Hydroxyapatite/poly(L-lactic acid)-chitosan Porous Scaffolds Prepared by Phase Separation Method

Hydroxyapatite/poly(L-lactic acid)–chitosan and poly(L-lactic acid)/chitosan porous scaffolds were prepared by phase separation technique using heated acetic acid–water as a common solvent of poly(L-lactic acid) and chitosan. The results show that the distribution of hydroxyapatite in the scaffolds is good. The porosity of the hydroxyapatite/poly(L-lactic acid)–chitosan scaffolds is nearly 85%. The hydroxyapatite particles in the scaffolds are beneficial for improving the compression property of the scaffolds. The in vitro bioactivity test shows that there is a low crystallinity of carbonate hydroxyapatite coating formed on the surface of the scaffold after immersing in simulated body fluid for 14 days, indicating that the hydroxyapatite/poly(L-lactic acid)–chitosan scaffolds have a good bioactivity.     

Crystalline,Thermal, and Biodegradable Properties of Poly(L-Lactic Acid)/Poly(D-Lactic Acid)/POSS Melt Blends

A ternary nanocomposite consisting of poly(L-lactic acid) (PLLA), poly(D-lactic acid) (PDLA), and epoxy cyclohexyl polyhedral oligomeric silsesquioxane (e-POSS) was prepared by reactive blending method. Scanning electron microscopy revealed that the feeding of three compositions in batches, i.e., PDLA incorporation at different times, was more beneficial for the even dispersion of POSS in matrix. POSS introduction improved the homocrystallinity and stereocomplex of the blends. Rheological properties and heat resistance were enhanced, which indicated potential extensive application of PLLA-based materials. The optimization of degradation stability in saline buffer was attributed to the various hydrophobic properties of blends caused by POSS structure.     

Assessment of Cytocompatibility of Bulk Modified Poly-L-lactic Acid Biomaterials

The cytocompatibility and hydrophilicity tests were performed by culturing mouse fibroblastic cells on films of poly-L-lactic acid (PLLA), poly(L-lactic-co-glycolide) (PLGA) and poly(L-lactide-co-glycolide)/ bioactive glass (PLGA/BG) or in the presence of extracts from these polymeric materials. The solvent casting method was used to prepare these films. PLLA films were most hydrophobic and PLGA/BG was least hydrophobic. Compared to the other films, PLLA showed the worst results in cytocompatibility. PLGA also showed favorable results for fibroblastic cells viability. PLGA/BG films also demonstrated improved cell compatibility due to the good biocompatibility of the bioactive glass particles. The results of this study indicate the promising biocompatibility of PLGA/BG as biomaterials in medical field.     

Preparation and properties of DNA/PLLA,whey protein/PLLA and collagen/PLLA composites

The poor flexibility, low toughness and thermal stability have restricted the applications of degradable poly(lactic acid) bioplastic. The introduction of deoxyribonucleic acid, whey protein or collagen with helical structures, which include numerous intermolecular hydrogen bonds, can produce changes in mechanical and thermal properties of poly(lactic acid) materials. Due to the presence of more –C?=?O and –NH groups with strong hydratability, different composites exhibited a higher heat resistance compared with the neat poly(l-lactic acid). Moreover, for collagen/poly(l-lactic acid) composites, the tensile strength and elongation at break were increased by 88.6 and 154.9% compared with the neat poly(l-lactic acid), respectively. The results provide a basis for the design of novel poly(lactic acid)-based composites and can expand the application areas of materials, including plastic films, taker-bags, textiles and so on.     

Synthesis and Characterization of Linear and Tri-Block PLLA–PEG–PLLA Blends

This study was conducted to synthesize poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) triblock copolymer (PEGLA) with different poly(L-lactide) block length, and explore its applicability in a blend with linear poly(L-lactide) (3051D NatureWorks) with the intention of improving heat seal and adhesion properties at extrusion coating on paperboard. Poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) was obtained by ring opening polymerization of L-lactide using poly(ethylene glycol) (molecular weight 6000 g mol^?1) as an initiator and stannous octoate as catalyst. The structures of the PEGLAs were characterized by proton nuclear magnetic resonance spectroscopy. The melt flow and thermal properties of all PEGLAs and their blends were evaluated using dynamic rheology and differential scanning calorimeter. All blends containing 10 wt% of PEGLAs displayed similar zero shear viscosities to neat poly(L-lactide), while blends containing 30 wt% of PEGLAs showed slightly higher zero shear viscosity. However, all blends displayed higher shear thinning and increased melt elasticity (based on tan δ). No major changes in thermal properties were distinguished from differential scanning calorimetric studies. High molecular weight PEGLAs could be used in extrusion coating with 3051D without problems.     

