###### Abstract
Expressed in almost all living organisms and being part of the innate immune system, AMPs are usually amphipathic short peptides (fewer than 100 amino acid residues), with a positive net charge (+2 to +9) at physiological pH [21,22]. These natural molecules are particularly interesting as therapeutic agents due to their high selectivity toward bacterial cells over mammalian cells [23,24], and low probability to elicit bacterial resistance [25]. Although the underlying mechanisms of action of AMPs are still under active study, it is widely accepted that the basic principle involves the electrostatic interaction of the cationic AMPs with negatively charged components of the bacterial cell membranes [20,26,27]. This electrostatic interaction leads to binding and accumulation of AMPs on the surface of the membranes, promoting membrane depolarization and permeabilization [28]. Several models have been proposed to explain the antimicrobial effect of AMPs and their interaction with the bacterial cell membrane. The most widely described models include the \"barrel stave\" model, the \"toroidal-pore\" model and the \"carpet\" model--several reviews are available on this subject [20,21,22,28,29,30]. Due to their broad antimicrobial activity, AMPs have been immobilized onto the surface of materials to confer contact-killing antimicrobial activity [31, 32, 33, 34]. Compared with soluble AMPs, the antimicrobial performance of surface-immobilized AMPs is generally reduced due to limited conformational freedom [35,36]. This can be compensated by increasing the density of immobilized AMPs or through introduction of flexible spacers [32,35]. Nevertheless, evidence with AMP-functionalized surfaces (e.g., films and coatings) indicates that the use of AMPs tethered into surfaces [37, 38, 39, 40, 41] or using genetically engineered fusion proteins for processing into films or coatings [8,10,12,42] results in surfaces with contact-killing antimicrobial activity by disrupting the integrity of bacteria membranes, resulting in the leakage of intracellular content. The cationic nature of the AMPs probably displaces the divalent cations that maintain the structural integrity of the negatively charged surface of the bacteria, disrupting its integrity; thus, this effect by itself might be sufficient to generate a lethal outcome [43,44]. Our research group is pioneering the formulation of antimicrobial ELR-based materials by genetically engineering an ELR, comprising 200 repetitions of the VPAVG sequence (A200), to include the DNA sequence of AMPs [8; 12; 45]. We have produced antimicrobial ELR-based films through functionalization with the antimicrobial peptides ABP-CM4 [12], a 35 amino acid peptide from the hemolymph of silkworm, and BMAP18 [8], an 18-amino acid truncated variant of bovine myeloid antimicrobial peptide-28. A200 is characterized by an acute thermal hysteresis behavior and the ability to self-assemble into spherical nanoparticles at temperatures above 33 \({}^{\circ}\)C [46; 47]; we explored this unique behavior for the purification of recombinant hepcidin [45], a 25 amino acid human liver antimicrobial peptide, and suggested its potential application as antimicrobial drug delivery platform. The aim of this study was to investigate the potential of using both ELRs and SELPs functionalized with AMPs for the development of new antimicrobial surfaces (e.g., films/coatings). Moreover, we also provide a comparison on the antimicrobial performance of SELP- and ELR-based materials obtained while using water and formic acid as solvents for processing. To achieve this, functional SELP hybrids were obtained by using SELP-59-A [6] as a structural module and the antimicrobial peptides ABP-CM4, BMAP18, hepcidin and Synoeca-MP, an antimicrobial peptide isolated from _Synoeca surinama_ social wasp [48], as antimicrobial functional modules. These AMPs were chosen due to their broad and potent antimicrobial activity against different microorganisms [49; 50; 51; 52; 53; 54].