## 8 Conclusions and Future Trends  
Unlike passive antibiofilm strategies discussed in Part I of the present review, active antibiofilm coatings do not impede bacterial adhesion but rather are designed to prevent biofilm development by killing bacteria or inhibiting their growth. To this purpose, an antimicrobial agent is either covalently tethered to the surface of the coating or physically entrapped within the bulk of the coatings being subsequently eluted from the coated device into the surrounding tissue. The covalent immobilization has the advantage of avoiding the depletion of the biodidal material, but on the other hand, the bactericidal action is restricted to the surface. Another major problem of contact-killing surfaces is the fact that usually, they are thought to be self-deactivating since the corpses of killed bacteria from a surface layer to which new incoming active microbes can adhere and subsequently proliferate on it. The non-covalent immobilization strategy extends the action area of the antimicrobial agent, but at the same time, the effect is limited in time. Moreover, leaching coatings may promote the development of bacterial resistance. Therefore, the next logical step was to combine the best elements of both passive and active strategies into one single platform. In this combined approach, the two strategies can be applied either simultaneously or sequentially. The appropriate mode of application of the two strategies must take into account their characteristics. For instance, if the contact killing and the antiadhesive strategies are to be combined, it is futile to apply them simultaneously because the active and passive elements dilute each other, and the bactericidal capability will be diminished compared to a pure contact killing surface [128]. Hence, it is much more profitable to apply them sequentially, that is to kill bacteria first and then to release the attached dead bacteria and to prevent further bacterial colonization as described in Section 7 (Applying Active and Passive Strategies One at a Time and Reversibly Switching between the Two Approaches). Through appropriate smart design, the converting process from bactericidal to non-fouling surface can be made reversible, allowing several killing/regeneration cycles to be performed, thereby greatly increasing the antimicrobial efficacy of these surfaces. Another milestone in the development of antib biofilm surfaces was achieved by designing smart coatings that provide triggered release of the antimicrobial payload in response to some changes in their microenvironment. Internal triggers like pH and temperature, as well as external triggers such as laser light, ultrasounds, and so on, can be used. The problem with this type of triggers is that in some situations, they can activate the release of the antibacterial agent even in the absence of any pathogens. Hence, the antimicrobial compound is uselessly lost and may cause unwanted side effects being also detrimental to beneficial bacteria. Consequently, a current trend that will continue in the future is the development of smart antib Biofilm surface coatings that become activated only in the presence of pathogens. The concept of self-defensive surfaces based on polyelectrolyte multilayers (PEMs) was first demonstrated by [PERSON] and co-workers [146]. Using the LbL technique, they prepared ultrathin hydrogel films that release antimicrobial agents in response to bacteria-triggered local acidification of the medium. [PERSON] et al. [147; 148] prepared PEM films based on the biocompatible and biodegradable polysaccharides HA as polyanion and CHI as polycation, respectively. Using the carbodiimide chemistry and the thiol-maleimide coupling reaction, they grafted bovine cateslytin (CTL), an endogenous antimicrobial peptide, on HA. To this end, cateslytin was previously modified by adding a \(C\)-terminal cysteine residue (C).