffusion. Further, the Ag⁺ ion release, antibacterial activity, and cytotoxicity of Ag-P(NiPAAm/IA) hydrogel nanocomposites were examined to evaluate their biomedical potential. All hydrogel nanocomposites showed an initial burst release of Ag⁺ ions (useful in preventing bacteria adherence and biofilm formation), followed by a slower release of the same (ensuring sterility for longer use). An antibacterial activity test against Escherichia coli and Staphylococcus aureus showed that Ag-P(NiPAAm/IA) hydrogel nanocomposites, with silver concentrations around 10 ± 1 ppm, successfully prevent bacterial growth. Finally, it was shown that the investigated hydrogel nanocomposites do not exhibit a cytotoxic effect on human keratinocyte HaCaT cells. Therefore, these multifunctional hydrogel nanocomposites may promote wound repair and show promising potential for application as functional wound dressing. Full article

Cyclic polymers have many interesting properties compared to their linear analogs, but there are very few examples of their synthesis. This is because most cyclic polymers have been synthesized by stepwise processes, including synthesizing homo- or hetero-telechelic end-functionalized precursor polymers and consecutive intramolecularly coupling of both ends of the polymers. This requires a complicated synthesis, and the product yields are very low because the target cyclic polymers are usually synthesized under highly dilute conditions, consequently, making it difficult to systematically analyze the properties of cyclic polymers. In the present research, we have synthesized cyclic polymers using a ring expansion polymerization method. Particularly, the ring expansion RAFT polymerization (RE-RAFT polymerization) that we have developed using a cyclic chain transfer agent is a smart method that can synthesize cyclic polymers very efficiently. In this paper, we successfully synthesized cyclic-poly(N-isopropylacrylamide), which is widely known as a thermo-responsive polymer, by RE-RAFT polymerization. Furthermore, we have compared the thermo-responsive properties of the cyclic-poly(N-isopropylacrylamide)s with those of their linear analogs. Full article

For the first time, we introduced chemomechanical self-oscillating poly(N-isopropylacrylamide)-based gels containing catalytically active Fe or Ru complexes both as crosslinkers and as pendant groups. All the obtained gels exhibited sustained autonomous oscillations driven by the Belousov–Zhabotinsky reaction within their structure. The Ru complex-based gels also demonstrated pronounced chemomechanical oscillations; they periodically swelled/shrunk when the catalyst was reduced/oxidized. It was found that the combination of catalytically active cross-linking and pendant Ru complexes in the same gel led to a change in the structure of the gel and a significant increase in the amplitude of its mechanical oscillations. The proposed approach allowed for increasing the amplitude of the mechanical oscillations of self-oscillating gels and opened up new possibilities for adjusting their characteristics. We believe that these gels hold potential for the development of soft actuators and systems capable of signal processing through propagating and interacting chemical waves. Full article

Natural polysaccharides can serve as carriers of genes owing to their intrinsic biocompatibility, biodegradability, and low toxicity. Additionally, they can be easily chemically modified, e.g., through grafting, leading to hybrid synthetic–biological copolymers with additional functionalities. In this work we report on the electrostatic interaction between a chitosan-g-poly(N-isopropylacrylamide) (Chit-g-PNIPAM) copolymer and DNA macromolecules of different lengths (i.e., 50 and 2000 bp), towards the construction of polyplexes that can serve as potential gene delivery systems. At the basic science level, the work aims to elucidate the effects of DNA length on the structural and physicochemical properties of the thermoresponsive hybrid macromolecular assemblies. The protonated amino groups on the chitosan backbone enable electrostatic binding with the anionic phosphate groups of the DNA molecules, while the PNIPAM side chains are expected to impart thermoresponsive properties to the formed polyplexes. Different amino to phosphate group (N/P) mixing ratios were examined, aiming to produce stable dispersions. The physicochemical properties of the resulting polyplexes were investigated by dynamic and electrophoretic light scattering (DLS and ELS), while their morphology was studied by scanning-transmission electron microscopy (STEM). Moreover, their response to changes in temperature and ionic strength, as well as their stability against biological media, was also examined. Finally, the binding affinity of the copolymer towards DNA was evaluated through fluorescence spectroscopy, using ethidium bromide quenching assays, while infrared spectroscopy was used to investigate the structure of the incorporated DNA chains. Full article