BURNSURGERY.ORG

Educating the burn care professionals around the world

Search Site

Nanocrystalline
Silver

IV. BIOLOGIC PROPERTIES OF NANOCRYSTALLINE SILVER COMPARED TO
OTHER
SILVER PRODUCTS

a) Antimicrobial Properties(3,4,16,17)
As can be seen in Table 3 the aqueous concentration of silver ions released from the
nanocrystalline film is approximately 3% of that released from a 0.5% silver nitrate or a 1%
silver sulfadiazine cream. However, the biological properties of the silver released from
nanocrystals are much greater. Silver resistance has been reported in the literature and is
mediated through one of two pathways. Either the silver is tied up in the cell wall and
membranes, or it is actively transported out of the cell. Bacterial organisms that have either one
of these resistance mechanisms, which are effective up to 1000 µg/mL Ag+, have been tested
against the nanocrystalline silver coated dressing Acticoat. These tests showed that these
organisms were susceptible to the silver produced by the nanocrystals, but not to Ag+ from
silver nitrate. These findings, as will be described, strongly suggest that other species of silver
besides Ag+ are released from the nanocrystals.

Table 3: Silver Concentration in Current Silver Products

Silver Nitrate 0.5% solution

Silver concentration 3180 µg Ag+/ml water
Ag+ availability 3180 µg Ag+/ml water
(immediate release)

Silver sulfadiazine 1% cream

Silver concentration 3030 µg Ag+/gram
Silver availability 3030 µg Ag+/gram
(release over 12 hours)

Silver Delivery (Rx Nanocrystal)

Silver concentration 13%
Silver availability 100 µg Ag+/ml water
(Stable release for at least 72 hours)

The lower amount Ag+ released should also decrease the potential of silver toxicity to cells, if it
exists, by a substantial margin when compared to the other silver agents.

Figure 1 Normal Silver Coated Membrane

Legend 1: Normal Silver Coated Membrane
When silver is sputtered under typical physical vapour deposition conditions, the resulting film,
is very dense with virtually no pores, allowing limited access to water and for silver release. The
crystals are smooth with crystal boundaries being the predominate feature. Crystal sizes range

Burn Prevention

http://www.burnsurgery.com/Modules/nano/p2/sec4.htm

1 z 4

2010-06-29 10:23

from 100nm to greater than 900nm with an average size of about 250nm.

Nanocrystalline Silver Coating (ACTICOAT)

Legend 3 : The antimicrobial properties of silver from the three silver
products,
against Staphylococcus aureus, is shown in this in vitro study. The
silver released
from the nanocrystals (100 µg/mL) killed more rapidly and more
completely than the Ag+
from AgNO3 (3180 µg/mL) and SSD (3030 µg/mL). This finding
suggests that
silver species other than Ag+ are released from the nanocrystals. (J
Burn Care Rehab

1999:20; 195)

18

In another study nanocrystalline silver was extracted from the silver delivery system Acticoat by
incubating the dressing in nanopure water at 37°C in a shaking incubator, and silver

Burn Prevention

http://www.burnsurgery.com/Modules/nano/p2/sec4.htm

2 z 4

2010-06-29 10:23

concentrations were measured using atomic absorption spectrophotometry. The minimum
inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were
determined using five bacterial isolates of clinical interest, and results were compared for
nanocrystal silver, silver nitrate and silver sulfadiazine, based upon total silver as shown in Table
4. Acticoat had similar MIC and MBC values when compared to three silver containing agents.
Kill kinetics were also studied, using 2.0 cm x 2.0 cm pieces of Acticoat dressing, and the same
sized pieced of dressing impregnated with either silver nitrate (100µl of 1% solution. This results
in a final concentration of 0.5% silver nitrate) or silver sulfadiazine (370mg of a 1% cream).
Bacterial survival was measured using a plate counting technique. Acticoat demonstrated the
fastest kill times for the five bacteria used. In most instances with Acticoat, bacterial survival
was undetectable 30 minutes after inoculation, whereas at least 2-4 hours elapsed before no
viable cells were detected with silver nitrate or silver sulfadiazine.

Table 4 Antimicrobial Activity of Silver Delivery Systems

Acticoat (Nanocrystalline

Silver)

Silver Sulfadiazine

Silver

Nitrate

Organism

MIC µg/ml

MBC µg/ml

MIC µg/ml

MBC

µg/ml

MIC

µg/ml

MBC

µg/ml

Staph Aureus

12.5

12.5

*

33

20

20

E. Coli

7.5

7.5

*

2.5

12

22

Klebsiella P.

5.0

5.0

*

25

8

8

Pseudomonas
Aeurginosa

7.5

7.5

*

25

12

12

* MIC's not determined for silver sulfadiazine's due to cloudiness of the
solution
MIC -minimal inhibitory concentration
MBC -minimal bactericidal concentration

These findings strongly suggest that silver species in addition to Ag+, are released from the
nanocrystalline film which are responsible for the more potent antimicrobial properties. To date
the nanocrystalline silver system kills all microbes found in a wound including fungi and all
current antibiotic resistant strains such as vancomycin resistant enterococcus (VRE) and
methicillin resistant Staphylococcus aureus (MRSA).18)

b) Pro-healing Properties
Although silver in an electro colloidal form, had been reported to improve the healing of indolent
wounds in the early 20th century, that finding disappeared with the use of silver salts and
complexes. Recently there have been several reported studies of improved re-epithelialization
rates across partial thickness wounds with silver in the nanocrystalline form. The mechanism,
although unknown at present, does not appear to be due to silver's antimicrobial action.(5,19,21)

c) Anti-inflammatory Properties
Increased wound inflammation not only accentuates pain but markedly impairs healing. Several
heavy metals have been reported to decrease surface inflammation, the most recognized being
gold. Wound surface inflammation has been reported to be decreased with the use of
nanocrystalline silver. Excess metaboproteinases (MMP) are known to increase inflammation by
both increasing inflammatory cell exudates and also leading to a non-healing chronic wound. A
characteristic of this type of wound is excess surface MMP activity, decreased inhibitory MMP
activity and degradation of growth factors by the MMP's.(9,2,23)

Nanocrystalline silver has been shown both in vitro and in vivo to decrease but not prevent
MMP activity as some activity is needed to remove devitalized tissue. The mechanism for this
action also remains unknown. Decreasing the necessary zinc activity required for MMP's, is one
possibility. The other is an effect on the expression or release of pro-inflammatory cytokines.

Burn Prevention

http://www.burnsurgery.com/Modules/nano/p2/sec4.htm

3 z 4

2010-06-29 10:23

Legend 3: Effect of standard collagenase inhibitors, phenanthrolene, and silver from Acticoat on
MMP suppression. Metalloproteinase is significantly inhibited by silver released from
nanocrystal silver delivery.

© Copyright 2002 Burnsurgery.org. All Rights Reserved

Burn Prevention

http://www.burnsurgery.com/Modules/nano/p2/sec4.htm

4 z 4

2010-06-29 10:23