Home About us Contact
|
Home About us Contact | ||
|
|
||
Lactide
Terms modified by Lactide Selected AbstractsDiscrete, Base-Free, Cationic Alkaline-Earth Complexes , Access and Catalytic Activity in the Polymerization of LactideEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2010Yann Sarazin Abstract Well-defined, base free cations of zinc and the alkaline-earth metals (Mg, Ca, Sr, Ba) supported by a multidentate phenolate ligand and stabilized by perfluorinated weakly coordinating counterions are readily available by simple procedures; the solid-state structures of the magnesium and calcium derivatives were elucidated. Upon treatment with an excess of iPrOH, these complexes generate highly efficient binary catalytic systems for the immortal ring-opening polymerization of L -lactide, yielding poly(L -lactide)s with controlled architectures and molecular features. [source] A Family of 1,1,3,3-Tetraalkylguanidine (H-TAG) Solvated Zinc Aryloxide Precatalysts for the Ring-Opening Polymerization of rac -LactideEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2010Julia J. Ng Abstract Reaction of [Zn(,-TAG){N(SiMe3)2}]2 {TAG = N=C[N(CH2CH3)2N(CH3)2] (DEDMG), N=C{[NCH2CH2CH2CdH2(N,Cd)]N(CH2CH3)2} (DEPYRG) and N=C{[NCH2CH2CH2CH2CeH2(N,Ce)]N(CH2CH3)2} (DEPIPG)} with 2 equiv. of ethanol (EtOH) and 2 equiv. of HOAr {OAr = OC6H3(CMe3)-2-(CH3)-6 (BMP) or OC6H2[C(CH3)3]2 -2,6-(CH3)-4 (4MeDBP)} results in dizinc alkoxides with the general formula [Zn(,-OEt)(OAr)(H-TAG)]2 (1,3). Et2Zn was additionally treated with 2 equiv. of 1,1,3,3-tetramethylguanidine (H-TMG) and H-BMP or HOC6H3(C6H5)2 -2,6 to yield [Zn(BMP)2(H-TMG)2] (4) and [Zn{OC6H3(C6H5)2 -2,6}2(H-TMG)2] (5). Complexes 1, 2, 4, and 5 were characterized by single-crystal X-ray diffraction. Polymerization of rac -lactide with 1,5 and [Zn(,-OMe)(4MeDBP)(H-TMG)]2 (6) were found to generate polylactide (PLA). The bulk powders for all complexes were found to be in agreement with the crystal structures based on elemental analyses, FTIR spectroscopy, and 1H and 13C NMR spectroscopic studies. [source] First Example of a Gold(I) N -Heterocyclic-Carbene-Based Initiator for the Bulk Ring-Opening Polymerization of L -LactideEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2006Lipika Ray Abstract Synthesis, structure, and catalysis studies of two Au- and Ag-based initiators, namely, [3-(N - tert -butylacetamido)-1-(2-hydroxycyclohexyl)imidazol-2-ylidene]AuCl (1c) and [3-(N - tert -butylacetamido)-1-(2-hydroxycyclohexyl)imidazol-2-ylidene]AgCl (1b), for the bulk ring-opening polymerization of L -lactide are reported. Specifically, gold complex 1c was obtained from silver complex 1b by the transmetalation reaction with (SMe2)AuCl. Silver complex 1b was synthesized by the treatment of 3-(N - tert -butylacetamido)-1-(2-hydroxycyclohexyl)imidazolium chloride (1a) with Ag2O. Compound 1a was synthesized directly from the reaction of N - tert -butyl-2-chloroacetamide, cyclohexene oxide, and imidazole. The molecular structures of 1a, 1b, and 1c have been determined by X-ray diffraction studies. The formation of neutral monomeric complexes with linear geometries at the metal centers was observed for both 1b and 1c. The Au and Ag complexes 1c and 1b successfully catalyzed the bulk ring-opening polymerization of L -lactide at elevated temperatures under solvent-free melt conditions to produce moderate to low molecular weight polylactide polymers with narrow molecular weight distributions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] In Vitro Characteristics of Surface-Modified Biphasic Calcium Phosphate/Poly(L -Lactide) BiocompositeADVANCED ENGINEERING MATERIALS, Issue 4 2010Weizhong Yang Abstract Surface-modified biphasic calcium phosphate (BCP)/poly(L -lactide) (PLLA) biocomposite is shown to have improved microstructure and mechanical properties compared to the unmodified system. In vitro biodegradation and bioactivity of the composite are investigated in simulate body fluid for up to four weeks. Weight changes of the samples and the pH changes of the SBF are recorded. Surface properties of the composite after immersion are characterized by XRD, SEM and EDX analyses. Cyto-compatibility was determined by MTT assay with L929 mouse fibroblasts. The difference of the degradation behavior between modified BCP/PLLA and the reference unmodified composite are investigated, and mBCP/PLLA composite is proved to be a better as a scaffold material. The surface formed bio-apatite layer after immersion shows the excellent bioactivity of the mBCP/PLLA composite. L929 cells show a high growth rate and proliferation, demonstrating the good cytocompatibility of mBCP/PLLA composite. [source] Photocurable Shape-Memory Copolymers of , -Caprolactone and L -LactideMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2010Minoru Nagata Abstract Biodegradable and photocurable block copolymers of , -caprolactone and L -lactide were