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ABSTRACT: A series of pH-responsive random copolymer poly(L-glutamic acid-co-L-lysine) [P(Glu-co-Lys)] were synthesized through the ring-opening polymerization (ROP) of γ-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) and 3-benzyloxycarbonyl-L-lysine N-carboxyanhydride (ZLys-NCA) and the subsequent deprotection. The chemical structure of the P(Glu-co-Lys)s was confirmed by nuclear magnetic resonance spectra (NMR). Critical micelle concentration (CMC) and transmission electron microscopy (TEM) measurements indicated that the P(Glu-co-Lys)s could self-assemble into micelles in phosphate buffer (PB). The surface charge of P(Glu-co-Lys) micelles was greatly affected by the solution's pH and L-glutamic acid/L-lysine ratio because the carboxyl and amino groups present on the P(Glu-co-Lys) micelles could be protonated or deprotonated to become charged. The pH value of the solution at which the surface charge of the P(Glu-co-Lys) micelles reversed could be manipulated by the feed ratio of BLG-NCA and ZLys-NCA. In vitro methyl thiazolyl tetrazolium (MTT) assays demonstrated that negatively charged P(Glu-co-Lys)s were non-toxic and biocompatible. Positive charged P(Glu-co-Lys)s showed some cytotoxicity to Hela cells. Cisplatin (CDDP) was used as a model anticancer drug to evaluate the charge-reversal drug delivery system. By the manipulation of CDDP loading content, the surface charge of the CDDP/P(Glu-co-Lys) nanoparticles could be reversed to positive from negative at tumor extracellular pH (pHe 6.5-7.2). An enhanced drug uptake and inhibition of cancer cell proliferation were observed for the tumoral pHe triggered charge-reversal CDDP/P(Glu-co-Lys) drug delivery system. These indicated that the CDDP/P(Glu-co-Lys) nanoparticles could be used as intelligent drug delivery systems for cancer therapy.
Biomacromolecules 05/2013; · 5.48 Impact Factor
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ABSTRACT: A novel glucose-sensitive nanogel was conveniently prepared through one-pot thiol-ene copolymerization of pentaerythritol tetra(3-mercaptopropionate), poly(ethylene glycol) diacrylate, methoxyl poly(ethylene glycol) acrylate and N-acryloyl-3-aminophenylboronic acid. The formation of core-shell nanogel was verified by proton nuclear magnetic resonance, dynamic laser scattering (DLS) and transmission electron microscopy. The successful incorporation of phenylboronic acid (PBA) in the nanogel was confirmed through Fourier transform infrared spectroscopy, inductively coupled plasma mass spectrometry and fluorescence technology. Owing to the presence of PBA, the nanogel exhibited high glucose sensitivity in phosphate-buffered saline determined by DLS and fluorescence technology. The increased amount of glucose causes an increase in the hydrodrodynamic radius and a decrease in the fluorescence intensity of PBA-alizarin red S (ARS) complex in the nanogel at pH 7.4 because of the competitive substitution of ARS to form the hydrophilic PBA-glucose complex. ARS and insulin were loaded into this glucose-sensitive nanogel. In vitro release profiles revealed that the drug release from the nanogel could be triggered by the presence of glucose. The more glucose in the release medium, the more drug was released and the faster the release rate. Furthermore, in vitro methyl thiazolyl tetrazolium assay, lactate dehydrogenase assay and hemolysis test suggested that the nanogel was biocompatible. Therefore, the PBA-incorporated nanogel with high glucose-sensitivity and good biocompatibility may have great potential for self-regulated drug release.
