Tissue Engineering And Nanotheranostics

b2815 Tissue Engineering and Nanotheranostics “9.61x6.69”

236 Tissue Engineering and Nanotheranostics

probes and biocompatible ligands for specific therapies. For drug

delivery, drug molecules can be encapsulated through the interior

pockets of dendrimers via non­covalent interactions such as electro­

static, hydrophobic, and hydrogen­bond interactions, while drug

molecules can also be conjugated by the surface functionalities via

covalent linkages. Additionally, the cationic dendrimers mainly includ­

ing polyamidoamine and poly(propyleneimine) with abundant tertiary

amine groups on the surface can efficiently condense nucleic acids into

nanomaterials for gene delivery.^1 31–137

2.4. Polymeric Micelle

In recent years, amphiphilic block copolymers forming self­assembled

micellar structure have gained much attention for their application in

drug delivery.138,139 The polymeric micelle has a hydrophobic core con­

sisting of polymer tails and hydrophilic head groups. The micelles are

formed through a process of self­assembly that occurs in a concentration­

dependent manner, referred to as critical micelle concentration. Like

other nanocarriers, the micelle used for drug delivery can improve the

drug tissue distribution and reduce off­target cytotoxicity. The fol­

lowing describes some typical micelles. Poloxamer (trade name

Pluronics) consists of a central poly(propylene oxide) (PPO) block

forming hydrophobic core that is flanked on both sides by two hydro­

philic chains of poly(ethylene oxides) (PEO) forming hydrophilic

corona, yielding a structure of (PEO)a–(PPO)b–(PEO). Poly(lactic)

acid (PLA), approved by the FDA, is used up in citric acid cycle to

produce water and carbon dioxide. In order to improve the weak

hydrophilicity of PLA, copolymerization of PEG–PLA was developed

for the self­assembly of micelles in water with the size range of

10–100 nm.140,141 The clinically approved micellar preparation of

paclitaxel, Genexol­PM has mPEG–PLA as the micelle­forming poly­

mer.142,143 Another class of amphiphilic polyester polymers, PEGy­

lated poly(caprolactone) (PEG–PCL) is an ideal candidate for drug

delivery with its amphiphilic property and ease to synthesis, and

exhibits good biocompatibility, biodegradability and low toxicity pro­

file.^1 44–146 PEG–lipid copolymers are the same as other diblock