Iron hydroxide nanoparticles coated with poly(ethylene glycol)-poly(aspartic acid) block copolymer as novel magnetic resonance contrast agents for in vivo cancer imaging

PEG-coated β-FeOOH nanoparticles were prepared through electrostatic complex formation of iron oxide nanoparticles with poly(ethylene glycol)-poly(aspartic acid) block copolymer [PEG-P(Asp)] in distilled water. By dynamic light scattering (DLS) measurement, the nanopaticle size was determined to be 70 nm with narrow distribution. The FT-IR and zeta potential experimental results proved that PEG-PAsp molecules bound to the surface of the iron oxide nanoparticles via the coordination between the carboxylic acid residues in the PAsp segment of the block copolymer and the surface Fe of the β-FeOOH nanoparticles. The PEG-coated nanoparticles revealed excellent solubility and stability in aqueous solution as well as in physiological saline. In vivo MRI experiments on tumor-bearing mice demonstrated that the PEG-coated nanoparticles prepared by the current approach achieved an appreciable accumulation into solid tumor, suggesting their potential utility as tumor-selective MRI contrast agents.     

Preparation, characterization and application of pyrene-loaded methoxy poly(ethylene glycol)–poly(lactic acid) copolymer nanoparticles

Pyrene-loaded biodegradable polymer nanoparticles were prepared by incorporating pyrene into the polymer nanoparticles formulated from amphiphilic diblock copolymer, methoxy poly(ethylene glycol)–poly(lactic acid) (MePEG–PLA). Their morphological structure and physical properties were characterized by nuclear magnetic resonance (NMR), dynamic light scattering, fluorescence spectroscopy, transmission electronic microscopy and zeta potential measurements. Further, MePEG–PLA nanoparticles containing pyrene as fluorescent marker were administered intranasally to rats, and the distribution of nanoparticles in the nasal mucosa and the olfactory bulb were visualized by fluorescence microscopy. NMR results confirmed that MePEG–PLA copolymer can form nanoparticles in water, and hydrophilic PEG chains were located on the surface of the nanoparticles. The particle size, zeta potential and pyrene loading efficiency of MePEG–PLA nanoparticles were dependent on the PLA block content in the copolymer. Following nasal administration, the absorption of nanoparticles across the epithelium was rapid, with fluorescence observed in the olfactory bulb at 5 min, and a higher level of fluorescence persisted in the olfactory mucosa than that in the respiratory mucosa. These results show that pyrene could serve as a useful fluorescence probe for incorporation into polymer nanoparticles to study tissue distribution and MePEG–PLA nanoparticles might have a great potential as carriers of hydrophobic drugs.     

Surface charge modulation of poly(ethylene glycol)–poly( , -lactide) block copolymer micelles: conjugation of charged peptides

Block copolymer micelles with aldehyde functionality were prepared in aqueous medium by dialyzing the N,N-dimethylacetamide solution of α-acetoxy-poly(ethylene glycol)-poly( , -lactide) block copolymer (acetal-PEG–PDLLA) against water, followed by mild acid treatment to convert the acetal moiety of the micelle to the aldehyde group. Peptidyl ligands (phenylalanine (Phe) and tyrosyl–glutamic acid (Tyr–Glu)) were then chemically conjugated to the micelle through Schiff base formation and successive reductive amination using NaBH₃CN. Micelles with peptidyl ligands thus prepared have a size of approximately 40 nm with extremely narrow distribution (μ₂/ ²<0.1) based on cumulant analysis of dynamic light scattering. A maximum 53% of the PEG-chain end of the micelle could be converted into peptidyl groups. Zeta potential values of Tyr–Glu derivatized micelles were well correlated with the amount of conjugated ligands, controllable over the range of 0 to−9 mV in sodium phosphate buffer (pH 7.4, 10 mM). These micelles with peptidyl ligands may have a utility for exploring the effect of the surface charge on the pharmacokinetic behavior of particulate systems as well as for modulated drug delivery where cellular peptidyl receptors play a substantial role.     

