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.     

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.     

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%.     

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.     

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.     

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.