Microencapsulation of dichromate and paracetamol with Eudragit Retard polymers using phase separation by nonsolvent addition

A coacervation technique for microencapsulation using Eudragit Retard polymers [poly(methyl methacrylates) substituted by quaternary ammonium groups] as wall material is described, based upon phase separation using a cold chloroform-cyclohexane mixture together with polyisobutylene as a stabilizer. The effect of various parameters on the nature and properties of the microcapsules of potassium dichromate and paracetamol has been studied, in particular the alteration in wall content and structure and release rate of contents. The microcapsules are discrete, their properties are reproducible, and various degrees of sustained release are obtained.     

Direct melting polycondensation and characterization of poly(ɛ-caprolactone-co-lactic acid)

A kind of biodegradable material, poly(ɛ-caprolactone-co-lactic acid) [P(CL-co-LA)] was synthesized via the direct melting polycondensation of lactic acid (LA) and ɛ-caprolactone (CL). The influences of the polycondensation time, and the catalyst type on the intrinsic viscosity of P(CL-co-LA) were also investigated. The results indicate that P(CL-co-dl-LA), with an intrinsic viscosity of 0.4733 dL/g, can be prepared by direct melting polycondensation with the molar ratio LA/CL = 3:7 at 180°C and 70 Pa for 12 h, using 0.5% (mass fraction) of SnCl₂ as the catalyst. Compared with lactide ring-opening polycondensation (ROP), the direct melting polycondensation of LA and CL is more practicable and simple. Translated from Journal of South China University of Technology, 2006, 34(7): 7–11 (in Chinese)     

Synthesis and characterization of functional l-lactic acid/citric acid oligomer

Oligomers of l-lactic acid and citric acid (PLCA) were synthesized by reacting lactic acid with citric acid in the presence of stannous chloride. The chemical compositions of these multicarboxylated oligomers were verified by FT-IR and ¹H-NMR spectroscopy. The thermal characteristics of the oligomers, such as glass transition temperature T_g, melting temperature T_m and melting enthalpy, were confirmed by DSC. The crystallinity of the oligomers were determined by DSC and WXRD. Meanwhile, the acid-base surface characteristics of PLCA have been determined by contact angle. The results implicated that these oligomers may be used to entrap the cospecies on PLLA surface in tissue engineering.     

Crystallization behavior of poly(l-lactic acid)

This article contains a detailed analysis of the crystallization behavior of poly(l-lactic acid) (PLLA). Crystallization rates of PLLA have been measured in a wide temperature range, using both isothermal and non-isothermal methods. The combined usage of multiple thermal treatments allowed to obtain information on crystallization kinetics of PLLA at temperatures almost ranging from glass transition to melting point. Crystallization rate of PLLA is very high at temperatures between 100 and 118 °C, showing a clear deviation from the usual bell-shaped curve. This discontinuity has been ascribed to a sudden acceleration in spherulite growth, and is not associated to morphological changes in the appearance of PLLA spherulites. Experimental data of spherulite growth rates of PLLA have been analyzed with Hoffman-Lauritzen method. Applicability and limitations of this theoretical treatment have been discussed.     

Biodegradation behaviour of poly(lactic acid) and (lactic acid-ethylene glycol-malonic or succinic acid) copolymers under controlled composting conditions in a laboratory test system

(Lactic acid, ethylene glycol, malonic or succinic acid) copolymers [(LA-EG-MA) and (LA-EG-SA) copolymers] were synthesized with different monomer feed ratios by direct polycondensation. The copolymers were characterized in terms of various properties such as acid value and number average molecular weight. The aerobic biodegradation under controlled composting conditions of commercially available and laboratory synthesized poly(l-lactic acid) (PLA) and synthesized copolymers was carried out according to ISO 14855-1:2005. The biodegradability of tested materials was found to be strongly dependent on the lactic acid content, ranging from 94% (method A) and 104% (method B) to 43% (method A) and 46% (method B) over the 110-days of the 50 °C composting.     

Stabilization of poly(lactic acid) by polycarbodiimide

Polycarbodiimide (CDI) was used to improve the thermal stability of poly(l-lactic acid) (PLA) during processing. The properties of PLA containing various amounts of CDI were characterized by GPC, DSC, rheology, and tensile tests. The results showed that an addition of CDI in an amount of 0.1-0.7 wt% with respect to PLA led to stabilization of PLA at even 210 °C for up to 30 min, as evidenced by much smaller changes in molecular weight, melt viscosity, and tensile strength and elongation compared to the blank PLA samples. In order to examine the possible stabilization mechanism, CDI was reacted with water, acetic acid, l-lactic acid, ethanol and low molecular weight PLA. The molecular structures of the reaction products were measured with FTIR. The results showed that CDI could react with the residual or newly formed moisture and lactic acid, or carboxyl and hydroxyl end groups in the PLA samples, and thus hamper the thermal degradation and hydrolysis of PLA.     

