## 2 Antibofilm Coatings Based on Polycationic Biocides  
### Tiggered Release Coatings  
Cationic compounds are known as strong biocides, with their activity relying on the electrostatic binding between the positively charged molecules of the biocide and the intrinsically negatively charged cell wall of bacteria, which results in the damage of the latter and subsequently cells death. A breakthrough in the field of contact-killing would be if the bacteria themselves triggered the killing process. It is known that the capacity of bacteria to secrete a series of extracellular metabolites like enzymes and exotoxins accounts for their pathogenicity. For instance, _Pseudomonas aeruginosa_, a pathogen responsible for most urinary tract infections, produces a toxin called pyocyanin. The reduced form of pyocyanin is a highly reactive free radical, which readily reacts with oxygen-producing reactive oxygen species (ROS) such as the superoxide anion and hydrogen peroxide, which in turn are capable of depolymerizing glycosaminoglycans like hyaluronic acid (HA) (Scheme 1).  
[PERSON] et al. [2] have nicely exploited this property of _P. aeruginosa_ to prepare multilayer coatings for bacteria biofilm prevention on urinary catheters. They used the layer-by-layer (LbL) assembly of polyelectrolytes to build up a multilayer film consisting of alternate layers of the anionic polyelectrolyte HA and sonochemically processes nanospheres prepared from the cationic polyelectrolyte 6-deoxy-6-(\(\omega\)-aminoethyl) amino cellulose (AC).  
The cationic polyelectrolyte AC was synthesized from microcrystalline cellulose as depicted in Scheme 2 through the intermediacy of a tosyl derivative of cellulose [3]. Next, AC nanospheres with a lipid core composed of sunflower oil, were prepared using an adapted sonochemical mediated synthesis previously developed by [PERSON] [4].  
The multilayer coatings were assembled on silicone supports in such a way that the outermost layer, which is in direct contact with bacteria, is the biocidal polycationic layer of AC nanospheres. To this purpose, the silicone support was the first surface-functionalized with amino groups by treatment with 3-(aminopropyl)triethoxysilane (APTES) in order to facilitate the deposition of the first HA layer through electrostatic interactions. Next, the first AC nanospheres layer was deposited, and the procedure was repeated identically until the number of alternate HA/AC bilayers reached the desired value. Pyocianin secreted by _P. aeruginosa_ destroyed the HA layer between two successive layers of AC nanospheres, thereby releasing the AC nanospheres immediately inward from the outermost layer. Hence, the local concentration of the polycationic antibacterial increased over time following the sequential degradation of each HA layer, which explains the improved antibacterial performance of the (HA/AC nanospheres)\({}_{\mathrm{n}}\) multilayer coating. Moreover, surface nanotopography was characterized by increased roughness due to the presence of massive defects caused by the nanospheres, which in turn facilitated bacterial attachment to the contact-killing surface. Multilayered coatings for which the value of n was as low as 5 were able to prevent the formation of _P. aeruginosa_ biofilms when incubated with bacteria. In the absence of bacteria, the multilayered coatings were quite stable. This is of notable importance since unnecessary elution and premature depletion of the biocidal agent, namely AC nanospheres from the active nanocoatings, is thereby avoided. Instead, the biocidal AC nanospheres are gradually released from the multi-layered coating following the bacteria-triggered stepwise degradation from the outside inward of the HA component of each HA/AC bilayer. Thanks to this ingenious design, long-lasting (up the seven days) antib Biofilm activity was achieved.