## 6 Combining Active and Passive Antibiofilm Strategies
The aim is to design smart surfaces that in response to some environmental changes are able to irreversibly switch from an antimicrobial status to a bacterial repelling status (the so-named \"kill and repel\" strategy) or reversely from a non-fouling status to a bacterial killing status (the so-called \"resist and kill\" strategy) [128]. Figure 8: Amphiphilic block-like copolymer membrane surface modifier for the creation of an integrated active-passive fouling release nanocoating. In the \"kill and repel\" approach, the surface is initially in the bactericidal status and kills bacteria on contact. Subsequently, the surface switches to the non-fouling status releasing the attached bacteria and preventing any further bacterial association with the surface. As an illustrative example, we mention here the pioneering work of [PERSON] et al. [129] who were the first to report a switchable polymer surface coating based on the contact killing polymer poly(carboxybetaine methacrylate ethyl ester) (PCBMAEE) which after pH-triggered irreversible hydrolysis turns into the non-fouling zwitterionic polymer poly(carboxybetaine methacrylate) (PCBMA). PCBMAEE killed more than 99.9% of _E. coli_ K12 in 1 h, and 98% of the dead bacterial cells could be released after its hydrolytic conversion to PCBMA [129]. [PERSON] et al. [130] conceived a wound dressing based on a modified CHI non-woven surface which can be kept in a bactericidal status during storage and undergoes a hydrolytic-driven switching to its non-fouling status before being used. A presynthesized copolymer bearing azlactone moieties and positively charged quaternary ammonium groups was attached to the CHI backbone through a \"grafting to\" methodology based on highly efficient \"click\" type ring-opening of pendant azlactones by the attack of the nucleophilic primary amino groups in CHI. In brief, copolymerization of 2-vinyl-4,4-dimethylazlactone (VDMA) with 2-chloroethyl acrylate (CEA) was conducted in the presence of AIBN as an initiator, and subsequently, methyl 3-(dimethylamino)propionate (MDAP) was \(N\)-alkylated with the pendant 2-chloroethyl acrylate groups in the resulting copolymer to afford the quaternized Q-poly(VDMA-_co_-CEA) copolymer as shown in Scheme 16. Next, dried CHI non-woven was dipped into dimethylsulfoxide (DMSO) solution of the quaternized copolymer for 24 h at 60 \({}^{\circ}\)C, rinsed with DMSO and ethanol, and dried at room temperature [130]. The antibacterial performance of the as-prepared modified CHI non-woven surface was estimated by counting the number of adhered _E. coli_ bacterial cells revealed by SEM imaging. The surface density of attached _E. coli_ on the quaternized CHI (Q-CHI) non-woven substrate was drastically reduced compared to a CHI non-woven reference demonstrating its strong antibacterial effect. Conversion of the bactericidal Q-CHI non-woven surface into the non-fouling zwitterionic CHI (Z-CHI) non-woven surface was achieved simply by basic hydrolysis in a solution containing 1.0 M NaOH and methanol with a pH value equal to 11.8. The Z-CHI non-woven surface-displayed very low hemolytic activity, reflecting low cytotoxicity. A hemolytic ratio as low as 0.44% was determined using blood freshly drawn from healthy rabbits. Furthermore, the reduced hemolytic activity translates into a good antithrombotic effect since hemolysis has been associated with increased platelet aggregation and accelerated clot formation. The blood clotting index of the Z-CHI non-woven surface determined after 1 h of incubation at 37 \({}^{\circ}\)C was larger than 95%, indicating good antithrombosis properties [130]. Temperature is another environmental stimulus that can be used to trigger the transition of a smart, functional coating from its bactericidal status to the non-adhesive status. To this purpose, [PERSON] et al.