###### Abstract  
Antibacterial resistance is a major worldwide threat due to the increasing number of infections caused by antibiotic-resistant bacteria with medical devices being a major source of these infections. This suggests the need for new antimicrobial biomaterial designs able to withstand the increasing pressure of antimicrobial resistance. Recombinant protein polymers (rPPs) are an emerging class of nature-inspired biopolymers with unique chemical, physical and biological properties. These polymers can be functionalized with antimicrobial molecules utilizing recombinant DNA technology and then produced in microbial cell factories. In this work, we report the functionalization of rPPs based on elastin and silk-elastin with different antimicrobial peptides (AMPs). These polymers were produced in _Escherichia coli_, successfully purified by employing non-chromatographic processes, and used for the production of free-standing films. The antimicrobial activity of the materials was evaluated against Gram-positive and Gram-negative bacteria, and results showed that the polymers demonstrated antimicrobial activity, pointing out the potential of these biopolymers for the development of new advanced antimicrobial materials. antimicrobial resistance; antimicrobial surfaces; antimicrobial films; recombinant protein polymers; silk-elastin proteins; elastin-like recombinamers; antimicrobial peptides +
Footnote †: journal: Applied Sciences  
1 CBMA (Centre of Molecular and Environmental Biology), Department of Biology, Campus de Gualtar, University of Minho, 4710-057 Braga, Portugal, [EMAIL_ADDRESS] (A.M.T.P.) [EMAIL_ADDRESS] (D.G.) [EMAIL_ADDRESS] (D.  
specific folding of building blocks that hierarchically assemble into well-defined structures. These building blocks have been used as design modules for the formulation of recombinant protein polymers (rPPs) with unique properties [1,3]. Recombinant DNA technology allows the biological synthesis of precisely defined rPPs with absolute control over size and composition. This technology is very powerful, enabling the design of multifunctional protein-based materials by fusing genes encoding for individual protein blocks, and even functional modules, into a single large gene [4]. For instance, the structure of rPPs can be genetically manipulated to incorporate the minimal consensus repeats of silk and elastin into the same molecule [5,6] and to include bioactive domains such as antimicrobial peptides (AMPs) [7, 8, 9]. The versatility of this approach allows custom design of the structure of rPPs to obtain functional protein materials that can be processed into different active materials such as coatings, films and fiber mats [7, 8, 9, 10, 11, 12, 13]. Due to the unique balance of mechanical properties, biocompatibility and thermostability, elastin-like polypeptides/recombinamers (ELPs/ELRs) and silk-elastin-like proteins/recombinamers (SELPs/SELRs) have been widely studied for the development of biotechnological applications [1,14,15]. ELRs are composed of repeating amino acid building blocks with a typical sequence of VPGXG (V--valine, P--proline, G--glycine, X is any amino acid except for proline) [16], characterized by a reversible temperature-dependent phase-transitional behavior [17,18]. SELPs are a group of copolymers consisting of alternate amino acid repetitions of silk blocks with sequence GAGAGS (A--alanine and S--serine) and elastin blocks, repeated in tandem [6]. These copolymers combine hard (silk) and soft (elastin) domains and can spontaneously form hydrogen-bonded antiparallel \(\beta\)-sheets, with the silk blocks imparting thermal and chemical stability and the elastin blocks reducing the overall crystallinity of the system, increasing its flexibility and water solubility [5,19]. Antimicrobial peptides (AMPs) are promising alternatives to classical antibiotics due to their broad antimicrobial activity and remarkable efficacy [20].