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.     

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.     

Biodegradable and conductive hyperbranched terpolymers based on aliphatic polyester,poly(D,L-lactide), and polyaniline used as scaffold in tissue engineering

Designing the novel conductive and biodegradable scaffolds based on star-like hyperbranched terpolymers of aliphatic polyester–poly(D,L-lactide)–polyaniline (S-HAP–PLA–PANI) was the purpose of this research. The electroactivity of tissue engineering scaffold, which in the current work was for the presence of PANI, is an essential factor in its performance because the electrical signals are the pivotal physiological stimuli that control the adhesion and differentiation of various cell types. Star-shaped polymers have attracted conspicuous attention, thanks to their low-cost, well-defined highly functionalized structures and low crystallinity, and they also could be an interesting alternative to the linear analogs for their interaction with surrounding tissue and faster degradation rate. In the present work, after 12 weeks, the mass loses for S-HAP–PLA–PANI sample were calculated to be 45%. Scaffolds based on S-HAP–PLA–PANI/PLA nanofibers having the average diameter of 70–200?nm and electrical conductivity of 0.05 S cm^?1 imitated the natural microenvironment of extra cellular matrix to regulate the cell attachment, proliferation, and differentiation.     

Preparation and characterization of carvedilol-loaded poly(d,l) lactide nanoparticles/microparticles as a sustained-release system

Carvedilol poly(d,l)-lactide nanoparticles/microparticles were prepared. The size and morphology of the developed particles were optimized to study the carvedilol release profile by studying the effect of organic solvents and polymer amount through atomic force microscopy analysis. Spherical particles were obtained with a minimum size of 125?nm in the case of acetone and a maximum size of 970?nm in the case of dichloromethane affording microparticles formation. The interaction was confirmed by differential scanning calorimeter and Fourier transform infrared. The in vitro release profile of the multicompartment system (pure carvedilol, loaded nanoparticles and microparticles) has shown a sustained release with Korsmeyer–Peppas with T lag model.     

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.     

Polymer-Biologically Active Principle Conjugates Obtained by Esterification of Poly(Vinyl Alcohol)

The paper deals with the study of some polymer-biologically active principle systems characterized by the controlled release of the bioactive component by hydrolyze followed by diffusion. The systems were obtained by coupling the 2-mercapto-benzotiazolyl-acetic acid and N-(m-nitrobenzoyl)-L-methionine on poly(vinyl alcohol) by means of esteric bonds in the presence of diciclohexylcarbodiimide as an activator. The influence of some coupling process parameters on the reaction efficiency was studied, such as the drug/support and activator/support ratios. The coupling products with a maximum content of biologically active compound were characterized by spectral measurements, also as regards the capacity of bioactive compound release under the conditions simulating those within the gastro-intestinal tract. The antibacterial activity of the conjugates against Staphylococcus aureus, Eschrichia coli, Sarcina lutea, and Bacillus subtilis was determined.     

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.     

Formation of a Polymer-Coated Inclusion Complex of D-Limonene and β-Cyclodextrin by Spray Drying

The polymer-coated inclusion complex powder formation of D-limonene and β-cyclodextrin obtained by spray drying was investigated with respect to the effects of various types of polymer coating agents on the powder particle size and morphology. The addition of the polymer coating agent affected the average particle size, morphology, and internal structures of the spray-dried powders. The average particle diameter of the uncoated spray-dried powders was approximately 5 µm. The powder particle size increased upon the addition of a polymer coating reagent. With the addition of 9 wt% of the polymer coating agent, an average diameter of approximately 80 µm was obtained for the spray-dried powder particles. However, further addition showed a negligible effect on the particle size. Inclusion complex crystals were observed on the surface and inside of the powder particles.     

Mechanistic studies of ruthenium(III)-catalyzed oxidation of DL-methionine by hexacyanoferrate(III) in an alkaline medium

The kinetics and mechanism of ruthenium(III) catalyzed oxidation of dl-methionine by alkaline hexacyanoferrate(III) (HCF(III)) in an alkaline medium were studied spectrophotometrically at 30±0.1°C. The reaction was first-order-dependent each on [HCF(III)] and [ruthenium(III)] and fractional-order-dependent on [alkali]. The rate of the reaction was found to be decreased with the increase in [methionine]. The main product of oxidation was methionine sulfone nitrile (3-(methylsulfonyl)propanenitrile) and it was identified and confirmed by FT-IR and mass spectral studies. Further, no effect of added reaction product was observed. A plausible mechanism was proposed involving complexation between methionine and ruthenium(III) species, [Ru(H₂O)₅OH]²⁺. Thermodynamic parameters for the reaction, E _a and Δ S ^#, were computed using linear least squares method and are found to be 65.83±1.03 kJ/mol and?249.58±3.35 J/K mol, respectively.

