Antimicrobial polymer
Polymers with the ability to kill or inhibit the growth of microorganisms such as bacteria, fungi, or viruses are classified as antimicrobial agents.
[5] The phospholipid bilayer is an important component of the cell membrane, which is composed of hydrophilic heads and a hydrophobic tail.
Positive residues on the polymer electrostatically interact with negative charges on the cell and induce secondary cellular effects.
[1][4] Secondary effects include disruption of solute and electron transport as well as disturbances to energy production pathways, which leads to cell death.
[1][9] The second mechanism is characterized by the release of low molecular weight antimicrobial agents from polymers.
When antimicrobial agents bind to proteins, structural changes occur to the cell membrane resulting in cellular death.
[9] Hydrophobic residues improve binding to the lipid bilayer and are utilized for insertion into the microbial cell wall.
Common agents added include N-halamine compounds, nitric oxide, and copper and silver nanoparticles.
Polymers may be chemically modified to induce antimicrobial behavior or they may be used as a backbone for the addition of organic or inorganic compounds.
[1] Polymers with inherent antimicrobial activity include chitosan, poly-ε-lysine, quaternary ammonium compounds, polyethylenimine, and polyguanidines.
[1] Optimal antimicrobial activity is generally seen in quaternary ammonium compounds with a long chain length, containing 8-18 carbon atoms.
[14] Polymer quaternary ammonium compounds containing nitrogen induce cell death through electrostatic interactions and the hydrophobic effect.
When attached to immobilized surfaces including glass and plastic, N-alkyl-polyethylenimine caused cell inactivation in almost 100% of airborne and waterborne bacteria and fungi.
[1] Antimicrobial polymers containing quaternary ammonium as a side group are commonly synthesized from methacrylic monomers.
[18] Polysiloxanes, which have a quaternary ammonium pendant group, have demonstrated activity against several strains of bacteria including Enterococcus hirae, E. coli, and P.
[1] Antimicrobial activity can also be induced through the addition of inorganic particles such as silver, copper, and titanium dioxide nanoparticles to a polymer.
The light source causes the titanium dioxide to be oxidized, which results in the release of highly reactive hydroxyl species that disrupt bacteria.
[1] Magainin and defensin are natural peptides, short polymers composed of amino acids, which display exceptional antimicrobial activity.
Extremely large molecular weight polymers will have trouble diffusing through the bacterial cell wall and cytoplasm.
Firstly, longer chains have more active sites available for adsorption with the bacteria cell wall and cytoplasmic membrane.
[25][26] A major disadvantage of antimicrobial polymers is that macromolecules are very large and thus may not act as fast as small molecule agents.
Biocidal polymers that require contact times on the order of hours to provide substantial reductions in pathogens, really have no practical value.
For example, a series of polyketones have been synthesized and studied, which show an inhibitory effect on the growth of B. subtilis and P. fluorescens as well as fungi, A. niger and T. viride.
[45] In order for an antimicrobial polymer to be a viable option for large-scale distribution and use there are several basic requirements that must be first fulfilled: Polymeric disinfectants are ideal for applications in hand-held water filters, surface coatings, and fibrous disinfectants, because they can be fabricated by various techniques and can be made insoluble in water.
In addition, because free chlorine ions and other related chemicals can react with organic substances in water to yield trihalomethane analogues that are suspected of being carcinogenic, their use should be avoided.
[51] Antimicrobial polymers are powerful candidates for controlled delivery systems and implants in dental restorative materials because of their high activities.
This can be ascribed to their characteristic nature of carrying a high local charge density of active groups in the vicinity of the polymer chains.
The field of antimicrobial polymers has progressed steadily, but slowly over the past years, and appears to be on the verge of rapid expansion.
[54] Modification of polymers and fibrous surfaces, and changing the porosity, wettability, and other characteristics of the polymeric substrates, should produce implants and biomedical devices with greater resistance to microbial adhesion and biofilm formation.
A number of polymers have been developed that can be incorporated into cellulose and other materials, which should provide significant advances in many fields such as food packaging, textiles, wound dressing, coating of catheter tubes, and necessarily sterile surfaces.
