Dual thermo-responsive and ion-recognizable monodisperse microspheres

Development of a Potassium-Ion-Responsive Star Copolymer with Controlled Aggregation/Dispersion Transition

Stimuli-responsive star polymers are promising functional materials whose aggregation, adhesion, and interaction with cells can be altered by applying suitable stimuli. Among several stimuli assessed, the potassium ion (K⁺), which is known to be captured by crown ethers, is of considerable interest because of the role it plays in the body. In this study, a K⁺-responsive star copolymer was developed using a polyglycerol (PG) core and grafted copolymer arms consisting of a thermo-responsive poly(N-isopropylacrylamide) unit, a metal ion-recognizing benzo-18-crown-6-acrylamide unit, and a photoluminescent fluorescein O-methacrylate unit. Via optimization of grafting density and copolymerization ratio of grafted arms, along with the use of hydrophilic hyperbranched core, microsized aggregates with a diameter of 5.5 μm were successfully formed in the absence of K⁺ ions without inducing severe sedimentation (the lower critical solution temperature (LCST) was 35.6 °C). In the presence of K⁺ ions, these aggregates dispersed due to the shift in LCST (47.2 °C at 160 mM K⁺), which further induced the activation of fluorescence that was quenched in the aggregated state. Furthermore, macrophage targeting based on the micron-sized aggregation state and subsequent fluorescence activation of the developed star copolymers in response to an increase in intracellular K⁺ concentration were performed as a potential K⁺ probe or K⁺-responsive drug delivery vehicle.

Programming Colloidal Self-Assembled Patterns (cSAPs) into Thermo-Responsible Hybrid Surfaces for Controlling Human Stem Cells and Macrophages

Hybrid surfaces with tunable topography, chemistry, and stiffness have potential to rebuild native extracellular matrix (ECM) and manipulate cell behavior in vitro. However, the fabrication of controllable hybrid surfaces is still challenging. In this study, colloidal self-assembly technology was used to program particles into highly ordered structures with hybrid chemistry and stiffness at biointerfaces. These colloidal self-assembled patterns (cSAPs), including unary, binary, and ternary cSAPs, composed of silicon (Si), polystyrene (PS), and/or poly(N-isopropylacrylamide) (pNIPAM) nanogels (PNGs), were fabricated using either coassembly or layer-by-layer (LBL) methods. The selected binary cSAPs (i.e., PS/PNG and PNG/PS) have a tunable surface topography and wettability between 25 and 37 °C; thus, they can be used as dynamic cell culture substrates. Human adipose-derived mesenchymal stem cells (hASCs), bone marrow-derived mesenchymal stem cells (hBMSCs), and macrophages (THP-1) were investigated on these hybrid cSAPs under a static or dynamic system. The results showed that hybrid cSAPs significantly influenced the focal adhesions, cell morphology, cell migration, and gene expressions of stem cells. In general, stem cells had more vinculin puncta, smaller spreading size, and faster migration speed than the TCPS control. Hybrid cSAPs up-regulated gene expressions of focal adhesion kinase (FAK) and chondrocytes (AGG and SOX9) under static culture, while they also up-regulated osteocytes (COL1 and RUNX2) under dynamic culture. THP-1 macrophages were at M0 state on all cSAPs under static culture. However, cells became sensitive under dynamic culture. For example, some M1 genes (i.e., IL6, CD68, and TNFα) and M2 genes (i.e., IL10 and CD206) were down-regulated, while other M1 genes (i.e., IL1β) and M2 genes (i.e., TGF-β and IL1ra) were up-regulated, depending on the particle combinations. In conclusion, new hybrid cSAPs with thermoresponsive surface properties are versatile materials for stem cells and macrophages manipulation.