synthesized by polycondensation of PLLA diol (,=,10,000,g,·,mol,1), PCL diol (,=,10,000,g,·,mol,1), and a chain extender bearing a coumarin group. The effect of copolymer composition on the thermal and mechanical properties of the photocured copolymers was studied by means of DSC and cyclic tensile tests. An increase in Young's modulus and a decrease in the tensile strain with increasing PLLA content was observed for the block copolymers. Block copolymers with high PCL content showed good to excellent shape-memory properties. Random copolymers exhibited Rf and Rr values above 90% at 45,°C for an extremely large tensile strain of 1,000%. [source] Synthesis of PLLA-MPEG Diblock Copolymers by Microwave-Assisted Copolymerization of L -Lactide and Methoxy Poly(ethylene glycol)MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 10 2007Chao Zhang Abstract PLLA-MPEG diblock copolymers with a controlled number-average molar mass ranging from 7,330 to 117,610 g,·,mol,1 and an L -lactide conversion ranging from 65.1 to 97.3% were synthesized effectively in 20 min at 100,°C by MPEG-initiated ROP of L -lactide under microwave irradiation. Prolonged microwave irradiation time led to the degradation of the copolymers because the ROP reaction and the thermal degradation reaction occurred simultaneously at the later stage of the reaction process. The differential scanning calorimetric and thermogravimetric study indicated that higher melting temperatures and thermal stability were obtained for PLLA-MPEG diblock copolymers with longer PLLA segments. [source] One-Pot Synthesis of Lactide,Styrene Diblock Copolymers via Catalytic Immortal Ring-Opening Polymerization of Lactide and Nitroxide-Mediated Polymerization of StyreneCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 5 2010Valentin Poirier Abstract An efficient, practical, and industrially relevant procedure for the production of polymer materials, in which a part of the oil-derived polyolefins has been replaced by a renewable, biodegradable, and biocompatible poly(lactide) block, is presented. Binary catalytic systems combining innocuous metals (yttrium, zinc, magnesium, or calcium) and bifunctional alcohols (acting as transfer agents) were developed to promote the immortal ring-opening polymerization of lactide directly in styrene. Up to 20,000,equivalents of lactide were polymerized (metal catalyst loading of 50,100,ppm) in a controlled fashion in the presence of 10,100,equivalents of a double-headed transfer agent to give as many end-functionalized poly(lactide) macromolecules that can be used eventually as macroinitiators for the controlled nitroxide-mediated polymerization of styrene. The specific use of the sterically shielded complex [BDI- iPr]Zn-N(SiMe3)2 ([BDI- iPr]=bis(diketiminate) ligand) allowed the efficient, catalytic, and controlled production of poly(lactide)- block -poly(styrene) materials in a one-pot, solvent-free sequential procedure, with nearly 100,% atom-efficiency. [source] Discrete, Base-Free, Cationic Alkaline-Earth Complexes , Access and Catalytic Activity in the Polymerization of LactideEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2010Yann Sarazin Abstract Well-defined, base free cations of zinc and the alkaline-earth metals (Mg, Ca, Sr, Ba) supported by a multidentate phenolate ligand and stabilized by perfluorinated weakly coordinating counterions are readily available by simple procedures; the solid-state structures of the magnesium and calcium derivatives were elucidated. Upon treatment with an excess of iPrOH, these complexes generate highly efficient binary catalytic systems for the immortal ring-opening polymerization of L -lactide, yielding poly(L -lactide)s with controlled architectures and molecular features. [source] A Family of 1,1,3,3-Tetraalkylguanidine (H-TAG) Solvated Zinc Aryloxide Precatalysts for the Ring-Opening Polymerization of rac -LactideEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2010Julia J. Ng Abstract Reaction of [Zn(,-TAG){N(SiMe3)2}]2 {TAG = N=C[N(CH2CH3)2N(CH3)2] (DEDMG), N=C{[NCH2CH2CH2CdH2(N,Cd)]N(CH2CH3)2} (DEPYRG) and N=C{[NCH2CH2CH2CH2CeH2(N,Ce)]N(CH2CH3)2} (DEPIPG)} with 2 equiv. of ethanol (EtOH) and 2 equiv. of HOAr {OAr = OC6H3(CMe3)-2-(CH3)-6 (BMP) or OC6H2[C(CH3)3]2 -2,6-(CH3)-4 (4MeDBP)} results in dizinc alkoxides with the general formula [Zn(,-OEt)(OAr)(H-TAG)]2 (1,3). Et2Zn was additionally treated with 2 equiv. of 1,1,3,3-tetramethylguanidine (H-TMG) and H-BMP or HOC6H3(C6H5)2 -2,6 to yield [Zn(BMP)2(H-TMG)2] (4) and [Zn{OC6H3(C6H5)2 -2,6}2(H-TMG)2] (5). Complexes 1, 2, 4, and 5 were characterized by single-crystal X-ray diffraction. Polymerization of rac -lactide with 1,5 and [Zn(,-OMe)(4MeDBP)(H-TMG)]2 (6) were found to generate polylactide (PLA). The bulk powders for all complexes were found to be in agreement with the crystal structures based on elemental analyses, FTIR spectroscopy, and 1H and 13C NMR