Biomedical Engineering Reference
In-Depth Information
were prepared in the pores of the template fi lm by the “surface sol-gel” methods [57]. For the
differential functionalization of nanotubes, the inner nanotube surface was treated with octadecyl-
triethoxysilane (C18-silane) while nanotubes were still embedded in the pores of the alumina tem-
plate. Free-standing magnetic nanotubes were obtained after polishing both sides of the template
fi lm mechanically and dissolving the alumina template in NaOH solution. After the template was
dissolved completely, magnetic nanotubes were collected by fi ltration. Both the magnetic nano-
tubes, with diameters of 60 and 200 nm, respectively, exhibited the superparamagnetic character-
istics, and their saturation magnetizations were 2.7 and 2.9 emu/g, respectively. Similar saturation
magnetization values were also reported for silica-magnetite nanoparticles [58] and MCM-48-Fe
particles [59]. However, this magnitude of saturation magnetization may not be suffi cient for the
targeting drug delivery, and further work needs to be done to enhance the magnetic property and
thus to improve the drug delivery effi ciency.
Lee et al. [56] also investigated the drug delivery behavior of magnetic nanotubes. 5-FU,
4-nitrophenol, and IBU were loaded as model drug molecules into the pores of magnetic nanotubes
functionalized with amino-silane (aminopropyl triethoxysilane, APTS) to study the effect of the
charged hydrogen-bonding interaction between drug and the inner pore surfaces on loading and
release. The amine-functionalized magnetic nanotubes were immersed in hexane (IBU) or etha-
nol (5-FU, 4-nitrophenol) solutions of drugs. The amine functional groups had strong ionic and/or
hydrogen-bonding interactions with the acid functional groups of drug molecules. Their experi-
ments showed that
10
7
IBU molecules per nanotube were loaded, and
10
6
for 4-nitrophenol and
∼
∼
10
7
for 5-FU. The value for IBU was about twice the monolayer coverage of the inner surface area
of a magnetic nanotube.
Santamaía et al. [60] synthesized nanocomposites consisting of magnetite and FAU zeolite with
a high surface area (442
.
9 m
2
/g) by a high-energy milling method. The magnetite nanoparticles had
diameters of 20-30 nm and were dispersed within larger zeolite particles (200 nm-1
.
2 µm long).
The resulting magnetic nanoparticles were covered by a thin aluminosilicate coating. The saturation
magnetization and coercivity were measured to be 16 emu/g and 94.2 Oe, respectively. The capacity
of the magnetite-zeolite composites to adsorb and release a specifi c drug (doxorubicin) was tested
using dispersions of the composites in human plasma. Because the molecular size of doxorubicin
used was larger than the mean pore size of the magnetic nanoparticles obtained (0.87 nm), the
adsorption occurred on the external surface of the nanocomposites and in the microvoids between
the magnetite cores and the zeolite shells. The initial uptake was very fast, with 77% of the initial
doxorubicin being adsorbed in 3.1 h. Adsorption of the remaining doxorubicin occurred at a slower
rate, and the adsorption process was essentially complete in approximately 25 h, at which time 92%
of the initial doxorubicin had been loaded. After removing nonadsorbed doxorubicin by washing,
the dried, drug-loaded nanoparticles were redispersed in human plasma. After washing, over 50%
of the initial doxorubicin was still adsorbed in the nanoparticles; it was progressively released by
desorption and diffusion to the plasma solution, and 77% of the doxorubicin loaded on the nanopar-
ticles was released in 12.6 h.
Wang et al. [61] synthesized tetraheptylammonium-capped nanoparticles of Fe
3
O
4
, Fe
2
O
3,
and
Ni by the electrochemical deposition method under oxidizing conditions. The synergistic effect of
these nanoparticles on the drug accumulation of the anticancer drug daunorubicin in leukemia cells
was investigated. The experiments showed that the presence of magnetic nanoparticles could facili-
tate the drug accumulation of daunorubicin inside leukemia cells and that the enhancement effect of
Fe
3
O
4
nanoparticles was much stronger than that of the other two magnetic nanoparticles.
Alexiou et al. [62] prepared iron oxide core covered by a layer of starch polymer. The starch
layer made the magnetic nanoparticles biocompatible and able to react with various end func-
tional groups for binding other molecules. The drug mitoxantrone was bound to phosphate groups
of starch derivatives. A successful application of the magnetic drug targeting was demonstrated
by experiments on New Zealand White Rabbits in which VX-2 squamous cell carcinoma was
placed at the medial portion of the left hind limb. Typically, 35 days after the treatment, the tumor
∼
