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Molecular biomaterials, such as biodegradable polymers, are the material basis for the development of nanomedicine. Although linear biodegradable polymers, such as poly(lactic-co -glycolic) (PLGA) and poly(lactide)-tocopheryl PEG succinate (TPGS), have been widely applied [1], branched biodegradable polymers, especially star-shaped block polymers, because of their technical simplicity in synthesis in comparison with others (e.g., hyperbranched polymers and dendrimers), have emerged as a new type of molecular biomaterial for nanomedicine development due to their high performance in sustained, controlled and targeted delivery of therapeutic and diagnostic agents. Synthesis of star-shaped polymers can be performed by either the 'core-first' or the 'arm-first' approach, in which the properties of the resulting star-shaped block polymers can be adjusted by changing the structure of the core and the arms [2]. Star-shaped block polymers have many characteristic properties desirable for nanoparticle-based drug delivery systems due to their unique structure. First, the star-shaped polymers have a lower solution viscosity, smaller hydrodynamic radius and higher density of functional groups in comparison with linear polymers of the same molar mass [3-5]. Second, the drug carriers based on star-shaped polymers showed high drug loading and high drug encapsulation efficiency in the literature [3]. Moreover, since the molecular structure can be engineered to prevent self-aggregation, star-shaped block polymers are an excellent candidate to form unimolecular micelles, which could result in a long half-life and high cellular uptake of the formulated drug [6,7]. A type of amphiphilic multiarm star-shaped block copolymer was successfully synthesized as an integrated platform for targeted delivery of therapeutic, as well as diagnostic, agents [8].
Star-shaped polymer-based nanomedicine for delivery of chemotherapeutic agents
Feng and colleagues conducted proof-of-concept research focused on nanomedicine based on linear vitamin E TPGS copolymers by using paclitaxel (PTX) and docetaxel, which have difficulties in formulation for clinical application, as model drugs [9]. More recently, the same group further developed a system of the cholic acid-functionalized star-shaped PLGA- b -TPGS (CA-PLGA-b -TPGS) nanoparticles for sustained and controlled delivery of docetaxel for treatment of cervical cancer, which were compared with the drug-loaded nanoparticles of the linear PLGA and PLGA-b -TPGS copolymers, respectively [3]. The in vitro and in vivo experiments demonstrated that the docetaxel-loaded CA-PLGA-b -TPGS nanoparticles exhibited significantly superior anti-tumor effects both in vitro and in...