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Section
III.
HOW CAN SILVER BE
DELIVERED TO THE WOUND?
There have
been and currently are several forms of silver used on a
wound. The delivery of elemental or ionic silver
(colloidal silver) without an added attached compound
has historically produced the best wound healing
and antibacterial results. Recent experience with
a new silver delivery system (releasing only silver) is
verifying the positive results described decades ago
with use of some silver alone.
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How
is Silver provided to the Wound?
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- Colloidal
silver (electrically charged) solutions
- Silver
Proteins
- Silver
salts
- Silver
compounds -- antibacterial silver sulfadiazine
- Silver
releasing systems (Acticoat)
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Colloidal
Silver Solutions
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- most
common delivery system prior to 1960
- infection
control and wound healing benefits, reported prior
to 1960 were from ionic silver solution
- 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
- highly
bacteriocidal, with no resistance,
- decreased
wound surface inflammation
- solutions
unstable when exposed to light, therefore not
practical
- silver
complexed to small proteins to improve stability in
solution
- much less
antibacterial action than pure ionic silver
- replaced
by silver salts in the 1960’s
- more
stable delivery system when silver complexed to AgCl,
AgNO3, AgSO4
- silver
nitrate most popular but dangerous in concentration
exceeding 2%
- silver
nitrate 0.5% is the standard solution for burns,
wounds (higher concentrations tissue toxic)
- nitrate
is toxic to wounds and to cells and appears to
decrease healing
- unstable
in light
- benefits
of silver alone compared by the addition of nitrate
- bacterial
resistance develops to AgNO3
- introduced
in 1970’s for burns and wounds as an antibacterial
- silver
complexed to propyleneglycol, stearyl alcohol, and
isopropyl myrislate
- silver
complex acts on the bacterial wall: not the energy
system as with silver ion
- bacterial
resistance develops
- toxicity
to bone marrow, propylene glycol poisoning not
silver
- impaired
re-epithelialization,
- pro
inflammatory not due to the silver, but to
the sulfadiazine complex
The current
data, on the silver products used in burns, would again
indicate that providing pure silver ions and radicals
produces the best anti-microbial results as well as
optimizing the wound healing environment.
The liver salts
and complexes used today were developed to maintain a stable
silver release system. It is clear that these products have
been very beneficial as antimicrobial agents, which would
indirectly improve healing. Using advanced technology a
current product has been developed which can provide silver
alone in a stable delivery system. This system again
captures both the positive antimicrobial and pro
healing effects if previously attributed to pure silver.
All these
salts dissolve in water. The most commonly used salt is
Silver nitrate. The reduction of nitrate to nitrite
causes oxidant induced cell damage. This effect is most
likely the reason for the impaired re-epithelialization
reported with its use in partial thickness burns or
donor sites. A concentration exceeding 1% is caustic to
tissues.
The toxicity
of this agent can be attributed to the sulfadiazine
component, including the bone marrow suppression
decreased healing of a partial thickness wound, and
fibroblast toxicity. Of major importance is the
increased inflammation caused by the water soluble cream
base itself. This surface inflammation increases
neutrophil exudate and increases protease activity on
the wound surface, which may be useful to break down
surface dead tissue but is deleterious to a viable
healing wound bed.
SILVER
CONCENTRATION IN CURRENT SILVER PRODUCTS
-
Silver
Nitrate 0.5% solution
Silver concentration 3180 ug Ag+/ml water
Ag+ availability 3180 ug Ag+/ml water
(immediate release)
-
Silver
sulfadiazine 1% cream
Silver concentration 3030 ug Ag+/gram
Silver availability 3030 ug Ag+/gram
(release over 12-24 hours)
-
Silver
Delivery (ACTICOAT)
Silver concentration 13%
Silver availability 100 ug Ag+/ml water
(Stable release for at least 48 hours)
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SILVER
DELIVERY DRESSING (ACTICOAT)
Acticoat
silver delivery dressings is a 3-ply gauze 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 coating
which consists of 0.24±0.4 mg silver per mg high
density polyethylene, is a binary alloy of silver (97%)
and oxygen with negligible contaminants (silver target
is 99.99% silver).
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. Handbook of Chemistry and Physics, 55th
ed., CRC Press, Cleveland, 1974, pp B-134.
  
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