Stability and Release Performance of a Series of Pegylated Copolymeric Micelles

Purpose. The aim of this work is to evaluate the capability of a series of biocompatible amphiphilic copolymers as a nano-sized drug carrier. Methods. The influences of the type of lactone monomer, the feed molar ratios of lactone/PEG, and the molecular weight of PEG on the performance and release behavior of micelles are investigated. Results. These pegylated amphiphilic copolymers efficiently form micelles with a low CMC value in the range of 10^–6-10^–7 M. The average particle size of micelles is 100 nm. The phenomenon of increasing particle size as increasing the chain length of poly(lactone) block is observed. The different hydrophobicity, based on chemical structure of poly(lactone), accounts for different interaction strength between indomethacin and hydrophobic inner core, which further influences the drug loading in copolymeric micelles and their release character. In addition, the PCL/PEG/PCL micellar solutions maintain their sizes at 4°C for 8 weeks without occurring significant aggregation or dissociation. Conclusions. A series of biocompatible pegylated amphiphilic copolymers have been elucidated possessing micellization potential to form nano-sized micelles in an aqueous environment, which enable incorporate hydrophobic drug and regulate drug release.     

多西他赛pH敏感嵌段共聚物胶束的制备

本文在合成pH敏感两亲性嵌段共聚物聚(2-乙基-2-噁唑啉)-聚乳酸(PEOz-PDLLA)的基础上，采用薄膜分散法制备多西他赛pH敏感嵌段共聚物胶束，利用芘荧光探针技术测定胶束的临界胶束浓度(CMC)；通过高效液相色谱测定胶束的载药量及包封率；分别利用透射电镜、动态光散射法和zeta电位分析仪对胶束的形态、粒径和表面电位进行了表征；采用透析法考察了载药聚合物胶束的体外释放行为。结果表明，胶束的临界胶束浓度值为1.0×10^-3 g·L^-1；载药量可达15.0%，包封率为91.1%；胶束的粒度分布很窄，平均粒径为28.7nm；胶束粒子为圆球形且分散良好，其表面zeta电位值为(1.19±0.12)mV；在pH 7.4释放介质中，多西他赛胶束具有缓释作用；而在pH 5.0条件下，胶束释药明显加快，体现出PEOz-PDLLA胶束释药行为的pH敏感性。综合上述研究可见，PEOz-PDLLA嵌段共聚物胶束作为疏水性抗肿瘤药物的给药系统具有很好的应用前景。     

Micelles of Different Morphologies—Advantages of Worm-like Filomicelles of PEO-PCL in Paclitaxel Delivery

Purpose

Worm-like and spherical micelles are both prepared here from the same amphiphilic diblock copolymer, poly(ethylene oxide)-b-poly (ε-caprolactone) (PEO [5 kDa]–PCL [6.5 kDa]) in order to compare loading and delivery of hydrophobic drugs.

Materials and Methods

Worm-like micelles of this degradable copolymer are nanometers in cross-section and spontaneously assemble to stable lengths of microns, resembling filoviruses in some respects and thus suggesting the moniker ‘filomicelles’. The highly flexible worm-like micelles can also be sonicated to generate kinetically stable spherical micelles composed of the same copolymer.

Results

The fission process exploits the finding that the PCL cores are fluid, rather than glassy or crystalline, and core-loading of the hydrophobic anticancer drug delivery, paclitaxel (TAX) shows that the worm-like micelles load and solubilize twice as much drug as spherical micelles. In cytotoxicity tests that compare to the clinically prevalent solubilizer, Cremophor^® EL, both micellar carriers are far less toxic, and both types of TAX-loaded micelles also show fivefold greater anticancer activity on A549 human lung cancer cells.

Conclusion

PEO–PCL based worm-like filomicelles appear to be promising pharmaceutical nanocarriers with improved solubilization efficiency and comparable stability to spherical micelles, as well as better safety and efficacy in vitro compared to the prevalent Cremophor^® EL TAX formulation.

