Liquid Oil Marbles: Increasing the Bioavailability of Poorly Water-Soluble Drugs

Liquid Marbles under Electric Fields: New Capabilities for Non-wetting Droplet Manipulation and Beyond

The study of liquid marbles (LMs) composed of stabilizing liquid droplets with solid particles in a gaseous environment has matured into an established area in surface and colloid science. The minimized "solid-liquid-air" triphase interface enables LMs to drastically reduce adhesion to a solid substrate, making them unique non-wetting droplets transportable with limited energy. The small volume, enclosed environment, and simple preparation render them suitable microreactors in industrial applications and processes such as cell culture, material synthesis, and blood coagulation. Extensive application contexts request precise and highly efficient manipulations of these non-wetting droplets. Many external fields, including magnetic, acoustic, photothermal, and pH, have emerged to prepare, deform, actuate, coalesce, mix, and disrupt these non-wetting droplets. Electric fields are rising among these external stimuli as an efficient source for manipulating the LMs with high controllability and a significant ability to contribute further to proposed applications. This Feature Article attempts to outline the recent developments related to LMs with the aid of electric fields. The effects of electric fields on the preparation and manipulation of LMs with intricate interfacial processes are discussed in detail. We highlight a wealth of novel electric field-involved LM-based applications and beyond while also envisaging the challenges, opportunities, and new directions for future development in this emerging research area.

Stimulus Responsive Remotely Rupturable Adhesive Marbles Realized through a Hybrid Nanoparticle Concept

Adhesive marbles, an innovative concept derived from liquid marble technology that is "remotely breakable on demand" by external stimuli, offer diverse application prospects. Therefore, a chemically linked superomniphobic hybrid perfluorinated carbon black-silica nanoparticle (PCBSN) was realized by functionalizing surface groups and used for encapsulating adhesives. PCBSN successfully encapsulated liquids and adhesives to form water (WM, contact angle 158°), epoxy (EM, contact angle 145°), and silicone (SM, contact angle 135°) marbles, regardless of the surface tension and polarity. Studies on the interface characteristics revealed that the work performed for marble formation maintained an inverse relationship with the surface energy of particles and the surface tension of encapsulated liquids. The marble formation energy was determined to be higher for EM (1.071 × 10^-17 J) and lower for SM (0.946 × 10^-17 J). Upon exposure to laser, marbles showed a rapid photothermal response, and the heat transferability on the surface of marbles followed the order SM > EM > WM. The marbles were remotely rupturable by regulating the applied laser power, with breaking time being tunable from <10 to 500 s. The photothermal efficiency (%) of marbles can be graded as good and falls in the range of 88.6 × 10^-3 (EM) and 162.9 × 10^-3 (SM) at 1.5 W laser power. The marbles possessed high mechanical integrity and repeated cyclability before breaking on the rolling impact test. These adhesive marbles formed from PCBSNs may represent attractive candidates for such applications as "bonding from a distance" through remote means.

Molecular Interactions in Solid Dispersions of Poorly Water-Soluble Drugs

Physicochemical characterization is a crucial step for the successful development of solid dispersions, including the determination of drug crystallinity and molecular interactions. Typically, the detection of molecular interactions will assist in the explanation of different drug performances (e.g., dissolution, solubility, stability) in solid dispersions. Various prominent reviews on solid dispersions have been reported recently. However, there is still no overview of recent techniques for evaluating the molecular interactions that occur within solid dispersions of poorly water-soluble drugs. In this review, we aim to overview common methods that have been used for solid dispersions to identify different bond formations and forces via the determination of interaction energy. In addition, a brief background on the important role of molecular interactions will also be described. The summary and discussion of methods used in the determination of molecular interactions will contribute to further developments in solid dispersions, especially for quick and potent drug delivery applications.

Occurrence and prevention of Pickering foams in pharmaceutical nano-milling

Particle size reduction to sub-micrometer dimensions in stirred media mills is an increasingly common formulation strategy used for improving the bioavailability of poorly aqueous soluble active pharmaceutical ingredients (APIs). Due to their hydrophobic character, the API particles need to be stabilised by a surfactant in order to form a stable nano-suspension. This work is concerned with the understanding of an undesired phenomenon often encountered during the development and scale-up of wet nano-milling processes for hydrophobic APIs - the formation of foams. We investigate the microstructure, rheology and stability of these foams, and find them to be Pickering foams stabilised by solid particles at the gas-liquid interface rather than by a surfactant. By exploring the effect of surfactant concentration on the on-set of foaming in conjunction with the milling kinetics, we find a relationship between the specific surface area of the nano-suspension, the quantity of surfactant present in the formulation and the occurrence of foaming. We propose a mechanistic explanation of foam formation, and find that in order to prevent foaming, a large surfactant excess of approx. 100x above the critical micelle concentration has to be present in the solution in order to ensure a sufficiently rapid coverage of freshly exposed hydrophobic surfaces formed during the wet nano-milling process.