## 6 Combining Active and Passive Antibiofilm Strategies
[131] fabricated smart thermoresponsive copolymer brushes based on diethylene glycol methyl ether methacrylate (MEO\({}_{2}\)MA), hydroxyl-terminated oligo(ethylene glycol) methacrylate (HOEGMA), and 2-hydroxyethyl methacrylate (HEMA) by SIATRP. The copolymer brushes were grown from plasma oxidized silicon wafers modified with the ATRP initiator, 2-bromo-2-methyl-propionic acid 3-trichlorosilanyl-propyl ester following the procedure of [PERSON] et al. [132]. The obtained poly[MEO\({}_{2}\)MA-_co_-HOEGMA-co_-HEMA] copolymer was further conjugated to an antimicrobial peptide derived from natural magainin I by introducing an additional cysteine residue at the C-terminus. Bioconjugation was achieved via a two-step process by using \(N\)-(\(p\)-maleimidophenyl)isocyanate (PMPI) as a heterolinker [133]. In the first step, PMPI-grafted brushes were obtained through the reaction of the isocyanate moiety in the heterolinker with the free pendant hydroxyl groups in the HOEGMA and HEMA segments. Subsequently, the reactive maleimide units in the PMPI-grafted copolymer brushes were utilized to conjugate the thiol group of the modified antimicrobial peptide MAG-Cys. At lower temperatures, the copolymer brush is in a swollen extended-chain conformation due to the hydration of the oligo(ethylene glycol) segments. Hence, in this extended-chain conformation, the copolymer brush exposes its grafted antimicrobial magainin I derivative molecules to bacteria enabling interaction with the bacterial cell membrane and inducing bacterial lysis. As the temperature is raised, dehydration occurs, and the copolymer brush collapses into a more compact structure. However, the transition from the extended-chain conformation to the collapsed conformation is not a sharp one but rather a gradual cooperative transition that occurs over a large range of temperatures and not sharply at one temperature. Collapse first occurs at the bottom of the swollen brush, and phase separation propagates upward to the top of the brush during the ongoing process. Hence, the outermost chain segments of the oligo(ethylene glycol) methacrylate-based brush are dehydrated later and collapse at a higher temperature than the inner bulk segments of the copolymer brush. The collapse transition temperature of the bulk of the poly[MEO\({}_{2}\)MA-\(co\)-HOEGMA-\(co\)-HEMA] copolymer brushes, \(T_{coll}^{bulk}\), grafted from silanized silicon wafer substrates, was determined by [PERSON] et al. [134] through quartz crystal microbalance with dissipation monitoring (QCM-D) measurements in water. \(T_{coll}^{bulk}\) can be finely tuned by varying the monomer composition of the polymerization mixture. For instance, increasing the molar composition of the copolymer brush in the more hydrophilic HOEGMA segments results in an increased \(T_{coll}^{bulk}\) as compared to the \(T_{coll}^{bulk}\) of a poly(McEO\({}_{2}\)MA) brush which equals 22.2 \({}^{\circ}\)C. By contrary, increasing the content of the copolymer brush in HEMA segments results in a decrease of the \(T_{coll}^{bulk}\). In fact, this is the great advantage this type of copolymer brushes has, since \(T_{coll}^{bulk}\) can be adjusted to a value very close to the physiological temperature [135]. A relevant example is a poly[MEO\({}_{2}\)MA-\(co\)-HOEGMA-\(co\)-HEMA] copolymer brush with a segment composition of 50:30:20 whose \(T_{coll}^{bulk}\) is equal to \(35\pm 1\)\({}^{\circ}\)C. On the other hand, the authors also determined the collapse transition temperature of the surface of the brush, \(T_{coll}^{surf}\), by measuring the equilibrium water contact angles, and found out that \(T_{coll}^{surf}\) is about 8 \({}^{\circ}\)C higher than \(T_{coll}^{bulk}\)[134; 131]. That means that at a temperature slightly higher than \(T_{coll}^{bulk}\), for instance, at 38 \({}^{\circ}\)C, the outermost oligo(ethylene glycol) segments still remain in a swollen hydrated state providing bacterial repellent properties.