Characterization of novel pH-sensitive polymeric micelles prepared by the self-assembly of amphiphilic block copolymer with poly-4-vinylpyridine block synthesized by mechanochemical solid-state polymerization

We fabricated novel pH-sensitive polymeric micelles consisting of amphiphilic block copolymer containing pyridyl groups as side chains in the hydrophobic block. The number average particle diameter of the polymeric micelles at pH 7 was approximately 200 nm. A decrease in pH resulted in deformation of the polymeric micelles over a very narrow pH range (between pH 5.7 and 5.6). Interestingly, micellization and demicellization occurred reversibly in this narrow pH range. Polymeric micelles incorporating 5-fluorouracil (5FU) were also prepared. Decreasing the pH of this polymeric micelle solution from 7 to 5.5 resulted in the rapid release of 5FU at pH 5.6; the drug was completely released within 30 min. These results suggest that deformation of the polymeric micelles caused the rapid release of 5FU.     

Biodegradable and thermosensitive micelles of amphiphilic polyaspartamide derivatives containing aromatic groups for drug delivery

The preparation, characterization, release, and in vitro cytotoxicity of a biodegradable polymeric micellar formulation of paclictaxel (PTX) were investigated. The micelles based on thermosensitive and degradable amphiphilic polyaspartamide derivatives containing pendant aromatic structures (phe‐g‐PHPA‐g‐mPEG) were prepared by a quick heating method without using toxic organic solvent. Dynamic light‐scattering results show that the micelles are stable upon dilution under physiological conditions and the destabilization of the micelles is pH‐dependent and the phe‐g‐PHPA‐g‐mPEG polymers are biodegradable. PTX was loaded into the phe‐g‐PHPAs‐g‐mPEG micelles with encapsulation efficiency of >90%, resulting in a high drug loading content (up to 29%). PTX‐loaded micelles had a mean size around 70 nm with narrow size distribution (polydispersity index, <0.1). The PTX‐loaded micelles showed sustained drug release and obvious anticancer activity similar to Taxol against HepG2 cells, whereas blank micelles were nontoxic. The present results suggest that the thermosensitive and biodegradable phe‐g‐PHPA‐g‐mPEG micelles are a promising delivery system for the hydrophobic drugs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3917–3924     

pH-Sensitive micelles with cross-linked cores formed from polyaspartamide derivatives for drug delivery

A series of polyaspartamide derivatives were synthesized by grafting O-(2-aminoethyl)-O'-methylpoly(ethylene glycol) 5000 (MPEG), 1-(3-aminopropyl) imidazole (API), and cinnamate onto polysuccinimide (PSI) with the respective degrees of substitution adjusted by the feed molar ratio. The chemical structure of the prepared polymer was confirmed using FT-IR and (1)H NMR spectroscopy. A new pH-sensitive polymeric micelle based on the synthesized polymer was prepared and characterized, and its pH-sensitive properties were characterized by the measurement of light transmittance and particle sizes at varying pH values. pH-dependent aggregation and deaggregation behavior was clearly observed in the polymer aqueous dispersion system. Photo-cross-linking of the cinnamate branches cross-linked the core of the micelles. The core cross-linked micelles showed high stability over a wider pH range and displayed obvious pH-dependent swelling-shrinking behavior instead of micelle-unimer transition behavior. This micelle system overcame the drawback of the facile disintegration of normal polymeric micelles and showed obvious delayed paclitaxel release in in vitro drug delivery experiments.     

