Zwitterionic polymeric sulfur ylides: antifouling coating with a synergistic effect
Bacteria that gather into biofilms on the surfaces of implants,
catheters, breathing tubes, and other medical components are a serious
health hazard. In the journal Angewandte Chemie, a research team
from the Netherlands has now introduced a new material based on
poly(sulfur ylides) that—when applied as coating—effectively inhibits
this process known as fouling. The coating minimizes the adhesion of
bacteria to surfaces and is also a bactericide while not affecting
mammalian cells.
© Wiley-VCH, re-use with credit to 'Angewandte Chemie' and a link to the original article.
Bacteria organized into biofilms are especially stubborn and often
resistant to antibiotics. It is estimated that 65% of infections
acquired in hospitals originate from biofilms. The cause is frequently
contamination with infectious bacteria from a patient’s skin or
pathogens that circulate in the bloodstream. The first step is adhesion
of the bacteria to a surface. To inhibit this, exposed surfaces are
given antifouling coatings, usually made of polyethylene glycol (PEG).
PEG binds to water molecules, which then form a hydration layer—an
effective barrier against the undesired adsorption of biomolecules and
bacterial cells. However, recent research has revealed that PEG also has
disadvantages in that it seems to trigger immune responses.
An alternative solution is offered by polybetaines, a class of
zwitterionic polymers. A zwitterion is a molecule that carries both
positive and negative charges. Recent studies suggest that the
antifouling performance enhances as the distance between the positive
and negative charges grows smaller. The most effective of these
substances should have the negatively charged atoms directly adjacent to
the positively charged ones—a requirement that cannot be met with a
conventional betaine structure. However, this is precisely the unique
structural feature of ylides. For example, in a sulfur ylide, a
positively charged sulfur ion is bound directly to a negatively charged
carbon atom.
A team led by Daniela A. Wilson and Kevin Neumann at Radboud
University in Nijmegen (Netherlands) produced zwitterionic polymers
based on sulfur ylides, poly(sulfur ylides) abbreviated as P(SY), which
display sulfur ylides as side chains on a backbone made of polystyrene.
The team showed that the new P(SY) had antifouling properties exceeding
those of PEG. This seems to be the result of a synergistic effect. Like
PEG, P(SY) produces a hydration layer that inhibits the adhesion of
bacteria and biomolecules. Unlike PEG, P(SY) also reduces the viability
of bacteria that overcome the barrier of the hydration layer.
Presumably, these initially bind to the ylide groups through
electrostatic attractions. Once they come into contact with the
hydrophobic polystyrene backbone, their cell membranes become porous,
and the bacterial cells die off. Mammalian cells, in contrast, are not
affected by P(SY); in fact, fibroblast cells, a type of connective
tissue, were grown on poly(sulfur ylide) coatings.
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About the Author
Dr. Kevin Neumann is
an Assistant Professor in the Systems Chemistry Department at Radboud
University in the Netherlands. His group conducts research in the field
of nanomedicine and polymer chemistry, where they focus on developing
innovative principles for drug delivery and activation, while also
applying principles from synthetic chemistry to design new
(bio)materials for medical applications.
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