OVERVIEW ON THE MAJOR RESEARCH ACTIVITIES ON CARBON NANOTUBES BEING DONE IN AMERICA, EUROPE AND ASIA - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 293

glomerular iltration system into the bladder. In their recent publication,
based on histological TEM evaluation in absence of any probe molecules, the
researchers indicated that factors including size, surface charge, shape of
materials and extent of aggregation play a crucial role in determining the fate
of their elimination and/or accumulation. The tubes used in these experiments
were MWCNTs with diameter of 20-30 nm and length of 0.5-2 μm, and they
were subjected to 1,3-dipolar cycloaddition reaction. Hence, tubes presented
lengths signiicantly larger than the dimensions of the glomerular capillary
wall (minimum diameter of fenestra is 30 nm, the thickness of the glomerular
basement membrane in rodents and humans is 200-400 nm, and the width
of the epithelial podocyte iltration slits is 40 nm). 178 Therefore, the only way
they could penetrate through such tiny system was by adopting a spatial
conformation in which the longitudinal CNT dimension is perpendicular to
the endothelial fenestrations, while the traverse dimension of CNT (cross
section of 20-30 nm) is small enough to allow permeation. Therefore, it was
shown that MWCNTs are capable of reorientation while in blood circulation
(Schematic representation in Fig. 9.28).

Bowman's space
(urine compartment)

Podocytes

Basal
membrane
(200-300
nm)

Fenestra
(>30 nm)

Capillary Lumen
(blood compartment)

Capillary Lumen
(blood compartment)

Capillary Lumen
(blood compartment)

Figure 9.28 Schematic representation of renal clearance of MWCNTs. MWCNT (in
black, with diameter ≤ 40 nm ) a few minutes after intravenous (tail vein) injection.
The tubes can crossthe renal iltration membrane after orienting perpendicularly. See
also Colour Insert.

Despite these results, the impact of administered CNTs on the physiological
functions of different organs and tissue is still to be addressed. That is why
the group has performed a short-term (24 hours) investigation on various
types of MWCNTs tail-vein injected in healthy mice. 179 Results indicated
that organ accumulation was proportional to the degree of ammonium
(NH 3 + ) functionalisation at the tubes' surface: the higher the degree of
functionalisation, the less their accumulation in tissues, without any
hazardous alteration even at the highest doses ever injected so far in vivo (20
mg/kg). Conversely, non-functionalised tubes accumulated almost entirely in
the lung and liver in form of large dark clusters. In a parallel study, 180 the