Phase transition behavior of novel pH-sensitive polyaspartamide derivatives grafted with 1-(3-aminopropyl)imidazole

New pH-sensitive polyaspartamide derivatives were synthesized by grafting 1-(3-aminopropyl)imidazole and/or O-(2-aminoethyl)-O'-methylpoly(ethylene glycol) 5000 on polysuccinimide for application in intracellular drug delivery systems. The DS of 1-(3-aminopropyl)imidazole was adjusted by the feed molar ratio, and the structure of the prepared polymer was confirmed using FT-IR and 1H NMR spectroscopy. Their pH-sensitive properties were characterized by light transmittance measurements, and the particle size and its distribution were investigated by dynamic light scattering measurements at varying pH values. The pH-sensitive phase transition was clearly observed in polymer solutions with a high substitution of 1-(3-aminopropyl)imidazole. The prepared polymers showed a high buffering capacity between pH 5 and 7, and this increased with the DS of 1-(3-aminopropyl)imidazole. The pH dependence of the aggregation and de-aggregation behavior was examined using a fluorescence spectrometer. For MPEG/imidazole-g-polyaspartamides with a DS of 1-(3-aminopropyl)imidazole over 82%, self aggregates associated with the hydrophobic interactions of the unprotonated imidazole groups were observed at pH values above 7, and their mean size was over 200 nm, while the aggregates of polymers were dissociated at pH values below 7 by the protonation of imidazole groups. These pH-sensitive polyaspartamide derivatives are potential basic candidates for intracellular drug delivery carriers triggered by small pH changes.     

Development and characterization of new insulin containing polysaccharide nanoparticles

A nanoparticle insulin delivery system was prepared by complexation of dextran sulfate and chitosan in aqueous solution. Parameters of the formulation such as the final mass of polysaccharides, the mass ratio of the two polysaccharides, pH of polysaccharides solution, and insulin theorical loading were identified as the modulating factors of nanoparticle physical properties. Particles with a mean diameter of 500 nm and a zeta potential of approximately −15 mV were produced under optimal conditions of DS:chitosan mass ratio of 1.5:1 at pH 4.8. Nanoparticles showed spherical shape, uniform size and good shelf-life stability. Polysaccharides complexation was confirmed by differential scanning calorimetry and Fourier transformed infra-red spectroscopy. An association efficiency of 85% was obtained. Insulin release at pH below 5.2 was almost prevented up to 24 h and at pH 6.8 the release was characterized by a controlled profile. This suggests that release of insulin is ruled by a dissociation mechanism and DS/chitosan nanoparticles are pH-sensitive delivery systems. Furthermore, the released insulin entirely maintained its immunogenic bioactivity evaluated by ELISA, confirming that this new formulation shows promising properties towards the development of an oral delivery system for insulin.     

Self-assembled micellar nanoparticles of a novel star copolymer for thermo and pH dual-responsive drug release

An amphiphilic star block copolymer comprised of a hydrophobic PMMA block and a hydrophilic tri-arm poly(NIPAAm-co-DMAEMA) block was synthesized by copolymerization of NIPAAm and DMAEMA, with Ce(4+) ions and tris(hydroxymethyl)methylamine as a redox initiatory system. The star copolymer undergoes self-assembly to the micellar nanoparticles with a core-shell structure and the thermo/pH dual-response, originated from the thermo-sensitivity of PNIPAAm and the pH-sensitivity of PDMAEMA. A fluorescence probe study showed the pH-dependent low CMCs (7.5 to 11.2 mg/L) of the micelles, confirming the formation of stable micelles. Morphological investigations showed that the blank and drug-loaded micelles both had spherical and uniform shapes. The sizes of the blank and drug-loaded nanoparticles were between 80 and 120 nm, depending on the given pH. The LCSTs of the star copolymer were determined to be 32 degrees C, 36.6 degrees C and 39.5 degrees C, corresponding to pH 5, pH 7.4 and pH 9, respectively, demonstrating a pH-dependent thermo-response. As a drug delivery, the micellar nanoparticles showed the dual-responsive release profiles in vitro, which were confirmed by the drug release studies. The obtained results showed the thermo-triggered accelerated release at pH 7.4, and the pH-triggered accelerated release at 37 degrees C, indicating the micelles nanoparticles would be a promising site-specific drug delivery for enhancing the accumulation of drug in targeting pathological areas.     