Synthesis and characterization of cobalt ferrite nanoparticles in hybrid micelles of poly[styrene-<Emphasis Type="Italic">block</Emphasis>-(ethylene oxide)] and sodium dodecyl sulfate

Cobalt ferrite nanoparticles are synthesized in hybrid micelles of poly[styrene-block-(ethylene oxide)] and sodium dodecyl sulfate in water at room temperature. The nanoparticles are prepared by the chemical precipitation method via the exchange reaction between iron and cobalt salts with sodium dodecyl sulfate and the redox reaction under the action of an aqueous solution of methylamine. As evidenced by small-angle X-ray scattering, transmission electron microscopy, and ferromagnetic resonance examination, cobalt ferrite nanoparticles occurring in hybrid micelles of the block copolymer and sodium dodecyl sulfate are polydisperse (their size is 0.3–50 nm) and ferromagnetic.     

Flash nanoprecipitation with Gd(III)‐based metallosurfactants to fabricate polylactic acid nanoparticles as highly efficient contrast agents for magnetic resonance imaging

Polylactic acid (PLA) nanoparticles coated with Gd(III)‐based metallosurfactants (MS) are prepared using a simple and rapid one‐step method, flash nanoprecipitation (FNP), for magnetic resonance imaging (MRI) applications. By co‐assembling the Gd(III)‐based MS and an amphiphilic polymer, methoxy poly(ethylene glycol)‐b‐poly(?‐caprolactone) (mPEG‐b‐PCL), PLA cores were rapidly encapsulated to form biocompatible T₁ contrast agents with tunable particle size and narrow size distribution. The hydrophobic property of Gd(III)‐based MS were finely tuned to achieve their high loading efficiency. The size of the nanoparticles was easily controlled by tuning the stream velocity, Reynolds number and the amount of the amphiphilic block copolymer during the FNP process. Under the optimized condition, the relaxivity of the nanoparticles was achieved up to 35.39 mM^?1 s^?1 (at 1.5 T), which is over 8 times of clinically used MRI contrast agents, demonstrating the potential application for MR imaging.     

Electrooptics of β-FeOOH Particles in Aqueous Media: 1. Reversing-Pulse Electric Birefringence in the Low Field Region

Reversing-pulse electric birefringence (RPEB) of a nearly monodisperse iron(III) hydroxide oxide sample in the β-form (β-FeOOH) was measured at 25°C and at a wavelength of 633 nm in aqueous media in the presence of NaCl. The concentrations of β-FeOOH and added NaCl varied between 0.00111 and 0.0555 g/L and 0.03 and 2.0 mM, respectively. Except for the suspensions with high salt concentrations, each RPEB signal showed a dip or minimum in the reverse process upon electric field reversal, together with a smooth rise in the buildup and a fall in the decay process. The observed signals were analyzed with a new RPEB theory, which takes into account not only the permanent electric dipole moment (μ) but also the root-mean-square ionic dipole moment (m^21/2) due to the ion fluctuation in ion atmosphere, in addition to the field-induced electronic (covalent) dipole moment Δα′ E. The results showed that the slowly fluctuating moment of m^21/2 is by far the most predominant one for the field orientation of the β-FeOOH particle, though the permanent dipole moment μ may not be completely excluded. The rotational relaxation time of the whole particle was evaluated from the decay signal, while the relaxation time for fluctuating ions was estimated from RPEB signal fitting. The sign of the steady-state birefringence for β-FeOOH suspensions was positive without exception under the present conditions. The birefringence signals in the steady state (δ/d) were proportional to the second power of the applied field strength (E) in the low field region; thus, the Kerr law was verified to hold for β-FeOOH suspensions. The specific Kerr constant was evaluated for each suspension by extrapolating the values of δ/d to zero field (E→0).     

Application of hydrophobically modified water‐soluble polyacrylamide conjugated with poly(oxyethylene)‐co‐poly(oxypropylene) surfactant as emulsifier

Hydrophobically modified polyacrylamide (PAAm) was prepared by grafting PAAm with block copolymer of poly(ethylene oxide) and poly(propylene oxide), PEO‐PPO‐PEO, by melt method in the presence of benzoyl peroxide as initiator. The chemical structure of the graft copolymer was determined by FTIR and ¹HNMR analyses. The surface tension, critical micelle concentration, and surface activities were determined at different temperatures. Surface parameters such as surface excess concentration (Γ_max), the area per molecule at interface (A_min), and the effectiveness of surface tension reduction (Π_CMC) were determined at different temperatures from the adsorption isotherms of the prepared surfactants. The prepared surfactant was tested as emulsifier for water with xylene, cyclohexane, or petroleum crude oil synthetic emulsions. Copyright © 2010 John Wiley & Sons, Ltd.     

