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Phospholipids, which are amphiphilic biomolecules composed of a polar head group and two nonpolar fatty acid tails, play a central role in cellular and body functions. The most common phospholipid is phosphatidylcholine (PC), which is also widespread used as a surfactant in colloidal systems, such as oil-in-water (O/W) emulsions, for several applications ranging from food to cosmetics. In these systems, PC tends to arrange at the interface between polar and nonpolar phases. Specific identification of these molecules at the interface is still an ambitious task. In this work, we propose immunofluorescence and confocal microscopy as valuable tools for the localization of PC at the interface of O/W emulsions, where phospholipids are used as surfactants. The protocol required the use of a primary antibody (TEPC-15), specific for choline, and a secondary fluorescently-labelled antibody, which selectively binds to the primary antibody. By using this approach, we were able to visualize choline-based phospholipids in cell membranes, lipid-based emulsions and in PC films and to estimate molecule concentration by image analysis techniques. We also investigated the interference of proteins on the staining procedure. We attributed this interference to possible molecular interactions close to the interface, which were found to depend on protein concentration. This innovative approach can have a relevant impact in a wide range of interfacial engineering applications, such as tuning emulsion microstructure and stability.

Gelatin gels are increasingly involved in many industrial applications due to several advantages including cost efficiency and biocompatibility. Generally, their production requires the use of aqueous solvents, which cause significant swelling, due to the ability of solvent molecules to penetrate through the gel microstructure and increase its volume. Since swelling mechanisms and their effect on the gel structure are not fully understood, further investigations are required. In this work, we combine macroscopic measurements of the swelling ratio (SR) with Nuclear Magnetic Resonance (NMR) and Confocal Laser Scanning Microscopy (CLSM) to investigate changes in the gelatin structure as a function of both polymer concentration and swelling time. SR values increase as a function of time until a maximum is reached and then show a slight drop for all the gelatin concentrations after 24 h swelling time, probably due to a network relaxation process. NMR allows determination of mass transport and molecular dynamics of water inside the gelatin pores, while CLSM is used to visualize the penetration of tracers (polystyrene microbeads) with a diameter much larger than the gel pores. Structural parameters, such as average pore size and tortuosity, are estimated. In particular, the pore size decreases for higher polymer concentration and increases during swelling, until reaching a maximum, and then dropping at longer times. The penetration of tracers provides evidence of the heterogeneity of the gel structure and shows that single microcarriers can be loaded in gelatin gels upon swelling.

Interaction of microstructured fluids with skin is ubiquitous in everyday life, from the use of cosmetics, lotions, and drugs, to personal care with detergents or soaps. The formulation of microstructured fluids is crucial for the control of the transdermal transport. In biomedical applications transdermal delivery is an efficient approach, alternative to traditional routes like oral and parenteral administration, for local release of drugs. Poor skin permeability, mainly due to its outer layer, which acts as the first barrier against the entry of external compounds, greatly limits the applicability of transdermal delivery. In this review, we focus on recent studies on the improvement of skin transport efficiency by using microemulsions (ME). Quantitative techniques, which are able to investigate both skin morphology and penetration processes, are also reviewed. ME are increasingly used as transdermal systems due to their low preparation cost, stability and high bioavailability. ME may act as penetration enhancers for many active principles, but ME microstructure should be chosen appropriately considering several factors such as ratio and type of ingredients and physic-chemical properties of the active components. ME microstructure is strongly affected by the flow conditions applied during processing, or during spreading and rubbing onto skin. Although the role played by ME microstructure has been generally recognized, the skin transport mechanisms associated with different ME microstructures are still to be elucidated and further investigations are required to fully exploit the potential of ME in transdermal delivery.