## 2 Co-Administration of Two Different Antimicrobial Polymers
### Nitric Oxide co-Administration Systems
aureus_ and _P. aeruginosa_[70]. The formation of dangerous bacterial biofilms on the surface of medical devices, such as catheters or implants, often leads to health complications, such as recurrent infections [79]. The treatment of biofilm-related infections is challenging because the bacteria cells are embedded in a polysaccharide matrix with embedded cells which makes them highly resistant to hostile environmental conditions and antibiotic treatment [14]. At this time, the synergy between NO-releasing agents and dendrimers remains uncertain since only a low cooperative effect has been observed. As a consequence, a comprehensive study is required to clarify a possible collaborative interaction, as well as the extent of such an impact. It may also be desirable to design new polymers to combine them with NO-releasing compounds and other biocidal agents. In summary, NO-releasing agents appear to be a promising research area for the development of novel antimicrobial materials to fight bacterial drug resistance. Figure 5: Comparison of the inhibition of viable colony forming units (CFU cm-2) of _S. aureus_ and _P. aeruginosa_ on the surface Carbosil of _S_-nitrooS-N acetylpenicillamine (SNAP) films, benzophenone based quaternary ammonium molecules (BPAM) films and SNAP-BPAM films. Reproduced with permission from reference [76]. Copyright 2017 RSC. Enhancing Efficiency of Antimicrobial Cationic Polymers by Incorporating Metal Oxides and Metal Nanoparticles  
Nanomaterials provide attractive structural and surface properties to fight bacterial infections due to their exceptional diffusivity and penetrability, as well as their ability to inhibit bacterial growth. During recent decades, substantial research on their biocide properties has been performed opening their application to several healthcare fields such as nanomedicine, drug delivery or pharmacy [80]. Thus, the use of combinations of nanoparticles (NPs) with cationic antimicrobial polymers represents a promising approach to reduce microbial resistance. In particular, NPs derived from silver, copper, gold, titanium oxide as well as zinc oxide have shown outstanding bactericidal behavior and a wide range of antimicrobial effects, and have arisen as attractive alternative materials to complement and enhance the performance of well-known antimicrobial polymers [81; 82; 83]. Thus far, the mechanisms of action of NPs against bacteria have not been precisely established and depend on many factors (size, concentration, surface modification, etc. ), but it is known that they cause damage on the cell membrane altering vital functions as permeability and respiration, and disturb functions of some proteins contained into bacteria [84]. It is well documented that silver possesses strong antimicrobial properties both in its salt and nanoparticle form. Hence, it has found a variety of applications in different fields [85; 86; 87]. In particular, silver nanoparticles (AgNPs), one of the predominant nanomaterials, display a broad-spectrum of antimicrobial activity against bacterial and fungal species, including antibiotic-resistant strains [88; 89]. Their proposed mechanisms of action involve the gradual release of silver ions that interfere in DNA functions, direct damage to the cell structure and the generation of reactive oxygen species (ROS) [86; 90]. In case of copper nanoparticles (CuNPs), their metallic and ionic forms produce toxic hydroxyl radicals that damage essential proteins and DNA [84]. Furthermore, gold nanoparticles (AuNPs) have shown to combat multi-drug-resistant pathogenic bacteria, and also, to exhibit enhanced properties in terms of physical and chemical stability with excellent biocompatibility [91; 92]. ZnO and TiO\({}_{2}\) NPs have also attracted considerable interest due to its good photocatalytic activity, nontoxicity and antibacterial properties for application in several fields such as cosmetics, depollution and protective medical clothes [93].