Synthesis, self-assembly, and drug-loading capacity of well-defined cyclodextrin-centered drug-conjugated amphiphilic A14B7 miktoarm star copolymers based on poly(ε-caprolactone) and poly(ethylene glycol)

Article abstract of DOI:10.1021/bm901371p

Novel drug-conjugated amphiphilic A₁₄B₇ miktoarm star copolymers composed of 14 poly(ε-caprolactone) (PCL) arms and 7 poly(ethylene glycol) (PEG) arms with β-cyclodextrin (β-CD) as core moiety were synthesized by the combination of controlled ring-opening polymerization (CROP) and "click" chemistry. ¹H NMR, FT-IR, and SEC-MALLS analyses confirmed the well-defined A₁₄B₇ miktoarm star architecture. These amphiphilic miktoarm star copolymers could self-assemble into multimorphological aggregates in aqueous solution, which were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Moreover, the drug-loading efficiency and drug-encapsulation efficiency of the drug-conjugated miktoarm star copolymers were higher than those of the corresponding non-drug-conjugated miktoarm star copolymers.

Full text of DOI:10.1021/bm901371p

934
Biomacromolecules 2010, 11, 934–943
Synthesis, Self-Assembly, and Drug-Loading Capacity of
Well-Defined Cyclodextrin-Centered Drug-Conjugated
Amphiphilic A14B7 Miktoarm Star Copolymers Based on
Poly(ε-caprolactone) and Poly(ethylene glycol)
Peng-Fei Gou, Wei-Pu Zhu,* and Zhi-Quan Shen
MOE Key Laboratory of Macromolecule Synthesis and Functionalization, Department of Polymer Science
and Engineering, Zhejiang University, Hangzhou 310027, China
Received December 3, 2009; Revised Manuscript Received February 20, 2010
Novel drug-conjugated amphiphilic A14B7 miktoarm star copolymers composed of 14 poly(ε-caprolactone) (PCL)
arms and 7 poly(ethylene glycol) (PEG) arms with ꢀ-cyclodextrin (ꢀ-CD) as core moiety were synthesized by
the combination of controlled ring-opening polymerization (CROP) and “click” chemistry. 1H NMR, FT-IR, and
SEC-MALLS analyses confirmed the well-defined A14B7 miktoarm star architecture. These amphiphilic miktoarm
star copolymers could self-assemble into multimorphological aggregates in aqueous solution, which were
characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Moreover, the
drug-loading efficiency and drug-encapsulation efficiency of the drug-conjugated miktoarm star copolymers were
higher than those of the corresponding non-drug-conjugated miktoarm star copolymers.
ε-CL-terminated PEG macromonomer.26,27 As the “click”
reaction has appeared to be an efficient method for the
Introduction
preparation of polymers with complex structures,28-34 Je´roˆme’s
group developed a facile strategy to synthesize PCL- and PEG-
based graft copolymers via the combination of “click” reaction
and ROP.35-37 Recently, Yuan et al. synthesized a cylindrical
brush copolymer with linear PCL-b-PEG as side chains and
studied its thermal and crystallization behaviors.38 As an
extension of this work, Wang et al. investigated in detail the
doxorubicin (DOX) loading capacity and release behavior of
these cylindrical brush copolymer micelles and found that they
were preferable potential drug carriers for efficient drug delivery
compared with their linear PCL-b-PEG micelle analogues.39
Quite interestingly, Dong et al. described the synthesis of novel
linear-dendron-like PCL-b-PEG copolymers composed of linear
PEG blocks and dendron-like PCL blocks.40 These new types
of copolymers provide an approach to fabricate worm-like DOX-
loaded nanoparticles which showed a higher drug loading
efficiency and a longer drug-release time than the linear
counterparts.41
Great interest has been evoked for the design of polymeric
micelles self-assembled from amphiphilic copolymers as drug
carriers due to their unique characteristics such as core-shell
structure, mesoscopic size range, and prolonged blood
circulation.1-4 Naturally, biodegradable and biocompatible
polymeric micelles are of special interest in the delivery
system.5 As a U.S. Food and Drug Administration (FDA)
approved biomedical polymer, poly(ε-caprolactone) (PCL)
is one of the most attractive and promising biodegradable
and biocompatible aliphatic polyesters that can be used as a
synthetic biomaterial or a controlled drug release matrix due
to its good drug permeability, biocompatibility, and nontox-
icity.6 Poly(ethylene glycol) (PEG) is also a FDA approved
hydrophilic and nonionic polymer that has been widely
investigated as a biocompatible polymer in both academia
and industry for chemical and biological applications.7
Polymeric micelles containing PEG as the hydrophilic shell
can prevent the adsorption of proteins and enzymes and thus
increase their residence time in systemic circulation.8,9
Star polymers consisting of several equal or unequal (mik-
toarm star) linear chains together at one central core have
attracted considerable attention of polymer chemists because
they are special types of branching polymers and always
showing particular bulk and solution properties.42,43 Moreover,
several recent publications also demonstrated that star polymers
have some advantages in gene and drug delivery compare to
the linear polymers.44-47 For example, Bae et al. investigated
the formation of doxorubicin hydrochloride encapsulated poly-
mersome from AB2 miktoarm star copolymers [PEG-b-(PLLA)2]
and observed sustained in vitro release of the loaded drug.48
Roovers et al. reported that micelles self-assembled from PCL-
and PEG-based multiarm star block copolymers exhibited high
drug loading capacity as well as facile release kinetics.49,50
Therefore, it is expected that developing new types of star
polymers with unique architectures may provide new insights
for fabricating superior drug carriers for special delivery system.
