Biomedical Engineering Reference
In-Depth Information
14.5.3 Controlled-drug Delivery Agents
Controlled delivery of the antibacterial agents from the surface involves re-
lease-based antibacterial mechanisms. Medical implant coatings can in-
clude antibacterial agents (such as antibiotics or metal ions) and the benefits
of such a local drug delivery approach compared to systemic drug therapy
are published elsewhere.
108
The similarity in properties, such as hydro-
phobicity between surface polymer and the intended drug for delivery, was
shown to produce homogenous distribution of the drug within the matrix.
11
Recent developments in this area of research include the use of bio-
degradable polymers (e.g., polyhydroxyalkanoates
109
) for the controlled de-
livery of drugs. Biodegradable surface coatings could actively discharge high
doses of antibiotics for a long time and the degradation end products are
easily metabolised by the human body.
109,110
Immunotherapy, which in-
volves the release of ex situ produced antibodies in a clinical setting, hold
promise for highly ecient killing of bacteria. Likewise, leachable anti-
microbial agents which are incorporated into polymers such as poly(b-amino
esters) with a tuneable discharge of the aminoglycoside antibiotic genta-
micin have been explored.
111
Moreover, antimicrobial peptides that can be
released from polyelectrolyte multi-layers have also been reported.
112
Re-
cently, emerging classes of polymers such as polynorbornenes or poly-
(phenylene ethylene) derived from antimicrobial peptides (such as defensin
or magainin) display excessive antibacterial activity but with low levels of
cytotoxicity.
113-115
Polyelectrolyte multi-layers are reported to be used for the
delivery of antimicrobial compounds such as silver including ionic and
nanoparticulate forms.
116-120
It was reported that a coating based on silver
nanoparticles fixed in a modified-chitosan layer deposited on methacrylic
thermosets was found to inhibit bacterial growth.
121
Silver-nanoparticle-
embedded antimicrobial paint based on vegetable oil which could have
biomedical application was also reported.
122
Silver, photocatalytic TiO
2
,ni-
tric oxide releasing nanoparticles and metal oxides such as zinc and mag-
nesium nanoparticles were also found to inhibit bacterial growth.
123,124
It
was reported that the bactericidal actions of nanoparticles are derived from
its electrostatic forces, basic character, oxidising power of halogens, gener-
ation of reactive oxygen species and accrual of nanoparticles near the cyto-
plasm which kills the cells.
123,125
Quaternary ammonium compounds, such
as cetrimide, were incorporated into polyelectrolyte multi-layers as leaching
agents to inactivate S. aureus and E. coli.
96
In spite of its antibacterial
properties, it was reported that some bacteria are capable of developing re-
sistance against surfaces coated with quaternary ammonium compounds.
126
Phosphate glasses offer potential alternatives to the existing means offered
for the treatment of infections since it can be used as localised antibacterial
delivery systems through the inclusion of ions known for its antibacterial
effects such as copper, silver and gallium.
127
Those materials could be
placed at a site of infection to release antibacterial ions as part of the
glass degradation, which could be valuable in wound healing applications.
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