Synthesis and physicochemical characterization of amphiphilic triblock copolymer brush containing pH-sensitive linkage for oral drug delivery

A novel and well-defined pH-sensitive amphiphilic triblock copolymer brush poly(lactide)-b-poly(methacrylic acid)-b-poly(poly(ethylene glycol) methyl ether monomethacrylate) (PLA-b-PMAA-b-PPEGMA) and its self-assembled micelles were developed for oral administration of hydrophobic drugs. The copolymer and its precursors were synthesized by the combination of activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) and ring-opening polymerization (ROP) techniques. The molecular structures and characteristics were confirmed by GPC, (1)H NMR, and FT-IR. The critical micelle concentration (CMC) values of PLA-b-PMAA-b-PPEGMA in aqueous medium varied from 1.4 to 2.6 mg/L, and the partition equilibrium constant (K(v)) of pyrene in micellar solutions ranged from 2.873 × 10(5) to 3.312 × 10(5). The average sizes of the self-assembled blank and drug-loaded micelles were 140-250 nm determined by DLS in aqueous solution. The morphology of the micelles was found to be spherical by SEM. Nifedipine (NFD), a poorly water-soluble drug, was selected as the model drug and wrapped into the core of micelles via dialysis method. The in vitro release behavior of NFD from the micelles was pH-dependent. In simulated gastric fluid (SGF, pH 1.2), the cumulative release percent of NFD was relative low, while in simulated intestinal fluid (SIF, pH 7.4), more than 96% was released within 24 h. All the results showed that the pH-sensitive PLA-b-PMAA-b-PPEGMA micelle may be a prospective candidate as oral drug delivery carrier for hydrophobic drugs with controlled release behavior.     

Evaluation of pH-sensitive poly(β-amino ester)-graft-poly(ethylene glycol) and its usefulness as a pH-sensor and protein carrier

In this study, some possible biomedical applications of a pH-sensitive and amphiphilic copolymer as a pH sensor and protein delivery system are reported. PAE-g-PEG was used as a pH-sensitive polymer that can exhibit a sharp pH-dependent transition. Various fluorescent dyes including pyrene and RITC can be used to label the pH-sensitive polymer PAE-g-PEG, which was evaluated for protein encapsulation. pH-sensing was possible by observing excimer formation of the labeled pyrene via pH-dependent expansion of the polymeric chain. Also, it was confirmed that FITC-BSA could be entrapped in RITC-labeled pH-sensitive micelles of PAE-g-PEG by FRET. As a result, PAE-g-PEG can be a pH sensor and carrier for protein delivery.     

pH sensitivities of egg phosphatidylcholine liposomes and dioleoylphosphatidylethanolamine liposomes triggered by poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide-co-methacrylic acid-co-octadecylacrylate)

Egg phosphatidylcholine (PC) liposomes bearing pH-sensitive polymers and dioleoylphosphatidylethanolamine (DOPE) liposomes including the same polymers were prepared by a sonication method. As pH-sensitive polymers, copolymers of N-isopropylacrylamide, methacrylic acid, and octadecylacrylate were used. The liposomes were stable in neutral pH ranges in terms of release. But the release became marked at pH 5.5, and it was accelerated as pH further decreased. For example, the degree of release from egg PC liposomes (polymer/lipid ratio is 3:10, w/w) for 120 s increased from 2% to 63% as pH decreased from 7.5 to 4.5. Under the same condition, the degree of release from DOPE liposomes increased from 4% to 80%. These results indicate that DOPE liposome is more pH-sensitive than egg PC liposome.     