Rapid controlled hydrolytic degradation of poly(l-lactic acid) by blending with poly(aspartic acid-co-l-lactide)

Although poly(lactic acid) is known as a biodegradable polymer, its hydrolytic degradation is extremely slow, taking years in water and in the human body. In this study the effects of blending oligomeric poly(aspartic acid-co-lactide) (PALs) on the hydrolytic degradation of poly(l-lactic acid) (PLLA) were studied in detail. It was found that the addition of PAL did not accelerate the hydrolysis of the PLLA in air (25 °C, 60% relative humidity), but significantly accelerated it in a phosphate buffer solution. The degradation rate becomes higher for the blends containing PAL with higher molar ratios of lactide to aspartic acid units, [LA]/[Asp], when PLLA/PAL blends prepared with different PALs are compared at the same PAL concentration. TEM results, in which the distribution of PALs with higher [LA]/[Asp] occurs at a smaller scale in blends, imply that higher miscibility of the PAL with PLLA results in higher contact area between the components, thereby accelerating the degradation efficiently.     

Quantitative evaluation of photodegradation and racemization of poly(l-lactic acid) under UV-C irradiation

To obtain details of poly(l-lactic acid) (PLLA) photodegradation behavior, PLLA films were irradiated by UV-C light (λ = 253.7 nm) to directly excite carbonyl groups, resulting in a rapid decrease in the molecular weight accompanying a gradual decrease in the optical purity of monomeric units in the chains. The racemization during the photodegradation was first detected as a result of the chain scission by irradiation. From quantitative analyses of the molecular weight and the monomeric unit composition, it was found that the chain scission ratio and the d-lactate unit ratio increased in parallel during the irradiation, suggesting that approximately one d-lactate unit formed for every chain scission. From a mechanistic consideration, the racemization equilibrium was proposed to occur at both carboxyl and hydroxyl chain ends.     

Tissue engineering and peripheral nerve regeneration (III)

The biodegradation rate and biocompatibility of poly (d, / -lactide) (PDLLA)in vivo were evaluated. The aim of this study was to establish a nerve guide constructed by the PDLLA with 3-D microenvironment and to repair a 10 mm of sciatic nerve gap in rats. The process of the nerve regeneration was investigated by histological assessment, electrophysiological examination, and determination of wet weight recovery rate of the gastrocnemius muscle. After 3 weeks, the nerve guide had changed from a transparent to an opaque status. The conduit was degraded and absorbed partly and had lost their strength with breakage at the 9th week of postoperation. At the conclusion of 12 weeks, proximal and distal end of nerves were anastomosed by nerve regeneration and the conduit vanished completely. The results suggest that PDLLA conduits may serve for peripheral nerve regeneration and PDLLA is a sort of hopeful candidate for tissue engineering.     

Synthesis of high-molecular-weight poly(l-lactic acid) through the direct condensation polymerization of l-lactic acid in bulk state

A strategy was attempted to produce high-molecular-weight poly(l-lactic acid) (PLLA) through the direct condensation polymerization of l-lactic acid in bulk state. Polymerizations were carried out with titanium(IV) butoxide (TNBT) as a catalyst employing different duration of decompression, esterification and polycondensation. The molecular weights were characterized by using the gel permeation chromatography (GPC). The stereosequences were analyzed from the ¹³C NMR spectra on the basis of the triad fractions.     

Immobilization ofLactobacillus bulgaricus in a hollowfiber bioreactor for production of lactic acid from acid whey permeate

Lactobacillus bulgaricus was immobilized in the shell side of an industrial hollow-fiber ultrafiltration module. Acid whey permeate, containing 46 g/L lactose supplemented with 10 g/L yeast extract, was pumped through the tube side at dilution rates of 0.2–2.5/h. At a cell concentration of 100 g/L, productivity was 1.5–5 g lactic acid/L/h.     

