“9.61x6.69” b2815 Tissue Engineering and Nanotheranostics
Multifunctional Nanomaterials for Cancer Theranostics 233
cellular uptake increases in positively modified particles by rising of
charge.95,96 The permeability of positively charged drug carriers to
gastrointestinal mucous barrier is easier than neutral and negatively
charged nanoparticles because of the presence of negatively charged
proteins in outer surface of gastrointestinal epithelial cells. The ani
onic nanomaterials can also affect their cellular uptake. For example,
by increasing the negative surface charge of carboxymethyl dextran
modified iron oxide nanoparticles, the nanomaterials can be taken
increasingly via nonspecific pathways.^97
Besides, the hydrophobic/hydrophilic character of nanomaterials
is also an important factor for cell uptake and blood circulation.98–100
If the hydrophobicity of the nanomaterials is stronger than the cell
membrane, the nanomaterials bind more easily to the cell surface
through protein adsorption to enhance uptake. However, such nano
materials cannot be used in vivo, especially via intravenous injection.
In contrast, hydrophilic nanoparticles will attract fewer of these pro
teins, which makes nanomaterial in vivo circulation adsorb protein
hardly. For this reason, nanocarriers are often PEGylated.101,102
Polyethylene glycol (PEG), a neutral and hydrophilic polymer mate
rial, can lead to the steric prevention, low opsonization, high blood
circulation time, and escape from reorganization by phagocytic sys
tem. PEG could be used to modulate the hydrophilicity of hydropho
bic nanomaterials significantly. Obviously, there are many factors that
interplay in the design of the nanoparticles for use in theranostic
systems. It must be explained that the above effects are only the
wealth of information available and reported, for a given system, and
each of these factors should be experimentally determined because
there is no way to predict the interactions occurring in a given system.
The following are some of the mainly introduced and frequentlyused
theranostics of organic systems and representatives of inorganic
systems.^73
2.1. Polymer
Polymeric nanomaterials are composed of a backbone that is synthe
sized from a monomer. Anticancer drugs’ conjugation with polymeric
