Biomedical Engineering Reference
In-Depth Information
optical imaging, nuclear medical imaging, ultrasound imaging, CT, MRI,
and photoacoustic imaging. Molecular imaging always requires an accu-
mulation of contrast agent in the target site, ot en achieved most ei ciently
by steering nanoparticles containing contrast agent into the target. h is
entails accessing target molecules hidden behind tissue barriers, necessitat-
ing the use of targeting groups. For imaging modalities with low sensitivity,
nanoparticles bearing multiple contrast groups provide signal amplii ca-
tion. h e same nanoparticles can in principle deliver both contrast medium
and drug, allowing monitoring of biodistribution and therapeutic activity
simultaneously (theranostics). Nanoparticles with multiple bioadhesive
sites for target recognition and binding will be larger than 20 nm diameter.
h ey share functionalities with many subcellular organelles (ribosomes,
proteasomes, ion channels, and transport vesicles) and are of similar sizes.
h e materials used to synthesize nanoparticles include natural proteins and
polymers, artii cial polymers, dendrimers, fullerenes and other carbon-
based structures, lipid-water micelles, viral capsids, metals, metal oxides,
and ceramics. Signal generators incorporated into nanoparticles include
iron oxide, gadolinium, l uorine, iodine, bismuth, radionuclides, quantum
dots, and metal nanoclusters. Diagnostic imaging applications, now appear-
ing, include sentinal node localization and stem cell tracking [187].
Nanomedicine has major potential applications in diabetes. h ese include
solving needs such as noninvasive glucose monitoring using implanted
nanosensors, with key techniques being l uorescence resonance energy
transfer (FRET) and l uorescence lifetime sensing, as well as new nanoen-
capsulation technologies for sensors such as layer-by-layer (LBL) i lms. h e
latter might also achieve better insulin delivery in diabetes by both improved
islet encapsulation and oral insulin formulations. An “artii cial nanopan-
creas” could be an alternative closed-loop insulin delivery system. Other
applications of nanomedicine include targeted molecular imaging
in vivo
(e.g., tissue complications) using quantum dots (QDs) or gold nanoparti-
cles, and single-molecule detection for the study of molecular diversity in
diabetes pathology [188]. Functionalized-quantum-dot-liposome (f-QD-
L) hybrid nanoparticles are engineered by encapsulating poly(ethylene
glycol)-coated QD in the internal aqueous phase of dif erent lipid bilayer
vesicles. Moreover, f-QD-L of er many opportunities for the development
of combinatory therapeutic and imaging (theranostic) modalities by incor-
porating both drug molecules and QDs within the dif erent compartments
of a single vesicle [189]. Other examples include measuring, understand-
ing, and manipulating stem cells using magnetic nanoparticles/quantum
dots for labeling,
in vivo
tracking, intracellular delivery of genes/oligonu-
cleotides, protein/peptides and engineered nanometer-scale scaf olds for
