Silver has long been used for its
antimicrobial properties. However, the delivery
systems available, often in the form of a salt,
have been the limiting factor to successful
biological use of this noble metal.
Nanotechnology and the ability to
deliver silver from a nanocrystalline structure
has and will markedly improve the biologic value
of silver. These advances in crystal chemistry
will likely have a dramatic impact on the
microbiology, as well as biology of wound
healing and control of inflammation.
We will describe the past,
present and future uses of silver in biologic
systems focusing on its biological properties on
“wounds”.
Silver has been used for
centuries to prevent and treat a variety of
diseases, most notably infections. Silver has
extremely potent antimicrobial properties with
levels in solutions exceeding 10 parts per
million. Silver ions appear to kill
micro-organisms instantly by blocking the
respiratory enzyme system (energy production),
as well as altering microbe DNA and the cell
wall, while having no toxic effect on human
cells in vivo.
Free silver ions, or radicals,
are known to be the active antimicrobial agent.
In order to achieve a bactericidal effect,
silver ions must be available in solution at the
bacterial surface. Efficacy depends on the
aqueous concentration of these ions.
However, crystalline silver is
quite insoluble in water and in dilute acids
making the available silver cation
concentration, inadequate for use as an
antimicrobial on a wound surface.
Beginning in the 1920’s, a small
electrical charge was passed through water and
silver crystals in order to obtain an effective
silver (electro-colloidal) ion solution to be
used topically on wounds. The charged silver
solutions (electro-colloidal) were approved in
the 1920’s by the FDA for use as an
antibacterial agent. These solutions are very
unstable and the concentration of silver may be
inadequate for an ideal antimicrobial agent.
Prior to 1940,
pure silver in the colloidal form was being
commonly used for wound infection as this period
predated the use of antibiotics. After 1940,
systemic antibiotics became prevalent.
Carl Moyer in 1965
introduced the use of a 0.5% silver nitrate
solution for burn wound management. The silver
nitrate was a more stable compound and replaced
colloidal silver. During the same time period,
Dr. Charles Fox developed another silver
compound for wounds and burns, silver
sulfadiazine. The sulfadiazine is composed of
propylene glycol, stearyl alcohol and
iso-propanol. This compound was formulated as a
water soluble cream to be applied twice a day to
a wound surface instead of a continuous soak
required of silver nitrate for continued silver
delivery.
Over the past 40
years silver sulfadiazine has become a very
popular anti-microbial silver delivery system.
However, both nitrate and sulfadiazine impair
fibroblast and epithelial proliferation,
impairing healing.
Advances in the field of
nanotechnology were required before a new form
of pure silver was available for use in
biological systems.