Smart hybrid magnetic self-assembled micelles and hollow capsules

Novel magnetic nano-composites are obtained by the self-assembly in water of polypeptide-based diblock copolymers polybutadiene-b-poly(glutamic acid) combined with hydrophobically modified γ-Fe₂O₃ nanoparticles. These hybrid supramolecular objects are either filled micelles (3-d) or hollow vesicles with a magnetic membrane (2-d), deformation of which under an applied magnetic field has been evidenced. These nanoparticles are also able to respond to stimuli such as pH and ionic strength due to the presence of the polypeptide block, thus forming what we called multi-responsive nanocapsules. These superparamagnetic hybrid self-assemblies offer attractive potentialities in biomedicine and biotechnology due to their dimensions (0.1–0.5 μm) small enough to stay for some time in the blood circulation, and due to the properties brought about by the iron oxide nanoparticles: possible manipulation by an external magnetic field gradient, local heating by a radio-frequency field for cancer radio-therapy, labeling of organs to enhance the contrast in Magnetic Resonance Imaging.     

Diblock‐Copolymer‐Mediated Self‐Assembly of Protein‐Stabilized Iron Oxide Nanoparticle Clusters for Magnetic Resonance Imaging

Superparamagnetic iron oxide nanoparticles (SPIONs) can be used as efficient transverse relaxivity (T₂) contrast agents in magnetic resonance imaging (MRI). Organizing small (D<10 nm) SPIONs into large assemblies can considerably enhance their relaxivity. However, this assembly process is difficult to control and can easily result in unwanted aggregation and precipitation, which might further lead to lower contrast agent performance. Herein, we present highly stable protein–polymer double‐stabilized SPIONs for improving contrast in MRI. We used a cationic–neutral double hydrophilic poly(N‐methyl‐2‐vinyl pyridinium iodide‐block‐poly(ethylene oxide) diblock copolymer (P2QVP‐b‐PEO) to mediate the self‐assembly of protein‐cage‐encapsulated iron oxide (γ‐Fe₂O₃) nanoparticles (magnetoferritin) into stable PEO‐coated clusters. This approach relies on electrostatic interactions between the cationic N‐methyl‐2‐vinylpyridinium iodide block and magnetoferritin protein cage surface (pI≈4.5) to form a dense core, whereas the neutral ethylene oxide block provides a stabilizing biocompatible shell. Formation of the complexes was studied in aqueous solvent medium with dynamic light scattering (DLS) and cryogenic transmission electron microcopy (cryo‐TEM). DLS results indicated that the hydrodynamic diameter (D_h) of the clusters is approximately 200 nm, and cryo‐TEM showed that the clusters have an anisotropic stringlike morphology. MRI studies showed that in the clusters the longitudinal relaxivity (r₁) is decreased and the transverse relaxivity (r₂) is increased relative to free magnetoferritin (MF), thus indicating that clusters can provide considerable contrast enhancement.     

Gold-copolymer nanoparticles: Poly(ε-caprolactone)/poly(N-vinyl-2-pyrrolydone) Biodegradable triblock copolymer as stabilizer and reductant

Block copolymers have been extensively used in the synthesis of many types of nanoparticles, where generally are considered as stabilizer and protective agent. In this work a double function of the biodegradable triblock copolymer poly(N-vinyl-2-pyrrolidone)-b-poly(ε-caprolactone)-b-poly(N-vinyl-2-pyrrolidone), (PVP–PCL–PVP) in the gold nanoparticle-copolymer synthesis is reported.Gold-copolymer composed nanoparticles were synthesized using the triblock copolymer (PVP–PCL–PVP) and potassium tetrachloro aurate (III), both in aqueous solution. The copolymer work as both, reductant and stabilizer agent. The obtained nanoparticles were characterized by FT-IR, dynamic light scattering (DLS), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The shape and the size of the obtained nanoparticles are dependent on the copolymer/salt of gold concentration ratio used in the synthesis.To complement the experimental results about the copolymer role in the nanoparticles synthesis, computational tools were used to characterize the reactivity of the reactant species.     