     

5-Fluorouracil-loaded microspheres prepared by spray-drying poly(D,L-lactide) and poly(lactide-co-glycolide) polymers: Characterization and drug release

5-Fluorouracil (5-FU), a hydrosoluble anti-neoplastic drug, was encapsulated in microspheres of poly(D,L-lactide) (PLA) and poly(lactide-co-glycolide) (PLGA) polymers using the spray-drying technique, in order to obtain small size microspheres with a significant drug entrapment efficiency. Drug-loaded microspheres included between 47?±?11 and 67?±?12?µg 5-FU?mg^?1 microspheres and the percentage of entrapment efficiency was between 52?±?12 and 74?±?13. Microspheres were of small size (average diameter: 0.9?±?0.4–1.4?±?0.8?µm microspheres without drug; 1.1?±?0.5–1.7?±?0.9?µm 5-FU-loaded microspheres) and their surface was smooth and slightly porous, some hollows or deformations were observed in microspheres prepared from polymers with larger T_g. A fractionation process of the raw polymer during the formation of microspheres was observed as an increase of the average molecular weight and also of T_g of the polymer of the microspheres. The presence of 5-FU did not modify the T_g values of the microspheres. Significant interactions between the drug and each one of the polymers did not take place and total release of the included drug was observed in all cases. The time needed for the total drug release (28–129?h) was in the order PLA?>?PLGA 75/25?>?PLGA 50/50. A burst effect (17–20%) was observed during the first hour and then a period of constant release rate (3.52?±?0.82–1.46?±?0.26?µg 5-FU?h^?1 per milligram of microspheres) up to 8 or 13?h, depending on the polymer, was obtained.     

Arginine-stabilized mPEG-PDLLA (50/50) polymeric micelles of docetaxel by electrostatic mechanism for tumor-targeted delivery

Abstract

Arginine-stabilized, docetaxel-loaded polymeric micelles (AR-DTX-PM) were prepared to enhance the physical stability of micelles and control the degradation of docetaxel (DTX). Amphiphilic diblock copolymers, methoxy-(Polyethylene Glycol)-block-Poly (D, L-lactide) (mPEG-PDLLA) were synthesized and used for the formulation of lyophilized DTX-PM powders. The micelles were found to have diameters of 20–30?nm with narrow polydispersity, and the entrapment efficiency was 90–100%. The accumulative release of AR-DTX-PM was higher than that of glucose-dispersed DTX-PM (Glu-DTX-PM). The results of both physical and chemical stability studies showed that the concentration of arginine required for optimum stability was 2.0?mg/ml. Preliminary investigation of the mechanisms of stabilization by arginine suggested that it is due to the electrostatic interaction as well as hydrogen bonds between DTX and arginine. The acute toxicity studies demonstrated that AR-DTX-PM was better tolerated in beagle dogs than DTX injection. However, the pharmacokinetic studies revealed no significant difference in C_max and AUC of AR-DTX-PM compared to DTX injection. When AR-DTX-PM was administrated at a dose of 30?mg/kg, the antitumor effect was stronger than that of commercial DTX injection at 10?mg/kg, and the increase of administration dose did not cause higher toxicity. The in vivo imaging test showed that the residence time of AR-DTX-PM at tumor sites was longer than its commercial formulation. In a word, it is expected that AR-DTX-PM can reduce systemic toxicity while retaining antitumor efficacy in cancer patients.     

Preparation of Biodegradable Microparticles Using Solution-Enhanced Dispersion by Supercritical Fluids (SEDS)

Purpose. We have evaluated a new process, involving solution-enhanced dispersion by supercritical fluids (SEDS), for the production of polymeric microparticles. Methods. The biodegradable polymers, Poly (DL-lactide-co-glycolide) : copolymer composition 50:50 (DL-PLG), Poly (L-lactide) (L-PLA), Poly (DL-lactide) (DL-PLA) and Polycaprolactone (PCL), were used for preparation of microparticles using SEDS. Solutions of the polymers in organic solvents were dispersed and sprayed with supercritical CO₂. Extraction of the organic solvents resulted in the formation of solid microparticles. The amounts of highly toxic solvents such as dichloromethane (MC) were reduced in the process. Results. Microparticles were obtained from all polymers. The mean particle size and shape varied with the polymer used. The morphology of the particles was strongly affected by the choice of polymer solvent. Discrete spherical microparticles of DL-PLG were produced with a mean volumetric diameter of 130 m. The microparticles of the L-PLA were almost spherical, and their size increased from 0.5 to 5 m as the density of supercritical CO₂ decreased. PCL formed microparticles with diameters of 30–210 m and showed a strong tendency to form films at high pressure. Conclusions. The SEDS process appears a promising method for production of microparticles from biodegradable polymers without the use of toxic solvents.     