新型壳聚糖基自组装纳米胶束紫杉醇药物释放载体

以N-胆甾醇琥珀酰基-O-羧甲基壳聚糖(CCMC, 胆甾醇基取代度6.9%)为原料, 在水溶液中通过探头超声处理制备其自组装凝胶纳米胶束, 采用稳态荧光探针法考察临界胶束浓度, 并通过透射电镜和动态激光散射仪检测胶束的形态大小. 以紫杉醇为模型药物, 采用透析法制备载药CCMC纳米胶束, 并通过高效液相色谱法(HPLC)考察其在纳米胶束中的包载及释放情况. 结果显示, CCMC为两亲性高分子, 在水溶液中能形成粒径为198.4 nm的规则球状胶束, 临界胶束浓度为0.018 mg/mL. 紫杉醇顺利包载于CCMC-纳米胶束内, 载药量高达34.9%; 随着载药量的增加, 胶束粒径呈增大的趋势. 体外释放实验结果显示, CCMC纳米胶束能延缓紫杉醇的释放, 释药速度和释放介质pH值密切相关.     

乙二醇-聚(咪唑丙基-天冬酰胺)-聚丙氨酸三嵌段共聚物的合成及其pH-响应性药物控制释放性能的研究

聚天冬氨酸及其衍生物是一种具有良好生物相容性和可生物降解性的高分子材料, 被广泛应用于生物医药领域. 本研究通过大分子引发剂ω-胺基-α-甲氧基聚乙二醇引发N-羧基-α-氨基环内酸酐开环聚合和N-(3-氨丙基)咪唑侧基改性, 制备了一种侧链含有咪唑丙基的聚乙二醇-聚(咪唑丙基-天冬酰胺)-聚丙氨酸三嵌段共聚物. 在水溶液中, 此聚合物可自组装形成一种核-壳-冠型的三层共聚物胶束, 其中疏水性的聚丙氨酸链段自聚集形成胶束的核, 聚(咪唑丙基-天冬酰胺)链段形成具有pH-响应性的壳层, 用于包埋和释放药物, 外围的聚乙二醇链段可以提供一个稳定的水合冠层, 延长药物的体内循环时间. 利用咪唑环与游离阿霉素之间的π-π相互作用和疏水相互作用可以在自组装的过程中将阿霉素包埋到胶束内. 研究发现, 载药胶束随环境pH 值的降低药物的释放速率显著增加. 这主要是由于咪唑环在酸性条件下的质子化导致链段亲疏水性质发生明显变化.     

pH-Responsive Self-assembled Nanoparticles of Simulated P(AA-co-SA)-g-PEG for Drug Release

Simulated graft copolymer of poly(acrylic acid-co-stearyl acylate) [P(AA-co-SA)] and poly(ethylene glycol) (PEG) was synthesized, where acrylic acid, stearyl acylate and PEG was employed as the pH-sensitive, hydrophobic and hydrophilic segment, respectively. Polymeric nanoparticles prepared by the dialysis of simulated graft copolymer solution in dimethylformamide against citrate buffer solution with different pH values were characterized by transmission electron microscopy (TEM), fluorescence technique and laser light scattering (LLS). TEM image revealed the spherical shape of the self-aggregates, which was further confirmed by LLS measurements. The critical aggregation concentration increased markedly (10 to 150 mg/L) with increasing pH (4.6 to 7.0), consistent with the de-protonation of carboxylic groups at higher pH. The hydrodynamic radius of polymeric nanoparticles decreased from 118 nm at pH 3.4 to 90 nm at pH 7.0. The controlled release of indomethacin from those nanoparticles was investigated, and the self-assembled nanoparticles exhibited improved performance in controlled drug release.     

Microgels formed by electrostatic and hydrophobic interaction of naphthaleneacetic acid with β-cyclodextrin-grafted polyethyleneimine

Microgels were prepared by physically cross-linking β-cyclodextrin-grafted polyethyleneimine (βCD-PEI) using a hydrophobic acidic compound, naphthaleneacetic acid (NAA). Under a strong acidic condition (e.g., pH 3.0), fibrous microgels were observed on a scanning electron microscope (SEM) possibly due to the intermolecular electrostatic interaction of NAA with PEI. In the range of pH 4.0 to pH 8.0, globular microgels were found possibly because an intramolecular electrostatic interaction prevails over an intermolecular interaction. At pH 9.0 and pH 10.0, neither fibrous nor globular microgels were observed due to lack of the electrostatic interaction and the hydrophobic interaction of NAA with βCD-PEI. The release of fluorescein isothiocyanate-dextran (FITC-dextran; M.W., 10,000) from the microgels increased with increasing pH. At pHs higher than pH 3.0, not only the diffusion of the solute, but also the dissolution of the microgels could contribute to the release.     