Selective preparation of glycosyl sulfone or glycal by treatment of phenyl thioglycoside of N-acetylneuraminic acid with m-chloroperbenzoic acid

Treatment of acetylated phenyl thioglycoside of N-acetylneuraminic acid with m-chloroperbenzoic acid (MCPBA) in CH₂Cl₂ affords quantitatively mixtures of the respective sulfone and glycal free from the sulfoxide. The outcome of the reaction does not depend on the anomeric configuration of the starting thioglycoside. The sulfone can be selectively prepared (yield 100%) by oxidation with an excess of MCPBA and NaHCO₃. In the presence of pyridine (2 equiv.) and MCPBA (2 equiv.), the major product is glycal (yields 81—88%). This version of the reaction can be regarded as a new method for the preparation of sialic acid glycals.     

Continuous production of L-aspartic acid

For the continuous production ofl-aspartic acid from fumaric acid and ammonia by the action of aspartase, the enzyme extracted fromEscherichia coli orE. coli cells having high aspartase activity were immobilized by various methods. In 1973 we succeeded in the industrial production ofl-aspartic acid usingE. coli cells immobilized with polyacrylamide gel. For the improvement of this process, we developed a novel technique using κ-carrageenan as the immobilizing matrix forE. coli cells. Further, EAPc-7 strain, having higher aspartase activity, was contracted from the parentE. coli by continuous cultivation with a definite medium. The aspartase activity was about seven times higher than that of the parent cells. In 1982 we changed from the conventional method to the improved method, using EAPc-7 strain immobilized with κ-carrageenan.     

Crystalline morphology of poly(l-lactic acid) thin films

Crystalline morphologies of spin-coated poly(l-lactic acid) (PLLA) thin films under different conditions are investigated mainly with atomic force microscopy (AFM) technique. When PLLA concentration in chloroform is varied from 0.01 to 1% gradually, disordered structure, rod-shape and larger spheres aggregates are observed in thin films subsequently. Under different annealing temperature, such as at 78, 102, 122 °C, respectively, we can find most rod-like crystalline aggregates. Interestingly, we observed that nucleation sites locate at the edge of the holes at the original crystalline stage. Then, these holes developed to form chrysanthemum-like and rods subsequently with annealing time meanwhile the size and the shape of crystalline aggregate are changed. In addition, effect of substrate and solvent on morphology is also discussed. On the other hand, the possible mechanism of crystalline morphology evolution is proposed.     

Production of propionic acid using a xylose utilizingPropionibacterium

The kinetics ofP. acidipropionici (ATCC25562), a xylose-utilizing rumen microorganism, was studied to assess its use for propionic acid production from wood hydrolyzates. Propionic acid has been shown to have a stronger inhibitory effect than acetic acid, with the undissociated acid form being responsible for the majority of the inhibitory effect. Thus, in batch tests with pH controlled at 6.0, the propionic acid concentration reaches 25 g/L and the acetic acid 7 g/L. Xylose uptake rate is dependent on the specific growth rate and glucose concentration. An immobilized cell columnar reactor at very high product yields (80%) proved adequate for propionic production. At cell concentrations of 95 g/L with high product concentration, volumetric productivities of 2.7 g/L·h were obtained in ultrafiltration cell recycle systems.     

Biobased myo-inositol as nucleator and stabilizer for poly(lactic acid)

myo-Inositol made from a biomass feedstock was used as an additive for poly (l-lactic acid) (PLLA) which was also made from biomass feedstock. The crystallization and stabilization of PLLA by the addition of myo-inositol were evaluated by the melt injection molding process. While the isothermal crystallization of PLLA at 100 °C had finished over 14 min after melting, that of PLLA with 5 wt% myo-inositol finished within 2 min. The crystal growth of PLLA started when the myo-Inositol crystal was added, and the crystallization was promoted. Furthermore, the molecular weight of PLLA with myo-inositol did not decrease during the melt-mixed at 200 °C, different from that of PLLA without the myo-inositol. myo-Inositol prevented the degradation of PLLA during the thermal melting process. The biomass carbon ratio measured by the accelerator mass spectroscopy method showed that the PLLA with 5 wt% myo-inositol was a fully biobased material. It was demonstrated that myo-inositol was a multi-functional biobased additive for the modification of PLLA without decreasing its mechanical properties.     