spectroscopic studies. [source] [Bis(guanidine)]zinc Complexes and Their Application in Lactide PolymerisationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 36 2007Janna Börner Abstract The bis(guanidine)-stabilised zinc complexes [N1,N2 -bis(1,3-dimethylimidazolidin-2-ylidene)ethane-1,2-diamine]dichloridozinc(II), [Zn(DMEG2e)Cl2] (C1), diacetato[N1,N2 -bis(1,3-dimethylimidazolidin-2-ylidene)ethane-1,2-diamine]zinc(II),[Zn(DMEG2e)(CH3COO)2] (C2), and bis[N1,N2 -bis(1,3-dimethylimidazolidin-2-ylidene)ethane-1,2-diamine]zinc(II) bis(trifluoromethanesulfonate), [Zn(DMEG2e)2](CF3SO3)2 (C3), have been synthesised and completely characterised by means of X-ray structure analysis, NMR spectroscopy and mass spectrometry. These [bis(guanidine)]zinc complexes were investigated regarding their activity in the bulk polymerisation of D,L -lactide. It could be shown that these compounds are able to act as initiators for lactide polymerisation, and polylactides with molecular weights (Mw) of around 18000,59000 g/mol could be obtained. Variation of the reaction temperature revealed that the molecular weights decrease with increasing temperature. Additionally, the correlation of the intrinsic viscosity with the molecular weight demonstrates that the obtained polymers are linear and structurally homogeneous.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] First Example of a Gold(I) N -Heterocyclic-Carbene-Based Initiator for the Bulk Ring-Opening Polymerization of L -LactideEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2006Lipika Ray Abstract Synthesis, structure, and catalysis studies of two Au- and Ag-based initiators, namely, [3-(N - tert -butylacetamido)-1-(2-hydroxycyclohexyl)imidazol-2-ylidene]AuCl (1c) and [3-(N - tert -butylacetamido)-1-(2-hydroxycyclohexyl)imidazol-2-ylidene]AgCl (1b), for the bulk ring-opening polymerization of L -lactide are reported. Specifically, gold complex 1c was obtained from silver complex 1b by the transmetalation reaction with (SMe2)AuCl. Silver complex 1b was synthesized by the treatment of 3-(N - tert -butylacetamido)-1-(2-hydroxycyclohexyl)imidazolium chloride (1a) with Ag2O. Compound 1a was synthesized directly from the reaction of N - tert -butyl-2-chloroacetamide, cyclohexene oxide, and imidazole. The molecular structures of 1a, 1b, and 1c have been determined by X-ray diffraction studies. The formation of neutral monomeric complexes with linear geometries at the metal centers was observed for both 1b and 1c. The Au and Ag complexes 1c and 1b successfully catalyzed the bulk ring-opening polymerization of L -lactide at elevated temperatures under solvent-free melt conditions to produce moderate to low molecular weight polylactide polymers with narrow molecular weight distributions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Functionalized Poly(D,L -lactide) for Pulmonary Epithelial Cell CultureADVANCED ENGINEERING MATERIALS, Issue 4 2010Yuan-Min Lin Functional groups on a material surface affect the response of many cell types. As part of our strategy aimed at engineering lung tissue, we introduced functional groups into the surface of Poly(D,L -lactide) (PDLLA) films to improve its suitability for the culture of mature pulmonary epithelial cells (A549 line) using two different methods. The first method, aminolysis, can introduce primary amines into PDLLA films by transesterification using 1,15% of ethylenediamine in isopropanol. The second method, a branching modification, can generate amine-terminated or carboxylic acid-terminated tree-like branched architectures. All modified PDLLA surfaces exhibited lower water contact angles, i.e. are more hydrophilic than unmodified PDLLA. PDLLA treated with 15% ethylenediamine exhibited a rougher surface than the control, and PDLLA with branching modification had a droplet-like surface topography as visualized by atomic force microscopy (AFM). PDLLA treated with 15% ethylenediamine and branching modification with two and three generations enhanced the attachment of pulmonary epithelial cells measured using Hoechst dye. Immunostaining demonsatrated that amine-terminated branched architectures allowed for better focal adhesion point formation than the control 24,h after cell seeding. Furthermore, they also induced higher A549 cell populations and levels of activity after 4 days in culture measured using Hoechst dye and WST1 cell proliferation reagents, respectively. In contrast, carboxylic acid-terminated branching architectures were found to reduce the cell population size after 4 days. It was concluded that the concentration, type and distribution of surface functional groups can affect significantly the behavior of pulmonary epithelial cells growing on a PDLLA surface, and PDLLA film modified with two or three generations of amine-terminated branched architectures is a suitable 2D scaffold for the culture of of pulmonary epithelial cells. [source] In Vitro