A poly(oxanorbornene)-based
polyzwitterion with primary ammonium
and carboxylate groups (PZI) has been reported previously as the first
simultaneously antimicrobial and protein-repellent polyzwitterion.
Here, additional physical and biological properties of three poly(oxanorbornene)-based
polyzwitterions with different functional groups (PZI, the polycarboxybetaine
(PCB), and the polysulfobetaine (PSB)) are compared to understand
the molecular origins of this unusual bioactivity. Additionally, the
three polyzwitterions and the antimicrobial polycationic SMAMP are
exposed to proteins, bacteria suspensions, human plasma, and serum.
These interactions are investigated by surface plasmon resonance spectroscopy.
In protein adhesion studies, neither fibrinogen nor lysozyme adhere
irreversibly to PZI, yet reversible interaction with lysozyme is observed
at pH 7 and 8. In the presence of bivalent cations, reversible fibrinogen
adhesion is observed on PZI and PSB but not on PCB. This might explain
why mammalian cells grow on PZI and PSB but not on PCB. PZI does not
show human plasma adhesion, whereas PCB and PSB have 0.27 and 0.48
ng mm–2 adhered plasma and SMAMP even at 6.3 ng
mm–2. Both PZI and SMAMP show strong serum adhesion,
whereas no serum adhered to PCB and only a little adhered to PSB.
This could be related to the pH difference between serum and plasma
to which the pH-responsive primary ammonium groups are susceptible
while the permanently charged NR4
+ groups are
unaffected. Both PZI and PCB showed no or only a little bacterial
adhesion. PCB is also intrinsically antimicrobial against E. coli and S. aureus bacteria and thus
is also simultaneously protein-repellent and antimicrobially active.
Thus, although the carboxylate groups of PZI and PCB seem to be a
prerequisite for the dual antimicrobial activity and protein-repellency,
the pH responsiveness of the primary ammonium group seems to make
the PZI molecule vulnerable for protein adhesion in fluids that are
slightly out of the physiological range.