Microgel Particles at Interfaces: Phenomena, Principles, and Opportunities in Food Sciences

The use of soft microgel particles for stabilizing emulsions has captured increasing attention across a wide range of disciplines in the past decades. Being soft, the nanoparticles, which are spherical in solution, undergo a structure change when adsorbed at the oil-water interface. This morphology change leads to the special dynamic properties of interface layers and packing structures, which then alter the interfacial tension and rheological properties of the interface. In addition, emulsions stabilized by these particles, known as Pickering emulsions, can be triggered by changing a variety of environmental conditions, which is especially desirable in industrial applications such as oil transportation processes and biphasic catalysis, where the emulsions can be stabilized and destabilized on demand. Although many studies of the behavior of soft microgel nanoparticles at interfaces have been reported, there are still many challenges in gaining a full understanding of the structure, dynamics, and effective interactions between microgels at the interface. In this Feature Article, we address some of the most important findings and problems in the field. They include the adsorption kinetics of soft microgel particles, particle conformation at the interface, pH and thermal responsiveness, and the interfacial rheological properties of soft-particle-occupied interfaces. We also discuss some potential benefits of using emulsions stabilized by soft particles for food applications as an alternative to conventional surfactant-based systems. We hope to encourage further investigation of these problems, which would be very beneficial to extending this knowledge to all other related soft matter systems.

Potassium-sensitive poly(N-isopropylacrylamide)-based hydrogels for sensor applications

In situcrosslinking polymerization of potassium sensitive hydrogels for advancedin vivosensor applications is studied in detail.

Characterizing Viscoelastic Modulations in Biopolymer Hydrogels by Coherence-Gated Light Scattering

pH-responsive hydrogels are of great interest for the controlled release of drugs. However, the changes in the structural and mechanical properties of hydrogels during the pH-responsive swelling/contraction process remains largely unknown. In this article, we demonstrate that coherence-gated dynamic light scattering can be used to in situ characterize the structural dynamics of chitosan (CS) hydrogels at different pH values and show that the CS hydrogels undergo viscoelastic modulations during the swelling/contraction/recovery process induced by pH changes. The conditions for the CS hydrogels to undergo these modulations are found by continuously monitoring the nonequilibrium, long-term dynamical process. Our findings are in a close correspondence to the macroscopic observations made at time points where the CS hydrogels are at equilibrium.

Synthesis and evaluation of pH-sensitive, self-assembled chitosan-based nanoparticles as efficient doxorubicin carriers

A novel pH-responsive polymer based on amphiphilic N-acetyl histidine and arginine-grafted chitosan was synthesized using N-acetyl histidine as hydrophobic segment and arginine as hydrophilic segment by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide-mediated coupling reactions as anticancer drug delivery system for doxorubicin. The structure of the synthesized polymer was confirmed by Fourier transform infrared and ¹H nuclear magnetic resonance analysis. Due to self-association behavior, N-acetyl histidine and arginine-grafted chitosan structured nanoparticles with in size range of 204 nm. N-acetyl histidine and arginine-grafted chitosan with different substitution degree of N-acetyl histidine were initially prepared and characterized. The critical micelle concentration decreased with increasing substitution degree of N-acetyl histidine. Furthermore, N-acetyl histidine and arginine-grafted chitosan nanoparticles exhibited an acidic pH-triggered aggregation and disassembling nature. The doxorubicin-encapsulated nanoparticles based on synthesized conjugate ( N-acetyl histidine and arginine-grafted chitosan/doxorubicin nanoparticles) showed a sustained drug release pattern, which could be hastened under acidic pH conditions but delayed with increasing substitution degree of N-acetyl histidine. Anticancer effects demonstrated that N-acetyl histidine and arginine-grafted chitosan/doxorubicin nanoparticles could suppress both sensitive and resistant human breast tumor cell line (MCF-7) efficiently in a dose- and time-dependent pattern. Confocal microscopy results evidenced increased cellular uptake and enhanced retention of the synthesized nanoparticles in drug-resistant cells demonstrating better efficacy of nanoparticles over native doxorubicin. These results suggest that N-acetyl histidine and arginine-grafted chitosan/doxorubicin nanoparticles might be promising carriers for delivery of hydrophobic drug doxorubicin against drug-resistant tumors.

Hydrogel adsorbents of poly(N-isopropylacrylamide-co-methacryloyloxymethyl-12-crown-4) for Li+ recovery prepared by droplet microfluidics

This article describes the synthesis and application of hydrogel adsorbents for lithium ion (Li⁺) recovery from seawater.

Novel thermo-responsive hydrogel microspheres with calixcrown host molecules as cross-links for highly specific binding and controllable release of cesium

Novel thermo-responsive hydrogel microspheres containing calixcrown molecules as covalent cross-links for highly-specific binding and thermo-triggered release of cesium in seawater.