In vitro controlled release of clove essential oil in self-assembly of amphiphilic polyethylene glycol-block-polycaprolactone

In this study, a micellar delivery system with an amphiphilic diblock copolymer of poly (ethylene glycol) and poly (?-caprolactone) was synthesised and used to incorporate hydrophobic clove essential oil (CEO). To determine an optimal delivery system, the effects of the copolymer’s hydrophobic block length and the CEO-loading content on the encapsulation of CEO were investigated. Percentages of entrapment efficiency (%EE), CEO loading (%CEO), and in vitro release profiles were determined. The size, size distribution, zeta potential, and morphology of the obtained micelles were determined by DLS, FE-SEM, and TEM. The %EE, %CEO, and in vitro release profiles of CEO incorporated in micelles were analysed by HPLC. The study revealed a sustained release profile of CEO from CEO-loaded micelles. The results indicate the successful formulation of CEO-loaded PEG-b-PCL micelle nanoparticles. It is suggested that this micelle system has considerably potential applications in the sustained release of CEO in intravascular drug delivery.     

Thermo-responsive shell cross-linked PMMA-b-P(NIPAAm-co-NAS) micelles for drug delivery

Thermo-responsive amphiphilic poly(methyl methacrylate)-b-poly(N-isopropylacrylamide-co-N-acryloxysuccinimide) (PMMA-b-P(NIPAAm-co-NAS)) block copolymer was synthesized by successive RAFT polymerizations. The uncross-linked micelles were facilely prepared by directly dissolving the block copolymer in an aqueous medium, and the shell cross-linked (SCL) micelles were further fabricated by the addition of ethylenediamine as a di-functional cross-linker into the micellar solution. Optical absorption measurements showed that the LCST of uncross-linked and cross-linked micelles was 31.0 °C and 40.8 °C, respectively. Transmission electron microscopy (TEM) showed that both uncross-linked and cross-linked micelles exhibited well-defined spherical shape in aqueous phase at room temperature, while the SCL micelles were able to retain the spherical shape with relatively smaller dimension even at 40 °C due to the cross-linked structure. In vitro drug release study demonstrated a slower and more sustained drug release behavior from the SCL micelles at high temperature as compared with the release profile of uncross-linked micelles, indicating the great potential of SCL micelles developed herein as novel smart carriers for controlled drug release.     

Polymeric Micelles Based on Amphiphilic Scorpion-like Macromolecules: Novel Carriers for Water-Insoluble Drugs

No HeadingPurpose. The objective was to evaluate amphiphilic scorpion-like macromolecules (AScMs) as drug carriers for hydrophobic drugs.Methods. Indomethacin (IMC) was incorporated into two AScM micelles (M₁₂P₅ and M₁₂P₂) by the O/W emulsion technique. The influences of IMC:polymer feed ratio and molecular weight of the hydrophilic block of AScMs on the micelle size, IMC entrapment efficiency and release behavior were investigated. Furthermore, cytotoxicity of the AScMs was evaluated with human umbilical vein endothelial cells (HUVEC).Results. The maximal IMC entrapment efficiency in M₁₂P₅ and M₁₂P₂ micelles (72.3 and 20.2%, respectively) was obtained at ratios of 0.1 to 1 for indomethacin:polymer. The sizes of IMC-loaded M₁₂P₅ and M₁₂P₂ polymeric micelles were <20 nm with a narrow size distribution. In vitro release studies revealed that IMC released from M₁₂P₅ and M₁₂P₂ polymeric micelles showed sustained release behavior during the 24 h of experiment. Additionally, M₁₂P₅ and M₁₂P₂ polymeric micelles did not induce remarkable cytotoxicity against HUVEC cells at concentrations up to 1 and 0.5 mM, respectively.Conclusions. The amphiphilic scorpion-like macromolecules may be useful as novel drug carriers because of their small size, ability to encapsulate hydrophobic drugs and release them in a sustained manner as well as low cytotoxicity.     