Toughening Behavior of Poly(L-Lactic Acid)/Poly(D-Lactic Acid) Asymmetric Blends

The L-configured poly(lactic acid) has exhibited vast appeal in the past decades. However, most previous researches reveal that L-configured poly(lactic acid) exhibits fragile behavior, which limits its applications. Present work clarified that the toughness of poly(lactic acid) depended on the content of crystallites and rigid component incorporated into the specimens. The elongation at break was remarkably high in the L-configured poly(lactic acid)/D-configured poly(lactic acid) with a small amount of D-configured poly(lactic acid) (≤15%). The stretching led to orientation of crystals and amorphous molecular chains and segments. The crystals did not vary, while the amorphous molecular chains transited to mesophase during stretching, and this mesophase formed homocrystallites during heating.     

Purification of L‐Phenylalanine from a Ternary Amino Acid Mixture Using a Two‐Zone SMB/Chromatography Hybrid System

Abstract

A two‐zone SMB/chromatography hybrid system was studied to separate L‐phenylalanine, which is the intermediate retained component, from a ternary amino acid mixture; glycine, L‐phenylalanine, and L‐tryptophane. PVP (poly‐4‐vinylpyridine) and deionized water were used as solid and liquid phases, respectively. Single component linear isotherms and mass transfer rates were obtained from multiple frontal tests. For the mass transfer rate, the Lapidus and Amundson linear dispersion model was used with an effective dispersion coefficient calculated from the mass transfer rate and the axial dispersion coefficient. This model was validated by comparing the frontal data with the simulation results from Aspen Chromatography 2004^®. A single objective genetic algorithm was employed to determine optimal operating condition. Experiments using the two‐zone SMB/chromatography system were conducted to purify L‐phenylalanine. The results show that the two‐zone system successfully removed 95.0% of glycine and 79.2% of L‐tryptophane from the ternary mixture producing a L‐phenylalanine product purity of 88.2%.     

Optimization of Process Parameters for Controlled Ring-Opening Polymerization of Lactide to Produce Poly(L-Lactide) Diols as Precursor for Polyurethanes

Series of poly(L-Lactide) diols with molecular weights (M_n) in 2,069–4,811?g mol^?1 were synthesized from L-Lactide using stannous octoate catalyst and 1,4-butanediol chain extender. Operating conditions, i.e., temperature, catalyst concentration, chain extender concentration, and reaction time, were optimized. Maximum monomer conversion and M_n were observed at 0.5?mol% SnOct₂ and 1.0?mol% 1,4 butanediol (BDO) at 145°C. Poly(L-Lactide) diols were analyzed by Fourier transform infrared, proton nuclear magnetic resonance, end-group analysis, and X-ray diffraction techniques. Fourier transform infrared confirmed the formation of poly(L-Lactide) diols. Poly(L-Lactide) diols’ % degree of crystallinity was determined by X-ray diffraction. M_n was calculated by proton nuclear magnetic resonance and end-group analysis.     

Electroelastic Response of Cylindrical Fiber with D∞ Symmetry Exposed to Local Electric Field Through Opposed Electrode Pair

To obtain practical information on the electroelastic behavior of poly-l-lactic acid microtweezers or catheters, a previously constructed analytical technique is used to obtain the electroelastic field solution of a poly-l-lactic acid cylindrical fiber exposed to a local electric field, which is applied through an opposed pair of square-sectioned electrodes. The numerical representation of the solution reveals the detailed field quantity distributions, their importance in the design of microtweezers and catheters, the overall deformation of such devices, and the effects of the electrode dimensions on the deformation.     

