Layer-by-layer assemblies for drug delivery

Hello, my name is Szczepan Zapotoczny, I work as a professor heading the Group of Nanotechnology of Polymers and Biomaterials at the Agilonian University Faculty of Chemistry in Krakow, Poland. I'm going to talk about the formation of layer by layer assemblies, such as films, capsules, and their applications in drug delivery.

I'm going to start with the introduction to the layer by layer assembly as the position technique enabling fabrication of multi layer films and capsules. I will particularly focus on capsules that can be formed using solid micro particles as well as liquid nano droplets serving as templates. Then encapsulation of drugs and their release from the capsules and films will be addressed, I will complete the talk with some examples of drug delivery systems based on LbL assemblies.

LbL assembly based on sequential absorption of oppositely charged polymers was introduced by Professor Decher in the 90s, but some first attempts with application of charge microparticles were already reported 30 years earlier. In a classical approach, polyelectrolytes are absorbed on oppositely charged surfaces by simple immersion of a substrate in an aqueous solution of polyelectrolyte, for example, poly-anion, followed by washing the coating to remove loosely bound macro-molecules, and subsequent deposition of another polyelectrolyte layer, in this case, polyketile. By repeating this procedure, a number of times multi layer films of desired thickness are formed, such a sequential absorption of thin layers of oppositely charged polyelectrolytes relies mainly on electrostatic forces acting cooperatively for high molecular weight compounds. This technique has a number of advantages with respect to other film fabrication methods. It is relatively simple and inexpensive, it can be applied on various charged substrates, both flat and curved, such as micro or nano particles. Importantly, various synthetic and natural polyelectrolytes can be used in LbL approach that is crucial for their potential biomedical applications. Thus typical synthetic polyelectrolytes such as poly(sodium-4-styrenesulfonate) abbreviated PSS, or poly(allylamine hydrochloride) PAH, but also biocompatible polysaccharides such as hyaluronic acid, chitosan, as well as charged polypeptides can be used in preparation of LbL coatings. LbL offers also high control over film thickness down to about one nanometer per layer, as well as its related properties such as permeability and density of the coating. Such coatings are pretty robust also in aqueous media, but can be further strengthened by cross linking of the polymer layers. The methodology is not limited to polyelectrolytes only since other charged objects, such as nanoparticles, nanotubes, or nanoplates can be applied. LbL can also be driven by other types of interactions, such as hydrogen bondings, host gas interactions that significantly broaden application of this film fabrication method.