Monolayer-protected gold nanoparticles by the self-assembly of micellar poly(ethylene oxide)-b-poly(epsilon-caprolactone) block copolymer

A study is presented of the preparation of gold nanoparticles incorporated into biodegradable micelles. Poly(ethylene oxide)-b-poly(epsilon-caprolactone) (PEO-b-PCL) copolymer was synthesized by ring-opening polymerization, and the hydroxyl end group of the PCL block was modified with thioctic acid using dicyclohexyl carbodiimide as the coupling reagent. The PEO-b-PCL-thioctate ester (TE) thus obtained was used in a later step to form monolayer protected gold nanoparticles via the thioctate spacer. Gold nanoparticles stabilized with the PEO-b-PCL block (named Au/Block (x/y), where x/y is the mole feed ratio between HAuCl4 and PEO-b-PCL-TE) were prepared and analyzed. Au/Block (1/1), Au/Block (2/1), and Au/Block (3/1) nanoparticles were found to form stable dispersions in the organic solvents commonly used to dissolve the unlabeled block copolymer. The average diameter of the nanoparticles was determined by transmission electron microscopy (TEM) and found to be 6+/-2 nm. Au/Block (4/1) nanoparticle dispersions in organic solvents, on the other hand, were not stable and produced large gold clusters (50-100 nm). Cluster formation was attributed to the low grafting density of the block copolymer, which facilitates agglomeration. For Au/Block (12/1), along the same trend, only an insoluble product was isolated. Micelles in water were prepared by the slow addition of the dilute Au/Block solution in dimethylformamide into a large excess of water with vigorous stirring. Au/Block (1/1) and Au/Block (2/1) formed nanosized structures of 5-7 nm. TEM images of stained Au/Block (1/1) micelles, made in water, clearly showed the formation of core-shell structures. Au/Block (3/1) micelles, on the other hand, were not stable and large agglomerates a few microns in size were observed. The study focuses on the synthesis, characterization, and aggregation behavior of gold-loaded PEO-b-PCL block copolymer micelles, a potential system for drug delivery in conjunction with tissue and subcellular localization studies.     

Preparation of highly dispersible and tumor-accumulative, iron oxide nanoparticles Multi-point anchoring of PEG-b-poly(4-vinylbenzylphosphonate) improves performance significantly

This paper describes the preparation of iron oxide nanoparticles, surface of which was coated with extremely high immobilization stability and relatively higher density of poly(ethylene glycol) (PEG), which are referred to as PEG protected iron oxide nanoparticles (PEG-PIONs). The PEG-PIONs were obtained through alkali coprecipitation of iron salts in the presence of the PEG-poly(4-vinylbenzylphosphonate) block copolymer (PEG-b-PVBP). In this system, PEG-b-PVBP served as a surface coating that was bound to the iron oxide surface via multipoint anchoring of the phosphonate groups in the PVBP segment of PEG-b-PVBP. The binding of PEG-b-PVBP onto the iron oxide nanoparticle surface and the subsequent formation of a PEG brush layer were proved by FT-IR, zeta potential, and thermogravimetric measurements. The surface PEG-chain density of the PEG-PIONs varied depending on the [PEG-b-PVBP]/[iron salts] feed-weight ratio in the coprecipitation reaction. PEG-PIONs prepared at an optimal feed-weight ratio in this study showed a high surface PEG-chain surface density (≈0.8 chainsnm(-2)) and small hydrodynamic diameter (<50 nm). Furthermore, these PEG-PIONs could be dispersed in phosphate-buffered saline (PBS) that contains 10% serum without any change in their hydrodynamic diameters over a period of one week, indicating that PEG-PIONs would provide high dispersion stability under in vivo physiological conditions as well as excellent anti-biofouling properties. In fact we have confirmed the prolong blood circulation time and facilitate tumor accumulation (more than 15% IDg(-1) tumor) of PEG-PIONs without the aid of any target ligand in mouse tumor models. The majority of the PEG-PIONs accumulated in the tumor by 96 h after administration, whereas those in normal tissues were smoothly eliminated by 96 h, proving the enhancement of tumor selectivity in the PEG-PION localization. The results obtained here strongly suggest that originally synthesized PEG-b-PVBP, having multipoint anchoring character by the phosphonate groups, is rational design for improvement in nanoparticle as in vivo application. Two major points, viz., extremely stable anchoring character and dense PEG chains tethered on the nanoparticle surface, worked simultaneously to become PEG-PIONs as an ideal biomedical devices intact for prolonged periods in harsh biological environments.     

