## 6 Combining Active and Passive Antibiofilm Strategies  
[PERSON] et al. [117] designed new surface coatings with dual functionality that are able to release a bacteria-killing agent and to repel the bacterial adhesion simultaneously. The synthetic procedure starts with a quite simple \"priming\" method through which an adhesive PDA film was deposited on a polycarbonate substrate by a dip-coating process. The method takes advantage of the chemical structural features of the PDA film. The catechol groups in PDA are redox-active and can get oxidized to quinone groups, thereby reducing metal ions like Ag\({}^{+}\)[118]. On the other hand, quinone functional groups can serve as anchor points for covalent grafting through Michael addition of hydrophilic polymers bearing nucleophilic end groups like poly(ethylene glycol) methyl ether thiol (mPEG-SH). Briefly, the successive synthetic steps followed by the authors were the next ones: (i) Coating PDA thin films on the polycarbonate substrates through direct immersion of the substrates in a freshly prepared solution of DA hydrochloride in bicine buffer (pH 8.5) for 18 h at room temperature; (ii) formation and incorporation of zero-valent silver nanoparticles into the PDA coatings by simply incubating the PDA-modified substrates with a solution of silver nitrate for 24 h at room temperature; (iii) deposition of a new PDA layer by repeating the first step under identical conditions except for the incubation time which was reduced to 4 h; and (iv) grafting PEG brushes by incubation of the silver nanoparticles incorporated PDA coatings in a solution of mPEG-SH in cloud point buffer for 6 h at 55 \({}^{\circ}\)C [117]. The prepared coatings exhibited sustained release of silver nanoparticles over at least 10 days. The performances of these coatings in terms of their antifouling and antimicrobial properties were evaluated on three bacterial strains: _E. coli_, _S. epidermidis_, and _P. aeruginosa_. The bacterial attachment was assessed using fluorescence imaging, while a live/dead staining assay was used to estimate the antibacterial activity. While unmodified polycarbonate substrates developed biofilms of all three bacterial strains, substrates modified with PDA, silver nanoparticles, and PEG brushes suppressed bacterial attachment for all the tested strains. When the PDA/Ag/PEG-modified polycarbonate substrates were inoculated with an inoculum suspension (20 \(\mu\)L; \(2.5\times 10^{9}\) CFU/mL) of each bacterial strain premixed with a live/dead stain and incubated at 37 \({}^{\circ}\)C for 24 h, almost all bacterial cells were found to be dead at the end of the incubation period except for _E. coli_ for which a slightly lower ratio of the area occupied by dead cells to the total area covered by bacterial cells (both live and dead) was observed [117]. [PERSON] and coworkers reported an ingenious and innovative approach to creating smart dual-functional surface coatings with both anti-adhesive and antibacterial agent releasing properties. They prepared monolayered films [119] as well as LbL self-assembled multilayer coatings [120] based on zwitterionic block copolymer micelles. Using a diblock copolymer composed of a polyzwitterionic poly[3-dimethyl] (methacryloyloxyethyl) ammonium propane sulfonate] block (\(\beta\)PDMA) imparting anti-biofouling properties and a pH-responsive poly[2-(diisopropylamino)ethyl methacrylate] (PDPA) block, the authors attained pH-induced micellization by increasing the pH of an aqueous acidic solution of the \(\beta\)DMA-\(b\)-PDPA diblock copolymer above the pK\({}_{\text{a}}\) value of about 6.4 of the PDPA block. By increasing pH, the PDPA block becomes uncharged due to gradual deprotonation. Hence, the hydrophobic association among the PDPA blocks is reinforced, and the \(\beta\)PDMA-\(b\)-PDPA diblock copolymer self-assembles in micellar aggregates with hydrophilic zwitterionic bacteria repelling \(\beta\)-PDMA coronae and hydrophobic PDPA cores, the latter serving as reservoirs to trap hydrophobic antimicrobial agents.