Characteristics of Surface-Modified Biphasic Calcium Phosphate/Poly(L -Lactide) BiocompositeADVANCED ENGINEERING MATERIALS, Issue 4 2010Weizhong Yang Abstract Surface-modified biphasic calcium phosphate (BCP)/poly(L -lactide) (PLLA) biocomposite is shown to have improved microstructure and mechanical properties compared to the unmodified system. In vitro biodegradation and bioactivity of the composite are investigated in simulate body fluid for up to four weeks. Weight changes of the samples and the pH changes of the SBF are recorded. Surface properties of the composite after immersion are characterized by XRD, SEM and EDX analyses. Cyto-compatibility was determined by MTT assay with L929 mouse fibroblasts. The difference of the degradation behavior between modified BCP/PLLA and the reference unmodified composite are investigated, and mBCP/PLLA composite is proved to be a better as a scaffold material. The surface formed bio-apatite layer after immersion shows the excellent bioactivity of the mBCP/PLLA composite. L929 cells show a high growth rate and proliferation, demonstrating the good cytocompatibility of mBCP/PLLA composite. [source] Matrix Assisted Pulsed Laser Evaporation (MAPLE) of Poly(D,L lactide) (PDLLA) on Three Dimensional Bioglass® StructuresADVANCED ENGINEERING MATERIALS, Issue 8 2009Valeria Califano Matrix assisted pulsed laser evaporation (MAPLE) was used to coat Bioglass-based tissue engineering scaffolds with poly(D,L lactide). The polymer penetrated to some extent from the surface producing a graded porous composite material. This structure can be beneficial for application in osteochondral tissue engineering, where composite scaffolds are required exhibiting two distinct regions, one for cartilage integration (biopolymer) and the other one for bone contact (bioactive glass). [source] Nanofibrous Patches for Spinal Cord RegenerationADVANCED FUNCTIONAL MATERIALS, Issue 9 2010Yiqian Zhu Abstract The difficulty in spinal cord regeneration is related to the inhibitory factors for axon growth and the lack of appropriate axon guidance in the lesion region. Here scaffolds are developed with aligned nanofibers for nerve guidance and drug delivery in the spinal cord. Blended polymers including poly(L -lactic acid) (PLLA) and poly(lactide- co -glycolide) (PLGA) are used to electrospin nanofibrous scaffolds with a two-layer structure: aligned nanofibers in the inner layer and random nanofibers in the outer layer. Rolipram, a small molecule that can enhance cAMP (cyclic adenosine monophosphate) activity in neurons and suppress inflammatory responses, is immobilized onto nanofibers. To test the therapeutic effects of nanofibrous scaffolds, the nanofibrous scaffolds loaded with rolipram are used to bridge the hemisection lesion in 8-week old athymic rats. The scaffolds with rolipram increase axon growth through the scaffolds and in the lesion, promote angiogenesis through the scaffold, and decrease the population of astrocytes and chondroitin sulfate proteoglycans in the lesion. Locomotor scale rating analysis shows that the scaffolds with rolipram significantly improved hindlimb function after 3 weeks. This study demonstrates that nanofibrous scaffolds offer a valuable platform for drug delivery for spinal cord regeneration. [source] Cell Imaging: (Generic Strategy of Preparing Fluorescent Conjugated-Polymer-Loaded Poly(DL -lactide- co -Glycolide) Nanoparticles for Targeted Cell Imaging) Adv.ADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Funct. A generic strategy for the fabrication of highly fluorescent poly(DL -lactide- co -glycolide) nanoparticles loaded with conjugated polymers is reported by B. Liu et al. This method may serve to produce a new generation of biocompatible, surface-functionalizable probes for targeted cancer cell imaging and diagnostics, as described on page 3535. [source] Generic Strategy of Preparing Fluorescent Conjugated-Polymer-Loaded Poly(DL -lactide- co -Glycolide) Nanoparticles for Targeted Cell ImagingADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Kai Li Abstract A general strategy for the preparation of highly fluorescent poly(DL-lactide- co -glycolide) (PLGA) nanoparticles (NPs) loaded with conjugated polymers (CPs) is reported. The process involves encapsulation of organic-soluble CPs with PLGA using a modified solvent extraction/evaporation technique. The obtained NPs are stable in aqueous media with biocompatible and functionalizable surfaces. In addition, fluorescent properties of the CP-loaded PLGA NPs (CPL NPs) could be fine-tuned by loading different types of CPs into the PLGA matrix. Four types of CPL NPs are prepared with a volume-average hydrodynamic diameter ranging from 243 to 272,nm. The application of CPL NPs for bio-imaging is demonstrated through incubation with MCF-7 breast cancer cells. Confocal laser scanning microscopy studies reveal that the CPL NPs are internalized in cytoplasm