Biomedical Engineering Reference
In-Depth Information
studies. Irradiation of the photosensitizing drug entrapped in nanoparticles with light of suitable
wavelength resulted in effi cient generation of singlet oxygen.
In vitro
studies showed the active
uptake of drug-doped nanoparticles into the cytosol of tumor cells. Signifi cant damage to such
impregnated tumor cells was observed upon irradiation with light of wavelength 650 nm.
Lee et al. [29] investigated the controlled release of lidocaine hydrochloride from the doped
silica-based xerogels with pore sizes from 0.84 to 1.45 nm and surface area from 95 to 649 m
2
/g.
In the xerogel preparation, tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), and prop-
yltriethoxysilane (PTES) were used as precursors, and a nonionic surfactant Igepal CO 720 was
used as a dopant. The release of lidocaine hydrochloride was controlled by partially substituting
TEOS with the organosilanes, and/or by adding the dopant. Adding the organosilane precursors
lowered the release of both the drug and the surfactant in the order of TEOS, MTES/ TEOS, and
PTES/TEOS xerogels. The release from the PTES/TEOS xerogels was much lower than that from
the other xerogels. The release of lidocaine hydrochloride was suppressed by the addition of Igepal
CO 720, while the release of Igepal CO 720 was slightly promoted by the addition of the drug. The
overall release process was diffusion-controlled.
Drug-loaded silica or titania porous microspheres with complex morphology were prepared
by sonication of nanoparticle suspensions confi ned within aqueous droplets of drug molecules in
toluene [30]. The drug molecules were incorporated during the assembly of nanoparticle-containing
microspheres. The charge and the amphiphilic nature of the drug molecules had a marked infl uence
on microsphere morphology. As a general rule, when the charge on the drug molecule was the same
as that of the inorganic nanoparticles, for example, for negatively silica/IBU or positively charged
titania/phenylephrine hydrochloride combinations, the microspheres exhibited smooth outer sur-
faces perforated with circular apertures that were usually less than a micrometre in diameter. When
fractured, these microspheres displayed an elaborate foam-like interior of spherical pores with
interconnecting mineralized walls, 50-100 nm in thickness. The strong interactions between the
drug molecules and the nanoparticles took place for silica/phenylephrine hydrochloride or titania/
IBU combinations, leading to the inhibition of the formation of the oil-in-water-in-oil micelles.
Intact nonperforated microspheres with compact, roughened, and creased surfaces and solid inte-
riors were produced. The release properties of IBU- or phenylephrine-loaded silica microspheres
were investigated in simulated body fl uid. In both the cases, release of the drugs occurred within
30 min, after which steady-state conditions corresponding to further release of residual drug mol-
ecules were observed up to 3 h after immersion.
The nanotubes are highly attractive since it is possible to differentially functionalize the inner
and outer surfaces to facilitate drug loading. Lee et al. [31] reported the template synthesis of
composite nanotubes containing silica and iron oxide. The inside of nanotubes were differentially
functionalized with amino-silane (aminopropyl triethoxysilane, APTS) to generate a polycationic
surface for drug loading using ionic interaction between drug molecules and nanotube inner surface.
For drug loading, 5-fl uorouracil (5-FU), 4-nitrophenol, and IBU were used. The amount of released
drug was monitored by measuring changes in absorbance at 264 nm (IBU), 400 nm (4-nitrophenol),
and 266 nm (5-FU). Drug release patterns varied with the drugs. For example, 10% of IBU was
released in 1 h and 80% was released after 24 h, whereas more than 90% of 5-FU and 4-nitrophenol
were released in 1 h. The total release percentage at the same time scale increased in the order of
IBU, 4-nitrophenol, and 5-FU.
The recent progress in the design and the development of nanodevices for drug delivery is note-
worthy. Sinha et al. [32] developed a high-precision nanoengineered device to yield long-term zero-
order release of drugs for therapeutic applications. The device contained nanochannels that were
fabricated between two directly bonded silicon wafers and therefore possessed a high mechanical
strength. The nanochannels were defi ned by selectively growing oxide and then etching that oxide
(sacr ii cial oxide), which was grown under dry thermal conditions. It was possible to control the
oxide thickness within
±
1 nm uniformity; therefore, the nanochannels were fabricated with less
than
±
1 nm size error. Diffusion through the nanochannels was the rate-limiting step for the release
