Biomedical Engineering Reference
In-Depth Information
Recently a study showed generation of “two-in-one” magnetic-fluorescent
nanocomposites comprising silica-coated magnetite nanoparticles, which get cova-
lently attached to a porphyrin moiety. In the presence of PMNC, initial co-incuba-
tion experiments were performed using THP-1 macrophage cells which showed a
distinct photobleaching of the porphyrin upon irradiation of light under a fluores-
cent microscope (Nowostawska et al. 2011).
3.4 Porphyrin Based Nanoparticles (Porphysomes)
The ideal nanomedicine formulation includes design of novel materials for drug
delivery application. Designing multicomponent and multifunctional nano-
particles via molecular self-assembly involves control upon nanoparticle size,
surface chemistry and geometry, it is especially useful in a process whereby
molecules self-associate in solution via weak intermolecular forces (Huynh and
Zheng 2013). The concept of activatable nanoparticles can be executed by cou-
pling dynamic structural changes with photophysical phenomena that occur at
the nanometer length scale. External stimuli leads to activation of these “smart”
agents which further elicit an effect at the nanoscale level. These activatable nan-
oparticles that get activated by external stimulus played useful role in PDT and
photodiagnosis. The specificity of action depends on preferential accumulation of
the photoactive agent into target versus normal tissues. Thus additional layer of
specificity can be included by activating the agent only in the target tissues into the
treatment process.
Porphysomes represents the self-assembled form of porphyrin lipid conju-
gate into liposome-like nanoparticles (100 nm diameter). The packing density
of porphyrin per particle (>80,000 per particle) is high, so their light absorp-
tion efficiency is extremely high. Induction of highly self-quenching porphyrin
excited states due to the packing density, their absorbed energy will be released
as heat, making them exceptionally useful as PTT agents. Unlike monomeric
porphyrins, this nanoassembly of porphyrin lipids (Porphyrosome) serves
as ideal for PTT enhancement rather than usual PDT agent. Recently a study
evaluated the mechanism of nanostructure-driven conversion of the PDT acti-
vated porphyrin photosensitizers to activated PTT transducers by performing in
vivo studies. It involves the PDT and PTT efficiency of porphysomes for treat-
ment of hyperoxic and hypoxic tumors. This was the first unique study which
showed the conversion of porphyrins from PDT to PTT, by comparing porphy-
rin nanoparticles with porphyrin monomers in vivo. Porphysomes exhibit fluo-
rescence quenching and photothermal properties when formulated mechanically
(Jin et al. 2013). This fluorescent lipid conjugated vesicle was capable of ROS
generation, and also stably chelate metals for radioimaging applications (Liu
et al. 2012). Thus it showed for the first time about the usage of organic PTT
agents with comparable optical absoprtions to GNPs for high photothermal
efficiency (Lovell et al. 2011).