around the nuclei with intense fluorescence. After conjugation with folic acid, cellular uptake of the surface-functionalized CPL NPs is greatly enhanced via receptor-mediated endocytosis by MCF-7 breast cancer cells, as compared to that for NIH/3T3 fibroblast cells, which indicates a selective targeting effect of the folate-functionalized CPL NPs in cellular imaging. The merits of CPL NPs, such as low cytotoxicity, high fluorescence, good photostability, and feasible surface functionalization, will inspire extensive study of CPL NPs as a new generation of probes for specific biological imaging and detection. [source] Conductive Core,Sheath Nanofibers and Their Potential Application in Neural Tissue EngineeringADVANCED FUNCTIONAL MATERIALS, Issue 14 2009Jingwei Xie Abstract Conductive core,sheath nanofibers are prepared by a combination of electrospinning and aqueous polymerization. Specifically, nanofibers electrospun from poly(, -caprolactone) (PCL) and poly(L -lactide) (PLA) are employed as templates to generate uniform sheaths of polypyrrole (PPy) by in-situ polymerization. These conductive core,sheath nanofibers offer a unique system to study the synergistic effect of different cues on neurite outgrowth in vitro. It is found that explanted dorsal root ganglia (DRG) adhere well to the conductive core,sheath nanofibers and generate neurites across the surface when there is a nerve growth factor in the medium. Furthermore, the neurites can be oriented along one direction and enhanced by 82% in terms of maximum length when uniaxially aligned conductive core,sheath nanofibers are compared with their random counterparts. Electrical stimulation, when applied through the mats of conductive core,sheath nanofibers, is found to further increase the maximum length of neurites for random and aligned samples by 83% and 47%, respectively, relative to the controls without electrical stimulation. Together these results suggest the potential use of the conductive core,sheath nanofibers as scaffolds in applications such as neural tissue engineering. [source] The Implications of Polymer Selection in Regenerative Medicine: A Comparison of Amorphous and Semi-Crystalline Polymer for Tissue RegenerationADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Michelle D. Kofron Abstract Biodegradable polymeric scaffolds are being investigated as scaffolding materials for use in regenerative medicine. While the in vivo evaluation of various three-dimensional (3D), porous, biodegradable polymeric scaffolds has been reported, most studies are ,3 months in duration, which is typically prior to bulk polymer degradation, a critical event that may initiate an inflammatory response and inhibit tissue formation. Here, a 6,month in vitro degradation and corresponding in vivo studies that characterized scaffold changes during complete degradation of an amorphous, 3D poly(lactide- co -glycolide)(3D-PLAGA) scaffold and near-complete degradation of a semi-crystalline3D-PLAGA scaffold are reported. Using sintered microsphere matrix technology, constructs were fabricated in a tubular shape, with the longitudinal axis void and a median pore size that mimicked the architecture of native bone. Long-term quantitative measurements of molecular weight, mechanical properties, and porosity provided a basis for theorization of the scaffold degradation process. Following implantation in a critical size ulnar defect model, histological analysis and quantitative microCT indicated early solubilization of the semi-crystalline polymer created an acidic microenvironment that inhibited mineralized tissue formation. Thus, the use of amorphous over semi-crystalline PLAGA materials is advocated for applications in regenerative medicine. [source] A Spring-Like Behavior of Chiral Block Copolymer with Helical Nanostructure Driven by CrystallizationADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Yeo-Wan Chiang Abstract The crystallization of helical nanostructure resulting from the self-assembly of a chiral diblock copolymer, poly(styrene)- b -poly(L -lactide) (PS-PLLA), is studied. Various crystalline PS-PLLA nanostructures are obtained by controlling the crystallization temperature of PLLA (Tc,PLLA), at which crystalline helices and crystalline cylinders occur while Tc,PLLA,<,Tg,PS (the glass transition temperature of PS) and Tc,PLLA,,,Tg,PS, respectively. As evidenced by selected-area electron diffraction and two-dimensional X-ray diffraction results, the PLLA crystallites under confinement reveal a unique anisotropic character regardless of the crystallization temperature. On the basis of observed uniaxial scattering results the PLLA crystallites grown within the microdomains are identified as crystals with preferential growth directions either along the [100] or along the [110]-axes of the PLLA crystalline unit cell, at which the molecular chains and the growth direction are normal and parallel to