## 3 Antibiofilm Coatings Based on Antimicrobial Peptides (AMPs)
### Contact Active Antimicrobial Surfaces Fabricated by Covalent Immobilization of AMPs
** Synthetic strategy to covalently immobilize the antimicrobial peptides (AMP), Cys-Lasio-III, on the surface of silicone Foley catheters [14]. Adapted from an open-access source. However, the immobilization technique described above suffers from a major drawback, which is the complicated surface activation method (plasma radiation). To overcome this limitation, [PERSON] et al. [16] applied a bioinspired facile conjugation technique previously developed by [PERSON] and coworkers [17]. In this immobilization strategy, the synthetic AMP CWR11 was attached to PDMS slides and Foley urinary catheters via an intermediate crosslinking mussel-inspired [18] polydopamine (PDA) film. It is well known that under weak alkaline conditions, dopamine (DA) undergoes oxidative self-polymerization [19; 20] (Scheme 6), forming PDA, a soft and sticky material able to adhere to almost any surface. The oxidative polymerization of DA involves catechol-quinone conversions, thereby facilitating covalent fixation of CWR11 either via Michael addition reactions of the biological amino and sulfhydryl nucleophiles in the peptide to the conjugated quinone systems or through the formation of Schiff bases. Briefly, commercially available Foley urinary catheters were covered with a layer of PDA using the dip-coating technique. The catheters were dipped in a solution of DA in 50 mM tris(hydroxymethyl)aminomethane-hydrochloride (TRIS) buffer (pH = 8.8), and the polymerization reaction was allowed to proceed for 72 h at room temperature. Next, the catheters were repeatedly rinsed with deionized water to remove any traces of unattached DA, and then were immersed for another 72 h in a solution of the CWR11 peptide in TRIS buffer at room temperature. Eventually, the peptide-immobilized catheters (Cat-PDA-CWR11) were thoroughly washed with water. The antibiofilm properties of Cat-PDA-CWR11 were assessed in comparison to bare catheter controls. The catheters were seeded into the intraluminal space with equal amounts (50 uL) of suspensions of the most relevant urinary tract infections bacteria (_E. coli_, _S. aureus_, and green fluorescent protein (GFP)-_P. aeruginosa_) each of the same concentration (\(5\times 10^{4}\) colony forming units (CFU), incubated for 3 h at room temperature, and then immersed in fresh medium for overnight culture. Bacterial adhesion to catheters was quantitatively assessed by fluorescence spectroscopy. There was up to 92% decrease in the amount of viable adherent (GFP)-_P. aeruginosa_ bacteria on Cat-PDA-CWR11 as compared to control (unmodified) catheters. Bacterial growth in the immersion medium was monitored by measuring the optical density at 600 nm (OD\({}_{600}\)). For the CWR11-functionalized catheters, no bacterial growth could be detected, whereas significant bacterial growth was evident in the control catheters. The stability of the functionalized catheters was tested by exposing the catheters for three days to various media (air, water, PBS, SU, and urine) and then assessing their antibacterial activity. The Cat-PDA-CWR11 maintained their antibacterial activity in all tested media. In water, the antibacterial activity of CWR11-functionalized catheters was kept unchanged up to 21 days. Figure 6: Oxidative self-polymerization of dopamine (DA). To assess the hemolytic activity of the Cat-PDA-CWR11 against RBC, the catheters were immersed in an erythrocyte solution, incubated at 37 \({}^{\circ}\)C for 1 h, and vigorously stirred. After centrifugation of the RBC solutions, the hemoglobin released into the supernatant was determined by measuring the optical density at 540 nm. The determined hemolytic activity corresponded to a level of acceptable amounts of hemolysis, as stipulated by ISO 10993 for medical devices.