Abstract

Development of colloidal drug delivery systems showed a fast increase in the last decade due to the demand for drug formulations able to target specific sites in the body and to control drug release kinetics after administration. Numerous systems in the sub-micronic size range were introduced to encapsulate or solubilize drugs and present them in the form of an aqueous “nano” dispersion. They include solid polymeric or lipidic nanoparticles, liposomes or other vesicles, micelles, nanoemulsions, microemulsions. All these objects have a size in the range from 1 nm to approximately 300 nm, and their complex structure is responsible for their behavior and their efficacy as drug delivery systems. Size distribution is an essential property for these systems; their distribution in the body and the drug delivery largely depends on this parameter. Light scattering is commonly used in that field. However, other scattering methods and especially Small Angle Neutron Scattering (SANS) allows retrieving complementary information on the structural organization of colloidal drug delivery systems. The size and shape of micelles, the thickness of a bilayer in liposomes or that of a polymeric shell in nanocapsules, the conformation of a polymer in solution, the structure of a microemulsion... are all examples of information that SANS can provide. Drug loading in the delivery system often leads to structural changes that can be investigated by SANS; the distribution of drug molecules in a micelle or a bilayer, the interactions between drug and carrier material are assessed by means of SANS. It is also a means to anticipate the behavior of the drug delivery systems in the body by studying the influence of dilution, variations of pH or salt concentration. SANS experiments carried under nonclassical conditions are quite uncommon in the field of drug delivery system characterization, although it may be a valuable tool to study dynamic phenomena with time resolution in the range of 100 ms.