# Innovative Antibacterial Polymer Coatings
## 2 Antibacterial Coatings
### Coatings That Release Antibacterial Compounds
The electrostatic interactions between two polymers: polycation carrying 3,4-dihydroxy-phenylalanine (DOPA) units used to anchor to stainless steel and for the formation andstabilization of silver nanoparticles (AgNPs) and a poly(styrene sulfonate) (PSS) polyanion were used for the formation of micelles. The chloride counteranion of the polycation also forms and stabilizes silver chloride nanoparticles (AgCl), known for their biocidal properties. Two layers of micelles, alternating with PSS and loaded with silver particles, effectively confer strong antibacterial activity on the surface against Gram-negative _E. coli_[39]. In a further investigation aimed at improving the adhesion of layer-by-layer (LbL) coatings to stainless steel, a stable aqueous suspension containing Ag\({}^{0}\) and AgCl nanoparticles was created by combining silver nitrate with a cationic polymer: poly(3,4-dihydroxy-L-phenylalanine)-co-poly(2-(methacryloxy)ethyl trimethylammonium chloride) [P(DOPA)-co-(DMAEMA\({}^{+}\))]/AgCl/Ag\({}^{0}\). This suspension was then applied layer by layer with a polystyrene sulfonate (PSS) polyanion onto a stainless steel substrate. The resulting coatings demonstrated strong antibacterial activity against Gram-negative _E. coli_ bacteria due to the release of silver ions into the surrounding environment [40]. Antibacterial activity on polymer surfaces such as PE, PET, and polycarbonates has been achieved by immobilizing silver ions in LbL films based on catechol-modified PEI and catechol-modified hyaluronic acid. The catechol groups in the coating enhance adhesion and reduce silver ions to metallic silver nanoparticles, providing antibacterial properties [41]. The presence of silver nanoparticles effectively prevents bacterial contamination of stored water in PET bottles, on whose inner walls a thiol/silver nanoparticle/polyopamine coating has been deposited [42]. PEM films have also been obtained, linked through hydrogen bonds (PAA/polyacrylamideamide), loaded with silver ions, which are reduced in situ to silver nanoparticles. The silver nanoparticles are released from the multilayer thin films and effectively kill both Gram-positive (_S. epidermidis_) as well as Gram-negative (_E. coli_) bacterial strains [43]. Silver bromide nanoparticles have also been incorporated as antibacterial agents in covalently crosslinked LbL polymer films made from synthetic methoxysilane polymers [44]. Extensively reported as effective carriers for coatings designed to deliver antibacterial compounds were also hydrogels, ceramics, and plasma-deposited polymers [45; 46]. The choice of coating materials ultimately depends on the chemical compatibility between the scaffold and the antibacterial agent, the specific functionalities required of the matrix, and the necessary release mechanism. Since each antibacterial agent and matrix system possesses unique properties, it is crucial to carefully consider the specific requirements of the target application when designing antibacterial coatings based on release. Figure 2: Antibacterial multilayer micelle films. Adapted from ref. [39] with permission from American Chemical Society, Copyright 2012.