Acta biomaterialia 02/2013; · 3.98 Impact Factor
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ABSTRACT: Biodegradable poly(ester amide)s have recently been used as biomaterials due to their desirable chemical and biological characteristics as well as their mechanical properties, which are amendable for material processing. In this study, electroactive tetraaniline (TA) grafted poly(ester amide)s were successfully synthesized and characterized. The poly(ester amide)s-graft-tetraaniline copolymers (PEA-g-TA) exhibited good electroactivity, mechanical properties, and biodegradability. The biocompatibility of the PEA-g-TA copolymers in vitro was systematically studied, which demonstrated that they were nontoxic and led to favorable adhesion and proliferation of mouse preosteoblastic MC3T3-E1 cells. Moreover, the PEA-g-TA copolymers stimulated by pulsed electrical signal could serve to promote the differentiation of MC3T3-E1 cells compared with TCPs. Hence, the biodegradable and electroactive PEA-g-TA copolymers possessed the properties in favor of the long-time potential application in vivo (electrical stimulation directly to the desired area) as bone repair scaffold materials in tissue engineering.
Biomacromolecules 08/2012; 13(9):2881-9. · 5.48 Impact Factor
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ABSTRACT: Biodegradable and pH-sensitive PEAs based on dual amino acids are designed, synthesized, and characterized. Insulin can be loaded into the PEA microspheres by a solid-in-oil-in-oil technique with high encapsulation efficiency. The feasibility of PEA microspheres as oral insulin delivery carriers is evaluated in vitro and in vivo. The hydrophobic leucine groups on PEA seem to play an important role in the pH-dependent release mechanism and cytotoxicity of PEA microspheres. Oral administration of insulin-loaded PEA microspheres to streptozotocin-induced diabetic rats at 60 IU kg(-1) is able to reduce fasting plasma glucose levels to 49.4%. These results indicate that PEA microspheres are potential new vehicles for insulin oral delivery.
Macromolecular Bioscience 02/2012; 12(4):547-56. · 3.89 Impact Factor
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ABSTRACT: Polylactide (PLA) is a biodegradable, aliphatic polyester derived from lactic acid. It has similar mechanical properties to polyethylene terephthalate, but has a significantly lower maximum continuous use temperature. PLA products can be recycled after use either by remelting and processing the material a second time or by hydrolyzing to lactic acid, the basic chemical. In this review, the technologies for polymerization of the lactic acid and the comparison of physical, thermal and mechanical properties, biodegradability, and biocompatibility of the PLA and copolymers with other similar polymers are described.
Biotechnology Journal 11/2010; 5(11):1125-36.
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Journal of Polymer Science Part A Polymer Chemistry 07/2010; 48(17):3758 - 3766. · 3.92 Impact Factor
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ABSTRACT: A series of biodegradable functional amino acid-based poly(ester amide)s (PEA-AG) were designed and synthesized by the solution co-polycondensation of amino acid (L-phenylalanine and DL-2-allylglycine) based monomers and dicarboxylic acid based monomers. Pendant carbon-carbon double bonds located in the DL-2-allylglycine were incorporated into these PEA-AGs, and the double bond contents could be adjusted by tuning the feed ratio of L-phenylalanine to DL-2-allylglycine monomers. Chemical structures of this new functional PEA-AG family were confirmed by FTIR and NMR spectra. The thermal properties of these polymers were investigated; increasing the methylene chain in both the amino acid and dicarboxlic acid segments resulted in a reduction in the polymer glass-transition temperature. The short-term in vitro biodegradation properties of PEA-AGs were investigated as a function of PEA-AG chemical structures and enzymes. Based on the weight loss data, PEA-AGs biodegraded much faster in an enzyme solution than in a PBS buffer solution. The utility of the pendant functional carbon-carbon double bonds in PEA-AG was demonstrated by synthesizing additional functional PEA derivatives. The incorporation of the functional pendant carbon-carbon double bonds along the PEA-AG chains could significantly expand the biomedical applications of these functional PEA-AGs via either their capability to conjugate bioactive agents or prepare additional useful functional derivatives.