Up to this date, although micelles self-assembled from PCL-
and PEG-based copolymers have been extensively studied for
biomedical applications, most of the work focused on utilizing
linear block copolymers.10-19 It has been proved that the
architecture of amphiphilic copolymer may influence the
morphology, stability, and dimensions of the micelles,20-23
which are important parameters to determine the drug loading
capacity, release behavior, and circulation in vivo.24,25 Therefore,
rational design and synthesis of PCL- and PEG-based copoly-
mers with novel architecture may provide promising drug carrier
candidates for clinical applications in delivery systems. Je´roˆme
and co-workers reported the synthesis and micellization of
comblike PCL- and PEG-based graft copolymers through the
ring-opening copolymerization (ROP) of ε-CL and a novel
* To whom correspondence should be addressed. Fax: +86 571
87953727. E-mail: carrols@163.com.
10.1021/bm901371p
 2010 American Chemical Society
Published on Web 03/12/2010

Amphiphilic A14B7 Miktoarm Star Copolymers
Biomacromolecules, Vol. 11, No. 4, 2010 935
Scheme 1. Synthetic Route of Cyclodextrin-Centered Drug-Conjugated Amphiphilic A14B7 Miktoarm Star Copolymers via the Combination
of Controlled Ring-Opening Polymerization (CROP) and “Click” Chemistry
Meanwhile, traditional polymeric micellar drug carrier system
by simple encapsulating hydrophobic drugs to the hydrophobic
core is hampered by either premature drug release before the
micelle reaches the targets or insufficient intracellular delivery
owing to the low drug loading capacity.51 To overcome these
shortcomings, conjugation of drugs to the polymer chains by
covalent bonds have been developed in recent years.52-60
Employing drug conjugated polymeric micelles as drug carriers
not only increases the drug loading capacity but also enhances
the controllability of the drug delivery system.
(PEG)7-D]. These new types of amphiphilic copolymers could
self-assemble into multimorphological aggregates in aqueous
solution which were composed of biocompatible PEG corona
surrounding with both biodegradable cyclodextrin core and PCL
arms. In addition, the hydrophobic drug ibuprofen-loaded
nanoparticles fabricated from these drug-conjugated copolymers
showed a higher drug loading efficiency than the non-drug-
conjugated counterpart. Furthermore, covalently linked drug may
prolong the drug release time, potentially making them promis-
ing carriers for the delivery of hydrophobic drugs.
In this paper, using per-6-(tert-butyldimethylsilyl)-ꢀ-CD
(CDSi) as a heteromultifunctional initiator, a facile strategy to
prepare amphiphilic drug-conjugated A14B7 miktoarm star
copolymer [CDS(PCL)14-(PEG)7-D] has been successfully de-
veloped via the combination of controlled ring-opening polym-
erization (CROP) and “click” reaction (Scheme 1). First, CDSi
with 14 secondary hydroxyl groups were first synthesized for
the CROP of ε-CL to generate 14-arm star PCL homopolymers
[CDS(PCL)14]. Second, model hydrophobic drug ibuprofen was
incorporated onto the end of the PCL chains in the presence of
DCC and DMAP at room temperature. Next, after desilylation
of the tert-butyldimethylsilyl ether groups from the ꢀ-CD core,
seven “clickable” azide groups were introduced by tandem
treating with 4-chlorobutyryl chloride and NaN3. Finally, alkyne-
terminated poly(ethylene glycol) (A-PEG) was coupled with the
14-arm drug-conjugated azide-functionalized star PCL [CD-
S(PCL)14-D-N3] by “click” reaction to produce the target
amphiphilic A14B7 miktoarm star copolymers [CDS(PCL)14-
Experimental Section
Materials. ꢀ-Cyclodextrin hydrate (ꢀ-CD) was dried over P2O5 at
80 °C under reduced pressure overnight before use. Pyridine, toluene,
and triethylamine (TEA) were dried over CaH2 and distilled just before
use. ε-Caprolactone (99%; Acros) and 2-propyny-1-ol (99%; Aladdin,
China) were distilled under reduced pressure prior to use. THF was
distilled from the ketyl prepared from sodium and benzophenone.
Methoxy poly(ethylene glycol)s (Fluka; Mn ) 1.1 K, 2 K) denoted as
mPEG25 and mPEG45 were dried by azeotropic distillation in the
presence of dry toluene. N,N,N′,N′′,N′′-Pentamethyldiethylenetriamine
(PMDETA; 99%; Aldrich), dicyclohexylcarbodiimide (DCC; 99%;
Fluka), 4-dimethylaminopyridine (DMAP; 99%; Fluka), 4-chlorobutyryl
chloride (98%; Acros), tert-butylchlorodimethylsilane (TBDMSCl;
98%; Acros), and ibuprofen (99%; Juhua Group Corporation, China)
were used as received. Succinic anhydride (99%; Fluka) was crystallized
from acetic anhydride. CuBr (99%; Acros) was purified by stirring
overnight in acetic acid. After filtration, it was washed with ethanol

936 Biomacromolecules, Vol. 11, No. 4, 2010
Gou et al.
and then dried in vacuum. Boron trifluoride diethyl etherate (BF3 ·Et2O;
48% BF3), stannous octoate [Sn(Oct)2; 97%], and other reagents were
purchased from Sinopharm Chemical Reagent Co., Ltd. (China), and
used as received.
Synthesis of Azide Functionalized Ibuprofen-Conjugated 14-Arm
Star Poly(ε-caprolactone)s [Scheme 1, CDS(PCL)14-D-N3]. A typical
procedure was as follows: CDS(PCL6)14-D-Cl (1.0 g, 0.47 mmol of
Cl group) was dissolved in DMF (50 mL) and sodium azide (306 mg,
4.7 mmol) was added. The reaction mixture was stirred for 48 h at 30
°C, then filtered and evaporated to remove DMF. Methylene chloride
(40 mL) was added, and the mixture was washed three times with
distilled water. The organic layer was dried with anhydrous MgSO4,
and the solvent was evaporated to obtain a white solid, which was dried
in vacuum to constant weight. Yield: 0.95 g (95% for polymer weight).
Synthesis of Ibuprofen-Conjugated A14B7 Miktoarm Star
Copolymer [CDS(PCL)14-(PEG)7-D] by “Click” Reaction. Ibuprofen-
conjugated A14B7 miktoarm star copolymer [CDS(PCL)14-(PEG)7-D]
was synthesized by “click” reaction between azide functionalized
ibuprofen-conjugated 14-arm star poly(ε-caprolactone)s [CDS(PCL)14-
D-N3] and alkyne-terminated PEG (A-PEG; see Supporting Informa-
tion). A typical example is given below. CDS(PCL6)14-D-N3 (400 mg,
0.19 mmol of azide group) and A-PEG25 (250 mg, 0.21 mmol of alkyne
group) were dissolved in argon-purged DMF (15 mL) in a flame-dried
ampule. CuBr (30 mg, 0.21 mmol) and PMDETA (36 mg, 0.21 mmol)
were added in order, and the reaction mixture was degassed by three
freeze-pump-thaw cycles, left in argon, and stirred at 45 °C for 48 h.
The solution was passed through an alumina column to remove the
copper salt. The polymer was recovered by precipitation into cold
diethyl ether and dried in vacuum. Yield: 540 mg (83% for polymer
weight).