Magnetite/poly(D,L-lactide-co-glycolide) and hydroxyapatite/poly(D,L-lactide-co-glycolide) prepared by W/O/W emulsion technique for drug carrier: Evaluation of in vitro release of dexamethasone from composite nanoparticles

Biocompatible polymeric carriers containing inorganic materials for delivering therapeutic agents to a targeted site are promising candidate for drug delivery. Two nanocomposite nanoparticles, magnetite/poly(D,L-lactide-co-glycolide) and hydroxyapatite/poly(D,L-lactide-co-glycolide) (Fe₃O₄/PLGA and HAp/PLGA, respectively), with different weight ratios of inorganics to polymer and different polymer molecular weights were prepared by water-in-oil-in-water (W/O/W) emulsion technique to determine incorporation and in vitro release profile of the small molecule drugs water-insoluble dexamethasone acetate (DEX-Ac) and water-soluble dexamethasone phosphate (DEX-P). The in vitro release for DEX-Ac nanoparticles showed an initial burst release followed by a continuous slower release, whereas DEX-P nanoparticles showed only rapid initial release behavior.     

Kinetics of L-Ascorbic Acid Degradation in Pineapple Drying under Ethanolic Atmosphere

The kinetics of L-ascorbic acid degradation during drying of pineapple in normal and modified atmosphere was studied. Drying experiments were carried out in a tunnel dryer at two drying temperatures and air velocities. The drying atmosphere was modified by the addition of ethanol (0.5% v/v). The presence of ethanol in the drying atmosphere promoted a more intense water evaporation compared to the conventional process. Although the L-ascorbic acid degradation rate during the pineapple drying (final moisture content of 27% wet basis) under ethanolic atmosphere was higher, these samples retained higher amounts of L-ascorbic acid. Moreover, the Weibull model was applied to fit the kinetics data.     

Research on the nonenzymatic browning reactions in model systems based on apple slices dried by instant controlled pressure drop drying

ABSTRACT

In this study, the influences of reducing sugar, amino acids, ascorbic acids, and phenolic compounds on the nonenzymatic browning reactions in model systems based on apple slices were studied. The browning components in apple slices were removed using water and ethanol sequently, and then infiltrated with different solutions. The browning ratio (BR) of apple slice model measured by a computer vision-based image analysis system was used to evaluate the nonenzymatic browning reactions. Compared to the solution containing reducing sugar and amino acids alone, the results showed that the reducing sugar and amino acid solution with the addition of (+)-catechin, L-epicatechin, and phlorizin resulted in a remarkable increment of BR in the apple slices. L-lysine, L-arginine, and L-cysteine showed higher positive effects on the formation of BR in models based on apple slices. This study was contributed to better understand the chemical reaction in real dehydrated apple slices.     

PLGA with less than 1 month of half-life time: Tensile properties in dry and wet states and hydrolytic degradation

In this study, the degradation mechanism and tensile properties of plasticized poly(D,L-lactide-co-glycolide) (PLGA) are evaluated. Purasorb PDLG 5010 is first extruded into rods with or without plasticizers, i.e, D,L-lactide or aspirin. Then, the hydrolytic degradation of such rods is studied in phosphate buffer solution. A very fast hydrolytic degradation (half-life time lower than 1 month) that is enhanced by the presence of plasticizer occurs through a heterogeneous mechanism and leads to the formation of hollow rods. The mechanical properties of these rods are studied in dry and wet states. Finally, water diffusivity in plasticized (or not) PLGA is estimated.     

Development and Assessment of Electrospun Poly(ε-caprolactone)–Poly(vinylalcohol) Blend Nanofibers for Pest Control in Stored Products

l-Carvone is a constituent of essential oil consisting of monoterpene ketone that possesses various medicinal properties. In this context, the present study focuses on the fabrication and assessment of electrospun poly(ε-caprolactone)–poly(vinylalcohol blend nanofibers imbibed with l-Carvone (5%, w/v) that served as a suitable polymeric carrier to preserve the antimicrobial and antioxidant activities of l-Carvone for a longer period of time. The fumigant potential of l-Carvone and C-PP fibers were assessed toward saw-toothed beetle, a major pest found in stored products. The prepared fragrant C-PP fibers displayed a promising potential formulation for the control of stored product pest such as saw-toothed beetle.     

Degradation of Poly(L-lactide) Films under Ultraviolet Irradiation and Water Bath

Poly(L-lactide) (PLLA) films were exposed to ultraviolet (UV) light (254 nm) and water bath of 60°C and 80°C. The limiting viscosity ([η]) of PLLA decreased from initial 187.4 dl/g to 42.2 dl/g after UV irradiation, and to 33.3 dl/g after soaking in 80°C water for 40 h, while the [η] of PLLA exposed to 60°C water remained at 115.6 dl/g after 40 h. Compared with the original PLLA, the degraded PLLA was bimodal in the GPC profile. FTIR analysis showed that the chain scission of PLLA acted by water molecules resulted in a C=C structure.     