Degradation behaviors of monomethoxy poly(ethylene glycol)‐b‐poly(ε‐caprolactone) nanoparticles in aqueous solution

Monomethoxy poly(ethylene glycol)‐b‐poly(ε‐caprolactone)(MPEG‐b‐PCL) diblock copolymers were synthesized via a ring‐opening polymerization. The polymeric nanoparticles prepared by precipitation/solvent evaporation exhibit a core–shell structure, characterized by dynamic light scattering (DLS), nuclear magnetic resonance (NMR), and atomic force microscopy (AFM). The hydrolytic degradation of those nanoparticles was studied by DLS, NMR, and gel permeation chromatography (GPC). It was found that the molecular weight of PCL block in a copolymer significantly affects the stability of nanoparticles in aqueous solution and nanoparticles with shorter PCL block length degraded faster. The degradation behaviors could be divided into two stages with slow degradation at the interface region via swelling effect and fast degradation at inner core via caves and channels formed by cleavage of ester bonds. Copyright © 2007 John Wiley & Sons, Ltd.     

Design of water-based ferrofluids as contrast agents for magnetic resonance imaging

We report the synthesis, characterization and relaxometric study of ferrofluids based on iron oxide, with potential for use as magnetic resonance imaging (MRI) contrast agents (CAs). The effect of different cost-effective, water-based surface modification approaches which can be easily scaled-up for the large scale synthesis of the ferrofluids has been investigated. Surface modification was achieved by silanization, and/or coating with non-toxic commercial dispersants (a lauric polysorbate and a block copolymer with pigment affinic groups, namely Tween 20 and Disperbyk 190) which were added after or during iron oxide nanoparticle synthesis. It was observed that all the materials synthesized functioned as negative contrast agents at physiological temperature and at frequencies covered by clinical imagers. The relaxometric properties of the magnetic nanoparticles were significantly improved after surface coating with stabilizers compared to the original iron oxide nanoparticles, with particular reference to the silica-coated magnetic nanoparticles. The results indicate that the optimization of the preparation of colloidal magnetic ferrofluids by surface modification is effective in the design of novel contrast agents for MRI by enabling better or more effective interaction between the coated iron oxide nanoparticles and protons present in their aqueous environment.     

Polymeric nanoparticles prepared using salt bridges between [(dimethylamino)propyl]-octadecanamide and poly(N-isopropylacrylamide-co-methacrylic acid)

Polymeric lipid nanoparticles were prepared in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer (pH 8.0, 10 mM) by taking advantage of salt bridges formed between poly(N-isopropylacrylamide-co-methacrylic acid) (P(NIPAM-co-MAA)) and N-[3-(dimethylamino)propyl]-octadecanamide (DMAPODA). The homogeneous nanoparticles of 200–250 nm were obtained when the copolymer was included in the preparation so that the relative mass of copolymer to lipid was more than 5. However, when the relative amount of copolymer was less than 5, large agglomerates more than 10 μm were observed together with nanoparticles. The protonated amino groups of DMAPODA will attach to the ionized carboxyl groups of P(NIPAM-co-MAA), and they would act as polymeric amphiphiles. It is believed that the hydrophilic copolymer can stabilize the hydrophobic core of the lipid. The critical association concentrations were determined to be 32, 112, and 158 mg/l, when the lipid/copolymer ratios were 1:5, 1:23, and 1:50, respectively.     

Optimization and ecofriendly synthesis of iron oxide nanoparticles as potential antioxidant

The present study involves the use of Box-Behnken design for optimization of the energy-efficient process variables, eco-friendly synthesis of nanoparticles of iron oxide using Coriandrum sativum L. (cilantro) leaf extract. The factors, which significantly influenced mean nanoparticle size, surface charge, and size distribution, were the volume of leaf extract, agitation speed, and temperature. The developed model using Box-Behnken design was validated by synthesizing the iron nanoparticles using optimized operational conditions i.e. 10 ml volume of leaf extract, 1500 rpm agitation speed and 30 °C temperature. This resulted in the formation of highly stable iron oxide nanoparticles with mean particle size 161.5 nm and polydispersity index 0.132 with a zeta potential of −19.5 mV. The free radical inhibitory activity of prepared iron oxide nanoparticles was found comparable to ascorbic acid. These results reveal that iron nanoparticles for a biomedical application can be prepared at ambient temperature in an eco-friendly manner.     

