Core Crosslinking of Biodegradable Block Copolymer Micelles Based on Poly(ester carbonate)

A biodegradable amphiphilic block copolymer, PEG-b-P(LA-co-MAC), was used to prepare spherical micelles consisting of a hydrophobic P(LA-co-MAC) core and a hydrophilic PEG shell. To improve their stability, the micelles were crosslinked by radical polymerization of the double bonds in the hydrophobic blocks. The crosslinked micelles had similar sizes and a narrow size distribution compared to their uncrosslinked precursor. The improved stability of the crosslinked micelles was confirmed by measurements of the CMC and a thermodynamic investigation. These micelles can internalize into Hela cells in vitro as demonstrated by inverted fluorescence microscopy and CLSM. These stabilized nanoscale micelles have potential use in biomedical applications such as drug delivery and disease diagnosis.

Cinnamate-Functionalized Poly(ester-carbonate): Synthesis and Its UV Irradiation-Induced Photo-Crosslinking

A functionalized. cyclic carbonate monomer containing a cinnamate moiety, 5-methyl-5-cinnamoyloxymethyl-1,3-dioxan-2-one (MC), was prepared for the first time with 1,1,1-tri(hydroxymethyl) ethane as a starting material. Subsequent polymerization of the new cyclic carbonate and its copolymerization with L-lactide (LA) were successfully performed with diethyl zinc (ZnEt2) as initiator/catalyst. NMR was used for microstructure identification of the obtained monomer and copolymers. Differential scanning calorimetry (DSC) was used to characterize the functionalized poly(ester-carbonate). The results indicated that the copolymers displayed a single glass transition temperature (T-g) and the T, decreased with increasing carbonate content and followed the Fox equation, indicative of a random microstructure of the copolymer. The photo-crosslinking of the cinnamate-carrying copolymer was also demonstrated.

Isothermal Crystallization Behavior of Poly(L-lactic acid)/Organo-Montmorillonite Nanocomposites

The isothermal crystallization behavior of poly(L-lactic acid)/organo-montmorillonite nanocomposites (PLLA/OMMT) with different content of OMMT, using a kind of twice-functionalized organoclay (TFC), prepared by melt intercalation process has been investigated by optical depolarizer. In isothermal crystallization from melt, the induction periods (t(i)) and half times for overall PLLA crystallization (100 degrees C <= T-c <= 120 degrees C) were affected by the temperature and the content of TFC in nanocomposites. The kinetic of isothermal crystallization of PLLA/TFC nanocomposites was studied by Avrami theory. Also, polarized optical photomicrographs supplied a direct way to know the role of TFC in PLLA isothermal crystallization process. Wide angle X-ray diffraction (WAXD) patterns showed the nanostructure of PLLA/TFC material, and the PLLA crystalline integrality was changed as the presence of TFC. Adding TFC led to the decrease of equilibrium melting point of nanocomposites, indicating that the layered structure of clay restricted the full formation of crystalline structure of polymer.

Layer-by-Layer Buildup of Poly(L-glutamic acid)/Chitosan Film for Biologically Active Coating

A new biocompatible film based on chitosan and poly(L-glutamic acid) (CS/PGA), created by alternate deposition of CS and PGA, was investigated. FT-IR spectroscopy, UV-vis spectroscopy and QCM were used to analyze the build-up process. The growth of CS and PGA deposition are both exponential to the deposition steps at first. After about 9 (CS/PGA) depositions, the exponential to linear transition takes place. QCM measurements combined with UV-vis spectra revealed the increase in the multilayer film growth at different pH (4.4, 5.0 and 5.5). The build-up of the multilayer stops after a few depositions at pH = 6.5. A muscle myoblast cell (C2C12) assay showed that (CS/PGA)(n) multilayer films obviously promote C2C12 attachment and growth.

In vivo mineralization and osteogenesis of nanocomposite scaffold of poly (lactide-co-glycolide) and hydroxyapatite surface-grafted with poly(L-lactide)

Nanocomposite of hydroxyapatite (HAP) surface-grafted with poly(L-lactide) (PLLA) (g-HAP) shows a wide application for bone fixation materials due to its improved interface compatibility, mechanical property and biocompatibility in our previous study. In this paper, a 3-D porous scaffold of g-HAP/poly (lactide-co-glycolide) (PLGA) was fabricated using the solvent casting/particulate leaching method to investigate its applications in bone replacement and tissue engineering. The composite of un-grafted HAP/PLGA and neat PLGA were used as controls. Their in vivo mineralization and osteogenesis were investigated by intramuscular implantation and replacement for repairing radius defects of rabbits. After surface modification, more uniform distribution of g-HAP particles but a lower calcium exposure on the surface of g-HAP/PLGA was observed. Intramuscular implantation study showed that the scaffold of g-HAP/PLGA was more stable than that of PLGA, and exhibited similar mineralization and biodegradability to HAP/PLGA at the 12-20 weeks post-surgery.