Critical Surface Tension of Acrylamide-Grafted Polypropylene Copolymer by the Contact Angle Method

The contact angles θ of polar liquids on PP-g-AM copolymer (AM content 0.19, 0.26, and 0.37 wt%) were measured. The critical surface tension γ_C of PP-g-AM films were evaluated by the Zisman plot (cos θ versus-γl), the Young-Dupre-Good-Girifalco plot (1 + cos θ) versus 1/γ^0.5 l, and the log(1 + cos θ) versus log-γl plot. The-γl values estimated by the plot log(1 + cos θ) versus log-γl were smaller than those obtained by the other plots.     

Elevation of flow temperature of poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid) gel by controlling its morphology and crystal form

Complex crystals (ε-crystals) of poly(l-lactic acid) (PLLA) with solvents such as N,N-dimethylformamide (DMF) induce gelation of PLLA by forming fibrous structure. Three procedures to elevate the flow temperature of the PLLA gel were described: formation of an additional network by immersion of a DMF solution of PLLA with lower molecular weight, changing the crystal form from ε-crystal to α-crystal by heating the gel at 46 °C, and increasing the concentration of the solution to form the gel followed by heating. Field emission electron microscopy and X-ray diffraction measurements were carried out to elucidate the structural change and driving force of the elevation of the flow temperature. Densification of the fibrous structure and change of the crystal form from ε-crystals to α-crystals with lower solubility at higher temperatures were observed in the gel after the formation of an additional network by immersion in a DMF solution of PLLA. The procedure to elevate the flow temperature, which has been developed in this study, can broaden the application of PLLA gels.     

Review of recent literature on the light absorption properties of black carbon: Refractive index,mass absorption cross section,and absorption function

Abstract

Knowledge of the optical properties of soot black carbon (BC) is required for the prediction of the radiative effects of freshly-emitted and aged BC particles. Here we review BC mass absorption cross section (MAC) and absorption function E(m) measurements, focusing on freshly-emitted BC. First, we review recently reported MACs at 550?nm wavelength as obtained from direct measurements of particulate absorption and mass concentration; we find an average of 8.0?±?0.7?m²/g from ten measurements, not significantly higher (p?>?0.26) than the widely used MAC of 7.5?±?1.2?m²/g recommended by Bond and Bergstrom [Bond, T. C., and R. W. Bergstrom. 2006. Light absorption by carbonaceous particles: An investigative review. Aerosol Sci. Technol. 40(1):27–67]. Second, we review recently reported E(m), whose retrieval is more complex due to the need to combine measurements with numerical models to estimate the contribution of scattering to extinction. Third, we review recent numerical studies that have aimed to predict the BC MAC using various complex refractive indices (m?=?n?+?ik). Most of these studies have used m?=?1.95?+?0.79i recommended by Bond and Bergstrom (2006), yet failed to predict a MAC as high as 7.5 or 8.0?m²/g at 550?nm wavelength. Fourth, we summarize a selected range of alternative values of m that has been reported by recent studies and place them in the context of measurements using a contour plot of E(m) on the n–k plane. We show that the widely used m?=?1.95?+?0.79i corresponds to an E(m) that is too low to be consistent with the measured MAC values. We conclude that the E(m) of BC in the visible and near infrared should be greater than 0.32, and that the commonly used BC models or the refractive index, or both, are still in need of improvement.     

Preparation and Performance of Poly(Lactic Acid)-γ-Cyclodextrin Inclusion Complex-Poly(Lactic Acid) Multibranched Polymers by the Reactive Extrusion Process

The poly(lactic acid)-γ-cyclodextrin inclusion complex-poly(lactic acid) multibranched polymers were prepared by reactive extrusion process with L-lactide as raw material, stannous octoate as catalyst and the carboxyl poly(lactic acid)-γ-cyclodextrin inclusion compound as cores prepared by ultrasonic coprecipitation and carboxylation reaction. It was shown that the comprehensive performance of poly(lactic acid)-γ-cyclodextrin inclusion complex-poly(lactic acid) had been significantly improved compared with liner poly(lactic acid) by the study of structure and properties. Thus, the novel poly(lactic acid)-γ-cyclodextrin inclusion complex-poly(lactic acid) multibranched polymers have a potential use in biomedical materials. This study provided a simple and feasible preparation method for improving the performance of poly(lactic acid).