the central axes of helices, respectively. The formation of this exclusive crystalline growth is attributed to the spatial confinement effect for crystallization. While Tc,PLLA,<,Tg,PS, owing to the directed crystallization by helical confinement, the preferential crystalline growth leads to the crystallization following a helical track with growth direction parallel to the central axes of helices through a twisting mechanism. Consequently, winding crystals with specific crystallographic orientation within the helical microdomains can be found. By contrast, while Tc,PLLA,,,Tg,PS, the preferential growth may modulate the curvature of microdomains by shifting the molecular chains to access the fast path for crystalline growth due to the increase in chain mobility. As a result, a spring-like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation of helices, resulting in crystalline cylinders that might be applicable to the design of switchable large-strain actuators. [source] Temperature-Induced Hydrogels Through Self-Assembly of Cholesterol-Substituted Star PEG- b -PLLA Copolymers: An Injectable Scaffold for Tissue Engineering,ADVANCED FUNCTIONAL MATERIALS, Issue 8 2008Koji Nagahama Abstract Partially cholesterol-substituted 8-arm poly(ethylene glycol)- block -poly(L -lactide) (8-arm PEG- b -PLLA-cholesterol) has been prepared as a novel star-shaped, biodegradable copolymer derivative. The amphiphilic 8-arm PEG- b -PLLA-cholesterol aqueous solution (polymer concentration, above 3,wt%) exhibits instantaneous temperature-induced gelation at 34,°C, but the virgin 8-arm PEG- b -PLLA does not, irrespective of concentration. Moreover, an extracellular matrix (ECM)-like micrometer-scale network structure has been created with favorable porosity for three-dimensional proliferation of cells inside the hydrogel. This network structure is mainly attributed to specific self-assembly between cholesterol groups. The 10 and 20,wt% hydrogels are eroded gradually in phosphate buffered saline at 37,°C over the course of a month, and after that the gel becomes completely dissociated. Moreover, L929 cells encapsulated into the hydrogel are viable and proliferate three-dimensionally inside the hydrogels. Thus, in-vitro cell culture studies demonstrate that 8-arm PEG- b -PLLA-cholesterol is a promising candidate as a novel injectable cellular scaffold. [source] Non-invasive Transdermal Delivery Route Using Electrostatically Interactive Biocompatible NanocapsulesADVANCED MATERIALS, Issue 6 2010Jinseob Shin A robust means of fabricating skin-penetrating and compatible nanocarriers comprising poly(D, L -lactide- co -glycolide) is reported. The resultant nanocapsules have the ability to load biologically active ingredients and selectively release them through the epidermis lipid layer. Their release of genistein (left figure) is determined to be diffusion-controlled, and they are shown to successfully deliver molecules, such as nile red (right figure), into biopsied skin samples. [source] Effects of ethyl benzoate on performance, morphology, and erosion of PLGA implants formed in situADVANCES IN POLYMER TECHNOLOGY, Issue 1 2008R. Astaneh Abstract An in situ forming implant (ISFI) is a novel drug delivery system used for protein and peptide delivery, especially for cancer treatment. An ISFI based on 33% (w/w) poly(D,L -lactide- co -glycolide)(PLGA; 50:50)/3% (w/w) leuprolide acetate (LA)/64% (w/w) N -methyl-2-pyrrolidone (NMP) was prepared for this study. After injection of the final formulation, which is a viscous liquid to an aqueous medium, it deforms to become a semisolid or solid matrix. The performance of this matrix was investigated on the basis of peptide release from it. Erosion and morphology of ISFI were also studied. The effects of adding 12.8% (w/w) ethyl benzoate (EB) as a rate-modifying agent on performance, erosion, and morphology of ISFI were assessed. The implant containing EB showed very low burst release (5.53% ± 0.82%) and the morphology turns to closed pore-like structures. After adding EB, the morphology turns to closed pore-like structures. This type of morphology has very close relation to the performance of the implant as well. Finally, the effect of EB on performance, erosion, and morphology is explained by means of solvent,nonsolvent affinity, water permeation, and the rate of phase inversion. