Role of Surface Energy of Nanoparticle Stabilizers in the Synthesis of Microspheres via Pickering Emulsion Polymerization

Reversible Cu-Nanoparticle Formation in Soft Hydrogel Composites: Towards Write-Erase Displays and Fluorescence Detection

In this study, we introduce a hydrogel-polymer microsphere (HPM) composite material constituted of PVA, glycerin, and polymer microspheres obtained from Pickering emulsions that are capable of adsorbing Cu2+ ions. The obtained HPM composite is soft, flexible, can be fully saturated with Cu2+ ions, and exhibits a reversible color transition from blue to black upon electrode contact or interaction with a reducing agent, due to in situ generation of copper nanoparticles (Cu-NPs). Because of the color contrast between the locally generated Cu-NPs and the background, the HPM can be used as substrate for stamping different shapes or writing text. Further, the surface can be erased by an acidic solution, which makes it interesting as flexible write-erase displays. A second feature of the HPM is that it can function as a fluorescence detector of cyanide ions. An HPM whose surface has been stamped with an electrode, upon contacting an aqueous solution containing cyanide ions, begins fluorescing a yellow-green light around the patterned area. The displayed luminescence is irreversible and is preserved even after HPM's drying or lyophilization. This work lays a foundational framework for future exploration of the HPM composites in various technological applications, for sensing, circuit printing, and flexible displays.

Emulsions delivery systems of functional substances for precision nutrition

Many functional substances are chemically unstable and exhibit variable water/oil solubility, reducing their bioavailability and efficacy. It is necessary to devise effective measures to improve the unfavorable properties of functional substances and maximize their potential benefits in nutritional interventions. Therefore, the development and application of edible emulsion-based delivery systems for these functional substances using food-grade materials would be highly beneficial for the food industry. In recent years, Pickering emulsions have garnered significant attention in the scientific community due to their characteristic of being free from surfactants. This section focuses on emphasizing the design and preparation of emulsion delivery systems based on functional substances. Additionally, we summarize the current applications of emulsion delivery systems in functional substances. This chapter also discusses the potential advantages of Pickering emulsion systems in the precise nutrition field, including high targeting specificity and nutritional intervention for various diseases. Well-designed Pickering emulsion delivery carriers for functional substances can enhance their stability in food processing and in vivo digestion. To meet the nutritional needs of specific populations for functional foods, utilizing emulsion delivery systems to improve the bioavailability of functional substances will provide a theoretical basis for the precise nutrition of functional substances in functional foods.

General approaches to biopolymer-based Pickering emulsions

Pickering emulsion is a type of emulsion that uses solid particles or colloidal particles as emulsifiers rather than surfactants to adhere at oil-water interface. Pickering emulsions have gathered significant research attention recently due to their excellent stability and wide range of potential uses compared to traditional emulsions. Major advancements have been made in development of innovative Pickering emulsions using different colloidal particles by various techniques including homogenization, emulsification and ultrasonication. Use of biopolymer particles gives Pickering emulsions a more escalating possibilities. In this review paper, we seek to present a critical overview of development in food-grade particles that have been utilized to create Pickering emulsions with a focus on techniques and application of Pickering emulsions. Particularly, we have evaluated protein, lipid, polysaccharide-based particles and microalgal proteins that have emerged in recent years with respect to their potential to stabilize and add novel functionalities to Pickering emulsions. Some preparation methods of Pickering emulsions in brief, applications of Pickering emulsions are also highlighted. Encapsulation and delivery of bioactive compounds, fat substitutes, film formation and catalysis are potential applications of Pickering emulsions. Pickering double emulsions, nutraceutical and bioactive co-delivery, and preparation of porous materials are among research trends of food-grade Pickering emulsions.

Water-Floating Hydrogel Polymer Microsphere Composites for Application in Hydrological Mining of Cu(II) Ions

Innovative materials and technologies capable of extraction and recovery of technologically relevant metal ions from various water sources, such as lakes, oceans, ponds, or wastewater reservoirs, are in great demand. Polymer beads are among the most well-known solid-phase adsorbents and ion exchangers employed in metal ion recovery. On the other hand, hydrogels are an emerging platform for producing innovative adsorbents, which are environmentally friendly and biocompatible materials. In this work, we take advantage of both technologies and produce a new type of material by loading nanostructured polymer microsphere adsorbent into a PVA matrix to obtain a hydrogel polymer microsphere (HPM) composite in the form of a block. The main role of the poly(4-vinylpyrridine-co-methacrylic acid) microspheres is to adsorb metal ions, such as Cu(II), from model water samples. The secondary role of these microspheres in the hydrogel is to change the hydrogel morphology by softening it and stabilizing it under a foam-like morphology. The foam-like morphology endows these composites with the capability of floating on water surfaces. In this work, we report, for the first time, an HPM composite capable of floating on water surfaces and extracting Cu(II) ions from model water samples. This could enable more environmentally friendly hydrological mining technologies by simply deploying adsorbents on water surfaces for metal ion extraction and recovery, thus eliminating the need for water pumping and mechanical processing steps.

