Biomedical Engineering Reference
In-Depth Information
disappeared completely [47]. No metastases or negative side effects were observed. Both rabbits
were treated with mitoxantrone. One rabbit was treated using magnetic drug targeting. Only 20%
of the systemic dose was necessary to achieve complete remission of the tumor after 16 days. The
second rabbit was treated with conventional local application (femoral artery) of mitoxantrone. To
obtain a complete remission of the tumor, 75% of the systemic dose was necessary. However, the
side effects of this treatment were atrophy of the left hind limb, alopecia, and ulcerations and weep-
ing infl ammation of the skin. The experiments also showed that ferrofl uids not only concentrated in
the cancer tissue but also penetrated into the tumor cells [62].
Giorgio et al. [63] developed an in vitro system to quantify the suitability of superparamagnetic
nanoparticles as a site-specifi c therapeutic vehicle for delivery through fl uid- and gel-based sys-
tems. The motion of magnetic nanoparticles was induced by an external magnetic fi eld. Magnetic
nanoparticles were capped with silica surface coating (135 nm radius) and 300 Da polyethylene
glyco (PEG) surface coating (145 and 400 nm radius). PEGylated nanoparticles with a 135 nm
radius moved through the extracellular matrix with an average velocity of 1.5 mm/h, suitable for
some clinical applications. However, a greater than 1000-fold reduction in magnetic mobility (less
than 0.01 mm/h) was observed when the nanoparticle radius was increased to 400 nm while main-
taining the same per nanoparticle magnetic susceptibility. The critical infl uence of nanoparticle size
on gel permeation was also observed in silica-coated 135 nm magnetic nanoparticles. Superpara-
magnetic nanoparticles enabled signifi cant free-solution mobility to specifi c sites within a cavity
and generated suffi cient force to penetrate common in vivo gels.
9.5 CONCLUDING REMARKS
Inorganic materials are promising for their applications in the development of new controlled drug
delivery systems, which constitute a rapidly evolving research fi eld of current interest. As reviewed
in this chapter, some interesting work has been done in recent years, and the research activities in
this fi eld continue to grow rapidly. In my opinion, one of the main future research directions in this
fi eld is the development of multifunctional (controllable drug loading capacity, controllable drug
release, targeting ability, biodegradability, etc.) nanostructured inorganic drug carriers with spe-
cifi c structures and morphologies. To prepare such multifunctional nanostructured drug carriers, it
is very important to explore new methods that are simple, inexpensive, and environment-friendly.
Another important research topic could be exploring new techniques for controllable drug release,
which not only control the release rate but more importantly control when and where to release the
drug (“start” and “stop” of drug release at the time and the location we want). Biodegradability,
which enables the drug-carrier materials to disappear after the drug release is complete, is also an
important desirable characteristic for drug carriers. In this case, the infl uence of the degradation
rate on the drug release rate should be investigated, and the degradation rate needs to be considered
for the design of the controlled biodegradable drug release systems.
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drug release, Chem. Rev. , 99, 3181, 1999.
3. Langer, R., Polymer-controlled drug-delivery systems, Accounts Chem. Res. , 26, 537, 1993.
4. Moghimi, S.M., Hunter, A.C., and Murray, J.C., Long-circulating and target-specifi c nanoparticles:
theory to practice, Pharmacol. Rev. , 53, 283, 2001.
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