Spectroscopic Study on Water Diffusion in Poly(ester urethane) Block Copolymer Matrix

The diffusion of water in a phase-separated biodegradable poly(ester urethane) shape-memory polymer with poly(E-caprolactone) (PCL) as the soft segment was investigated using time-resolved FTIR-ATR. On the basis of the band fitting and water ordering in drawn films, the broad water band in the 3800-2800 cm(-1) region was decomposed into four bands located at 3620, 3510, 3400, and 3260 cm(-1), and the first two components at 3620 and 35 10 cm(-1) were assigned to the vibrations of antisymmetric and symmetric stretching of water hydrogen bonded with the C=O group of the soft segment. The other two were associated with water bonded to the urethane hard segments in the forms of N-H:O-H:O=C bridge hydrogen bond and double hydrogen bonds with two C=O groups, respectively. Furthermore, band fitting and two-dimensional correlation analyses revealed that in the diffusion process, water first diffuses into the continuous soft-rich PCL phase and then into the hard-rich urethane domains, forming double hydrogen bonds with two C=O groups prior to the bridge hydrogen bond in the form of N-H:O-H:O=C.

Hydrogen Bonding and Crystallization in Biodegradable Multiblock Poly(ester urethane) Copolymer

The hydrogen bonding and crystallization of a biodegradable poly(ester urethane) copolymer based on poly(L-lactide) (PLLA) as the soft segment were investigated by FTIR. On slow cooling from melt, the onset and the progress of the crystallization of the urethane hard segments were correlated to the position, width, and relative intensity of the hydrogen-bonded N-H stretching band. The interconversion between the "free" and hydrogen-bonded N-H and C=O groups in the urethane units in the process was also revealed by 2D correlation analysis of the FTIR data. The crystallization of the PLLA soft segments was monitored by the ester C=O stretching and the skeletal vibrations. It was revealed that the PLLA crystallization was restricted by the phase separation and the urethane crystallization, and at cooling rates of 10 degrees C/min or higher, the crystallization of the PLLA soft segments was prohibited.

Synthesis and Characterization of Hyperbranched Poly(ether amide)s with Thermoresponsive Property and Unexpected Strong Blue Photoluminescence

A facile and efficient strategy for the syntheses of novel hyperbranched poly(ether amide)s (HPEA) from multihydroxyl primary amines and (meth)acryloyl chloride has been developed. The chemical structures of the HPEAs were confirmed by IR and NMR spectra. Analyses of SEC (size exclusion chromatography) and viscosity characterizations revealed the highly branched structures of the polymers obtained. The resultant hyperbranched polymers contain abundant hydroxyl groups. The thermoresponsive property was obtained from in situ surface modification of abundant OH end groups with N-isopropylacrylamide (NIPAAm). The study oil temperature-dependent characteristics has revealed that NIPAAm-g-HPEA exhibits an adjustable lower critical solution temperature (LCST) of about 34-42 degrees C depending on the grafting degree. More interestingly, the work provided an interesting phenomenon where the HPEA backbones exhibited strong blue photoluminescence.

Poly(ethylene glycol-co-propylene glycol) as a Macromolecular Plasticizing Agent for Polylactide: Thermomechanical Properties and Aging

Finding a Suitable plasticizer for polylactide (PLA) is necessary to overcome its brittleness and enlarge its range of applications. In this study, commercial PLA was melt-blended with a new plasticizer, an ethylene glycol/propylene glycol random copolymer [poly(ethylene glycol-co-propylene glycol) (PEPG)] with a typical number-average molecular weight of 1.2 kDa and an ethylene glycol content of 78.7 mol %. The thermal properties, crystallization behavior, and mechanical properties of the quenched blends and the properties of the blends after storage for 2 months under the ambient conditions were investigated in detail. The advantage of using PEPG is that it does not crystallize at room temperature and has good compatibility with PLA. The quenched PLA/PEPG blends were homogeneous and amorphous systems. With an increase in the PEPG content (5-20%), the glass-transition temperature, tensile strength, and modulus of the blends decreased, whereas the elongation at break and crystallizability increased dramatically. The cold crystallization of PLA resulted in phase separation of the PLA/PEPG blends by annealing of the blends at the crystallization temperature.

Crystallization Behavior and Mechanical Properties of Crosslinked Plasticized Poly(L-lactic acid)

Enhancing the stability of plasticized poly(L-lactic acid) (PLLA) with poly (ethylene glycol) (PEG) is necessary for its practical application. In this study, plasticized PLLA (PLLA/PEG 80/20 wt/wt) was crosslinked under I-ray (Co-60) in the presence of triallyl isocyanurate (TALC) as crosslinking agent. FTIR analysis revealed that PLLA, PEG, and TALC formed a cocrosslinking structure. Crystallization behavior and mechanical properties of the crosslinked plasticized PLLA were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and tensile tests. Experimental results indicated that the crystallization behaviors of both PEG and PLLA in the blends were restrained after irradiation. The melting peak of PEG in the crystallized samples disappeared at a low irradiation doses about 10 kGy. Although PLLA still owned the behavior of crystallize, its cold crystallization temperature and glass transition temperature shifted to higher temperature. Mechanical properties of the plasticized PLLA were strengthened through crosslinking. Both yield strength and elastic modulus of the samples increased after crosslinking.