具有pH-响应性的聚天冬氨酸类载药胶束的制备和释放能力研究

通过大分子引发剂ω-氨基-α-甲氧基聚乙二醇引发N-羧基-α-氨基环内酸酐开环聚合和水合肼侧基改性,制备了一系列聚乙二醇-聚氨基酸类三嵌段共聚物.其中聚氨基酸链段包括具有酰肼基的聚天冬氨酸衍生物(PAHy),以及疏水性的聚丙氨酸链段.引入具有pH响应性的腙键键合阿霉素,利用键合阿霉素与游离阿霉素之间的π-π叠合作用,在聚合物自组装形成胶束过程中通过化学键合+物理包埋的方式充分负载药物.该胶束以聚丙氨酸链段为核心,以PEG链段为冠层,以PAHy链段为包裹药物的壳层.载药胶束的粒径在170 nm左右.研究不同pH值条件下载药胶束的药物释放能力,随环境pH值的降低药物的释放速率显著增加.     

Photo-crosslinked and pH sensitive polymersomes for triggering the loading and release of cargo

Crosslinkable and pH-sensitive amphiphilic block copolymers are promising candidates to establish pH-stable and permeable vesicles for synthetic biology. Here, we report the fabrication of crosslinked and pH-stable polymersomes as swellable vesicles for the pH-dependent loading and release of small dye molecules.     

Novel polymeric vesicles with pH-induced deformation character for advanced drug delivery

pH-responsive amphiphilic graft macromolecules consisting of a polyphosphazene backbone, hydrophilic PEG branches and pH-sensitive DPA were successfully synthesized and characterized. The copolymer can self-assemble into vesicles in an aqueous solution with unique inner structure and homogeneously encapsulate both lipophilic and hydrophilic molecules. The pH-dependent structure change of vesicles was also observed by DLS and TEM. Dox-loaded vesicles exhibit a sharp pH-responsive drug release profile and dramatically enhance the cytotoxicity of Dox against Dox-resistant MCF-7/adr cells. These results suggest such vesicles based on pH-responsive polyphosphazene hold great potential for specific drug therapy.     

Drug-loaded and superparamagnetic iron oxide nanoparticle surface-embedded amphiphilic block copolymer micelles for integrated chemotherapeutic drug delivery and MR imaging

We report on the fabrication of organic/inorganic hybrid micelles of amphiphilic block copolymers physically encapsulated with hydrophobic drugs within micellar cores and stably embedded with superparamagnetic iron oxide (SPIO) nanoparticles within hydrophilic coronas, which possess integrated functions of chemotherapeutic drug delivery and magnetic resonance (MR) imaging contrast enhancement. Poly(ε-caprolactone)-b-poly(glycerol monomethacrylate), PCL-b-PGMA, and PCL-b-P(OEGMA-co-FA) amphiphilic block copolymers were synthesized at first by combining ring-opening polymerization (ROP), atom transfer radical polymerization (ATRP), and post- modification techniques, where OEGMA and FA are oligo(ethylene glycol) monomethyl ether methacrylate and folic acid-bearing moieties, respectively. A model hydrophobic anticancer drug, paclitaxel (PTX), and 4 nm SPIO nanoparticles were then loaded into micellar cores and hydrophilic coronas, respectively, of mixed micelles fabricated from PCL-b-PGMA and PCL-b-P(OEGMA-co-FA) diblock copolymers by taking advantage of the hydrophobicity of micellar cores and strong affinity between 1,2-diol moieties in PGMA and Fe atoms at the surface of SPIO nanoparticles. The controlled and sustained release of PTX from hybrid micelles was achieved, exhibiting a cumulative release of ~61% encapsulated drugs (loading content, 8.5 w/w%) over ~130 h. Compared to that of surfactant-stabilized single SPIO nanoparticles (r(2) = 28.3 s(-1) mM(-1) Fe), the clustering of SPIO nanoparticles within micellar coronas led to considerably enhanced T(2) relaxivity (r(2) = 121.1 s(-1) mM(-1) Fe), suggesting that hybrid micelles can serve as a T(2)-weighted MR imaging contrast enhancer with improved performance. Moreover, preliminary experiments of in vivo MR imaging were also conducted. These results indicate that amphiphilic block copolymer micelles surface embedded with SPIO nanoparticles at the hydrophilic corona can act as a new generation of nanoplatform integrating targeted drug delivery, controlled release, and disease diagnostic functions.     

