Multi-stimuli responsive nanofluid with easy-to-visualize structural color patterns

Magnetic nanofluids (Ferrofluids): Recent advances, applications, challenges, and future directions

Impelled by the need to find solutions to new challenges of modern technologies new materials with unique properties are being explored. Among various new materials that emerged over the decades, magnetic fluids exhibiting interesting physiochemical properties (optical, thermal, magnetic, rheological, apparent density, etc.) under a magnetic stimulus have been at the forefront of research. In the initial phase, there has been a fervent scientific curiosity to understand the field-induced intriguing properties of such fluids but later a plethora of technological applications emerged. Magnetic nanofluid, popularly known as ferrofluid, is a colloidal suspension of fine magnetic nanoparticles, has been at the forefront of research because of its magnetically tunable physicochemical properties and applications. Due to their stimuli-responsive behaviour, they have been finding more applications in biology and other engineering disciplines in recent years. Therefore, a critical review of this topic highlighting the necessary background, the potential of this material for emerging technologies, and the latest developments is warranted. This review also provides a summary of various applications, along with the key challenges and future research directions. The first part of the review addresses the different types of magnetic fluids, the genesis of magnetic fluids, their synthesis methodologies, properties, and stabilization techniques are discussed in detail. The second part of the review highlights the applications of magnetic nanofluids and nanoemulsions (as model systems) in probing order-disorder transitions, scattering, diffraction, magnetically reconfigurable internal structures, molecular interaction, and weak forces between colloidal particles, conformational changes of macromolecules at interfaces and polymer-surfactant complexation at the oil-water interface. The last part of the review summarizes the interesting applications of magnetic fluids such as heat transfer, sensors (temperature, pH, urea detection, cations, defect detection sensors), tunable optical filters, removal of dyes, dynamic seals, magnetic hyperthermia-based cancer therapy and other biomedical applications. The applications of magnetic nanofluids in diverse disciplines are growing day by day, yet there are challenges in their practical adaptation as field-worthy or packaged products. This review provides a pedagogical description of magnetic fluids, with the necessary background, key concepts, physics, experimental protocols, design of experiments, challenges and future directions.

Interferon-gamma carrying nanoemulsion with immunomodulatory and anti-tumor activities

The therapeutic administration of cytokines has been introduced aiming to modulate the immune response system, seeking for different approaches to face pathologies such as cancer, auto immune and infectious diseases. The objective of this study was to investigate the effects of a stable oil-in-water (O/W) nanoemulsion system carrying the cytokine Interferon gamma (IFN-γ) on the activity of phagocytes and MCF-7 human breast cancer cells. Nanoemulsions were prepared through ultra-homogenization, and they consisted of distilled water, triglycerides of capric acid/caprylic, sorbitan-oleate, polysorbate 80, and 1-butanol. IFN-γ (100 ng ml^-1 ) was incorporated into two O/W nanoemulsion formulations, and these formulations were characterized in terms of their preliminary and accelerated physicochemical stability, rheological properties, droplet size, polydispersity and surface charge. We identified the most optimal IFN-γ nanoemulsion (IFN-γNE2), which remained stable under extreme temperature variations for 90 days, contained an average dose of 97 ng ml^-1 of IFN-γ and exhibited a biocompatible pH and a relative stable rheological profile. Cell viability and intracellular Ca²⁺ release assays conducted showed that IFN-γNE2 reduced the cell viability of MCF-7 cells without affecting the cell viability of phagocytes. Furthermore, IFN-γNE2 was able to induce cellular activity of phagocytes as evidenced by increased intracellular Ca²⁺ release in these cells. Our findings on this IFN-γ nanoemulsion suggest that it can be a promising therapeutic agent for immunostimulation and cancer treatment.

Structural Colored Balloon Composed of Temperature-Responsive Polymers Showing LCST Behavior

Structural colored balloons (SCBs) consisting of polymer thin film developed structural color by thin-layer interference on the shell. Thermoresponsive SCBs were prepared with poly(diethylene glycol monomethyl ether methacrylate)- co-poly( N-phenylacrylamide), which shows lower critical solution temperature (LCST) behavior. When cooling gelatin aqueous solution in which osmotic pressure was not operated, only hydration of the copolymer progressed due to LCST transition. The optical path length of the SCB increased due to swelling by water and subsequently decreased due to dissolution. The structural color changed according to the change in optical path length. In cold pure water, in addition to the hydration, osmotic pressure was operated to induce an influx of the outer solvent and the resulting diameter change also affected the shell thickness. The structural color change was analyzed to reveal that the dissolution of the polymer had significant effect on the developed structural color.

Study on influencing factors of Pickering emulsions stabilized by hydroxyapatite nanoparticles with nonionic surfactants

Emulsions were prepared using hydroxyapatite nanoparticles and nonionic surfactant sorbitan monooleate (Span 80) as emulsifier. Effects of Span 80 concentration, emulsification time, emulsification rate, poly(l-lactic acid) (PLLA) concentration and the surface chemical properties of hydroxyapatite nanoparticles on emulsion properties were systematically studied. The results showed that emulsion would undergo a phase inversion from oil-in-water (O/W) type to water-in-oil (W/O) type with an increase in Span 80 concentration. All of the above factors are closely related to emulsion type and stability. SEM results indicated that cured materials with different structures were obtained using these emulsions as templates via in situ evaporation; especially, open-cell porous structures were obtained by a mixture of hydroxyapatite and a moderate concentration of Span 80. The mechanism of this emulsion system is proposed in relation to the emulsion properties and cured material structure, which should be attributed to the formation of hydrogen bonds between hydroxyapatite and Span 80 by hydroxyl groups as well as their location changes in the emulsion.

Effects of Salt-Controlled Self-Assembly of Triblock Copolymers F68 on Interaction Forces between Oil Drops in Aqueous Solution

Nonionic triblock copolymers, surfactant Pluronic F68 (PEO76-PPO29-PEO76), are widely used in industrial processes, such as foaming, emulsification, and stabilization. The behaviors of triblock copolymers such as the salt-dependent self-assembly in bulk solution and the irreversible adsorption at the oil/water interface are mainly focused to explore their effects on the interaction forces between nano-spacing interfaces of oil droplets. In this study, the atomic force microscopy (AFM) technique was employed to measure the drop interaction forces with different F68 bulk concentrations. All selected bulk concentrations (≥100 μM) of copolymers can ensure the formation of a stable layer structure of stretched polymer chains ("brush") at the oil/water interface, which behaved as a mechanical barrier at the interface. This study quantified the forces caused by the space hindrance of F68 copolymers both in the bulk phase and at the interface of oil/F68 aqueous solution during drop interaction. The effects of monovalent electrolyte (NaCl)-induced self-assembly behavior of triblock copolymers F68 in bulk solution on drop interaction forces were measured through the AFM technique.