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III. HOW CAN SILVER BE DELIVERED TO THE BURN WOUND?
As presented in the historical
review, silver delivery to a burn has changed dramatically
over the years. The initial pure colloidal silver delivery was
somewhat effective, but very impractical to use on large
wounds or for extended time periods due to instability.
However, the pure silver was observed to have benefits
to wound healing in addition to antimicrobial activity,
although no formal study on silver and wound healing was ever
performed until recently.(1-4)
The development
of the delivery systems silver nitrate and silver sulfadiazine
were more practical, as the compounds were quite stable and
effective as antimicrobials.
However, some of the benefits of pure silver appeared
to be lost. In fact, these silver products were noted to
retard rather than improve healing not due to the silver, but
rather the nitrate and sulfadiazine.(17,20)
Now pure silver delivery systems(5)
are again available. Described are the common delivery systems
used in the past and the present.
DELIVERY
OF SILVER TO BURNS
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How
is silver provided to the wound?
- Colloidal
silver (electrically charged) solutions
- Silver
salts
- Silver
compounds, e.g., silver sulfadiazine
Pure
silver releasing systems, e.g., Acticoat |
Colloidal silver solutions
- Most
common delivery system prior to 1960
- Charged
pure silver particles (3-5 ppm) were held in
suspension by small electric current
- Positive
ions repelled each other thereby remaining in
solution when applied topically to a wound
- Solutions
unstable when exposed to light, therefore not
practical
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Silver salts
- More
stable delivery system when silver complexed to
AgCl, AgNO3, AgSO4
- Silver
nitrate most popular but dangerous in
concentrations exceeding 2%
- Silver
nitrate 0.5% is the standard solution for burns
wounds
- Nitrate
is toxic to wound cells and appears to decrease
healing
- Unstable
in light
Continual
applications necessary to maintain activity
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Silver
Sulfadiazine
- Introduction
of silver sulfadiazine in 1965 for burns and
wounds as an antibiotic
- Silver
complexed to propyleneglycol, stearyl alcohol, and
isopropyl myristate
- Silver
complex acts on the bacterial wall, not the energy
system, as with silver ion
- Application
usually twice a day
- Toxicity
to bone marrow may occur due to propylene glycol
poisoning not silver
- Impairment
of re-epithelialization and collagen deposition
may occur
- Inflammation
may occur due to sulfadiazine complex, not silver
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Silver
nanocrystalline delivery system
- A
three-ply dressing consisting of inner
rayon/polyester core between two layers of
silver-coated mesh
- Nanocrystalline
silver placed onto a bilayer of polyethylene for
controlled release
- Ionic
silver and silver radicals released in high
concentrations when exposed to water
- Maintains
moisture layer for healing between wound and
silver membrane
- Decreases
exudates formation (anti-inflammatory)
- Highly
bactericidal
- Can
remain active and in place for days
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Silver
Nanocrystalline Delivery Dressing
The silver delivery dressing
developed by Dr. Burrell is a 3 layer wound dressing
consisting of an absorbent rayon/polyester core laminated
between an upper and lower layer of silver coated high density
polyethylene mesh. The laminations are held in place with
ultrasound welds. The silver coating, which consists of 0.24±0.4
mg silver per mg high-density polyethylene, is a binary alloy
of silver and oxygen with negligible contaminants (content is
99.99% silver).(21-25)
The coatings are highly porous
and consist of nanocrystals organized into coarse columnar
structures.
This unique physical structure,
in combination with the oxygen atoms/molecules that are
trapped in the crystal lattice, contribute to the enhanced
solubility of the films which continue to release silver until
the concentration in solution reached 66 mg/L a level that is
50 to 100 times higher than is expected from typical bulk
pieces of silver metal.
The silver crystals
coat both sides of the product with a polyester core between
the sheets to maintain the moisture needed for silver release. Either side of the silver dressing can be placed onto the
wound surface. The silver coating when wet with sterile water,
produces a continual release of Ag+ and likely other silver
radicals for days. The
delivery system readily molds to the wound producing wound
occlusion as well as maintaining a wound surface moisture
layer. Current published data indicates that this silver
release product produces a rapid and complete killing of
essentially all pathogens found on a wound.
The silver delivery system is represented
Both silver layers release the silver ion ryson
exposure to water.
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Silver
concentration in current silver products |
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Silver
Nitrate 0.5% solution |
-Silver
concentration 3180µg
Ag+/mL water
-Ag+
availability 3180µg
Ag+/mL water
-Immediate
release |
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Silver
sulfadiazine 1% cream |
-Silver
concentration 3030µg
Ag+/gram
-Silver
availability 3030µg
Ag+/gram
-Release
over 12-24 hours |
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Silver
delivery (Nanocrystals) |
-Silver
concentration 13%
-Silver
availability 100µg
Ag+/mL water
-Stable
release for at least 48 hours |
Although
the nanocrystal silver delivery membrane has less total
silver, a more rapid and sustained release appears to occur
due to the nanocrystalline structure.
This process markedly increases the surface area of the
silver when exposed to the wound. This physical property may
explain its more rapid bactericidal action.
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