Liquid marbles: principles and applications

The ability of particles to adhere to a fluid–fluid interface can stabilize the formation of an emulsion. When the encapsulated fluid is a liquid and the fluid in which it is immersed is air, the object formed is called a “Liquid Marble”. Here we discuss how liquid marbles can be created, their fundamental properties and their transport and potential uses. We show how they arise naturally as an insect waste disposal system, from impact of droplets on powders and on hydrophobic soil, and in the mixing of particulate containing liquids. Our principal aim is to review research on macroscopic single marbles and their potential uses in sensors and droplet microfluidics. However, we also illustrate the similarity between liquid marbles, Pickering emulsions and “Dry Water”, and the potential application of assemblies of liquid marbles within cosmetics and pharmaceutical formulations. Finally, we discuss how modifying the surface structure of particles and providing heterogeneous surface chemistry on particles (e.g. Janus particles) might provide new types of liquid marbles and applications

An introduction to superhydrophobicity

This paper is derived from a training session prepared for COST P21. It is intended as an introduction to superhydrophobicity to scientists who may not work in this area of physics or to students. Superhydrophobicity is an effect where roughness and hydrophobicity combine to generate unusually hydrophobic surfaces, causing water to bounce and roll off as if it were mercury and is used by plants and animals to repel water, stay clean and sometimes even to breathe. The effect is also known as The Lotus Effect® and Ultrahydrophobicity. In this paper we introduce many of the theories used, some of the methods used to generate surfaces and then describe some of the implications of the effect

Controlled motion of electrically neutral microparticles by pulsed direct current

A controlled motion of electrically neutral microparticles in a conductive liquid at high temperatures has not yet been realized under the uniform direct electric current field. We propose a simple method, which employs pulsed direct current to a conductive liquid metal containing low-conductivity objects at high temperature. The electric current enables the low-conductivity particles to pass from the centre towards the various surfaces of the high-conductivity liquid metal. Most interestingly, the directionality of microparticles can be controlled and their speed can be easily regulated by adjusting pulsed current density. We find that the movement may arise from the configuration of electrical domains which generates a driving force which exceeds the force of gravity and viscous friction. All of these features are of potential benefit in separating the particles of nearly equal density but distinctly different electrical conductivities, and also offer considerable promise for the precise and selective positioning of micro-objects or the controlled motion of minute quantities of surrounding fluids

Exocytosis of mesoporous silica nanoparticles from mammalian cells: from asymmetric cell-to-cell transfer to protein harvesting

The exocytosis of mesoporous silica nanoparticles (MSNs) from mammalian cells is demonstrated for the first time. The differences in the degree of exocytosis of MSNs between healthy and cancer cells are shown to be responsible for the asymmetric transfer of the particles between both cell types. The exo­cytosis of highly adsorbent magnetic MSNs proves to be useful as a means for harvesting biomolecules from living cells

In Vitro Mineralization Models: Examining The Formation Of Calcium Phosphate In A Hydrogel Based Double Diffusion System.

In biomineralization, both crystal nucleation and growth are under tight regulation. The components required for biomineralization are: the controlled delivery of reagents required for crystal growth to the site of mineralization, a nucleating substrate, a growth medium (often a hydrogel-like matrix), and growth-modifying elements (often acidic biomacromolecules). Using synthetic analogs of components found in biology, in vitro models can be created to study various aspects of biomineralization. Depending on what one wants to model, the type of in vitro system can vary greatly: from solution growth of hydroxyapatite using a constant composition set-up, to in vitro mineralization using cells, to synthetic growth in hydrogels. Traditionally, crystal growth in hydrogels is a technique used by crystallographers to grow large crystals. For those seeking to model biomineralization, hydrogels are also excellent models of the extracellular matrix (ECM) microenvironment. In this thesis, I use an optimized hydrogel-based double diffusion system (DDS) (Chapt. 1) to explore interesting questions in biomineralization such as: What are the effects of various types of hydrogels (in which ions have different diffusivities) on both the crystal morphology and degree of mineralization in an environment where the rate of diffusion is controlled by changing the experimental setup (Chap. 2)? What i is the role of substrates in mineralization within an ECM-like matrix, and how can such a substrate be fabricated and introduced into a hydrogel-based DDS (Chap. 3)? What are the effects regulating gradients of inhibitors, using enzymes strategically placed in a DDS, on mineral formation within an ECM-like environment (Chap. 4)? By evaluating the DDS in the context of classical diffusion theory, an optimized system was designed and tested (Chap. 1). Using an innovative layered hydrogel design, differences in ion diffusivities within different hydrogels were eliminated. These experiments showed that both collagen and gelatin gels produce similar crystal morphology, while both agarose and collagen have increased mineral content over that of gelatin (Chap. 2). Placing porous silicon substrates into the DDS, revealed that cooperative behavior of proteins and substrates has an effect on both the morphology and the quantity of mineral in the hydrogel (Chap. 3). Finally, by modulating a gradient of mineral inhibitors, mineral gradients within the hydrogel are formed. The resulting "sharpness" in the mineral/hydrogel interface is proportional to the steepness of the inhibitor gradient (Chap. 4). Taken together these results provide insight into the formation of calcium phosphate in biological systems. i