Characterization of Poly(glycolide-co-D,L-lactide)/Poly(D,L-lactide) Microspheres for Controlled Release of GM-CSF

Purpose. This study describes the preparation and characterization of a controlled release formulation of granulocyte-macrophage colony-stimulating factor (GM-CSF) encapsulated in poly(glycolide-co-D,L-lactide) (PLGA) and poly(D,L-lactide) (PLA) microspheres. Methods. GM-CSF was encapsulated in PLGA/PLA microspheres by a novel silicone oil based phase separation process. Several different blends of PLGA and low molecular weight PLA were used to prepare the microspheres. The microspheres and the encapsulated GM-CSF were extensively characterized both in vitroand in vivo. Results. Steady release of GM-CSF was achieved over a period of about one week without significant 'burst' of protein from the microspheres. Analysis of microsphere degradation kinetics by gel permeation chromatography (GPC) indicated that low molecular weight PLA enhanced the degradation of the PLGA and thereby affected release kinetics. GM-CSF released from the microspheres was found to be biologically active and physically intact by bioassay and chromato-graphic analysis. Analysis of serum from mice receiving huGM-CSF indicated that the GM-CSF was biologically active and that a concentration of greater than 10 ng/mL was maintained for a period lasting at least nine days. MuGM-CSF was not detected followingin vivo administration of muGM-CSF microspheres. The tissues of mice receiving muGM-CSF microspheres were characterized by infiltration of neutrophils, and macrophages which were in significant excess of those found in mice administered with placebo controls (i.e. microspheres without GM-CSF). Conclusions. This study demonstrates the influence of formulation parameters on the encapsulation of GM-CSF in PLGA/PLA microspheres and its controlled release in biologically active form. The intense local tissue reaction in mice to muGM-CSF microspheres demonstrates the importance of the mode of delivery on the pharmacologic activity of GM-CSF.     

Andrographolide-loaded PLGA-PEG-PLGA micelles to improve its bioavailability and anticancer efficacy

Background: Andrographolide (ADG) isolated from Andrographis paniculata exhibits anti-inflammatory and anticancer activities, but high hydrophobicity and poor bioavailability greatly restricts its clinical application.

Objectives: In this study, ADG was encapsulated in a micelle formulation based on poly (D,L-lactide-co-glycolide)-b-poly (ethylene glycol)-b-poly (D,L-lactide-co-glycolide) (PLGA-PEG-PLGA) amphiphilic triblock copolymers, in order to enhance the anticancer efficacy and bioavailability in vivo.

Methods: The physicochemical properties of the ADG-loaded PLGA-PEG-PLGA micelles were investigated for encapsulation efficiency, particle size, zeta potential and critical micelle concentration. These micelles were further evaluated for in vitro cytotoxicity, including proliferation inhibition, cell cycle arrest and pro-apoptosis effects against human breast cancer MAD-MB-231 cells, cellular uptake and pharmacokinetics study in rat.

Results: ADG-loaded PLGA-PEG-PLGA micelles had a high encapsulation and loading efficiency of about 92 and 8.4% (w/w), respectively, and a stable particle size of 124.3 ± 6.4 nm. In vitro cytotoxicity testing demonstrated that ADG-loaded PLGA-PEG-PLGA micelles exhibited higher proliferation inhibition, cell cycle arrest at the G2/M phase and pro-apoptosis effects in MAD-MB-231 cells, which would be contributed to higher efficiency of cellular uptake and intracellular transport. Further, the plasma AUC_{(0 – ∞)} and mean resident time of ADG-loaded PLGA-PEG-PLGA micelles were increased by 2.7- and 2.5-fold, respectively, when compared to the raw suspension.

Conclusion: All of these investigations suggest that PLGA-PEG-PLGA micelles may be a potential drug delivery strategy for improving ADG bioavailability and efficacy in cancer therapy.     

Stabilization and Controlled Release of Bovine Serum Albumin Encapsulated in Poly(D,L-lactide) and Poly(ethylene glycol) Microsphere Blends

