BIOMEDICAL AND BIOMEDICINE APPLICATIONS OF CNTs - Bio-Inspired and Nanoscale Integrated Computing - page 507

A recent study probing the effects of CNT size on toxicity conducted in vitro
and in vivo experiments with 220-nm and 850-nm oxidized MWCNTs. As opposed
to the previously mentioned study, an order of magnitude lower MWCNT
concentration was used to test toxicity against human acute monocytic leukemia
cells in vitro. These studies observed an induced inflammation-associated gene
expression with no size correlation in vitro, while in vivo, subcutaneous adminis-
tration of the larger MWCNTs generated a heightened inflammatory response.
Increased inflammation was associated with an inability of the macrophages to
effectively engulf the larger MWCNTs.
More recently, an in vitro study was conducted on human dermal fibroblasts
involving sidewall functionalized SWCNTs with phenyl-SO 3 H, phenyl-SO 3 Na,
and phenyl-(COOH) 2 groups, as well as unmodified SWCNTs dispersed in the
block-copolymer Pluronic F108. Sidewall functionalized SWCNTs contained
varying degrees of functionalization density, and toxicity substantially decreased
with increasing sidewall functionalization density. Furthermore, in all cases,
sidewall functionalization resulted in less toxicity than the surfactant coated
SWCNTs.
All of the in vitro studies mentioned in the above discussion of CNT
applications found low or no toxicity for the doses of functionalized CNTs that
were employed. In vitro studies offer valuable insight for specific cellular level
toxicity and therapeutic properties of functionalized CNTs; however, whole
animal in vivo studies are crucial to determine targeting specificity as well as
potential side effects.
A recent in vivo animal study employed ammonium and indium-labeled
dimethylentriamine pentaacetic functionalized SWCNTs and MWCNTs adminis-
tered intravenously into mice. The data showed that the SWCNTs were not
retained in any reticuloendothelial organs and were completely cleared from the
animals through the renal excretion route without any toxic side effects. The
development of blood-compatible CNTs has been reported recently. MWCNTs
were functionalized with glycosaminoglycan (GAG), which is commonly found on
the luminal surface of the endothelium. Further developments involving intrave-
nous administration of carbon nanotubes are on the horizon.
Several reviews regarding nanoparticle toxicity are emerging that offer
comparisons between clinically relevant nanoparticles. CNTs offer unique proper-
ties as therapeutic materials over other nanoparticles, and it is reasonable to
expect that their toxicity can be effectively managed.
18.7. CONCLUSIONS
Although there may be a long process of getting some of the above-mentioned
biomedical products to the market, the research on some of these aspects are
already on the floor. In future, many of these developed devices could save
millions of lives, and therefore gives companies and institutions the incentives to
hasten their research.