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250 Tissue Engineering and Nanotheranostics
6. Therapy
In this section, several therapeutic methods including PTT, photody
namic therapy as well as combined therapy are mainly discussed.
Controlled drug delivery in the previous section has been mentioned.
6.1. Photothermal Therapy
PTT is a therapeutic strategy in which photon energy is converted
into heat for the treatment of many medical conditions, including
cancer. It is known that NIR light is harmless to the human body. So,
ideal photothermal agents should exhibit strong absorbance in the
NIR region, and should efficiently transfer the absorbed NIR optical
energy into heat. Various types of NIRabsorbing nanomaterials, such
as carbonbased nanomaterials, goldbased nanomaterials, copper
sulfide nanoparticles as well as organic polymers have been widely
explored.309–318 For example, CNTs have been developed as effective
photothermal conversion agents for the PTT of cancer.319–321 The
results indicated that PEGylated CNTs exhibited excellent biocom
patibility, low cost, nontoxic and stabilization.185,322,^323 Due to their
strong NIR absorption, gold nanotubes have also been extensively
explored in PTT.324,325 Even so, the potential toxicity of carbonbased,
goldbased nanomaterials, is still an unresolved debate, which will inevi
tably limit future clinic applications of PTT. These nondegradable or
slowly degradable nanoparticles easily accumulate in bodily organs,
resulting in increased oxidative stress, inflammatory cytokine produc
tion and cell death. Fe 3 O 4 nanoparticles have received tremendous
attention for their excellent magnetic, biocompatible and potentially
nontoxic properties. Iron is a nutrient and is readily metabolized by
cellular regulation using the transferrin pathway. Thus, Fe 3 O 4 nano
particles are easily degradable and pass in and out of cells across the
plasma membrane. Shen et al. firstly reported photothermal effect of
nanoFe 3 O 4 clusters for the photothermal ablation of tumors.
Compared with individual magnetic Fe 3 O 4 nanoparticles, clustered
Fe 3 O 4 nanoparticles can result in a significant increase in the NIR
absorption.^326