Purpose. The acidic microclimate in poly(D, L-lactide-co-glycolide) 50/50 microspheres has been previously demonstrated by our group as the primary instability source of encapsulated bovine serum albumin (BSA). The objectives of this study were to stabilize the encapsulated model protein, BSA, and to achieve continuous protein release by using a blend of: slowly degrading poly(D, L-lactide) (PLA), to reduce the production of acidic species during BSA release; and pore-forming poly(ethylene glycol) (PEG), to increase diffusion of BSA and polymer degradation products out of the polymer. Methods. Microspheres were formulated from blends of PLA (Mw 145,000) and PEG (Mw 10,000 or 35,000) by using an anhydrous oil-in-oil emulsion and solvent extraction (O/O) method. The polymer blend composition and phase miscibility were examined by FT-IR and DSC, respectively. Microsphere surface morphology, water uptake, and BSA release kinetics were also investigated. The stability of BSA encapsulated in microspheres was examined by losses in protein solubility, SDS-PAGE, IEF, CD, and fluorescence spectroscopy. Results. PEG was successfully incorporated in PLA microspheres and shown to possess partial miscibility with PLA. A protein loading level of 5% (w/w) was attained in PLA/PEG microspheres with a mean diameter of approximately 100 m. When PEG content was less than 20% in the blend, incomplete release of BSA was observed with the formation of insoluble, and primarily non-covalent aggregates. When 20%-30% PEG was incorporated in the blend formulation, in vitro continuous protein release over 29 days was exhibited. Unreleased BSA in these formulations was water-soluble and structurally intact. Conclusions. Stabilization and controlled relaease of BSA from PLA/PEG microspheres was achieved due to low acid and high water content in the blend formulation.     

Near Infrared with Principal Component Analysis as a Novel Analytical Approach for Nanoparticle Technology

Purpose. To progress in the characterization of a poly(MePEGcyanoacrylate-co-hexadecylcyanoacrylate) (poly(PEGCA-co-HDCA) copolymer and the nanoparticles formed from this copolymer. Methods. Poly(PEGCA-co-HDCA) at a MePEG/hexadecyl ratio of 1:4 was investigated by ¹H-NMR and near infrared spectroscopy. The nanoparticle suspensions, obtained by the methods of nanoprecipitation or emulsion—solvent evaporation, as well as the crude nanoparticles and their dispersion medium—were analyzed by MePEG measurement, ¹H-NMR, and near infrared spectroscopy. Results. The ¹H-NMR results showed that the (poly(PEGCA-co-HDCA) copolymer obtained bore lateral hydrophilic MePEG chains and lateral hydrophobic hexadecyl chains in a final ratio of 1:4. However, this ratio, although reproducible from batch to batch, represented only a mean value for different molecular species. Indeed, our results demonstrated the formation of more hydrophobic poly(alkylcyanoacrylate) oligomers (with a higher content of hexadecyl chains) and other more hydrophilic oligomers (with a higher MePEG content). Only the more hydrophobic oligomers were able to form solid pegylated nanoparticles. As far as these nanoparticles were concerned, determination of their MePEG content allowed the calculation of a distance of 1.2 nm and 1.05 nm between 2 grafted MePEG chains at the nanoparticle surface, when obtained by nanoprecipitation and emulsion-solvent evaporation, respectively. Moreover, when the same copolymer batch was used, different nanoparticles were obtained according to the preparation method, as seen by near infrared spectroscopy. Conclusions. The nanoparticles obtained by nanoprecipitation or emulsion-solvent evaporation of poly(PEGCA-co-HDCA) 1:4 copolymer displayed a different supramolecular organization, as evidenced by the near infrared spectroscopy results. Moreover, these nanoparticles showed surface characteristics compatible with a long circulating carrier.     

Environmental-sensitive micelles based on poly(2-ethyl-2-oxazoline)-b-poly(L-lactide) diblock copolymer for application in drug delivery

Anticancer drug doxorubicin (DOX) was physically loaded into the micelles prepared from poly(2-ethyl-2-oxazoline)-b-poly(L-lactide) diblock copolymers (PEOz-PLLA). PEOz-PLLA consists of hydrophilic segment PEOz and hydrophobic segment PLLA showed pH-sensitivity in the aqueous solution. The DOX-loaded micelle exhibited a narrow size distribution with a mean diameter around 170 nm. The micellar structure can preserve hydrophobic drug DOX under the physiological condition (pH 7.4) and selectively release DOX by sensing the intracellular pH change in late endosomes and secondary lysosomes (pH 4-5). At 37 degrees C, the cumulated released rate of DOX from micelles was about 65% at pH 5.0 in the initial 24 h. Additionally, polymeric micelles had low cytotoxicity in human normal fibroblast HFW cells for 72 h by using MTT assay. Moreover, DOX-loaded micelles could slowly and efficiency decrease cell viability of non-small-cell lung carcinoma CL3 cells. Taken together, PEOz-b-PLLA diblock polymeric micelles may act as useful drug carriers for cancer therapy.     