Synthesis
of
Cyclodextrin-Centered
14-Arm
Star
Poly(ε-caprolactone)s [CDSiS(PCL)14] by Controlled Ring-Opening
Polymerization (Scheme 1). CDSiS(PCL)14 was synthesized by con-
trolled ring-opening polymerization of ε-CL using per-6-(tert-butyldim-
ethylsilyl)-ꢀ-CD (CDSi; see Supporting Information) as the multifunc-
tional initiator in the presence of Sn(Oct)2. A typical polymerization
procedure was as follows: CDSi (0.773 g, 5.6 mmol of OH group)
was dried at 70 °C under reduced pressure overnight and transferred
into a flame-dried ampule. Then, ε-CL (3.88 g, 34 mmol) and a
magnetic stirring bar were added to the ampule under an argon
atmosphere. After CDSi was dissolved in ε-CL completely, the tube
was then connected to a Schlenk-line, where an exhausting-refilling
process was repeated three times. A total of 20 mg Sn(Oct)2 in 1 mL
of dry toluene was added to the mixture, and the exhausting-refilling
process was carried out again to remove the toluene. The ampule was
put into an oil bath at 125 °C for 24 h bulk polymerization. The crude
polymer was dissolved in THF and poured into excess methanol to
precipitate the product, which was dried in vacuum to constant weight.
Yield: 4.58 g (98%).
Synthesis of Ibuprofen Conjugated Cyclodextrin-Centered
14-Arm Star Poly(ε-caprolactone)s [Scheme 1, CDSiS(PCL)14-D]. The
hydroxyl end groups of the CDSiS(PCL)14 were blocked by ibuprofen.
A typical procedure was as follows: CDSiS(PCL6)14 (3.0 g, 3.53 mmol
of OH group), ibuprofen (1.45 g, 7.06 mmol), DCC (3.20 g, 15.5 mmol),
and DMAP (172 mg, 1.41 mmol) were dissolved in 80 mL of anhydrous
THF, and the reaction was performed at room temperature for 48 h
under an argon atmosphere. The byproduct dicyclohexylcarbodiurea
was removed by filtration. After evaporating most of the solvent, the
ibuprofen-terminated 14-arm star poly(ε-caprolactone) [CDSiS(PCL6)14-
D] was precipitated by the addition of cold diethyl ether, which was
dried in vacuum to constant weight. Yield: 3.17 g (85% for polymer
weight).
Desilylation of CDSiS(PCL)14-D (Scheme 1). The primary hydroxyl
groups on the cyclodextrin-core were recovered by desilylation of the
tert-butyldimethylsilyl ether groups in the presence of BF3 ·Et2O. A
typical procedure was as follows: BF3 ·Et2O (0.5 mL, 2 mmol) in 10
mL of anhydrous CH2Cl2 was added dropwise to a solution of
CDSiS(PCL6)14-D (2.0 g, 0.95 mmol of tert-butyldimethylsilyl group)
in 80 mL of anhydrous CH2Cl2 under stirring. The reaction mixture
was stirred for 12 h under an argon atmosphere at room temperature
and then washed successively with NaHCO3 (100 mL, 1 M) and distilled
water. The organic phase was dried over anhydrous MgSO4. The
concentrated solution was poured into cold methanol to precipitate the
product. The resulting white solid (denoted as CDS(PCL6)14-D, Scheme
1) was dried in vacuum at room temperature for 24 h. Yield: 1.69 g
(90% for polymer weight).
Pure CDS(PCL)14-(PEG)7-D was obtained by dialysis (dialysis
membrane, MWCO 14000) and lyophilization. Typically, a 540 mg
mixture of CDS(PCL6)14-(PEG25)7-D and linear A-PEG25 was first
dissolved in 20 mL of THF, and then the distilled water (ca. 10 mL)
was added dropwise to the solution with vigorous stirring. Then the
solution was stirred overnight and dialyzed against distilled water over
7 days at room temperature to remove THF and the excess unreacted
A-PEG. The final solid-state sample was recovered by lyophilization.
Yield: 440 mg (81.9% for polymer weight).
Non-ibuprofen-conjugated A14B7 miktoarm star copolymers [CD-
S(PCL)14-(PEG)7] were synthesized using the similar methods (see
Supporting Information).
Micelles/Aggregates Formation. Typically, CDS(PCL)14-(PEG)7-D
or CDS(PCL)14-(PEG)7 (25 mg) was dissolved in 5 mL of THF, and
then distilled water (ca. 5 mL) was added dropwise to the solution
with vigorous stirring. The micelle solution was stirred overnight and
dialyzed against distilled water over 48 h to remove THF. The final
concentration of the micelle solution was adjusted to 1.0 × 103 mg/L.
Preparation of Drug-Loaded Micelles/Aggregates of
CDS(PCL)14-(PEG)7-D and CDS(PCL)14-(PEG)7 Miktoarm Star
Copolymers. CDS(PCL)14-(PEG)7-D or CDS(PCL)14-(PEG)7 (50 mg)
and the calculated amount of ibuprofen were dissolved in 10 mL of
THF, and then distilled water (ca. 5 mL) was added dropwise to the
solution under vigorous stirring to induce the hydrophobic ibuprofen
incorporated into the micellar core. The micelle solution was stirred
overnight and dialyzed against distilled water over 48 h to remove THF.
The unloaded ibuprofen precipitate was filtered through 0.45 µm filter,
and the solid-state drug-loaded miktoarm star copolymers were
recovered by lyophilization. The drug-loading capacity of the samples
Synthesis of Chloride Functionalized Ibuprofen-Conjugated
14-Arm Star Poly(ε-caprolactone)s [Scheme 1, CDS(PCL)14-D-Cl]. A
typical procedure was as follows: CDS(PCL6)14-D (1.4 g, 0.71 mmol
of OH group) was dissolved in 40 mL anhydrous THF, followed by
the introduction of triethylamine (TEA; 0.72 g, 7.1 mmol, 1.0 mL) via
a syringe. 4-chlorobutyryl chloride (1.0 g, 7.1 mmol, 0.8 mL) in 5 mL
of anhydrous THF was added dropwise to the vigorously stirred solution
at 0 °C over 30 min. The reaction mixture was stirred at room
temperature overnight. The precipitated byproduct was removed by
filtration, and the solution was evaporated to dryness. The crude product
was dissolved in 40 mL of methylene chloride, and then washed
successively with 1 M NaHCO3 aqueous solution and 40 mL of distilled
water, and finally dried over anhydrous MgSO4. The concentrated
solution was poured into methanol to precipitate the product. The
resulting white solid was dried in vacuum at room temperature for 24 h.
