Biomedical Engineering Reference
In-Depth Information
3.2.2.2 Nonreleased Antibacterial Agents
A different approach relates to the usage of insoluble disinfectants that can inactivate target micro-
organisms by contact without leaching from the carrier material. This mechanism is based on immo-
bilized bactericides, which have the advantage of being chemically stable and nonvolatile
[28]
. One
example was the usage of triclosan that induced bacterial death presumably by acting on the cell wall of
the bacteria
[29]
. Consequently, triclosan incorporation in a restorative composite might be better than
chlorhexidine, fluoride, or benzalkonium chloride in the long run because of its nonreleasing nature.
To overcome the disadvantages of antibacterial materials based on releasing of antiseptic agents
or small-molecule antimicrobial agents, a possible solution is the usage of polymeric macromolecules
with antimicrobial groups.
3.3
ANTIMICROBIAL MACROMOLECULES
An alternative approach gaining interest in recent years is the development of macromolecular mate-
rials that have antimicrobial properties without releasing an agent into the solution. As compared
with small-molecule antibacterial agents, macromolecular materials have some advantages, such as
being nonvolatile, chemically stable, and sustaining long-term antibacterial activity
[5]
. Furthermore,
insoluble polymeric contact disinfectants may inactivate or remove target microorganisms by contact
without releasing any biocide from the bulk phase. For example, Imazato et al. reported of an anti-
bacterial monomer covalently bonded to the polymer network of a restorative composite. This MDPB
was found to have a long-lasting antibacterial effect without altering the mechanical properties and
the curing behavior
[13,14]
.
Polymeric antimicrobials may also possess high antimicrobial activity due to the high local den-
sity of the active groups. Particularly, polycationic antimicrobials, which bear quaternary ammonium,
have high charge density and excellent processibility, exhibiting high antimicrobial activity
[30]
.
3.3.1
Polycationic Disinfectants
Cationic polymer disinfectants include ion-exchange fibers
[31]
, alkoxysilanes
[32]
, insoluble
pyridinium-type polymers
[33,34]
, polyionenes
[35]
, polymer surfaces derivatized with poly(vinyl-
N
-pyridinium)
[36,37]
and immobilized
N
-alkylated PEI
[38-40]
. Specifically, cationic polymers
bearing quaternary ammonium groups, mainly crosslinked anion-exchange resins including quater-
nary ammonium-type resins, exhibit high antibacterial activity.
In view of the fact that cell surface of bacteria is negatively charged, polymers comprising cations
or retaining positive charges on their surfaces may have a contact disinfectant effect. A number of
polymers that exhibit antibacterial properties were developed for this purpose including soluble and
insoluble pyridinium-type polymers
[37,41]
. Water-soluble pyridinium-type polycations have been
previously reported to have bactericidal properties. Furthermore, hexyl-poly(vinyl-
N
-pyridinium) sur-
face coating has proven to kill 90-99% of Gram-negative and Gram-positive bacteria, through either
air or water
[36]
. Most of these compounds bearing quaternary ammonium groups appear to act pri-
mary by interacting with the cell wall and disrupting negatively charged cell membrane of bacterial.
A structure-activity relationship analysis has revealed that in order to create antibacterial surfaces,
immobilized long polymeric chains have to be positively charged and moderately hydrophobic
[39]
.
