# Biofilms: Novel Strategies Based on Antimicrobial Peptides
## 4 Nanoparticles Coated with AMPs  
Nanotechnology through the combination of AMPs and nanoparticles (NPs) could improve the antimicrobial action of the peptides but also overcome their disadvantages [49; 50; 51]. Nanotechnology offers a number of promising opportunities to develop antimicrobial nanosystems that break the biofilm barrier and penetrate over significantly larger distances into biofilm, killing its microorganisms more than conventional antibiotics or AMPs. Both the multidrug resistance and protective character of biofilms could make common antibiotics thousands-fold less potent. Despite the initial enthusiasm for AMPs as alternative candidates to antibiotics, disadvantages have limited their development and clinical use. Thanks to nanotechnology, many nanomaterials (1-100 nm) have been developed with powerful capability of delivering drugs. Among them, NPs are widely exploited in different fields. According to the application, the NP composition can vary and for biomedical applications, various biocompatible materials have been exploited. Many NPs have been demonstrated to have anti-biofilm activities by themselves, but nonetheless, they can carry antimicrobial agents such as AMPs and show enhanced properties. Silver NPs, gold NPs, quantum dots (QD) NPs have anti-biofilm activities even though their toxicity remain a serious issue which prevents their full application. Functionalization of NPs surface with AMPs is attracting growing interest for three main reasons: (i) NPs can facilitate delivery; (ii) NPs make peptides more resistant towards degradation; (iii) peptides form a protecting/coating shell on the NPs, which can reduce their toxic effect. Thus, when conjugated, peptides and NPs combine the antimicrobial activity of both components and are also able to overcome their drawbacks. Thus, functionalization of NPs with AMPs might represent a novel approach to overcome some problems related to the limited clinical use of AMPs, as reported in Figure 2.  
Covalent immobilization of AMPs and their analogues is widely exploited. Although being a promising strategy, covalent immobilization appears to produce new properties and functions that are not owned by their building blocks [52], which may influence their interaction with cell membranes and their activity. As a consequence, the antimicrobial activity may be affected because the charge distribution will be different from that of single peptide molecules. A novel strategy to develop nanosystems coated with AMPs is represented by the use of self-assembled peptides for the obtainment of on demand supramolecular nanostructures (nanotubes, nanobelts, fibrils, nanosviescles, gels, and nanocages), which can disassemble upon contact with the bacteria and release the AMP. Recently, a novel versatile platform was developed in our laboratory to immobilize an analogue of the marine antimicrobial peptide myxnidin (WMR) on a peptide based biomaterial [53]; the AMP sequence was located on the periphery of the nanofiber, and was able to increase their effective local concentration compared to soluble peptides and was the driving force for improved antibacterial activity [54; 55; 33; 56]. The presence of WMR on self-assembled nanostructures improved anti-biofilm activity against the Gram-negative bacterium _P. aeruginosa_ and the fungus _C. albicans_; the fibers were able both to inhibit the biofilm formation and to eradicate pre-formed biofilms [53; 57]. [PERSON] et al. showed that RBRBR-CS-NPs, a polymeric NPs functionalized with RBRBR, cationic ultrashort AMPs, were active against wild-type and the multidrug-resistant clinical isolated strains of Gram-positive bacteria compared to the peptide-unloaded nanoparticles [58]. The antimicrobial effect is very powerful also against clinical isolates of the resistant strains of _S. aureus_ compared to free RBRBR. [PERSON] et al.