“9.61x6.69” b2815 Tissue Engineering and Nanotheranostics
Multifunctional Nanomaterials for Cancer Theranostics 235
2.2. Liposome
The liposome with its capacity to selfassemble into a bilayer structure
is composed of both hydrophobic and hydrophilic component, is the
most widely used for targeted drug delivery.^1 21–124 The lipid bilayer can
be composed of cationic, anionic, or neutral (phospho)lipids and cho
lesterol. To improve liposome stability and enhance their circulation
times in the blood, some hydrophilic polymers, such as PEG are often
chosen for obtaining stericallystabilized liposome.125,126 Its unique
structure gives the liposome a powerful drug loading function.
Hydrophobic drugs can be inserted into the bilayer membrane, with
the hydrophilic molecules trapped in the aqueous center. Moreover,
owing to the large aqueous center and biocompatible lipid exterior, a
variety of macromolecules, such as DNA, proteins and imaging agents
can also be delivered by means of the liposome. The use of the
liposomes as drug vesicles have been shown to be beneficial for stabi
lizing therapeutic drugs, overcoming obstacles to cellular and tissue
uptake, and improving biodistribution of drug. Moreover, the
liposomes are biocompatible, their surface properties can be easily
modified according to the need of active targeting to tumor site, and
their particle sizes can be precisely controlled. Despite these advan
tages, the liposome nanocarriers also have shortcomings, including
poor stability, low loading efficiency, and poor release profiles.
2.3. Dendrimers
Dendrimers are constituted of successive branched layers with dis
crete, highly compact and treelike nanostructures. Their size is well
controlled with the increase of the dendrimer generation. Dendrimers
as drug carriers also possess a lot of advantages.^127 For instance,
because of the excellent monodispersity, the dendrimers loaded anti
cancer drugs provide a good promise for reproducible pharmacody
namic and pharmacokinetic behaviors.^128 The nanosize and unique
structure of dendrimers ensure drug delivery applications in vivo.129,130
The sufficient functional groups on the surface of dendrimers can be
modified with various ligands such as targeting moieties, imaging