Yield: 1.13 g (75% for polymer weight).
1
was investigated by H NMR spectra. The loading capacity and the
encapsulation efficiency were calculated using eqs 1 and 2, respectively.
loading capacity(%) ) (WDM - WDC)/WP
(1)
(2)
encapsulation efficiency(%) ) (WDM - WDC)/WDt
1
where WDM is the weight of ibuprofen measured by H NMR spectra,
WDC is the weight of conjugated ibuprofen [for CDS(PCL)14-(PEG)7,
WDC ) 0], Wp is the weight of the star copolymer, and WDt is the total
weight of ibuprofen used in drug-loading experiment.

Amphiphilic A14B7 Miktoarm Star Copolymers
Biomacromolecules, Vol. 11, No. 4, 2010 937
Characterization. Proton Nuclear Magnetic Resonance
1
Spectroscopy (1H NMR). H NMR spectra were recorded on a Bruker
Avance DMX500 spectrometer in CDCl3 with tetramethylsilane as
internal standard.
ESI-PositiVe Mass Spectrometry (MS). ESI-MS was performed using
Bruker Esquire 3000 plus spectrometer with an ESI interface.
Size Exclusion Chromatography (SEC). The molecular weight and
molecular weight distribution were determined by size-exclusion
chromatography/multiangle laser light scattering (SEC-MALLS). The
SEC system consisted of a Waters degasser, a Waters 1515 Isocratic
HPLC pump, a Wyatt Optilab DSP interferometric refractometer, a
Wyatt DAWN DSP multiangle laser light scattering detector, and
columns: Styragel, HT 3, HT 4. Tetrahydrofuran (THF) was used as
the mobile phase at a flow rate of 0.8 mL ·min-1 at 30 °C. Polystyrenes
with the Mw ranging from 580 to 600000 were used as calibration
standards. The refractive-index increment (dn/dc) was determined with
a Wyatt Optilab DSP differential refractometer at 690 nm.
Figure 1. 1H NMR spectrum (500 MHz) of CDSiS(PCL18)14 in CDCl3.
Dynamic Light Scattering (DLS). The hydrodynamic diameter and
size distribution of micelles were determined by dynamic light scattering
(DLS) at 90° angle to the incident beam and at 25 °C on a Brookhaven
90 Plus particle size analyzer. All micellar solutions had a final polymer
concentration of 300 mg/L and were filtered through a 0.45 µm filter.
Transmission Electron Microscopy (TEM). TEM images were
obtained using JEM-1230 operating at an acceleration voltage of 60
kV. A drop of 300 mg/L micellar solution was placed onto the surface
of Formvar-carbon film-coated copper grids. Excess solution was
quickly wicked away with a filter paper. All grids were finally
negatively stained by 2 wt % phosphotungstic acid.
Fluorescence Spectroscopy. The critical micelle concentration (CMC)
was determined by fluorescence measurement using pyrene as a
fluorescent probe. Fluorescence excitation spectra were recorded on
Hitachi F-4500 fluorescence spectrometer at 390 nm emission wave-
length and 2.5 nm slit width. The pyrene concentration in the solution
was chosen to be 6.0 × 10-7 M.
additional signals of the per-6-(tert-butyldimethylsilyl)-ꢀ-CD
core moiety, that is, signals corresponding to methyl protons
(Hb) and tert-butyl protons (Ha) of the tert-butyldimethylsilyl
ether groups. The triplet at 3.65 ppm (Hg) is assigned to the
PCL methylene protons conjoint with the hydroxyl end groups.
Notably, the ratio of peak areas of Ha and Hg (Ia/Ig) is 2.15,
which is close to the theoretical value (2.25). This result clearly
demonstrates the 14-arm star structure of the samples prepared.
The number average molecular weight of the CDSiS(PCL)14
(Mn,NMR) can be calculated by the integral of signals at 4.05
ppm (Hf) of the PCL repeat units and that of signals at 0.89
ppm (Ha) of the tert-butyldimethylsilyl ether groups, which are
close to the values calculated by observed conversion and [CL]0/
[CDSi] (Mn,Cal; see Table 1). All these observations confirm that
CDSiS(PCL)14 with designed chemical structure and molecular
weight has been successfully synthesized.
SEC traces (Figure 2) of the resulting 14-arm star PCL
[CDSiS(PCL)14] homopolymers reveal unimodal elution peaks
with reasonably narrow polydispersity (<1.20), although slight
tailing was detected in the low-molecular-weight region, which
was attributed to unavoidable chain transfer side reactions during
the polymerization. Furthermore, the actual molecular weights
of the CDSiS(PCL)14 homopolymers (Mn,MALLS) measured by
connecting a multiangle laser light scattering detector to the
SEC have confirmed the values obtained from 1H NMR
spectroscopy (Mn,NMR; Table 1). These results demonstrate that
CDSiS(PCL)14 with well-defined architectures have been suc-
cessfully prepared and their molecular weights can be controlled
by adjusting the molar ratio of the monomer to the initiator. It
should be pointed out that only CDSiS(PCL)14 homopolymers
with relatively low molecular weight have been prepared in this
paper. This is due to the fact that the tailing in the low-
molecular-weight region increased with the increasing of
molecular weigh (data not shown), leading to ill-defined
structures. On the other hand, it is difficult to functionalize the
ꢀ-CD core moiety of the CDSiS(PCL)14 homopolymers with
high molecular weight in the following steps.
Synthesis of Ibuprofen Conjugated Cyclodextrin-Centered
14-Arm Star Poly(ε-caprolactone)s [CDSiS(PCL)14-D]. The
reactive hydroxyl groups at the end of the PCL arms provide
opportunities for covalent attachment of functional groups or
biological molecules (such as biotin, folic acid, and drug).62
Ibuprofen is a nonsteroidal anti-inflammatory drug that is
commonly used for the relief of symptoms of arthritis and fever.