Biomaterials 02/2010; 31(14):3745-54. · 7.40 Impact Factor
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ABSTRACT: A series of enolic Schiff base aluminum(III) complexes LAlR (where L=NNOO-tetradentate enolic Schiff base ligand) containing ligands that differ in their steric and electronic properties were synthesized. Their single crystals showed that these complexes are five-coordinated around the aluminum center. Their coordination geometries are between square pyramidal and trigonal bipyramidal. Their catalytic properties in the solution polymerization of racemic lactide (rac-LA) were examined. The modifications in the auxiliary ligand exhibited a dramatic influence on the catalytic performance. Lengthening the backbone from C(2) alkylene to C(3) alkylene resulted in remarkable enhancement of both the stereoselectivity and the polymerization rate because of the increasing flexibility of the diimine backbone. Electron-withdrawing substituents in the diketone also highly improved the activity and the stereoselectivity. Among these complexes, 4 b had the highest activity and the stereoselectivity owing to the C(3) alkylene backbone and the two gem-methyl groups on the middle carbon atom. The value of the polymerization rate constant (k(p)) catalyzed by 4 b in 70 degrees C was 1.90 L mol(-1) min(-1), the activation energy of the polymerization (35.4 kJ mol(-1)) was calculated according to the Arrhenius equation. Other factors that influenced the polymerization, such as the polymerization time, the temperature, and the monomer concentration, are also discussed in detail.
Chemistry 02/2008; 14(10):3126-36. · 5.93 Impact Factor
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Journal of Polymer Science Part A Polymer Chemistry 12/2007; 46(2):643 - 649. · 3.92 Impact Factor
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Journal of Polymer Science Part A Polymer Chemistry 09/2007; 45(22):5050 - 5056. · 3.92 Impact Factor
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Journal of Polymer Science Part A Polymer Chemistry 10/2005; 43(24):6605 - 6612. · 3.92 Impact Factor
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ABSTRACT: A single-site ethyl aluminum complex, [2,2- diethyl-1,3-propylenebis(3,5-di-tert-butyl-salicylideneiminato)] ethyl aluminum (2), with a geminal diethyl substitutent on the diamino bridge was synthesized by the reaction of AlEt3 with 1 equiv of N,N′-(2,2-diethyl-1,3-propylene)bis(3,5-di-tert-butylsalicylideneimine). X-ray diffraction showed that complex 2 contained a five-coordinate aluminum atom with a distorted trigonal bipyramidal geometry in the solid state. 1H-NMR and 13C-NMR spectra indicated that the two conformational enantiomers of 2 tautomerized quickly on the NMR timescale in solution. In the presence of isopropyl alcohol, the ring-opening polymerization (ROP) of rac-lactide with complex 2 produced a crystalline stereoblock polylactide (PLA). The stereoblocks contained an average of 12 units (L̄ = 12) of enantiomerically pure lactic acid. There was a linear relationship between the monomer conversion and number-average molecular weights of the polymer. An induction period was observed for the polymerization. The induction period increased with decreasing concentration of catalyst 2 and isopropyl alcohol. In the presence of poly(ethylene glycol) (PEG), a PLA/PEG/PLA stereocomplex was prepared directly by the ROP of rac-lactide with complex 2, which was confirmed by NMR, gel permeation chromatography, wide-angle X-ray diffraction, and differential scanning calorimetry. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 102–108, 2005
Journal of Applied Polymer Science 07/2005; 98(1):102 - 108. · 1.29 Impact Factor
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Journal of Polymer Science Part A Polymer Chemistry 10/2004; 42(23):5974 - 5982. · 3.92 Impact Factor
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ABSTRACT: A series of aluminum ethyls and isopropoxides based upon N,N,O,O-tetradentate Schiff base ligand framework have been prepared. X-ray diffraction analysis and 1 H NMR confirmed that these Schiff base aluminum ethyls and isopropoxides were all monomeric species with a five-coordinated central aluminum in their solid structures. Compared to the aluminum ethyls which all retain their monomeric structure in the solution, the dinucleating phenomenons of aluminum isopropoxides with less steric hindered substituents in the solution have also been observed. The activities and stereoselectivities of these complexes toward the ring-opening polymerization of rac-lactide have been investigated. Polymerization experiments indicated that (SB-2d)AlO i Pr [(SB-2d)) 2,2-dimethyl-1,3-propylenebis(3,5-di-tert-butylsalicylideneiminato)] exhibited the highest stereoselectivity and (SB-3b)AlO i Pr [(SB-3b)) 2,2-dimethyl-1,3-propylenebis(3,5-dichlorinesalicylideneiminato)] possessed the highest activity among these aluminum isopropoxides. The substituents and the mode of the bridging part between the two nitrogen atoms both exerted significant influences upon the progress of the polymerizations, influencing either the tacticity of isolated polymers or the rate of polymerization. The polymerization kinetics using (SB-3b)AlO i Pr as a catalyst were studied in details, and the experimental results revealed that the rate of polymerization was first-order in [LA] and 1.81th-order with respect to (SB-3b)AlO i Pr, which indicated that the propagating species was not uniform in the system without the protection of steric hindered substituents. Furthermore, the polymerization by initiating with (SB-3b)AlO i Pr could be progressed at low temperatures (0 °C) without the change of stereoselectivity.