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 27:17,26, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20114 [source] Application of the biodegradable diblock copolymer poly(L -lactide)- block -poly(L -cysteine): Drug delivery and protein conjugationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010Jing Sun Abstract A novel approach to self-assembled and shell-crosslinked (SCL) micelles from the diblock copolymer poly(L -lactide)- block -poly(L -cysteine) to be used as drug and protein delivery carriers is described. Rifampicin was used as a model drug. The drug-loaded SCL micelles were obtained by self-assembly of the copolymer in the presence of the drug in aqueous media. Their morphology and size were studied with dynamic light scattering and field emission scanning electron microscopy. The rifampicin loading capacity and encapsulation efficiency were studied with ultraviolet,visible spectrophotometry. The drug-release rate in vitro depended on the oxidizing and reducing environment. Moreover, a straightforward approach to the conjugation of the copolymer with bovine serum albumin (BSA) was developed, and a gel electrophoresis test demonstrated that this conjugated BSA could be reversibly released from the copolymer substrate under reducing conditions. In conclusion, this L -cysteine copolymer can be used in drug delivery and in protein fixation and recovery. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Compatibilization method applied to the chitosan-acid poly(L -lactide) solutionJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Nugraha Edhi Suyatma Abstract We are testing the compatibilization of the chitosan/PLA blends by addition of diisocyanate and at studying the effect of several MDI concentrations (0.5 and 2.5% of the global blend mass, w/w). To evaluate the MDI efficiency as a compatibilizer of chitosan/PLA blends, we worked with the following methods: IRTF spectra with higher peak at 1558 cm,1 is due to the NH bonds that exist in urea and urethane, thermal properties shows that the temperature of the endothermic peaks of the chitosan/PLA blends with MDI is very close to the temperature of pure chitosane and SEM micrography shows that MDI addition decreases the PLA particles size in the chitosan mixture; they also comply with the compatibilization theory. After that the mechanical properties have been characterized: we can notice that the MDI compatibilized chitosan/PLA blends have a higher Young's modulus than the noncompatibilized blends. we are showed that the use of 0.5% MDI is not enough sufficient to obtain a compatibilization, because a part of the MDI can be consumed by water. The addition of MDI increases the performance of the mechanical properties of the blends. Therefore, with this compatibilization, we could obtain some chitosan/PLA blends that would be water-resistant and that would also keep their mechanical properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Effect of process parameters on properties of wet-spun poly(L,D -lactide) copolymer multifilament fibersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2009Marja Rissanen Abstract Poly(L,D -lactide) [P(L,D)LA], LL/D ratio 96/4, and poly(L,DL -lactide) [P(L,DL)LA], L/DL ratio 70/30, multifilament fibers were prepared by wet-spinning and the effects of the spin draw ratio and the coagulant on the morphological, thermal, and mechanical properties of the filaments were studied. The hydrolytic degradation of filaments was studied in vitro. The filament diameter and the mechanical properties of filaments were highly dependent on the spin draw ratio, whereas the coagulant had no or minor effect. The filament diameters were in the range of 11,36 ,m and the maximum tenacity of 150 MPa was obtained at the spin draw ratio of 7.0 for both copolymers. The copolymer had the main importance on the crystallinity of filaments, but it was also affected by the duration of the coagulation process. The crystallinities of P(L,D)LA 96/4 filaments were in the range of 5,16%, whereas P(L,DL)LA 70/30 filaments were totally amorphous. The degree of crystallinity had effect on the hydrolytic degradation of filaments. The tenacity loss of P(L,D)LA 96/4 filaments was about 10% and that of P(L,DL)LA 70/30 filaments was as high as 50% after 24 weeks in vitro. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Solubility and phase separation of poly(L,D -lactide) copolymersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008Marja Rissanen Abstract In this study, the solubility and precipitation properties of medical-grade stereocopolymers were investigated. The solubility of the polymers was tested with eight different organic solvents and four nonsolvents. The solubility of poly(L,D -lactide) stereocopolymers was highly dependent on the L/D ratio of the copolymer. The phase-separation ability was tested by cloud-point titration with a solvent and a nonsolvent. The solvent was in all cases dichloromethane, and the nonsolvents were n -hexane, methanol, ethanol, and isopropyl alcohol. The results showed that n -hexane was the most efficient nonsolvent. Methanol and ethanol showed quite similar precipitation properties. Isopropyl alcohol was the least efficient nonsolvent of those studied. Also, the L/D ratio of the copolymer had an effect on the precipitation properties. The precipitation happened most easily when the L content was high. The molecular weight of the copolymer had only a slight effect on the phase