Layer-by-layer Polymeric Deposition as an Efficient Strategy to Sustain Drug Release

The ability to control and sustain the release of drugs avoiding under and overdosing, maintaining the drug concentration within therapeutic range, is a well-established discipline in pharmaceutics with many commercial products and many other challenges that should be overcome [1-3]. Indeed, despite the very good results obtained in many applications, several critical points come from the fact that pure diffusion mechanism is the main phenomenon involved, then drug release is generally too quick due to the high clearance present within animal bodies [4-6]. A common strategy used to decelerate the release involves the formation of covalent bonds between drug molecules and polymeric chains; these are commonly known in literature as biorthogonal strategies [7-9]. This approach guarantees the controlled and sustained release molecules on one hand, but on the other hand, the chemical modification of active principles may change their efficacy. Another interesting alternative is represented by multilayer deposition onto a single device where different coatings one onto another can decrease the release rates of drugs. In this framework, in the last decade, layer-by-layer self-assembly (LbL) technique has shown extremely promising properties in many different biomedical fields [10-12]. It consists of the alternate adsorption of oppositely charged macromolecules over a charged substrate. Here, the good adhesion achieved between the neighboring layers and the surface is so based on electrostatic interactions and the use of macromolecules rather than small molecules guarantees a certain number of ionic bonds. For this reason, this technique is often referred to as electrostatic self-assembly (ESA) [13, 14]. In principle, when the polyionic molecules approach an opposite charged substrate or layer, within a sufficiently small distance (Debye length), the local electric field is so strong that it attracts the polyionic molecules to the surface, starting the adsorption process.