In this present work, as a model drug, ibuprofen was conjugated
to the hydroxyl end groups of the 14-arm star poly(ε-caprolac-
tone)s [CDSiS(PCL)14] in the presence of DCC and DMAP at
Results and Discussion
Synthesis of Cyclodextrin-Centered 14-Arm Star
Poly(ε-caprolactone)s [CDSiS(PCL)14] by Controlled
Ring-Opening Polymerization. In our previous work, we
described the synthesis of well-defined seven-arm star poly(ε-
caprolactone)s initiated from the seven primary hydroxyl groups
of ꢀ-CD with stannous octoate as catalyst.61 Very recently, we
found that the 14 secondary hydroxyl groups of ꢀ-CD were also
suitable as the initiating sites for the controlled ring-opening
polymerization (CROP) of ε-CL. Thereby, in this paper, per-
6-(tert-butyldimethylsilyl)-ꢀ-CD (CDSi) with 14 s hydroxyl
groups was designed as the multifunctional initiator to generate
14-arm star poly(ε-caprolactone)s [CDSiS(PCL)14], as shown
in Scheme 1. tert-Butyldimethylsilyl ether groups as hydroxyl
protecting groups not only increased the solubility of ꢀ-CD in
ε-CL, which permits the simultaneous initiating of all the 14
secondary hydroxyl groups for the CROP of ε-CL, but also
provided a convenient platform to design A14B7 miktoarm star
copolymers in the following steps. The chemical structure of
CDSi was fully characterized by 1H NMR and MS (see
Supporting Information), which demonstrate that it has designed
chemical structure and can be used as initiator for the following
polymerization. Then, using CDSi as a multifunctional initiator,
CDSiS(PCL)14 were synthesized by the controlled ring-opening
bulk polymerization of ε-CL in the presence of Sn(Oct)2 at
125 °C. Two different monomer/initiator ratios were utilized
to achieve CDSiS(PCL)14 with different polymerization degrees.
Figure 1 exhibits a representative 1H NMR spectrum of
CDSiS(PCL)14 [CDSiS(PCL18)14]. It clearly shows that besides
the major proton signals of PCL chains (Hc-f), there are

938 Biomacromolecules, Vol. 11, No. 4, 2010
Gou et al.
PDIe
Table 1. Characterization of Cyclodextrin-Centered 14-Arm Star PCL Homopolymers
c
d
e
f
[CL]0/[CDSi]
(molar ratio)
convb
(%)
dn/dc
(mL/g)
Mn,Cal
Mn,NMR
Mn,SEC
Mn,MALLS
samplea
(g·mol-1
)
(g·mol-1
)
(g·mol-1
)
(g·mol-1
)
CDSiS(PCL6)14
CDSiS(PCL18)14
85
255
98.2
97.8
0.065
0.061
11400
30400
11900
30700
14000
36300
11200
29200
1.19
1.11
a Polymerization conditions: bulk, 125 °C, 24 h; 6 and 18 represent the polymerization degree (DP) of each PCL arm determined by 1H NMR; 14
represents the number of arms of the star PCL. b Conversion was calculated on the basis of gravimetric method. c Calculated from the equation: Mn,Cal
) ([CL]0/[CDSi]) × 114 × conversion (%) + MCDSi
.
d This calculation is based on the integral of the CL units as compared to that of the tert-butyl protons
of the CD-core in 1H NMR spectra: Mn,NMR ) ((If)/(2)) × ((9 × 7)/(Ia)) × 114 + MCDSi (see Figure 1). e Determined by SEC analysis with polystyrene
standards. f Measured by connecting a multiangle laser light scattering detector to the SEC (Mn,MALLS ) Mw,MALLS/PDI).
Figure 2. SEC traces of the cyclodextrin-centered 14-arm star PCL
homopolymers.
Figure 4. 1H NMR spectra (500 MHz) of CDS(PCL18)14-D-Cl (A) and
CDS(PCL18)14-D-N3 (B) in CDCl3.
(Hb) assigned to the methyl protons of the tert-butyldimethylsilyl
ether groups have totally disappeared, indicating that the seven
tert-butyldimethylsilyl ether groups on the ꢀ-CD core moiety
have been completely removed. In addition, the major proton
signals of PCL chains (Hc-f) and conjugated ibuprofen (Hh-j
)
remain essentially intact, which suggests there was no degrada-
tion of the PCL arms occurred.
Synthesis of Chloride Functionalized Ibuprofen-
Conjugated
14-Arm
Star
Poly(ε-caprolactone)s
[CDS(PCL)14-D-Cl]. Considering the steric hindrance of the
seven primary hydroxyl groups on the ꢀ-CD core moiety of
CDS(PCL)14-D, highly efficient “click” reaction between an
azide and an alkyne should be the best way to introduce the
seven hydrophilic PEG arms onto the presynthesized ibuprofen-
conjugated 14-arm star poly(ε-caprolactone) [CDS(PCL)14-D].
There are roughly two strategies to convert hydroxyl group into
azide group: one can resort to blocking the hydroxyl group with
tosyl chloride and followed by nucleophilic substitution reaction
with NaN3; the alternative way is to construct halogenated ester
group by capping the hydroxyl group with acyl halide and
subsequently treated with NaN3. In this work, the latter approach
was employed and 4-chlorobutyryl chloride was used to
introduce a four atom spacer group between the bulky ꢀ-CD
core and the chlorine atom, which could minimize the steric
hindrance in the following “click” reaction step. A large excess
of 4-chlorobutyryl chloride was used to ensure all the hydroxyl
groups could be capped. The 1H NMR spectrum of a representa-
tive chloride functionalized ibuprofen-conjugated 14-arm star
poly(ε-caprolactone) [CDS(PCL18)14-D-Cl] was shown in Fig-
ure 4A. After esterification, new signals corresponding to
chloromethylene protons (Ha) of the 4-chlorobutyl ester group
appeared at 3.60 ppm, which is partially overlapped with that
of the methine proton of ibuprofen moiety. By comparing the
integral of the methylene protons of PCL chain at 4.05 ppm
(Hg) to that of the methylene protons of 4-chlorobutyl ester
group at 2.10 ppm (Hb), the esterification efficiency was
Figure 3. 1H NMR spectra (500 MHz) of CDSiS(PCL18)14-D (A) and
CDS(PCL18)14-D (B) in CDCl3.
room temperature. Other hydrophobic drugs with carboxyl group
(such as ketoprofen, naproxen, and indomethacin) could also
1
be conjugated using the similar method. From the H NMR
spectrum shown in Figure 3A, resonance of the phenyl protons
at 7.09 ppm (Hj) and 7.20 ppm (Hi) indicate that ibuprofen has
been linked to the end of the PCL arms. Furthermore, the
integral of Hi+j is in well agreement with the theoretical value,
suggesting the successful and efficient synthesis of ibuprofen-
conjugated 14-arm star poly(ε-caprolactone)s [CDSiS(PCL)14-
D].
