## 6 Combining Active and Passive Antibiofilm Strategies
Since at infections sites, the surrounding milieu is slightly acidic, the authors concluded that besides their bacterial anti-adhesive properties, the pH-induced release of antibacterial agents is another important advantage of these mono and multilayered coatings [120]. [PERSON] et al. [124] prepared new hydrogels with non-fouling and controlled drug release properties based on a graft copolymer derivative of HA. HA is a linear polyanionic polysaccharide composed of repeating units of \(D\)-glucuron acid (GlcUA) and \(D\)-2-\(N\)-acetyl-glucosamine (GlcNAc), which are linked together by \(\beta\)-1,4, and \(\beta\)-1,3 glycosidic bonds. The graft copolymer was prepared by ATRP. The synthesis depicted in Scheme 15 starts with the activation of some of the primary alcohol functionalities in the tetrabutylammonium salt of HA (HA-TBA) as \(p\)-nitrophenyl carbonate derivatives followed by displacement of the very good leaving group \(p\)-nitrophenyl by ethylenediamine (EDA). The grafted amino groups served as nucleophilic counterparts for reaction with the activated N-hydroxysuccinidyl (NHS) ester of 2-bromo-2-methylpropionic acid (BMP) to eventually yield the ATRP macroinitiator, HA-TBA-EDA-BMP [125; 126]. The next step was the graft polymerization of sodium methacrylate (MANa), which occurred from the modified HA backbone in the presence of copper bromide Cu(I)Br as a catalyst and of 2,2'-bipyridyl (Bpy) as a ligand to afford the graft copolymer HA-TBA-EDA-BMP-MANa. The newly synthesized HA derivative bore both pendant unreacted ethylenediamine groups and carboxylic moieties from the newly grafted short segments of polymethacrylate. When dispersed in aqueous buffers at various pH values (3.0, 6.0, and 7.4) and concentrations ranging from 5 to 10% (_w/v_), the polycarboxylic/amino-functionalized derivative of HA formed transparent hydrogels, which were used to enclose the antibiotic vancomycin. Depending on the initial pH of the dispersing medium, the corresponding final pH values of the obtained hydrogels were 5.0, 6.0, and 7.0 at a polymer concentration of 10% _w/v_. For the preparation of vancomycin-loaded hydrogels, the antibiotic was first dissolved in each of the above three dispersing media, and then appropriate volumes of each of the resulted solutions were mixed with lyophilized copolymer powders in the right ratios to produce final formulations containing 2% _w/v_ vancomycin and 10% _w/v_ copolymer. In vitro release studies were performed on Franz diffusion cells for all the three medicated hydrogels prepared from the graft copolymer derivative of HA. The cumulative amount of vancomycin released during a period of time by each hydrogel as compared to the total amount of antibiotics released over the same period of time from a vancomycin formulation prepared similarly except that unmodified HA was used. **Scheme 14. ** Synthetic pathway for the preparation of zwitterionic \(\beta\)PDMA-\(b\)-PDPA diblock copolymer micelles, the building blocks for further construction of mono and multilayered films. All the three hydrogels obtained from the HA-TBA-EDA-BMP-MANa graft copolymer showed a much-diminshed burst effect as compared to the sample prepared using HA. The lower the final pH of the hydrogel, the more important the effect on burst release reduction. For instance, the hydrogel with the final pH equal to 5.0 released about 24% of vancomycin after 5 h, while 45% of the drug was released during the same time interval from the hydrogel formulated at pH 7.0. For comparison, after 5 h, the formulation obtained using unmodified HA released 85% of the embedded vancomycin. Moreover, after the initial burst effect, all three hydrogel formulations based on the HA-TBA-EDA-BMP-MANa graft copolymer showed sustained release profile, the hydrogel with the lowest pH value being the most effective in slowing down drug release rate and exhibiting extended-release up to 48 h [124].