AB₂ Miktoarm Star Polymers [PLGA-(MPEG)₂] as Nanocarriers for Drug Delivery

Among many biodegradable and biocompatible polymers, poly(Lactide-co-glycolide) (PLGA) copolymers are most widely investigated for various biomedical applications such as vaccination, drug and gene delivery, and tissue engineering (Danhier et al., 2012) . Several innovative products of these polymers are in clinical use today. The biodegradability and biocompatibility of these polymers and, thus, bioresorption of degradation products remains as the primary attraction for further exploration. However, due to its high hydrophobicity, PLGA has some limitation in practical release formulation. Research focus over the last two decades has since been directed towards various approaches to overcome the disadvantages of these polymers. One important strategy is to conjugate PLGA with Poly(ethylene glycol) (PEG) through copolymerization, producing PLGA/PEG based AB diblock (Beletsi et al., 1999), ABA (Kissel et al., 2002) or BAB triblock (Jeong et al., 2000), multi-block (Huh and Beae, 1999 and Bae
et al., 2000), branched block (Hrkach et al., 1997), star-shaped block (Breitenbach et al., 2000) and graft block (Jeong et al., 2000) copolymers, which has enabled a broader application in drug delivery and tissue engineering. This novel improvement in PLGA material performance is attributed to PEG having good hydrophilicity, antiphagocytosis against macrophages, resistance to immunological recognition, noncombination with proteins, chain flexibility, in addition to being biocompatible and biodegradable. Research has also shown that PLGA-PEG block copolymers are able to self-assemble into nanomicelle,
with PLGA as its hydrophobic core and PEG as its hydrophilic corona shell. The PLGA core of the micelles can be loaded with poorly water soluble drugs, while the PEG shell provides colloidal stability in vitro and in vivo. In fact, the prospective utility of polymeric micelles as nanocarriers for drug and gene
delivery has been largely demonstrated through preclinical and clinical trials.