Development and characterization of new insulin containing polysaccharide nanoparticles

A nanoparticle insulin delivery system was prepared by complexation of dextran sulfate and chitosan in aqueous solution. Parameters of the formulation such as the final mass of polysaccharides, the mass ratio of the two polysaccharides, pH of polysaccharides solution, and insulin theorical loading were identified as the modulating factors of nanoparticle physical properties. Particles with a mean diameter of 500 nm and a zeta potential of approximately −15 mV were produced under optimal conditions of DS:chitosan mass ratio of 1.5:1 at pH 4.8. Nanoparticles showed spherical shape, uniform size and good shelf-life stability. Polysaccharides complexation was confirmed by differential scanning calorimetry and Fourier transformed infra-red spectroscopy. An association efficiency of 85% was obtained. Insulin release at pH below 5.2 was almost prevented up to 24 h and at pH 6.8 the release was characterized by a controlled profile. This suggests that release of insulin is ruled by a dissociation mechanism and DS/chitosan nanoparticles are pH-sensitive delivery systems. Furthermore, the released insulin entirely maintained its immunogenic bioactivity evaluated by ELISA, confirming that this new formulation shows promising properties towards the development of an oral delivery system for insulin.     

Self‐Assembly of Amphiphilic Drug–Dye Conjugates into Nanoparticles for Imaging and Chemotherapy

An amphiphilic drug–dye conjugate ( PTX‐Pt‐BDP ) was designed and synthesized with a platinum compound as the hydrophilic head. The precursor of PTX‐Pt‐BDP was obtained under mild conditions by means of a three‐component Passerini reaction. PTX‐Pt‐BDP could self‐assemble into nanoparticles ( PTX‐Pt‐BDP NPs) in aqueous solution via a nanoprecipitation method. The obtained nanoparticles exhibited favorable structural stability in both water and physiological environment. PTX‐Pt‐BDP NPs could be endocytosed by cancer cells as revealed by confocal laser scanning microscopy and exert potent cytotoxicity. This work highlights the potential of nanomedicines from amphiphilic drug–dye conjugates for cancer cell imaging and chemotherapy.     

Effect of temperature and pH on the aggregation and the surface hydrophobicity of bovine κ-casein

κ-Casein (κ-CN) aggregation by heating has been studied at pH 7.2 and 5.2 using UV-visible spectrophotometry, sodium dodecyl sulfate polyacrylamide gel electrophoresis, spectrofluorometric study of the 1–8 aniline naphtalene sulfonate (ANS)–κ-CN binding and circular dichroism (CD) spectroscopy. The aggregation process to form aggregates like micelles or submicelles and the structural characteristics of these aggregates were pH dependent. Far-UV CD showed that the aggregates obtained by heating presented changes in the κ-CN secondary structure. Near-UV CD spectra showed a certain degree of tertiary organization in the Tyr environment for the protein heated or unheated, only at pH 5.2. ANS binding at both pH was quite different and depends on the self-association process. Heating produced exposition of hydrophobic binding sites only at pH 7.2, including those in the neighborhood of the κ-CN Trp residue.