Synthesis of conductive magnetic nickel microspheres and their applications in anisotropic conductive film and water treatment

Synthesized conductive magnetic Ni microspheres not only can be used for anisotropic conductive films, but also can be used for rapid waste removal and detoxification extraction with a very simple and efficient procedure.

Controlled stimulation-burst targeted release by smart decentered core-shell microcapsules in gravity and magnetic field

By combining gravity and magnetic force, we have developed a versatile and facile microfluidic method for forming magnetic decentered core-shell microcapsules in which the directions of the oil core and the magnetic nanoparticles are either opposed or the same. When the temperature rises above the LCST of the PNIPAm, the shell shrinks rapidly and the core targets burst release towards the converse or the same direction as the magnet. By adjusting the direction of the magnet, the release direction of the active substance could be correspondingly accurately controlled.

In situ fabrication of a temperature- and ethanol-responsive smart membrane in a microchip

Here we report a simple and versatile strategy for the in situ fabrication of nanogel-containing smart membranes in microchannels of microchips. The fabrication approach is demonstrated by the in situ formation of a chitosan membrane containing poly(N-isopropylacrylamide) (PNIPAM) nanogels in a microchannel of a microchip. The PNIPAM nanogels, that allow temperature- and ethanol-responsive swelling-shrinking volume transitions, serve as smart nanovalves for controlling the diffusional permeability of solutes across the membrane. Such self-regulation of the membrane permeability is investigated by using fluorescein isothiocyanate (FITC) as a tracer molecule. This approach provides a promising strategy for the in situ fabrication of versatile nanogel-containing smart membranes within microchips via simply changing the functional nanogels for developing micro-scale detectors, sensors, separators and controlled release systems.

Temperature-Responsive Fluorescence Polymer Probes with Accurate Thermally Controlled Cellular Uptakes

Poly(N-isopropylacrylamide) (PNIPAAm)-based temperature-responsive fluorescence polymer probes were developed using radical polymerization, with 3-mercaptopropionic acid as the chain-transfer agent, followed by activation of terminal carboxyl groups with N-hydroxysuccinimide and reaction with 5-aminofluorescein (FL). The lower critical solution temperatures (LCSTs) of the resulting fluorescent polymer probes differed depending on the copolymer composition, and had a sharp phase-transition (hydrophilic/hydrophobic) boundary at the LCST. The cellular uptakes of the fluorescent polymer probes were effectively suppressed below the LCST, and increased greatly above the LCST. In particular, the cellular uptake of a copolymer with N,N-dimethylaminopropylacrylamide, P(NIPAAm-co-DMAPAAm2%)-FL (LCST: 37.4 °C), can be controlled within only 1 °C near body temperature, which is suitable for biological applications. These results indicated that the cellular uptakes of thermoresponsive polymers could be accurately controlled by the temperature, and such polymers have potential applications in discriminating between normal and pathological cells, and in intracellular drug delivery systems with local hyperthermia.

Response mechanism of the phase transitions of poly(n-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) using infrared spectroscopy

The thermal and ionic effects on the phase transitions of poly(N-isopropylacrylamide) (PNIPAAm) and its copolymer with benzo-18-crown-6-acrylamide, poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (PNIPAAm-co-BCAm), were investigated using infrared (IR) spectral variations of methyl (CH3), C=O, and amine (NH) groups. Subsequently, perturbation correlation moving-window two-dimensional correlation infrared spectroscopy (PCMW 2D-IR) was applied to clarify the differences in the phase-transition mechanisms of the polymers. The dominant influence on the phase-transition mechanism of PNIPAAm is whether the anion is evenly distributed in the bulk solution. The results show that the phase transition shifts to a lower temperature with increasing barium chloride (BaCl2) concentrations. In addition, the effect of the anion on the chemical group is homogeneous upon heating. As a result, the relevant transition temperature ranges have remain approximately constant. In contrast, the dominant influence on the phase-transition mechanism of PNIPAAm-co-BCAm is the interactions of the polymer chains with barium ions (Ba(2+)). The hydrophilic BCAm-Ba(2+) complexes distributed in the PNIPAAm-co-BCAm chain prevent the water molecules from leaving the polymer chains, which leads to an increase in the transition temperature and the complicated variation of the transition temperature range, as environmental stimuli-response behavior, with increasing BaCl2 concentrations.