Novel Redox-Responsive Amphiphilic Copolymer Micelles for Drug Delivery: Synthesis and Characterization

A novel redox-responsive amphiphilic polymer was synthesized with bioreductive trimethyl-locked quinone propionic acid for a potential triggered drug delivery application. The aim of this study was to synthesize and characterize the redox-responsive amphiphilic block copolymer micelles containing pendant bioreductive quinone propionic acid (QPA) switches. The redox-responsive hydrophobic block (polyQPA), synthesized from QPA-serinol and adipoyl chloride, was end-capped with methoxy poly(ethylene glycol) of molecular weight 750 (mPEG₇₅₀) to achieve a redox-responsive amphiphilic block copolymer, polyQPA-mPEG₇₅₀. PolyQPA-mPEG₇₅₀ was able to self-assemble as micelles to show a critical micelle concentration (CMC) of 0.039% w/v (0.39 mg/ml, 0.107 mM) determined by a dye solubilization method using 1,6-diphenyl-1,3,5-hexatriene (DPH) in phosphate-buffered saline (PBS). The mean diameter of polymeric micelles was found to be 27.50 nm (PI = 0.064) by dynamic light scattering. Furthermore, redox-triggered destabilization of the polymeric micelles was confirmed by ¹H-NMR spectroscopy and particle size measurements in a simulated redox state. PolyQPA-mPEG₇₅₀ underwent triggered reduction to shed pendant redox-responsive QPA groups and its polymeric micelles were swollen to be dissembled in the presence of a reducing agent, thereby enabling the release of loaded model drug, paclitaxel. The redox-responsive polyQPA-mPEG₇₅₀ polymer micelles would be useful as a drug delivery system allowing triggered drug release in an altered redox state such as tumor microenvironments with an altered redox potential and/or redox enzyme upregulation.KEY WORDS: amphiphilic polymer, micelle, redox-responsive polymer, targeted drug delivery, trimethyl-locked quinone propionic acid     

聚（2-乙基-2-噁唑啉）-聚乳酸胶束的血液相容性和细胞相容性研究

合成的二嵌段共聚物聚（2-乙基-2-噁唑啉）-聚乳酸（PEOz-PLA）可自组装形成胶束,其在药物输送领域的应用与口俱增。然而,其与血液和细胞之间的相互作用迄今未知。本研究拟对PEOz-PLA胶束的血液相容性和细胞相容性进行评价,为PEOz-PLA胶束的潜在应用提供数据支持。通过溶血、凝血时间、血小板激活以及与白蛋白的相互作用评价了PEOz-PLA胶束的血液相容性。结果表明,PEOz-PLA胶束的血液相容性良好。SRB的实验结果表明,PEOz-PLA胶束与KBv细胞孵育后并未出现明显的细胞毒性,显示出良好的细胞相容性。总之,PEOz-PLA胶束是血液和细胞相容的药物载体,可用于静脉给药。     

Clonazepam release from core-shell type nanoparticles of poly(-caprolactone)/poly(ethylene glycol)/poly(-caprolactone) triblock copolymers

The triblock copolymer based on poly(-caprolactone) (PCL) as hydrophobic part and poly(ethylene glycol) (PEG) as hydrophilic one was synthesized and characterized. Core-shell type nanoparticles of poly(-caprolactone)/poly(ethylene glycol)/poly(-caprolactone) (CEC) block copolymer were prepared by a dialysis technique. According to the amphiphilic characters, CEC block copolymer can self-associate at certain concentration and their critical association concentration (CAC) was determined by fluorescence probe technique. CAC value of the CEC-2 block copolymer was evaluated as 0.0030 g/l. CAC values of CEC block copolymer decreased with the increase of PCL chain length, i.e. the shorter the PCL chain length, the higher the CAC values. From the observation of transmission electron microscopy (TEM), the morphologies of CEC-2 core-shell type nanoparticles were spherical shapes. Particle size of CEC-2 nanoparticles was 32.3±17.3 nm as a monomodal and narrow distribution. Particle size, drug loading, and drug release rate of CEC-2 nanoparticles were changed by the initial solvents and the molecular weight of CEC. The degradation behavior of CEC-2 nanoparticles was observed by ¹H NMR spectroscopy. It was suggested that clonazepam (CNZ) release kinetics were dominantly governed by diffusion mechanism.     

