## 3 Antibiofilm Coatings Based on Antimicrobial Peptides (AMPs)
### Contact Active Antimicrobial Surfaces Fabricated by Covalent Immobilization of AMPs  
[PERSON] et al. [13] addressed catheter-associated urinary tract infections (CAUTIs) by covalently immobilizing AMPs on the surface of silicone (polydimethylsiloxane) (PDMS) urinary catheters. The immobilization strategy was based on tethering peptide moieties to an allyl glycidyl ether (AGE) polymer brush synthesized as depicted in Scheme 4. The polymer brush was obtained using the \"grafting from\" technique. In this polymerization method, the polymerization initiators are immobilized on the surface being subsequently activated or surface-attached reactive species like free radicals, cations, or anions, able to initiate the polymerization reaction are generated in situ through plasma or UV/ozone treatment. In other words, the polymer chains grow from the surface and, therefore, the method is also named surface-initiated polymerization (SIP). Two new short peptides (RK1 and RK2) have been engineered by the authors for enhanced antimicrobial properties and resistance against media with increased salinity, which is thought to reduce the efficacy of the endogenous cationic host defense peptides. The primary structures of these peptides were: Arg-Trp-Lys-Arg-Trp-Trp-Arg-Lys-Lys (RK1) and Arg-Lys-Lys-Arg-Trp-Trp-Arg-Arg-Lys-Lys (RK2), respectively. Covalent immobilization of RK1 and RK2 endowed PDMS urinary catheter surfaces with antibiofilm properties against _Escherichia coli_, _S. aureus_, and _C. albicans_ in both PBS and urine media. Almost 100% inhibition of bacterial colonization was observed for both bacteria. The immobilized peptides showed no cytotoxicity toward mammalian cells. In a closely related approach, [PERSON] et al. [14] immobilized the potent AMP, Lasioglossin-III (Lasio-III), on silicone Foley catheters. To achieve an effective surface concentration, the authors used a heterotelechelic poly(ethylene glycol) (PEG) spacer to attach the peptide to the PDMS-AGE polymer brush. The spacer had an amine-reactive succinimidyl ester (i.e., \(N\)-hydroxysuccinimidyl (NHS) ester) at one end and a sulfhydryl-reactive group (i.e., maleimide (Mal)) at the other end. The polymer brush  
Figure 4: Synthesis of polydimethylsiloxane (PDMS)-allyl glycidyl ether (AGE) polymer brushes and tethering of antimicrobial peptides RK1 and RK2. was connected at the NHS-terminal end of the spacer via an ethylenediamine (EDA) linker, while the Mal moiety at the opposite end was used to attach the AMP. To facilitate sulfhydryl coupling, the \(N\)-terminal end of the peptide chain was chemically modified with a cysteine residue. The whole synthetic pathway is shown in Scheme 5. The peptide immobilized catheters were inoculated with two prevalent bacteria in urinary tract infections, i.e., the Gram-negative _E. coli_ and the Gram-positive _E. faecalis_, and their antibiofilm activity was assessed by XTT and immersion-based killing assays. The AMP coatings on the surface of the catheters reduced the biofilm development by 60% and 40% for _E. faecalis_ and _E. coli_, respectively. Moreover, stability tests, more specific adenosine triphosphate (ATP) leakage assays showed that in SU environment, the catheters with immobilized AMPs preserved their activity against _E. coli_ cells for at least four days. Furthermore, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolzolium bromide (MTT) cytotoxicity assay revealed good biocompatibility of the Cys-Lasio-III-functionalized catheters. The immobilization of the AMP led to a reduced hemolytic effect on human red blood cells (RBC) and THP-1 monocytic cell lines. The development of a urinary catheter that simultaneously shows strong activity against CAUTIs, chemical stability, and good biocompatibility represents a quite remarkable achievement in the field. Using the same synthetic strategy, the AMP WR11 engineered with an \(N\)-terminal cysteine (CWR11; Cys-Trp-Phe-Trp-Lys-Trp-Trp-Arg-Arg-Arg-Arg-Arg-NH\({}_{2}\)) was immobilized on PDMS slides [15]. **Scheme 5.