# Innovative Antibacterial Polymer Coatings
## 2 Antibacterial Coatings
### Anti-Adhesive Coatings
#### 2.3.1 Hydrophilic Coatings  
In recent years, surface hydrophilization has emerged as an innovative method for eliminating the spread of microorganisms. Hydrophilic surfaces are known to prevent bacterial attachment by being covered with a layer of water molecules, thereby inhibiting bacteria from adhering to the hydrophilic surface. The surface water layer formed by hydrophilic polymers imparts antifouling properties, acting as an energy and physical barrier. This barrier effectively inhibits biofouling processes, including protein attachment, initial bacterial adhesion, and subsequent biofilm growth [58].  
The highly preferred polymer is poly(ethylene glycol) (PEG) due to its water solubility, high flexibility, non-toxicity, biocompatibility, low immunogenicity, approval for internal use, and ability to achieve exceptionally large exclusion volumes. Its effective bacteria-repelling properties arise from its expanded hydration layer (and resulting large exclusion volume effect), rapid configurational changes, and spatial repulsion [59]. In recent years, PEG and its derivatives have been deposited on surfaces using various methods, mainly through simple adsorption or covalent grafting. Nevertheless, it has been proven that covalently bonded PEG chains provide long-term bacterial repellent action, which is not observed with physically adsorbed PEG polymers [57]. PEG-silanes with different polymer chain lengths (350-200,000 Da) have been effectively grafted onto stainless steel arches for dental applications, showing a significant reduction in the initial adhesion of acidogenic bacteria [57]. PEG films can also be easily deposited on various substrates through polydopamine-mediated binding. A multilayer antifouling coating based on polydopamine and PEG-catechol has been designed [60].  
As illustrated in Figure 5, solid substrates are initially coated with a polydopamine (PDA) film, followed by the deposition of a PEG-catechol (PEG-C) layer. These layers are then crosslinked through catechol-Fe\({}^{3+}\)-catechol interactions to enhance stability [60].  
Additionally, surfaces functionalized with zwitterionic polymers, which have equally distributed anionic and cationic groups along their backbone, also exhibit antifouling properties. This effect is attributed to a tightly bound water layer adsorbed onto the surface,  
Figure 5: Formation of multilayer PEG films on PDA-coated substrates and the chemical structure of PEG-catechol (PEG-C). Adapted from ref. [60] with permission from American Chemical Society Copyright 2017.  
which acts as both a physical and energetic barrier, reducing bacterial adhesion. In addition to the steric hindrance provided by the hydration layer, the cationic groups can also kill bacteria on contact, further enhancing the value of zwitterionic polymers as antibacterial coatings. Typical anionic groups included in zwitterionic polymers are carboxylate, sulfonate, and phosphate, while quaternary ammonium, phosphonium, pyridinium, and imidazolium are commonly used cationic groups in these polymers [57]. Zwitterionic polymers have been employed to create antibacterial coatings for membranes, fibers, and hydrogels. Hydrogels based on poly(sulfobetaine methacrylate) and PEG have been developed as promising candidates for the next generation of wound dressings due to their antibacterial and enhanced mechanical properties [61]. The LbL technique has also been used to fabricate zwitterionic polymeric surfaces on various substrates (including stainless steel, textiles, and wood) for long-lasting anti-corrosion and antifouling applications [62]. For this purpose, a primary layer of polydopamine is initially deposited on the substrates, which improves anti-corrosion properties and facilitates the binding of subsequent layers in the coating.