# Innovative Antibacterial Polymer Coatings
## 2 Antibacterial Coatings
### Coatings That Release Antibacterial Compounds  
Release-based coatings exhibit antibacterial efficacy by gradually releasing antibacterial compounds, effectively targeting both adhered bacteria and those around them. This release mechanism occurs through processes such as diffusion into the surrounding aqueous environment, material erosion or degradation, and hydrolysis of covalent bonds. Unlike conventional antibiotic delivery methods, the direct release from the material's surface enables localized delivery of high concentrations of antibacterial agents, thereby minimizing the risk of systemic toxicity. This approach guarantees that antibacterial activity is concentrated precisely where it is required, thus reducing the risk of resistance development and preventing potentially adverse effects. However, due to the inherently limited reservoirs of antibacterial agents in these coatings, their effectiveness is ultimately temporary. The initial generation of release-based coatings primarily comprises devices infused with antibiotics or silver compounds [28]. A comprehensive review of the literature from the last ten years indicates conflicting results concerning the efficacy of this initial generation of coatings. The emergence of these materials has been associated with a significant reduction in hospital-acquired infections [29; 30; 31]. However, various clinical studies have demonstrated only modest success or have highlighted complications [32; 33]. Common challenges associated with these coatings include limited reservoir capacity, inadequate long-term effectiveness, cytotoxicity, inflammatory responses, and increased resistance among bacterial strains [34; 35]. In recent decades, a diverse array of antibacterial compounds has been developed for use in release systems. The most traditional and frequently employed method for delivering these compounds is through surface coating, which can be achieved by simple impregnation, soaking a porous material, or directly applying the antibacterial agent to the surface. However, the absence of a specific binding mechanism in the coating process leads to the fast consumption of the antibacterial agent [35]. Since then, release systems have evolved to include a wide variety of carrier materials (i.e., any material that can be loaded with an antibacterial compound) and deposition methods. The most frequently utilized carriers consist of poly(methacrylic acid), polyacrylic acid, poly(lactic-co-glycolic acid), hydroxyapatite, polyurethane, hyaluronic acid, and chitosan [36; 37]. The primary limitation of these coatings is their finite effective lifespan. Antibacterial agents can only be incorporated into the system in a predetermined quantity, leading to a loss of effectiveness once the agents are completely released. Consequently, ensuring controlled release and long-term stability has emerged as a significant concern and challenge in the development of these coatings. A novel approach to controlling the release of antibacterial agents from coatings involves the use of multilayered polyelectrolyte systems (PEMs), which can be achieved through a \"layer-by-layer\" (LbL) deposition technique, consisting of the sequential assembly of alternating layers with opposite charges. This method is recognized as one of the most effective for integrating antibacterial compounds into coatings due to its simplicity, versatility, and cost-effectiveness [38]. Antibacterial agents can be incorporated either between the layers or as an integral component of the coating by substituting one of the charged layers. Silver is extensively utilized as a bactericidal agent. Various forms, such as silver ions, silver nanoparticles, and silver halide nanoparticles, have been integrated into LbL films in order to eliminate bacteria as a result of their release into environments. Antibacterial coatings for stainless steel have been obtained by sequential deposition of micelles consisting of positive polyelectrolyte with included Ag nanoparticles and polyanion (Figure 2).