     

Production and evaluation of vildagliptin-loaded poly(dl-lactide) and poly(dl-lactide-glycolide) micro-/nanoparticles: Response surface methodology approach

A laboratory scale spray dryer was used to encapsulate vildagliptin (VLG), an antihyperglycemic drug, into different polymers such as poly(dl-lactide) (PDLA), poly(dl-lactide-glycolide)-50:50 (PLGA 50:50), and poly(dl-lactide-glycolide)-75:25 (PLGA 75:25). Response surface methodology (RSM) was employed to evaluate the effects of process and formulation factors on the encapsulation efficiency (EE). The physicochemical properties of the drug-loaded micro-/nanoparticles, mainly the drug loading (DL), particle size distribution, surface morphology, drug–polymer compatibility, and release rate were investigated. % EE of drug-loaded micro-/nanoparticles were in the range of 57.10% to 76.44%. PLGA50:50 micro-/nanoparticles showed highest EE as compared to PDLA and PLGA75:25 micro-/nanoparticles. The mean particle size of the micro-/nanoparticles containing PLGA 50:50, PLGA 75:25, and PDLA polymers were 428?nm, 640?nm, and 1.22 µm, respectively. Surface morphology study revealed smooth, spherical and nonporous surface structures of the micro-/nanoparticles. Fourier transform infrared spectroscopy studies confirmed the drug–polymer compatibility. Powder X-ray diffraction analysis of micro-/nanoparticles revealed that VLG was present in the amorphous form within the micro-/nanoparticles formulations. In vitro release study demonstrated that VLG is slowly released from micro-/nanoparticles for 12?h and the drug release rate was influenced by type and viscosity of polymers used. This work suggests that PDLA, PLGA 50:50, and PLGA75:25 polymers are able to sustain the VLG release rates from micro-/nanoparticles.     

Application and Comparison of High-Speed Countercurrent Chromatography and High Performance Liquid Chromatography in Preparative Enantioseparation of α-Substitution Mandelic Acids

This paper is mainly about extending research on application and comparison of preparative high-speed countercurrent chromatography (HSCCC) and preparative high performance liquid chromatography (HPLC) in chiral separations. Preparative enantioseparations of α-cyclopentylmandelic acid and α-methylmandelic acid by HSCCC and HPLC were compared using hydroxypropy-β-cyclodextrin (HP-β-CD) and sulfobutyl ether-β-cyclodextrin (SBE-β-CD) as the chiral mobile phase additives. In preparative HPLC the enantioseparation was achieved on the ODS C₁₈ reverse phase column with the mobile phase composed of a mixture of acetonitrile and 0.10 mol L^?1 phosphate buffer at pH 2.68 containing 20 mmol L^?1 HP-β-CD for α-cyclopentylmandelic acid and 20 mmol L^?1 SBE-β-CD for α-methylmandelic acid. The maximum sample size for α-cyclopentylmandelic acid and α-methylmandelic acid was only about 10 mg and 5 mg, respectively. In preparative HSCCC the enantioseparations of these two racemates were performed with the two-phase solvent system composed of n-hexane-methyl tert.-butyl ether-0.1 molL^?1 phosphate buffer solution at pH 2.67 containing 0.1 mol L^?1 HP-β-CD for α-cyclopentylmandelic acid (8.5:1.5:10, v/v/v) and 0.1 mol L^?1 SBE-β-CD for α-methylmandelic acid (3:7:10, v/v/v). Under the optimum separation conditions, totally 250 mg of racemic α-cyclopentylmandelic acid could be completely enantioseparated by HSCCC with HP-β-CD as a chiral mobile phase additive in a single run, yielding 114-116 mg of enantiomers with 98-99% purity and 89-92% recovery. But, no complete enantioseparation of α-methylmandelic acid was achieved by preparative HSCCC with either of the chiral selectors due to their limited enantioselectivity. In this paper, preparative enantioseparation by HSCCC and HPLC was compared from various aspects.     

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.     

Glass transition behavior and dynamic fragility in polylactides containing mobile and rigid amorphous fractions

The segmental dynamics of polylactide chains covering the T_g − 30 °C to T_g + 30 °C range was studied in absence and presence of a crystalline phase by dynamic mechanical analysis (DMA) using the framework provided by the WLF theory and the Angell's dynamic fragility concept. An appropriate selection of stereoisomers combined with a thermal conditioning strategy to promote crystallization (above T_g) or relaxation of chains (below T_g) was revealed as an efficient method to tune the ratio of the rigid and mobile amorphous phases in polylactides. A single bulklike mobile amorphous phase was taken for poly(d,l-lactide) (PDLLA). In turn three phases, comprising a mobile amorphous fraction (MAF, X_MA), a rigid amorphous fraction (RAF, X_RA) and a crystalline fraction (X_c) were determined in poly(l-lactide) (PLLA) by modulated differential scanning calorimetry (MDSC) according to a three-phase model. The analysis of results confirms that crystallinity and RAF not only elevate the T_g and the breadth of the glass transition region but also yields an increase in dynamic fragility parameter (m) which entails the existence of a smaller length-scale of cooperativity of polylactide chains in confined environments. Consequently it is proposed that crystallinity is acting in polymeric systems as a topological constraint that, preventing longer range dynamics, provides a faster segmental dynamics by the temperature dependence of relaxation times according to the strong-fragile scheme.     

Synthesis and Characterization of Novel Thermotropic Aromatic-Aliphatic Biodegradable Copolyesters Containing D,L-Lactic acid (LA), Poly(butylene terephthalate) (PBT) and Biomesogenic Units

In this study, the copolyesters based on 4-hydroxybenzoic acid (HBA) and vanillic acid (VA), lactic acid (LA) and poly(butylene terephthalate) (PBT) were synthesized via melt polymerization and fully characterized by various measurements. The influences of content of HBA and VA units on thermal behavior, structure and degree of crystallinity of copolyesters were discussed in more detail. It was found that the copolymerization of aliphatic and aromatic units together could make the best use of advantages of the respective polyesters. Moreover, the copolyesters with more than 40 mol% of HBA and VA units could show liquid crystallinity in broad temperature range.     

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.