Civil Engineering Reference
In-Depth Information
single step. Additionally, it was demonstrated that colloidal protectors such as gelatin
and polyvinylpyrrolidone (PVP), or polydopamine to which Ag
+
has high ai nity play
a key role in particle size, shape and distribution homogeneity [219, 221, 222], or in the
case of heterogeneous functionalization of the membranes surface [228], can limit the
deposition of Ag NPs only to one of the sides of the membrane with obvious advantages
for biomedical applications. BC/Ag NPs hybrid materials show a characteristic broad
absorption band at 410-420 nm (e.g., [211, 213]) characteristic of the surface plasmon
resonance of Ag NPs, which results in BC/Ag NPs nanocomposites with a typical trans-
lucent yellow-brownish aspect (Figure 2.21). Furthermore, the presence of Ag NPs and
the Ag content is easily coni rmed by energy dispersive X-ray analysis (e.g., [212, 225,
226]) and its distribution and shape by SEM imaging, (e.g., [211-213]), whereas par-
ticle size and distribution is also frequently assessed by TEM (e.g., [213, 225]). Similar
approaches are also followed for the other inorganic NPs-based composites described
below.
In most BC/Ag hybrid materials, Ag NPs appear in spherical shapes with average
sizes ranging from 5 to 20 nm [213, 217, 225-227, 299]. Only two studies reported
the formation of cubic shape Ag NPs [219, 229], which interestingly showed much
higher average sizes (40-100 nm). However, it was demonstrated that the average size of
the NPs could be controlled by several factor, namely through the reducing agent/Ag
+
ratio [213, 217] and also by the 3D BC template, which ultimately can be af ected by
the fermentation and biosynthetic conditions and particularly by the monosaccharide
used as carbon source [225]. It is well known that silver, both in ionic form but also
as a metal and particularly in NPs form, exhibits strong cytotoxicity towards a broad
range of microorganisms. h erefore, the combination of this unique feature with BC,
particularly bearing in mind the potential biomedical applications mentioned above,
would obviously widen the potentiality of BC/derived materials and has been therefore
the object of a vast number of studies.
One of the i rst studies demonstrating the antibacterial activity of BC/Ag NPs was
reported by Maneerung
et al.
[213]. However, at erwards the strong activity of these
materials has been largely reported against the Gram positive
Staphylococcus aureus
[213, 217, 220, 225-227, 299-301]
, Bacillus subtilis
[220, 221]; and the Gram nega-
tive
Escherichia coli
[213, 217, 221, 222, 227-230],
Klebsiella pneumonia
[221] and
Pseudomonas aeruginosa
[299].
Figure 2.21
Typical yellow-brownish aspect of a BC/Ag NPs (b) compared with pristine BC (a).
Reproduced with permission from [220].
