Nano-droplet Systems by Surfactant Self-assembly and Applications in the Pharmaceutical Industry
Carlos Rodríguez-Abreu and Ana Vila
Affiliation: International Iberian Nanotechnology Laboratory, Braga 4715-330, Portugal.
Keywords: Microemulsions, nano-emulsions, surfactants, drugs, pharmaceuticals.
Liquid systems containing droplets with size in the nanoscale range are attractive from both scientific and technological
points of view as they have many current and potential applications in several industries and products. The formation
and stabilization of nano-droplet systems are mostly based on the self-assembly of surfactant (amphiphilic) molecules
at interfaces, driven by the solvophobic effect. Surfactants are involved in both top-bottom (high energy) and bottom-
up (low energy) methods. Several devices have also been developed to aid in liquid fragmentation down to the
nanometer scale. Nano-droplet systems can be both thermodynamically stable (microemulsions) or metastable (nanoemulsions),
and appropriate formulation is a key for optimum product design in terms of droplet size, maximum solubilization,
colloidal stability, and optical and rheological properties, among others. Such characteristics are determined by
molecular packing, interfacial curvature, droplet-droplet interactions, film elasticity and nature of the dispersed and continuous
phase. These properties can be engineered by proper understanding of the molecular structure and phase behavior
of the multicomponent systems involved and by a range of experimental characterization techniques. Nano-droplet systems
can help to solve specific issues in pharmaceutical products such as processing, limitations in drug solubility or stability,
control on drug release, drug targeting and absorption; there are many examples to prove that. However, several
practical aspects should be considered for preclinical and clinical tests and product development.
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