Biomedical Engineering Reference
In-Depth Information
that microbial contamination of the contact lenses can be resolved by storing the contact
lenses inside the DLC-coated cases. Work by Butter and Lettington [120] indicated that
microneedles coated with DLC causes the least possible distortion during an ophthalmic
surgery. Next, hydrogenated DLC coatings have been investigated for implants in oral
cavity [121, 122]. It was observed that the CVD-deposited C-H layers over DLC showed
significant biointegration and resistance to saliva and other oral cavity elements [122].
Biomedical Applications of Fullerenes
Functionalized fullerenes have been extensively used in major areas of biomedicine such
as drug delivery, reactive oxygen species quenching (ROS), and as magnetic resonance
imaging (MRI) contrast agent, and they are all discussed in detail below.
Functionalized Fullerenes as Drug Delivery Agents
Paclitaxel-embedded buckysomes (PEBs) are spherical nanostructures in the order of
~200 nm and composed of the amphiphilic fullerene embedding the anticancer drug
paclitaxel inside its hydrophobic pockets [123]. Similar to Abraxane®, the US Food and
Drug Administration-approved drug for treating diseases such as metastatic breast
cancer, the water-soluble fullerene derivatives enable the uptake of paclitaxel negat-
ing nonaqueous solvents, which can cause patient discomfort and other unwanted side
effects. However, work by Partha et al. [124] indicated that PEBs are capable of deliver-
ing even higher amounts of paclitaxel than those delivered via Abraxane. By delivering
an increased amount of paclitaxel, it is expected that infusion times were shortened and
results in higher tumor uptake leading to greater anticancer efficacy. Another advantage
of fullerene-based delivery vectors is that their nanoscale dimensions favor passive target-
ing and enables them to accumulate at tumor sites by entering through leaky vasculature
present in the endothelial cells of the tumor tissue. Moreover, the fullerene moiety can be
easily functionalized to attach targeting agents that facilitate active targeting. PEBs also
provide an easy route to attach targeting groups to their fullerene moieties. In PEBs, both
liposomal and nanoparticle technologies are combined together to create nanostructures
that serve as novel drug carriers. This is an innovative approach because it will improve
circulation times in the blood, shields the anticancer drug against enzymatic degradation,
and reduces uptake by the reticuloendothelial system. Furthermore, the size of the PEBs is
designed to be less than 200 nm to avoid reticuloendothelial system uptake. The presence
of dendritic groups outside the PEBs can also provide stealth function to reduce the clear-
ance. Fullerenes are capable of producing an ideal lipophilic slow release system and pro-
vide three-dimensional scaffolding for covalent attachment of multiple drugs, which will
be used to create single dose “drug cocktails.” Zakharian et al. [125] designed a fullerene
paclitaxel conjugate to slowly release the drug for aerosol liposome delivery of paclitaxel
for lung cancer therapy [125]. The aggregate size range for this conjugate was in the order
of 120 nm and the size did not vary with concentration. This conjugate was designed to
release paclitaxel via enzymatic hydrolysis with a half-life of release of 80 min in bovine
plasma. A dilauroylphosphatidylcholine-based liposome formulation of the conjugate
was reported to have a half maximal inhibitory concentration value virtually identical
to the half-maximal inhibitory concentration (IC
50
) for a paclitaxel-dilauroylphosphati-
dylcholine formulation in human epithelial lung carcinoma A549 cells. They concluded
that together with clinically relevant kinetics of hydrolysis and significant cytotoxicity in
tissue culture, the fullerene-paclitaxel conjugate had potential for enhanced therapeutic
© 2011 by Taylor & Francis Group, LLC