Desilylation of CDSiS(PCL)14-D. In order to recover the
seven primary hydroxyl groups on ꢀ-CD core moiety for further
modification and avoid any damage to PCL arms or conjugated
ibuprofen moieties, the tert-butyldimethylsilyl ether groups had
to be removed under mild conditions. Herein, boron trifluoride
diethyl etherate (BF3 ·Et2O) was employed to desilylate the tert-
1
butyldimethylsilyl ether groups at room temperature. The H
NMR spectrum of
a
representative desilylated CD-
SiS(PCL18)14-D [denoted as CDS(PCL18)14-D] is shown in
1
Figure 3B. Compared with the H NMR spectrum of CD-
SiS(PCL18)14-D in Figure 3A, after desilylation, there is obvious
decrease of the signals at 0.89 ppm, and signals at 0.04 ppm

Amphiphilic A14B7 Miktoarm Star Copolymers
Biomacromolecules, Vol. 11, No. 4, 2010 939
Figure 6. 1H NMR spectrum (500 MHz) of CDS(PCL18)14-(PEG25)7-D
in CDCl3.
Figure 5. FT-IR spectra of CDS(PCL18)14-D-Cl, CDS(PCL18)14-D-
N3, CDS(PCL18)14-(PEG25)7-D, and A-PEG25.
calculated to be about 91.5%. It is therefore demonstrated that
nearly all the primary hydroxyl groups on the ꢀ-CD core moiety
of CDS(PCL18)14-D have been acylated. In addition, the integral
of the PCL arms has not been changed, suggesting that no
hydrolysis of the PCL arms occurred.
are summarized in Table 2. Although a four atom spacer
between the bulky ꢀ-CD core moiety and the azide group was
introduced to decrease the steric hindrance in the “click”
coupling process, 10% excess A-PEG precursor and a slightly
high reaction temperature (45 °C) were both adopted to prepare
well-defined CDS(PCL)14-(PEG)7-D. After the “click” reaction,
linear unreacted A-PEG was removed by dialysis. From the 1H
NMR spectrum of CDS(PCL18)14-(PEG25)7-D (Figure 6), the
signal at 7.72 ppm (Hq) due to the proton of the triazole ring
and signal at 5.20 ppm (Hr) due to the methylene protons of
A-PEG conjoint to the triazole ring indicate the formation of
A14B7 miktoarm star architecture. Notably, compared with the
IR spectra of CDS(PCL18)14-D-N3 and A-PEG25 (Figure 5),
the characteristic absorption peak related alkyne group at 3295
cm-1 and azide group at 2094 cm-1 completely disappear from
the IR spectrum of CDS(PCL18)14-(PEG25)7-D, which also
confirms the successful synthesis of well-defined A14B7 mik-
toarm star copolymers by “click” reaction.
Synthesis of Azide Functionalized Ibuprofen-Conjugated
14-Arm Star Poly(ε-caprolactone)s [CDS(PCL)14-D-N3]. The
chloride groups of the CDS(PCL)14-D-Cl were converted to the
azide form in the presence of excess NaN3 in DMF at 30 °C.
1
The H NMR spectrum of CDS(PCL18)14-D-N3 is shown in
Figure 4B. It is noteworthy that the signal of the chlorometh-
ylene protons [Figure 4A (Ha)] has entirely disappeared, whereas
the new signal corresponding to methylene protons connected
with azide groups [Figure 4B (Ha)] appears at 3.36 ppm, which
indicates that the chloride groups have been converted into azide
groups entirely. SEC analysis proved that the molecular weight
and polydispersity (Mw/Mn) of the samples were not obviously
decreased after substitution, which suggests that no degradation
of the PCL arms occurred during the substitution process.
FT-IR measurements were performed to further confirm the
azide functionalized ibuprofen-conjugated 14-arm star poly(ε-
caprolactone) [CDS(PCL)14-D-N3]. As shown in Figure 5,
compared with the IR spectrum of CDS(PCL18)14-D-Cl, a new
absorption peak related to azide group at 2097 cm-1 has
appeared, which convincingly verifies the successful synthesis
of CDS(PCL)14-D-N3.
Synthesis of Ibuprofen-Conjugated A14B7 Miktoarm Star
Copolymers [CDS(PCL)14-(PEG)7-D] by “Click” Reaction.
“Click” chemistry strategy was employed to prepare ibuprofen-
conjugated A14B7 miktoarm star copolymers [CDS(PCL)14-
(PEG)7-D] between CDS(PCL)14-D-N3 and alkyne-terminated
PEG (A-PEG, characterization results see Supporting Informa-
tion) using CuBr/PMDETA as catalyst in DMF solution, and
the detailed results for miktoarm star copolymers preparation
Figure 7 shows the representative SEC traces of the miktoarm
star coplymers [CDS(PCL6)14-(PEG25)7-D and CDS(PCL6)14-
(PEG45)7-D] in comparison with those of the corresponding
CDS(PCL6)14-D-N3 homopolymer and A-PEG precursors. After
“click” reaction, the unimodal and symmetrical traces (PDI <
1.20) shifted to higher molecular mass region, indicating the
incorporation of PEG macromolecules. Meanwhile, not any trace
of A-PEG precursors were found, which demonstrates that the
excess A-PEG had been completely removed by simple dialysis.