separation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Microencapsulation of doxycycline into poly(lactide- co -glycolide) by spray drying technique: Effect of polymer molecular weight on process parametersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Pradip Patel Abstract Poly(lactide- co -glycolide) (PLGA) polymers with three different molecular weights were prepared, and microparticles were produced by spray drying and water-in-oil-water (w/o/w) double emulsion techniques to encapsulate 86% of doxycycline (DXY), an antibiotic drug, for the use of periodontitis. Placebo and drug-loaded microspheres and pristine DXY were analyzed by Fourier transform infrared spectroscopy, which indicated no chemical interactions between DXY and PLGA. X-ray diffraction of drug-loaded microspheres confirmed the molecular level dispersion of DXY in PLGA. Scanning electron microscopy confirmed spherical nature and smooth surfaces of the microspheres. Mean particle size as measured by laser light scattering technique ranged between 10 and 25 ,m. In vitro release of DXY performed in 7.4 pH media continued up to 72 h and depended on molecular weight of PLGA and extent of DXY loading. Antimicrobial studies performed on one formulation and placebo microspheres suggested that drug concentrations during in vitro release are above the minimum inhibitory concentration (MIC) for Staphylococcus aureus growth. Overall, the release studies depended on the molecular weight of PLGA, extent of drug loading, and the method used to prepare microspheres. Statistical analyses of release data performed using the analysis of variance (ANOVA) method agreed well with experimental observations. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Compatibility of liquid deproteinized natural rubber having epoxy group (LEDPNR)/poly (L -lactide) blendJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Phan Trung Nghia Abstract Reaction after mixing of liquid epoxidized natural rubber/poly(L -lactide) blend was performed to enhance the compatibility of the blend. The liquid epoxidized natural rubber was prepared by epoxidation of deproteinized natural rubber with peracetic acid in latex stage followed by depolymerization with peroxide and propanal. The resulting liquid deproteinized natural rubber having epoxy group (LEDPNR) was mixed with poly(L -lactide) (PLLA) to investigate the compatibility of the blend through differential scanning calorimetry, optical light microscopy, and NMR spectroscopy. After heating the blend at 473 K for 20 min, glass transition temperature (Tg) of LEDPNR in LEDPNR/PLLA blend increased from 251 to 259 K, while Tg and melting temperature (Tm) of PLLA decreased from 337 to 332 K and 450 to 445 K, respectively, suggesting that the compatibility of LEDPNR/ PLLA blend was enhanced by a reaction between the epoxy group of LEDPNR and the ester group of PLLA. The reaction was proved by high-resolution solid-state 13C NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Comparative study of the hydrolytic degradation of glycolide/L -lactide/,-caprolactone terpolymers initiated by zirconium(IV) acetylacetonate or stannous octoateJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Janusz Kasperczyk Abstract A series of copolymers have been synthesized by the ring-opening polymerization of glycolide, L -lactide, and ,-caprolactone with zirconium(IV) acetylacetonate [Zr(Acac)4] or stannous octoate [Sn(Oct)2] as the catalyst. The resulting terpolymers have been characterized by analytical techniques such as proton nuclear magnetic resonance, size exclusion chromatography, and differential scanning calorimetry. Data have confirmed that Sn(Oct)2 leads to less transesterification of polymer chains than Zr(Acac)4 under similar conditions. The various copolymers have been compression-molded and allowed to degrade in a pH 7.4 phosphate buffer at 37°C. The results show that the degradation rate depends not only on the copolymer composition but also on the chain microstructure, the Sn(Oct)2 -initiated copolymers degrading less rapidly than Zr(Acac)4 -initiated ones with more random chain structures. The caproyl component appears the most resistant to degradation as its content increases in almost all cases. Moreover, caproyl units exhibit a protecting effect on neighboring lactyl or glycolyl units. The glycolyl content exhibits different features: it decreases because of faster degradation of glycolyl units, which are more hydrophilic than caproyl and lactyl ones, remains stable in the case of abundant CGC sequences, which are very resistant to degradation, or even increases because of the formation of polyglycolide crystallites. Terpolymers can crystallize during degradation if the block length of one of the components is sufficiently long, even though they are amorphous initially. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] | |||||||||||||||||||||||||||||||