Selection and microencapsulation of an “NADH-oxidizing” bacterium and its use for NAD regeneration

An alternative approach to the regeneration of coenzymes is described here using immobilized microorganisms possessing “NADH-oxidase” function. Bacteria containing NADH-oxidase activity are immobilized by microencapsulation within artificial cells. In this form, the microencapsulated bacteria can recycle NADH back to NAD in the presence of molecular oxygen as an electron acceptor. The only byproduct of the recycling reaction is water. In order to perform the biological regeneration of NAD, the activity of NADH-oxidase was investigated in 13 strains of aerobic bacteria and yeast. The NADH-oxidizing bacteriaLeuconostoc mesenteroides exhibited the highest activity among the microorganisms tested. The permeabilized bacteria showed 10% of their initial activity after microencapsulation. Light and electron microscopy studies of bacteria loaded microcapsules have been done. Enzymatic properties of microcapsule-immobilized bacteria were investigated in comparison with those of the free enzyme complex.Leuconostoc mesenteroides, containing NADH-oxidase, has been microencapsulated together with 3α-hydroxysteroid dehydrogenase (3α-HSDH) for stereospecific steroid oxidation. In a batch reactor, 2 mg of NAD, with recycling, allowed the same substrate consumption as 4.4 mg of NAD without recycling. The microencapsulated system can be used repeatedly. The system is functional for 10 h, during which time each molecule of NAD has been used 7.6 times.     

Chemical recycling of poly(lactic acid)-based polymer blends using environmentally benign catalysts

Typical poly(l-lactic acid) (PLLA)-based polymer blends, PLLA/polyethylene (PE) and PLLA/poly(butylene succinate) (PBS), were degraded into each repolymerizable oligomer using environmentally benign catalysts, clay catalysts and enzymes, with the objective of developing a selective chemical recycling process. Two routes to selective chemical recycling of PLLA/PE blend were tested. One is the direct separation of PLLA and PE first by their different solubilities in toluene, followed by the chemical recycling of PLLA using montmorillonite K5 (MK5). The other is the selective degradation of PLLA in the PLLA/PE blend by MK5 in a toluene solution at 100 °C for 1 h forming the LA oligomer with a molecular weight of M_n = 200-300 g/mol, which is the best M_n for repolymerization. Thus regenerated PLLA had a M_w of greater than 100,000 g/mol. The PE remained unchanged and was quantitatively recovered by the reprecipitation method for material recycling. In a similar procedure, chemical recycling of PLLA/PBS blend was also carried out and compared by two routes. One is the direct separation of PLLA and PBS by solubility in toluene. The other route is the sequential degradation of PLLA/PBS blend using a lipase first to degrade PBS into cyclic oligomer, which was then repolymerized to produce a PBS. Next, PLLA was degraded into repolymerizable LA oligomer by MK5. The former procedure was carried out using a single solvent; however, the latter required mixed solvents, which decreased the efficient recycling use of solvents.     

On the specificity of the amide VI band for the secondary structure of proteins

In this work we analyzed the specificity of the amide VI band for different types of secondary structure elements in protein structures. This band involves the bending motion of the CO group of the peptide chain that is typically observed in the spectral region from 590 to 490 cm⁻¹. The infrared absorbance spectra of a set of polypeptide model compounds of well known secondary structure was obtained at defined pH, including poly (l-lysine), poly (l-tyrosine), poly (l-alanine) and poly (l-histidine). In addition spectra of membrane proteins from the respiratory chain, namely the NADH:ubiquinone oxidoreductase, the cytochrome c oxidase and its Cu_A fragment, the cytochrome bc₁ complex, a Rieske-type protein and in addition myoglobin, have been comparatively investigated. The systematic analysis of the amide VI band of the polypeptides and the proteins allowed correlating the signal appearing at ∼525 cm⁻¹ to α-helical structures and signals at ∼545 cm⁻¹ to β-sheet contributions. Random coils have been found to contribute at ∼535 cm⁻¹ while the β-turns were observed at ∼560 cm⁻¹.     

In-site mineralization of amorphous calcium carbonate particles: A facile and efficient approach to fabricate poly(l-lactic acid) based hybrids

The aim of this investigation is to obtain a polymer-based hybrid material with biodegradability, biocompatibility, and good mechanical properties and this object was realized via. in-situ introduction of the unmodified calcium carbonate (CaCO₃) into a poly(l-lactic acid) (PLLA) matrix. As verified by the measurements from scanning electron microscopy (SEM), optical microscopy, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), the hybrid films which possesses a uniform dispersion of calcium carbonate CaCO₃ in nano-meter scale, mechanically robustness and thermal stability could be fabricated by a mineralization-alike process. For example, the storage modulus increases from 441 MPa of neat PLLA to 1034 MPa of hybrid film containing 2% (w/w) CaCO₃. In addition, the hybrid films display a significant improvement in its UV-exposure resistance.