As for CDS(PCL18)14-(PEG25)7-D and CDS(PCL18)14-(PEG45)7-
D, similar results were observed as listed in Table 2. From the
detailed information of the miktoarm star copolymers sum-
marized in Table 2, the actual molecular weights obtained by
1H NMR spectra (Mn,NMR) and SEC-MALLS (Mn,MALLS
Mw,MALLS/PDI) are in agreement with the calculated values
)
Table 2. Characterization of CDS(PCL)14-(PEG)7-D and CDS(PCL)14-(PEG)7 Miktoarm Star Copolymers via “Click” Reactiona
c
d
e
f
sampleb
Mn,Cal (g·mol-1
)
Mn,NMR (g·mol-1
)
Mn,SEC (g·mol-1
)
Mn,MALLS (g·mol-1
)
PDIe
yield (%)g
CDS(PCL6)14-(PEG25)7-D
CDS(PCL6)14-(PEG45)7-D
CDS(PCL18)14-(PEG25)7-D
CDS(PCL18)14-(PEG45)7-D
CDS(PCL6)14-(PEG25)7
CDS(PCL6)14-(PEG45)7
23200
29500
42000
48300
20300
26600
21400
31600
40300
46100
19300
27500
19200
22100
37700
40500
18100
22600
23500
30300
39700
48000
1.10
1.07
1.11
1.15
1.12
1.14
81.9
78.2
72.1
66.3
83.8
80.2
a “Click” reaction condition: [CuBr]/[PMDETA]/[azide]/[alkyne] ) 1:1:1:1.1, DMF, 45 °C, 48 h. The synthetic process of CDS(PCL)14-(PEG)7 was described
in Supporting Information. b CDS(PCL6)14-(PEG25)7-D, 6 and 25 represent the polymerization degree of PCL and PEG, respectively; 14 and 7 represent the
number of arms of the PCL and PEG, respectively; D represents the drug-conjugated sample. c Calculated from the equation: Mn,Cal ) MCDS(PCL)
or MCDS(PCL)
-
14
-D-N
14
3
N
3 + MA-PEG × 7. d This calculation is based on the integration of the CL units as compared to that of the methyl protons of A-PEG: Mn,NMR ) MCDS(PCL)
3 or
-D-N
14
MCDS(PCL) 3 + DPCDSiS(PCL) × (Ix)/(Ig) × (28)/(3) × MA-PEG
.
e Determined by SEC analysis with polystyrene standards. f Measured by connecting a multiangle
-N
14
laser light scattering detec1to4 r to the SEC (Mn,MALLS ) Mw,MALLS/PDI). g The yield of these purified copolymers were determined gravimetrically after dialysis.

940 Biomacromolecules, Vol. 11, No. 4, 2010
Gou et al.
technique using pyrene as a probe.63 Pyrene will preferentially
incorporate into hydrophobic microdomains showing strong
fluorescence intensity while weak fluorescence intensity and a
shift of excitation peak in a polar environment (aqueous
solution). In addition, the sharp rise in intensity ratio of peaks
at 338 and 333 nm of pyrene in the excitation spectra indicates
the on-set of micellization (CMC) for amphiphilic copolymer.
Figure 8 shows the relationship of the intensity ratios (I338/I333
)
as a function of copolymer concentration at room temperature.
It can obviously be observed that the CMC values of these
amphiphilic miktoarm star copolymers were relatively low
(ranging from 1.35 to 6.46 mg/L), increasing as the weight
fraction of PEG increased (Table 3), which was probably due
to the highly branched architecture. These results indicate that
the aggregates in the aqueous solution are stable and the
conjugated hydrophobic drug moieties could be fully protected
by the PEG shell.
Figure 7. SEC traces of A-PEG25, A-PEG45, CDS(PCL6)14-D-N3,
CDS(PCL6)14-(PEG25)7-D, and CDS(PCL6)14-(PEG45)7-D.
(Mn,Cal) within the error of measurements, which convincingly
confirmed the well-defined structure of these miktoarm star
copolymers.
The morphologies of the self-assembled aggregates from these
amphiphilic A14B7 miktoarm star copolymers were investigated
by DLS and TEM as shown in Figure 9 and Table 3. Generally
speaking, with the decreasing of the weight fraction of the PEG
segment, CDS(PCL)14-(PEG)7-D prefers to form large ag-
gregates because the short hydrophilic PEG segment could not
evade the hydrophobic interaction and van der Waals interaction
between exposed hydrophobic domains of the aggregates.64
Nearly spherical micelles with number average mean diameters
ranging from 10-20 nm were observed when the weight fraction
of the PEG segment is 46.2% for CDS(PCL6)14-(PEG45)7-D
(Figure 9B) and 32.8% for CDS(PCL6)14-(PEG25)7-D (Figure
Self-Assembly Behaviors of Amphiphilic Ibuprofen-
Conjugated
A14B7
Miktoarm
Star
Copolymers
[CDS(PCL)14-(PEG)7-D]. These synthesized drug-conjugated
amphiphilic A14B7 miktoarm star copolymers provide an op-
portunity to form aggregates in water. The hydrophilic PEG
arms serve as the shell stabilizing the nanoparticles, and the
hydrophobic PCL arms and drug moieties constitute the core
domain. The critical micelle concentration (CMC) of am-
phiphilic copolymer was usually measured by fluorescence
Figure 8. Plots of fluorescence intensity ratio I338/I333 from pyrene excitation spectra vs log C for CDS(PCL6)14-(PEG45)7-D, CDS(PCL6)14
-
(PEG25)7-D, CDS(PCL18)14-(PEG45)7-D, and CDS(PCL18)14-(PEG25)7-D.
Table 3. Characterization of Amphiphilic CDS(PCL)14-(PEG)7-D and CDS(PCL)14-(PEG)7 Miktoarm Star Copolymer Aggregates
samplea
weight fraction of PEG (%)
particle sizeb (nm)
PDIc
CMC (mg ·L-1
)
CDS(PCL6)14-(PEG25)7-D
CDS(PCL6)14-(PEG45)7-D
CDS(PCL18)14-(PEG25)7-D
CDS(PCL18)14-(PEG45)7-D
CDS(PCL6)14-(PEG25)7
CDS(PCL6)14-(PEG45)7
32.8
46.2
19.4
29.2
33.6
47.3
17.3
11.8
61.3
59.4
16.5
10.5
0.301
0.270
0.232
0.312
0.275
0.215
2.69
6.46
1.35
2.24
2.95
6.53
a CDS(PCL6)14-(PEG25)7-D, 6 and 25 represent the polymerization degree of PCL and PEG arms, respectively; 14 and 7 represent the number of
arms of the PCL and PEG, respectively; D represents the drug-conjugated sample. b Number-average mean diameters measured by dynamic light scattering
(DLS). c PDI denotes the polydispersities of aggregates in aqueous solution.

Amphiphilic A14B7 Miktoarm Star Copolymers
Biomacromolecules, Vol. 11, No. 4, 2010 941
Figure 9. TEM micrography of micelles/aggregates from (A) CDS(PCL6)14-(PEG45)7, (B) CDS(PCL6)14-(PEG45)7-D, (C) CDS(PCL18)14-(PEG45)7-
D, (D) CDS(PCL6)14-(PEG25)7, (E) CDS(PCL6)14-(PEG25)7-D, and (F) CDS(PCL18)14-(PEG25)7-D.