A novel, smart microsphere with K(+)-induced shrinking and aggregating properties based on a responsive host-guest system

A novel type of smart microspheres with K(+)-induced shrinking and aggregating properties is designed and developed on the basis of a K(+)-recognition host-guest system. The microspheres are composed of cross-linked poly(N-isopropylacrylamide-co-acryloylamidobenzo-15-crown-5) (P(NIPAM-co-AAB15C5)) networks. Due to the formation of stable 2:1 "sandwich-type" host-guest complexes between 15-crown-5 units and K(+) ions, the P(NIPAM-co-AAB15C5) microspheres significantly exhibit isothermally and synchronously K(+)-induced shrinking and aggregating properties at a low K(+) concentration, while other cations (e.g., Na(+), H(+), NH4(+), Mg(2+), or Ca(2+)) cannot trigger such response behaviors. Effects of chemical compositions of microspheres on the K(+)-induced shrinking and aggregating behaviors are investigated systematically. The K(+)-induced aggregating sensitivity of the P(NIPAM-co-AAB15C5) microspheres can be enhanced by increasing the content of crown ether units in the polymeric networks; however, it is nearly not influenced by varying the monomer and cross-linker concentrations in the microsphere preparation. State diagrams of the dispersed-to-aggregated transformation of P(NIPAM-co-AAB15C5) microspheres in aqueous solutions as a function of temperature and K(+) concentration are constructed, which provide valuable information for tuning the dispersed/aggregated states of microspheres by varying environmental K(+) concentration and temperature. The microspheres with synchronously K(+)-induced shrinking and aggregating properties proposed in this study provide a brand-new model for designing novel targeted drug delivery systems.

pH-sensitive nano-systems for drug delivery in cancer therapy

Nanotechnology has been widely used in the development of new strategies for drug delivery and cancer therapy. Compared to traditional drug delivery systems, nano-based drug delivery system have greater potential in a variety of areas, such as multiple targeting functionalization, in vivo imaging, combined drug delivery, extended circulation time, and systemic control release. Nano-systems incorporating stimulus-responsive materials have remarkable properties which allow them to bypass biological barriers and achieve targeted intracellular drug delivery. As a result of the active metabolism of tumor cells, the tumor microenvironment (TME) is highly acidic compared to normal tissues. pH-Sensitive nano-systems have now been developed in which drug release is specifically triggered by the acidic tumor environment. Studies have demonstrated that novel pH-sensitive drug delivery systems are capable of improving the efficiency of cancer treatment. A number of these have been translated from bench to clinical application and have been approved by the Food and Drug Administration (FDA) for treatment of various cancerous diseases. Herein, this review mainly focuses on pH-sensitive nano-systems, including advances in drug delivery, mechanisms of drug release, and possible improvements in drug absorption, with the emphasis on recent research in this field. With deeper understanding of the difference between normal and tumor tissues, it might be possible to design ever more promising pH-responsive nano-systems for drug delivery and cancer therapy in the near future.

Aromatic organic contaminant removal from an aqueous environment by p(4-VP)-based materials

p(4-vinylpyridine) (p(4-VP)) hydrogels were prepared in bulk (macro, 5 × 6 mm) and in nanosizes (370 nm) dimensions. The prepared hydrogels were used to remove organic aromatic contaminates such as 4-nitrophenol (4-NP), 2-nitrophenol (2-NP), phenol (Ph) and nitrobenzene (NB) from an aqueous environment. Important parameters affecting the absorption phenomena, such as the initial concentration of the organic species and the absorbent, absorption rate, absorption capacity, pH and the temperature of the medium, were evaluated for both hydrogel sizes. The absorption capacity of bulk and microgels were found to be 4-NP>2-NP>Ph>NB. Furthermore, p(4-VP) microgels were embedded in poly(acrylamide) (p(AAm)) bulk hydrogel as a microgel-hydrogel interpenetrating polymer network and proved to be very practical in overcoming the difficulty of using the microgels in real applications. Moreover, it was demonstrated that separately prepared magnetic ferrite particles inserted inside p(4-VP) microgels during synthesis allowed for trouble-free removal of p(4-VP)-magnetic composite microgels from the aqueous environment by an externally applied magnetic field upon completion of their task.