## 5 Coating Materials with Embedded Antibiotics and Other Antibofilm Agents
### Antibiotic Based Antib Biofilm Coatings
In order to optimize the performances of the fabricated hydrophilic multilayer coatings in terms of loading capacity and sustained release the authors studied: (i) The effect of the concentration of Ca\({}^{2+}\) ions in the coating solutions on MH loading and release, (ii) the effect produced by incorporation of Ca\({}^{2+}\) ions into MH and GA layers on MH release kinetics, and (iii) the effect of the numbers of DS+Ca\({}^{2+}\)/MH/GA and DS+Ca\({}^{2+}\)/MH+Ca\({}^{2+}\)/GA+Ca\({}^{2+}\) trilayers on MH release. The optimal configuration that ensures the highest drug density of 645 \(\upmu\)g/mm\({}^{3}\) and the best release kinetics characterized by a low initial burst effect followed by a slow, stable release for over 35 days was found to be (DS+Ca\({}^{2+}\)/MH+Ca\({}^{2+}\)/GA+Ca\({}^{2+}\))\({}_{8}\) and was prepared at the optimal concentration of 7.2 mM Ca\({}^{2+}\) in the coating solutions. The thickness of (DS+Ca\({}^{2+}\)/MH+Ca\({}^{2+}\)/GA+Ca\({}^{2+}\))\({}_{8}\) film was 402 \(\pm\) 19 nm corresponding to an average trilayer thickness of 50 nm. After drug release, the thickness of the film was decreased only by about 100 nm, indicating that MH release from the LbL coating was not due to the degradation of the LbL film. The antibioticfilm activity of the (DS+Ca\({}^{2+}\)/MH+Ca\({}^{2+}\)/GA+Ca\({}^{2+}\))\({}_{8}\) film was tested against several bacterial strains including _E. coli_ ATCC 25922, _E. coli_ 0157:H7, _Acinetobacter baumantii_ ATCC 19606, _S. aureus_ ATCC 25923, MRSA USA300, _S. epidermidis_ ATCC 12228, and a clinical isolate _A. baumantii_ by comparison with bare polystyrene substrate and substrate coated with a (DS+Ca\({}^{2+}\)/GA+Ca\({}^{2+}\))\({}_{8}\) film. The XTT assays demonstrated that coatings with incorporated MH inactivated bacteria in all tested biofilms. Furthermore, a live/dead cell double staining assay using SYTO 9 and propidium iodide dyes revealed complete elimination of multi-drug resistant _A. baumantii_ biofilm on coatings loaded with MH. Figure 1: Chemical structures of minocycline hydrochloride (**a**), 2:1 Ca\({}^{2+}\)/minocycline hydrochloride chelate (**b**), and dextran sulfate sodium salt (**c**). Another strategy that exploits variations in pH to control the loading and release of antimicrobial compounds consists of the development of polyelectrolyte multilayer microcapsules with pH-tunable permeability [31; 32; 33; 34; 35]. [PERSON] et al. [35] accomplished pH-controlled ciprofloxacin hydrochloride (CH) encapsulation in and release from polyelectrolyte multilayer microcapsules fabricated by LbL deposition of poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) on poly(styrene sulfonate) (PSS)-doped calcium carbonate particles as sacrificial templates. Spherical PSS doped CaCO\({}_{3}\) microparticles with a diameter of \(6\pm 0.5\)\(\upmu\)m were prepared by co-precipitation of CaCl\({}_{2}\) and Na\({}_{2}\)CO\({}_{3}\). The dopant PSS was dissolved in the Na\({}_{2}\)CO\({}_{3}\) solution prior to mixing equal amounts of the two solutions [33; 34; 35]. Since the CaCO\({}_{3}\) microparticles have been synthesized in the presence of the anionic polyelectrolyte PSS, their surface was negatively charged, as evidenced by zeta potential measurement [33]. Hence, the first layer deposited on the surface of the CaCO\({}_{3}\) microspheres templates was the positively charged polyelectrolyte PAH followed by deposition of the oppositely charged polyelectrolyte PMA and the iterative procedure was repeated until four PAH/PMA bilayers were deposited. The negatively charged PSS molecules adsorbed on the surface of the template also play the role of preventing the recrystallization of CaCO\({}_{3}\) into the more stable rhombohedral calcite polymorph [34]. CaCO\({}_{3}\) particles have been chosen to template the synthesis of the polyelectrolyte multilayer microcapsules because they can be easily removed with a chelating agent like ethylenediaminetetraacetic acid (EDTA).