## 3 Nanotechnology Solutions for Biofilm Control  
Nanotechnology offers promising solutions and innovative strategies for overcoming the problem of biofilm resistance and tolerance [7]. Based on our present knowledge of biofilm properties and formation mechanism, three main strategies to combat biofilm development emerged (see Figure 1): passive strategies, active strategies, and a combination of these two strategies. All these strategies involve various modifications of the surface properties of the implanted biomaterial or its bulk chemistry.  
The passive concept aims to prevent adhesion by using antifouling coatings that inhibit the adherence of microorganisms without interfering with the proliferation or the metabolism of the microorganisms. Bacterial attachment can be impeded by controlling the surface hydrophobicity, the surface nanotopography and roughness, the surface stiffness, and the surface electrostatic charge [95].  
The active concept uses coatings with intrinsic antimicrobial properties. Two different strategies fall in this category, i.e., non-release-based antimicrobial systems that are thought to act by contact killing and release-based (drug-eluting) coatings [95; 96]. The first one relies on the covalent immobilisation of the biocidal compounds onto biomedical device surfaces, rendering them antimicrobial properties. The second strategy is based on physical immobilisation of the biocides into matrix coatings from which after implantation, the biocides are gradually released into the surrounding environment through various mechanisms such as bulk and surface erosion, diffusion, and osmotic pressure. Different encapsulation techniques such as solvent displacement, emulsion-solvent diffusion, emulsion-solvent evaporation, salting out, coacervation, and layer-by-layer assembly can be used to incorporate the active ingredients into the antimicrobial coatings. The antibacterial activity may rely on different mechanisms and compounds: polycations that are able to disrupt the bacterial cell wall allowing the cell contents to spill out; antimicrobial peptides; antimicrobial enzymes that are able to degrade the chemical constituents of the biofilm matrix (DNA, polysaccharides, proteins); antibiotics that interfere with microbes vital metabolic processes such as cell respiration, cell division, or cell wall synthesis; antiseptics; and QS inhibitors that interfere with the bacterial sensing network [96; 97]. Antimicrobial coatings targeting inhibition of the transition of the planktonic phenotype of bacteria into a sessile type represent another promising strategy [98]. Multifunctional coatings that combine the above two approaches exhibiting both antiadhesive and antimicrobial properties have also been designed.  
The present review given in two parts will highlight the most recent and significant achievements in the field of antimicrobial coatings, emphasising the functional principles, the synthetic strategies, and the antibacterial and antifouling performances of these materials. Smart stimuli-responsive and multifunctional materials are also included.  
Figure 1: Schematic representations of various currently used strategies to design anti-infective nanostructured surfaces.