Asymmetrically Nanostructured 2D Janus Films Obtained from Pickering Emulsions Polymerized in a Langmuir-Blodgett Trough

Low-dimensional structures, such as two-dimensional (2D) Janus films, can be useful in studying fundamental interactions or in applications at the nanoscale. In this work, we report the fabrication of 2D polymer Janus films consisting of one smooth and another nanostructured facet on which silica nanoparticles (NPs) are self-assembled in a compact monolayer shield. The 2D films are made from Pickering emulsions of monomers in water, stabilized by NPs, which are spread over the surface of the water in a Langmuir-Blodgett trough. Following the spreading of the colloidosomes, oil droplets stabilized by NPs collapse, and the interfaces reorganize such that the NP monolayer is found exclusively at the oil/water interface. Upon compression followed by UV polymerization, a 2D solid film is formed, with one smooth and another nanostructured face. The film can be removed from the surface of the water and handled with tweezers. The 2D films exhibit different surface properties on the two sides, such as differences in water wettability. On the nanostructured side, water wettability can be tuned by tuning the surface energy of the nanoparticles, namely by changing their surface functional groups. Upon removal of NPs, the surface can be patterned with an array of circular traces.

Monitoring the Surface Energy Change of Nanoparticles in Functionalization Reactions with the NanoTraPPED Method

Performing chemical functionalization on the surface of nanoparticles underlies their use in applications. Probing that a physicochemical transformation has indeed occurred on a nanoparticles' surface is rather difficult. For this reason, we propose that a macroscopic parameter, namely the surface energy γ, can monitor the physicochemical transformations taking place at the surface of nanoparticles. Determining the surface energy of macroscopic surfaces is trivial, but it is very challenging for nanoparticles. In this work we demonstrate that the Nanoparticles Trapped on Polymerized Pickering Emulsion Droplet (NanoTraPPED) method can be successfully deployed to monitor the evolution of surface energies γ, with its γ^p polar and γ^d dispersive components of the silica nanoparticles at each stage of two surface reactions: (i) amination by siloxane chemistry, coupling reaction of a 2,4-dihydroxy benzaldehyde and formation of a Schiff base ligand, followed by coordination of metal ions and (ii) epoxide ring opening and formation of azide. The change in surface energy and its components are discussed and analyzed for each step of the two reactions. It is observed that large variations in surface energy are observed with the complexity of the molecular structure attaching to nanoparticle surface, while functional group replacement leads to only small changes in the surface energies.

The Role of Microsphere Structures in Bottom-Up Bone Tissue Engineering

Bone defects have caused immense healthcare concerns and economic burdens throughout the world. Traditional autologous allogeneic bone grafts have many drawbacks, so the emergence of bone tissue engineering brings new hope. Bone tissue engineering is an interdisciplinary biomedical engineering method that involves scaffold materials, seed cells, and "growth factors". However, the traditional construction approach is not flexible and is unable to adapt to the specific shape of the defect, causing the cells inside the bone to be unable to receive adequate nourishment. Therefore, a simple but effective solution using the "bottom-up" method is proposed. Microspheres are structures with diameters ranging from 1 to 1000 µm that can be used as supports for cell growth, either in the form of a scaffold or in the form of a drug delivery system. Herein, we address a variety of strategies for the production of microspheres, the classification of raw materials, and drug loading, as well as analyze new strategies for the use of microspheres in bone tissue engineering. We also consider new perspectives and possible directions for future development.

A Review of Pickering Emulsions: Perspectives and Applications

Pickering emulsions are systems composed of two immiscible fluids stabilized by organic or inorganic solid particles. These solid particles of certain dimensions (micro- or nano-particles), and desired wettability, have been shown to be an alternative to conventional emulsifiers. The use of biodegradable and biocompatible stabilizers of natural origin, such as clay minerals, presents a promising future for the development of Pickering emulsions and, with this, they deliver some advantages, especially in the area of biomedicine. In this review, the effects and characteristics of microparticles in the preparation and properties of Pickering emulsions are presented. The objective of this review is to provide a theoretical basis for a broader type of emulsion, in addition to reviewing the main aspects related to the mechanisms and applications to promote its stability. Through this review, we highlight the use of this type of emulsion and its excellent properties as permeability promoters of solid particles, providing ideal results for local drug delivery and use in Pickering emulsions.

Extraction of Metal Ions by Interfacially Active Janus Nanoparticles Supported by Wax Colloidosomes Obtained from Pickering Emulsions

Most common wastewater treatment technologies for ion extraction and recovery rely on pumping wastewater through ion-exchange columns, filled with surface-functionalized polymer microspheres. To avoid the energetically intensive process of pumping large quantities of water through ion-exchange columns, alternative technologies are being developed, such as water-floating membranes containing ligands. In this context, innovative materials could be deployed. Here, we report nanostructured paraffine wax microspheres capable of floating on water, a design based on Pickering emulsion technology, where Janus nanoparticles act both as emulsion stabilizers and as ligand carriers. In the process of emulsification of molten wax in water, followed by cooling, the branched polyethylenimine (bPEI) carrying Janus nanoparticles are trapped at the molten wax/water interface, forming spherical microspheres or colloidosomes decorated with nanoparticles. The paraffine wax colloidosomes stabilized by ligand-carrying Janus nanoparticles are capable of floating on water and show high metal ion extraction capacities towards Cr(VI), Co(II), Ni(II), Cu(II) and Zn(II). In addition, we demonstrate that the ions can be recovered from the colloidosomes and that the colloidosomes can withstand several extraction/recovery cycles with little or no loss in the absorption capacity.