A Graphical Method for the Determination of the Mode of Hydrolysis of Biodegradable Polymers

Purpose. To develop a qualitative method for the determination of the mode of scission in the hydrolysis of biodegradable polymers. Methods. The method requires determination of the molar fraction of monomer (m₁ by ¹HNMR or HPLC, and the degree of polymer degradation () determined by ¹HNMR. Results. If the scission of the backbone bonds is completely random, the molar fraction of the monomer must equal the square of the degree of degradation as predicted by Kuhn (1). If the degradation follows an exclusive chain-end unzipping mechanism then, m₁ = . Experimental data falling on the theoretical curves (m₁ vs. ) confirm the corresponding mode of scission. If the data fall between the two curves, it suggests a faster chain-end scission than random scission. When data fall below both of these curves, it suggests the chain-end bonds are less reactive than the internal bonds. Conclusions. The acid catalyzed hydrolysis of a poly(ortho ester) and the base catalyzed hydrolysis of poly(D,L-lactide) (PLA) were by a random scission mechanism, while acid catalyzed hydrolysis of PLA demonstrated faster chain-end scission.     

Solubilization of an amphiphilic drug by poly(ethylene oxide)-block-poly(ester) micelles.

The purpose of this study was to investigate the solubilization of an amphiphilic drug, i.e, amiodarone (AMI) in methoxy poly(ethylene oxide)-block-poly(ester) micelles of different core structure. The effect of core-forming block structure as well as molecular weight, applied drug to polymer ratios and assembly condition on AMI solubilization; stability of the solubilized formulation upon dilution in phosphate buffer and the hemolytic activity of solubilized AMI against rat red blood cells were assessed and compared to those parameters for the commercial intravenous formulation of AMI. In general, polymeric micelles of different core structure were found to be more efficient in retaining their AMI content upon dilution than surfactant micelles in the commercial formulation of AMI for injection. Micelles with a poly(epsilon-caprolactone) (PCL) core were more efficient than poly(D,L-lactide) and poly(L-lactide) cores in the solubilization and stabilization of encapsulated AMI within the carrier. Encapsulation of AMI by methoxy poly(ethylene oxide)-block-poly(epsilon-caprolactone) (MePEO-b-PCL) micelles having higher PCL chains increased the level of AMI solubilization and decreased its hemolytic activity. Compared to O/W emulsion, application of solvent evaporation method led to higher encapsulation efficiency and lower hemolytic activity for AMI in micelles. An increase in the level of AMI added to the co-solvent evaporation process led to an increase in the solubilized AMI levels, but made the formulation more hemolytic. In conclusion, PEO-b-PCL micelles, particularly those with longer PCL chains, were found to be efficient carriers in encapsulating amphiphilic AMI, retaining encapsulated AMI within the carrier and reducing its hemolytic activity.     

Formulation and Lyoprotection of Poly(Lactic Acid-Co-Ethylene Oxide) Nanoparticles: Influence on Physical Stability and In Vitro Cell Uptake

Purpose. To investigate the feasibility of producing freeze-dried poly-(ethylene oxide) (PEO)-surface modified nanoparticles and to study their ability to avoid the mononuclear phagocytic system (MPS), as a function of the PEO chain length and surface density. Methods. The nanoparticles were produced by the salting-out method using blends of poly(D,L-lactic acid) (PLA) and poly(D,L-lactic acid-co-ethylene oxide) (PLA-PEO) copolymers. The nanoparticles were purified by cross-flow filtration and freeze-dried as such or with variable amounts of trehalose as a lyoprotectant. The redispersibility of the particles was determined immediately after freeze-drying and after 12 months of storage at –25° C. The uptake of the nanoparticles by human monocytes was studied in vitro by flow cytometry. Results. PLA-PEO nanoparticles could be produced from all the polymeric blends used. Particle aggregation after freeze-drying was shown to be directly related to the presence of PEO. Whereas this problem could be circumvented by use of trehalose, subsequent aggregation was shown to occur during storage. These phenomena were possibly related to the specific thermal behaviours of PEO and trehalose. In cell studies, a clear relationship between the PEO content and the decrease of uptake was demonstrated. Conclusions. The rational design of freeze-dried PEO-surface modified nanoparticles with potential MPS avoidance ability is feasible by using the polymer blends approach combined with appropriate lyoprotection and optimal storage conditions.