## 4 Passive Anti-Biofouling Nanoc Coatings
### Fouling Resistance Strategies. Hydrophilic and Zwitterionic Polymers
existing between the substrata stiffness and the adhesion of viable bacteria: the higher the elastic modulus of the substrate (i.e., the stiffer the material), the larger the degree of bacterial adhesion. Due to the very strong electrostatic interactions existing in zwitterionic polymers, they have a very tightly bound hydration layer resulting in \"superhydrophilicity\" and high anti-bioadhesion properties [100]. Using a grafting from strategy, [PERSON] et al. [109] prepared surface grafted poly(sulfobetaine methacrylate) (pSBMA) brushes by atom transfer radical polymerisation (ATRP). Self-assembled layers of polydopamine (PDA) and organosilane were used as a surface anchor on stainless steel coupons (SUS) for the coupling of pSBMA brushes. The synthetic procedure is depicted in Scheme 2. Cleaned SUS 316L coupons were subjected to UV irradiation for 20 min, followed by cleansing with ethanol and deionised water. For PDA as an anchoring agent, SUS coupons were dipped in buffered ((tris(hydroxymethyl))aminomethane or TRIS) aqueous dopamine solution followed by rinsing with ethanol and deionised water to remove excess unbound dopamine. For organosilane as an anchoring agent, SUS coupons were immersed in a solution of 3-aminopropyl trimethoxysilane (APTMS) in hexane at 40 \({}^{\circ}\)C for 2 h, followed by cleansing with ethanol and deionised water. Next, SUS 316L coupons were reacted with 2-bromoisobutyryl bromide (BiBB) under an inert atmosphere, in the presence of the hydrobromic acid scavenger, triethylamine, when the self-assembled anchor layers of the ATRP initiators SUS-D-BiBB, and SUS-Si-BiBB, respectively, were obtained (see Scheme 1). Eventually, ATRP of [2-(Methacryloyloxy)ethyl]-dimethyl(3-sulfopropyl)-ammonium hydroxide (SBMA) was carried out for 24 h, in the presence of Cu(I) bromide as a catalyst, and of 2,2'-bipyridine as a ligand, with deoxygenation (under nitrogen stream). The prepared grafted zwitterionic polymer brushes SUS-D-pSBMA and SUS-Si-pSBMA showed good antibiofouling properties being able to resist fibrinogen, blood platelets, and leukocytes adsorption. Hence, they are promising candidates for thrombogenic coatings. Moreover, only 0.8% _E. coli_ adhesion and 0.02% _S. epidermidis_ adhesion were observed on SUS-D-pSBMA [109]. Antiadhesive polymer brush coatings with higher mechanical strength and ability to self-regenerate have been prepared by [PERSON] et al. [110] based on hydrophobic polyurethane with hydrophobic poly(carboxy betaine) esters as side chains, which can be converted into the corresponding nonfouling zwitterionic poly(carboxybetaines) through hydrolysis. The advantage of this approach resides in combining in one material the mechanical strength and hardness imparted by the hydrophobic polymer matrix with the antifouling and self-healing abilities brought by the zwitterionic poly(carboxybetaine) segments formed at the outer surface of the polyurethane film through the hydrolysis of the poly(carboxybetaine) ester side chains. The synthetic pathway comprises three steps: (1) the synthesis of the carboxybetaine ester analog (CB-ester), (2) the synthesis of the dihydroxy-terminated poly(carboxybetaine) ester analog (PCB-ester(OH)2) side chains, and (3) the synthesis of polyurethane with PCB side chains (PCB-ester-PUR). The first synthetic step involves the Michael addition of 2-(methylamino) ethanol to ethyl acrylate followed by the reaction of the resulted intermediate addition product with methacryloyl chloride at 0 \({}^{\circ}\)C, in the presence of triethylamine (see Scheme 3). The second step consists in the free radical polymerisation of CB-ester in the presence of azobisisobutyronitrile (AIBN) as an initiator and of 3-mercapto-1,2-propanediol as a chain transfer agent to control the polymerisation degree, m. The stepwise polycondensation reactions of the macrodiol PCB-ester(OH)2 with 4,4'-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (1,4-BD) as a chain extender complete the synthesis. The eventual polycondensation reactions were carried out under nitrogen atmosphere.