Microbe-repelling surfaces

In applications where self-polishing is not possible, the combination of a microbe-repelling surface and a release system seems to be desirable. One example of a design for such a surface is shown in Fig. 8. The depicted coating is based on a hydrophilic polymer network that contains polyethyleneimine crosslinkers, which are capable of selectively taking up silver ions and acting as a template for silver nanoparticles [90], This reloadable co-network was surface-modified with PEG,... 

Fig. 9 Example of a contact-killing and microbe-repelling surface, (a) Antimicrobial cationic polyW.iV-dimethyl-iVTethoxycarbonylmethyll-iV-P -tniethacryloyloxylethyll-ammonium bromide) left structure) effectively kills bacteria, (b) The polymer is converted into the corresponding nonfouling zwitterionic derivative (right structure) upon hydrolysis, (c) Dead bacteria remaining on the surface are repelled from the nonfouling surface, (d) The zwitterionic surface itself is highly resistant to bacterial adhesion. Reproduced and adapted from [136]...

Besides the numerous synthetic and natural polymers that are suited for repelling microbes from surfaces (summarized in [8]), the negatively charged protein albumin can also reduce bacterial adhesion [30], Further, the nature of the surface-attached repelling polymer and its mechanical properties both seem to play a role in the attraction of microbes. This was demonstrated by Lichter et al., who investigated poly(allylammonium hydrochloride) (PAH) and poly(acrylic acid) (PAA) multilayers and found that the stiffness of the coating positively correlated with the adhesion of E. coli. [31],... 

More recently, Chen et al. described a surface modification whereby the polymer poly(Ar,Ar-dimethyl-Af-(ethoxycarbonylmethyl)-Ar-[2/-(methacryloyloxy)ethyl]-ammonium bromide) was grafted from a surface via ATRP [136], The cationic polymer effectively kills E. coli and is subsequently converted into a zwitterionic polymer by hydrolysis of the head group (Fig. 9). It then repels all attached cells dead or alive. This is the first example of a surface that can kill microbes on contact and repels them after that. The only downside of this elegant system is that it will eventually exhaust and turn into a more or less effective repelling surface. 

The most critical microbial infection is the biofilm, which is formed by adhesion and proliferation of planktonic microbial cells. Once formed, it is highly resistant, hard to remove, and often a deadly thread to other living forms. To avoid such biofilm formation, nature has developed two major strategies to avoid such infections, microbe killing and repelling surfaces. Most commonly and adapted by nearly all living forms, such as animals, plants, and even bacteria and fungi themselves, is the release of... 

The functions of phenylpropanoid derivatives are as diverse as their structural variations. Phenylpropanoids serve as phytoalexins, UV protectants, insect repellents, flower pigments, and signal molecules for plant-microbe interactions. They also function as polymeric constituents of support and surface structures such as lignins and suberins [1]. Therefore, biosynthesis of phenylpropanoids has received much interest in relation to these functions. In addition, the biosynthesis of these compounds has been intensively studied because they are often chiral, and naturally occurring samples of these compounds are usually optically active. Elucidation of these enantioselective mechanisms may contribute to the development of novel biomimetic systems for enantioselective organic synthesis. 

Repelling microbes or killing them on contact are obviously the optimal ways for an antimicrobial surface to function. However, most moist and biologically contaminated areas contain large amounts of material that nonspeciflcally attach to a surface and deactivate it fully. Furthermore, high concentrations of microbes will eventually cover any surface with dead cells, which also deactivate the surface. In the latter case, only surfaces that release biocides will retain their activity. 

Therefore, besides strict hygienic rules during insertion of the device, the development of new materials able to counteract microbial adhesiveness and colonization has become a critical issue in recent years. The two principal approaches to prevent microbial adhesiveness are (1) the development of polymers with antifouling properties, and (2) the development of polymers with antimicrobial properties. Such materials either repel microbes (antifouhng) or kill bacteria (antimicrobial) present in the surface proximity. 

---