Biocide-releasing polymers

Antimicrobial polymers have been classified in three different major groups. There are biocide-releasing polymers, polymeric biocides, and biocidal polymers (Figure 15.2). 

In general, biocide-releasing polymers have no influence over their intrinsic antimicrobial activity. The polymers are simply acting as carriers for biocides or antibiotics. The biocidal molecules, which are incorporated in the polymer matrix and/or tethered to the polymer backbone, are released. One of the major advantages of these systems is that the release of the embedded antimicrobial active substances is controlled by the used polymeric system. Therefore, the rates of release are adjustable and polymers can release the biocides very close to the cell, which makes them efficient. However, the polymers still release biocides into the environment and will eventually become inactive. Polymeric biocides contain biocidal repeating units. Such macromolecules often show the same mode of action as their repeating units with somewhat lower activity, due to the steric hindrance caused by the polymeric backbone. Biocidal polymers distinguish themselves by the fact that they act as a whole molecule. Further, biocidal polymers have been found to show a lower tendency to build up bacterial resistance. ... 

Thamizharasi et al. started with sulfamethoxazole and introduced me-thaciylic, aciylic, and maleimide groups. The resulting polymers revealed in some cases even better activities than the low molecular weight monomers. Similar to biocide-releasing polymers, there is the opportunity to use antibiotics instead of biocides. Moon et al. prepared an aciyl monomer containing a norfloxacin moiety. This polymer was blended with other common synthetic polymers. These samples reduced the viable cell number of microbial cells in shake flask tests. ... 

In the first three approaches, the polymer acts as a carrier for the antimicrobial agent that once released can exert its action (antimicrobial agent-releasing polymers). In the first case the antibiotic is adsorbed mainly on the device surface, in the second case the drug is physically entrapped, while in the third case the antibiotic is grafted by labile bonds. In the fourth approach, the whole polymer (the bulk and the surface) is intrinsically antimicrobial and exerts its killing action when microorganisms contact the surface. These polymers are often called biocidal polymers. 

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