Study on the Single Crystals of Poly(3-octylthiophene) Induced by Solvent-Vapor Annealing

Needle-like single crystals of poly(3-octylthiophene) (P3OT) have been prepared by tetrahydrofuran-vapor annealing. The morphology and structure of the crystals were characterized with optical microscopy, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, and wide-angle X-ray diffraction. It is observed that the P3OT molecules are packed with the backbones parallel to the length axis of the crystal and the alkyl side chains perpendicular to the substrate. The field effect transistor based on the P3OT single crystal exhibited a charge carrier mobility of 1.54 x 10(-4) cm(2)/(Vs) and on/off current ratio of 37, and the molecular orientation of the crystal is ascribed to account for the device performance. The time-dependent morphological evolution demonstrated that the crystals underwent Ostwald ripening when annealed.

Oxygen Carrier Based on Hemoglobin/Poly(L-lysine)-block-poly(L-phenylalanine) Vesicles

An oxygen carrier was prepared by encapsulating carbonylated hemoglobin (CO-Hb) molecules into polypeptide vesicles made from poly(L-lysine)-block-poly(L-phenylalanine) (PLL-b-PPA) diblock copolymers in aqueous medium at pH 5.8. The encapsulation was confirmed by confocal laser scanning microscopy (CLSM). The morphology and size of the Vesicles were studied by field-emission scanning electron microscopy (ESEM). They had a spherical shape with it mean diameter of about 4 to 5 mu m. The encapsulation efficiency of hemoglobin was 40 wt %, and the hemoglobin content in the vesicles was 32 wt %. The CO-Hb encapsulated in the PLL-b-PPA vesicles was more stable than free CO-Hb under ambient conditions, In the presence of a O-2 atmosphere, the CO-Hb in the vesicle could be converted into oxygen-binding hemoglobin (O-2-Hb) under irradiation of visible light for 2 h. Therefore, the CO-Hb/PLL-b-PPA vesicles are expected to be used its red blood cell substitutes.

Preparation, Surface Properties and Biological Activity of the Composite of Poly (lactide-co-glycolide) and Bioglass Nanoparticles Surface Grafted with Poly(L-lactide)

SiO2-CaO-P2O5 gel bioglass (BG) nanoparticles with the diameter of 40 nm were synthesized by sol-gel approach. The surface of BG nanoparticles was grafted through the ring-open polymerization of the L-lactide to yield poly (L-lactide) (PLLA) grafted gel particle (PLLA-g-BG). The PLLA-g-BG was further blended with poly(lactide-co-glycolide) (PLGA) to prepare the nanocomposites of PLLA-g-BG/PLGA with the various blend ratios of two phases. PLLA-g-BG accounted 10%, 20% and 40% in the composite, respectively. TGA, ESEM and EDX were used to analyze the graft ratio of PLLA-g-BG, the dispersion of nano-particles and the surface elements of the composites respectively. The rabbit osteoblasts were seeded and cultured on the thin films of composites in vitro. The cell adhesion, spreading and growth of osteoblasts were analyzed with FITC staining, NIH Image J software and MTT assay. The change of cell cycle was monitored by flow cytometry (FCM). The results demonstrated that the Surface modification of BG with PLLA could significantly improve the dispersing of the particles in the matrix of PLGA. The nanocomposite with 20% PLLA-g-BG exhibited superior surface properties, including roughness and plenty of silicon, calcium and phosper, to enhance the adhesion, spreading and proliferation of osteoblasts.

NOVEL COMPOSITES OF POLY(L-LACTIDE) AND SURFACE MODIFIED BIOACTIVE SiO2-CaO-P2O5 GEL NANOPARTICLES: MECHANICAL AND BIOLOGICAL PROPERTIES

Bioactive SiO2-CaO-P2O5 gel (BAG) nanoparticles with 40 nm in diameter were synthesized by the sol-gel route and further modified via the ring-opening polymerization of lactide on the surface of particles. Surface modified BAG (mBAG) was introduced in poly(L-lactide) (PLLA) matrix as bioactive filler. The dispersibility of mBAG in PLLA matrix was much higher than that of rough BAG particles. Tensile strength of the mBAG/PLLA composite could be increased to 61.2 MPa at 2 wt% filler content from 53.4 MPa for pure PLLA. The variation of moduli of the BAG/PLLA and mBAG/PLLA composites always showed an enhancement tendency with the increasing content of filler loading. The SEM photographs of the fracture surfaces showed that mBAG could be homogeneously dispersed in the PLLA matrix, and the corrugated deformation could absorb the rupture energy effectively during the breaking of materials. In vitro bioactivity tests showed that both BAG and mBAG particles could endow the composites with ability of the calcium sediment in SBF, but the surface modification of BAG particles could weaken this capability to some extent. Biocompatibility tests showed that both BAG and mBAG particles could facilitate the attachment and proliferation of the marrow cells on the surface of the composite.