Multipod structures of lamellae‐forming diblock copolymers in three‐dimensional confinement spaces: Experimental observation and computer simulation

The three‐dimensional (3D) confinement effect on the microphase‐separated structure of a diblock copolymer was investigated both experimentally and computationally. Block copolymer nanoparticles were prepared by adding a poor solvent into a block copolymer solution and subsequently evaporating the good solvent. The 3D structures of the nanoparticles were quantitatively determined with transmission electron microtomography (TEMT). TEMT observations revealed that various complex structures, including tennis‐ball, mushroom‐like, and multipod structures, were formed in the 3D confinement. Detailed structural analysis, showed that one block of the diblock copolymer slightly prefers to segregate into the particle surface compared with the other block. The observed structures were further elaborated using cell dynamics computer simulation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1702–1709     

Step-by-Step Design of New Theranostic Nanoformulations: Multifunctional Nanovectors for Radio-Chemo-Hyperthermic Therapy under Physical Targeting

While investigating the possible synergistic effect of the conventional anticancer therapies, which, taken individually, are often ineffective against critical tumors, such as central nervous system (CNS) ones, the design of a theranostic nanovector able to carry and deliver chemotherapy drugs and magnetic hyperthermic agents to the target radiosensitizers (oxygen) was pursued. Alongside the original formulation of polymeric biodegradable oxygen-loaded nanostructures, their properties were fine-tuned to optimize their ability to conjugate therapeutic doses of drugs (doxorubicin) or antitumoral natural substances (curcumin). Oxygen-loaded nanostructures (diameter = 251 ± 13 nm, ζ potential = −29 ± 5 mV) were finally decorated with superparamagnetic iron oxide nanoparticles (SPIONs, diameter = 18 ± 3 nm, ζ potential = 14 ± 4 mV), producing stable, effective and non-agglomerating magnetic nanovectors (diameter = 279 ± 17 nm, ζ potential = −18 ± 7 mV), which could potentially target the tumoral tissues under magnetic driving and are monitorable either by US or MRI imaging.     

Synthesis of poly(2-acetamidoacrylic acid) and its PEGMA block copolymer via ATRP in water

Controlled polymerization of a captodative monomer, 2-acetamidoacrylic acid (AAA), was studied for the first time in the literature. Salt of the monomer in water was polymerized using ATRP method and influence of several factors, including solvent composition, halogen exchange and additives like pyridine and halide salts were investigated to improve the control. Captodative monomers form very stable radicals favoring the active species over the dormant one. Depolymerization at room temperature under ATRP conditions was determined as the major obstacle in front of the high molecular weight polymers and block copolymer formation. Nevertheless, poly(AAA-b-(AAA-co-PEGMA)) block polymers were prepared through ATRP and possible applications were discussed. As an example, pH responsive nature and ability to coat superparamagnetic iron oxide nanoparticles were demonstrated.     

Clonazepam release from core-shell type nanoparticles composed of poly(γ-benzyl L-glutamate) as the hydrophobic part and poly(ethylene oxide) as the hydrophilic part

Block copolymers consisting of poly(γ-benzyl L -glutamate) (PBLG) as the hydrophobic part and poly(ethylene oxide) (PEO) as the hydrophilic part were synthesized and characterized. Core shell type nanoparticles of the block copolymers (abbreviated GEG) were prepared by the dialysis method. Under fluorescence spectroscopy measurement, the GEG block copolymers were associated in water to form core shell type nanoparticles as polymeric micelles and the critical micelle concentrations (CMC) values of the block copolymers decreased with increasing PBLG chain length in the block copolymers. Transmission electron microscopy (TEM) observations revealed nanoparticles of spherical shapes. From dynamic light scattering (DLS) study, sizes of nanoparticles of GEG-1 and GEG-2 copolymer were 64.3 ± 28.7 nm and 28.9 ± 7.0 nm. The drug-loading contents of GEG-1 and GEG-2 nanoparticles were 15.2 and 8.3 wt %, respectively. These results indicated that the drug-loading contents were dependent on PBLG chain length in the copolymer. Then, the longer the PBLG chain length, the more the drug-loading contents. Release of clonazepam (CNZ) from the nanoparticles was slower in higher loading contents of CNZ than lower loading contents due to the hydrophobic interaction between PBLG core and CNZ. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 415–423, 1998