Biomedical Engineering Reference
In-Depth Information
clinical use but mixed with 1%
Nano Silver
it probably is.
NanoSilver
refers to par-
ticles of 5-50 nm with an active surface of 4 m
2
/g and a porosity around 90% (0%
in commercial silver powder). At the concentration of 1%, no bacterial growth is
allowed (Fig. 5 of a paper by Alt et al. [
239
]).
For coatings an in situ deposition of a polymer-Ag composite was used [
240
].
Biocompatible, chemically inert, insoluble, mechanically and thermally stable films
can be deposited on stainless steel and titanium Kirschner nails by plasma poly-
merization using as precursor hexamethyldisiloxane. The films consist of an SiO
x
plasma polymer. Silver porous clusters, size of clusters around 10 nm, were formed
using inert gas evaporation. They can be produced either by deposition on the
bare metal (type A) followed by a plasma polymer layer, or embedded between
two plasma polymer layers (type B). As shown in Fig.
6.4
, a percolating path runs
between the Ag islands. The polymer film on top of these islands makes contact with
the metal surface in between the Ag nanoparticles assuring a well adhering coating.
The results are shown in Fig.
6.5
for 6 repetitions. The strain on duty for in vitro
tests is
S.epidermidis
. Uncoated wires show uninhibited bacterial proliferation with
negligible delay (vertical axis). Type A (columns 3 and 4) shows complete inhibition
with only a small exception for Ti in column 4. The same story for Ti with coating B
but B is ineffective on SS. It might be concluded that technique A exhibits promising
bactericidal activity on both stainless steel and titanium. Why type B on SS is not
effective remains unclear.
The discussion of bactericidal Ag coatings and a reference to Ag fillings is merely
a random choice out of an abundant list of items in the literature. It is giving just
a taste of what is going on in this part of the biomaterial world and what might
be on the menu in the years to come. Moreover, the use of nanosilver particles as
well as nanoparticles in general should be handled with care because they figure
high on the list of the emerging new branch in toxicity testing. Histopathological
examinations of rats exposed to inhalation of silver nanoparticles indicated dose-
dependent increases in internal lesions. Target organs were considered to be lungs
and liver [
241
].
Fig. 6.4
Transmission
electron microscopy of Ag
clusters deposited on the
metal surface (type A). From
[240
], by courtesy of Springer
Ve r l a g