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Journal of Organometallic Chemistry 692(25):5605-5613. · 2.38 Impact Factor
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ABSTRACT: Flower- or cake-shaped particles with uniform particle size ranging from nanometers to micrometers were prepared from the stereo multiblock copoly(rac-lactide)s (smb-PLAs) by precipitating the polymer from its solution in methylene chloride/ethanol via three different methods: slowly lowering the solution temperature, slowly evaporating the solvent, and slowly adding a nonsolvent. Under the same condition, sheet-shaped crystals in 10 mum size but not particles were obtained from the pure PLLA with almost the same molecular weight. Electron diffraction and WAXD data demonstrated that the stereocomplex particles belonged to the monoclinic system. All three methods resulted in particles with identical morphology and almost the same particle size. At a given stereoregularity of 88%, as the molecular weight of the polymer increased from 8700 to 23,200 Da, the crystallinity decreased, the particle morphology changed from flower-shaped to cake-shaped, and the diameter and height of the particles increased from 0.8 and 0.45 to 3.6 microm and 2.0 microm, respectively. The initial concentration of the polymer solution influenced the particle size slightly but affected the morphology markedly. On the basis of the above experimental observations, it was proposed that the smb-PLA particles of flower- or cake-shape were formed in four steps: (1) complexation in solution of the smb-PLA chains; (2) particle nucleation; (3) particle growth in the width direction; and (4) particle growth in the height direction. The curvature of the paired smb-PLA chains and the inner stress governed the particle size, and the interconnection between the neighboring particles determined the layered structure and the package density of the particles formed.
Biomacromolecules 6(5):2843-50. · 5.48 Impact Factor
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ABSTRACT: A monoethylaluminum Schiff base complex (2) with formula LAlEt (L = N,N'-(2,2-dimethylpropylene)bis(3,5-di-tert-butylsalicylideneimine) was synthesized and employed for the stereoselective ring-opening polymerization of rac-lactide (rac-LA). The complex 2 was characterized by nuclear magnetic resonance, crystal structure, and elemental analysis. It contains a five-coordinate aluminum atom with distorted trigonal bipyramidal geometry in the solid state. In the presence of 2-propanol, 2 showed high stereoselectivity for the polymerization of rac-LA. The polymerization yielded crystalline poly(rac-LA) with a high melting temperature (193-201 degrees C). NMR, differential scanning calorimetry, and wide-angle X-ray diffraction indicated that the poly(rac-LA) was highly isotactic, and a stereocomplex was formed between poly-l- and poly-d-lactide block sequences. By the analysis of electrospray-ionization mass spectrometry and (1)H NMR, the polymer was demonstrated to be endcapped in both terminals with an isopropyl ester and a hydroxy group, respectively. The polymerization was of first order in rac-LA concentration. The relationship between the rac-LA conversion and molecular weights of the polymer was linear so that the polymerization could be well controlled.
Biomacromolecules 5(3):965-70. · 5.48 Impact Factor