9E). Nevertheless, in the case of CDS(PCL18)14-(PEG45)7-D
having a similar PEG weight fraction (29.2%) compared with
CDS(PCL6)14-(PEG25)7-D, wormlike aggregates were observed
(Figure 9C). With further decreasing of the weight fraction of
the PEG segment, band-like aggregates appeared from CD-
S(PCL18)14-(PEG25)7-D (PEG weight fraction 19.4%, Figure
9F). It should be pointed out that the sizes of these wormlike
and band-like aggregates measured by DLS are not in ac-
cordance with the TEM results (Table 3), which is attributed to
the fact that the basic equations to calculate the hydrodynamic
diameter in DLS measurement are originated from the correla-
tion function cumulant analysis based on the assumption that
the particles are noninteracting spheres and not anisotropic
objects.65 As a comparison, the morphologies self-assembled
from non-drug-conjugated samples CDS(PCL6)14-(PEG25)7 and
CDS(PCL6)14-(PEG45)7 were also investigated, but similar
results were observed compared with the drug-conjugated
samples (Figure 9D,A). Therefore, from these results we could
conclude that both the architecture of the copolymers and the
PEG composition affect the morphology and dimension of the
self-assembled aggregates, and the conjugated drug moieties
have no apparent effect on the morphology of the aggregates
in aqueous solution. However, the influence of the A14B7
miktoarm star architecture on the morphology of aggregates is
still unclear, which deserves to be further investigated in the
near future.
aggregates. In the meantime, the corresponding non-ibuprofen-
conjugated samples [CDS(PCL6)14-(PEG25)7 and CDS(PCL6)14-
(PEG45)7] were also included as comparisons. The initial weight
ratio of ibuprofen to copolymer was kept equal to 3:10, and
the results were summarized in Table 4. Briefly, with the
decreasing of the weight fraction of the hydrophilic PEG
segment, both the drug-loading efficiency and the drug-
encapsulation efficiency increase. Moreover, it is worth noting
that the drug-loading efficiency and drug-encapsulation ef-
ficiency of the ibuprofen-conjugated miktoarm copolymers are
significantly higher than those of the corresponding non-
ibuprofen-conjugated counterparts. These results could be
attributed to the following factors: first, the conjugated ibuprofen
may enhance the hydrophobicity of the miktoarm star copoly-
mers, leading to an increase of drug loading amount; on the
other hand, the presence of covalently bonded ibuprofen may
have interactions (such as π-π aromatic stacking force) with
the free ibuprofen, which force the free ibuprofen to incorporate
into the micellar core. Typical TEM images of the ibuprofen-
loaded micelles were shown in Figure 10. It can be clearly
observed that the loaded hydrophobic drug influenced the final
morphology and dimension of the self-assembled aggregates.
In the case of CDS(PCL6)14-(PEG45)7-D, the number average
mean diameters of the spherical micelles slightly increased after
the drug-loading process (Figure 10A,B). As for CDS(PCL6)14-
(PEG25)7-D, spherical micelles have transformed into wormlike
aggregates after the drug-loading process (Figure 10C,D). These
results indicate that the loaded ibuprofen increases the hydro-
phobic property of the micellar core, leading to the formation
of larger aggregates with more stable morphologies.
Drug-Loading Capacity of Ibuprofen-Conjugated A14B7
Miktoarm
Star
Copolymer
[CDS(PCL)14-(PEG)7-D]
Aggregates. Ibuprofen was employed as a model drug to
evaluate the drug-loading capacity of CDS(PCL)14-(PEG)7-D

942 Biomacromolecules, Vol. 11, No. 4, 2010
Gou et al.
Table 4. Preparation and Properties of Ibuprofen-Loaded Aggregates from CDS(PCL)14-(PEG)7-D and CDS(PCL)14-(PEG)7 Miktoarm Star
Copolymers
weight fraction
of PEG (%)
encapsulation
efficiencyb (%)
weight fraction of
samplea
load efficiencyb (%)
conjugated drugb (%)
CDS(PCL6)14-(PEG25)7-D
CDS(PCL6)14-(PEG45)7-D
CDS(PCL6)14-(PEG25)7
CDS(PCL6)14-(PEG45)7
CDS(PCL18)14-(PEG25)7-D
CDS(PCL18)14-(PEG45)7-D
32.8
46.2
33.6
47.3
19.4
29.2
8.2
6.1
3.5
2.3
13.8
10.2
27.3
20.3
11.7
7.7
46.0
34.0
12.3
9.5
N/A
N/A
6.7
6.0
a The initial weight ratio of ibuprofen to copolymer (drugwt/polymerwt) was kept equal to 3:10. CDS(PCL6)14-(PEG25)7-D, 6 and 25 represent the
polymerization degree of PCL and PEG arms, respectively. D represents the drug-conjugated sample. b Determined by 1H NMR. For the ibuprofen-
conjugated sample, the weight of conjugated ibuprofen has been deducted from the 1H NMR results.
Figure 10. TEM micrography of aggregates before and after the drug-loading process.
were higher than those of the corresponding nondrug-conjugated
miktoarm star copolymers. Moreover, the drug release behavior
could be controlled not only by the loaded free drug molecules,
but also by the hydrolysis of conjugated drug moieties from
PCL arms within long periods of time. Further investigations
on release behaviors of these copolymers are ongoing in our
laboratory.
Conclusions
Well-defined cyclodextrin-centered drug-conjugated am-
phiphilic A14B7 miktoarm star copolymers [CDS(PCL)14-(PEG)7-
D] have been successfully synthesized via the combination of
CROP and “click” chemistry. 1H NMR, SEC-MALLS, and FT-
IR analyses confirmed the designed structures. These copolymers
could self-assemble into various morphologies in aqueous
solution, which can be controlled by both the macromolecular
architecture and the composition of the copolymer. Therefore,
a promising strategy to synthesize novel highly branched
biocompatible and biodegradable copolymers as potential mul-
tifunctional nanodrug carriers in delivery system has been
developed. The drug-loading efficiency and drug-encapsulation
efficiency of the drug-conjugated miktoarm star copolymers
Acknowledgment. The authors are grateful for the financial
support from the National Natural Science Foundation of China
(20704036), special fund from the Major State Basic Research
Project (2005CB623802), and the Committee of Science and
Technology of Zhejiang Province.

Amphiphilic A14B7 Miktoarm Star Copolymers
Biomacromolecules, Vol. 11, No. 4, 2010 943
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