Biocompatibility Assessment of Polylactic Acid (PLA) and Nanobioglass (n-BG) Nanocomposites for Biomedical Applications

Scaffolds based on biopolymers and nanomaterials with appropriate mechanical properties and high biocompatibility are desirable in tissue engineering. Therefore, polylactic acid (PLA) nanocomposites were prepared with ceramic nanobioglass (PLA/n-BGs) at 5 and 10 wt.%. Bioglass nanoparticles (n-BGs) were prepared using a sol–gel methodology with a size of ca. 24.87 ± 6.26 nm. In addition, they showed the ability to inhibit bacteria such as Escherichia coli (ATCC 11775), Vibrio parahaemolyticus (ATCC 17802), Staphylococcus aureus subsp. aureus (ATCC 55804), and Bacillus cereus (ATCC 13061) at concentrations of 20 w/v%. The analysis of the nanocomposite microstructures exhibited a heterogeneous sponge-like morphology. The mechanical properties showed that the addition of 5 wt.% n-BG increased the elastic modulus of PLA by ca. 91.3% (from 1.49 ± 0.44 to 2.85 ± 0.99 MPa) and influenced the resorption capacity, as shown by histological analyses in biomodels. The incorporation of n-BGs decreased the PLA crystallinity (from 7.1% to 4.98%) and increased the glass transition temperature (T_g) from 53 °C to 63 °C. In addition, the n-BGs increased the thermal stability due to the nanoparticle’s intercalation between the polymeric chains and the reduction in their movement. The histological implantation of the nanocomposites and the cell viability with HeLa cells higher than 80% demonstrated their biocompatibility character with a greater resorption capacity than PLA. These results show the potential of PLA/n-BGs nanocomposites for biomedical applications, especially for long healing processes such as bone tissue repair and avoiding microbial contamination.     

Radiation synthesis of acrylic acid onto poly(tetraflouroethylene-perflourovinyl ether) film: Chemical modifications and electrical conductivity

Graft-polymerization of acrylic acid (AAc) monomer onto poly(tetraflouroethylene-perflouro vinyl ether) (PFA) copolymer film was carried out using gamma irradiation technique to synthesize grafted copolymer film PFA-g-PAAc (PFA-COOH). The effect of the dose on the degree of grafting of AAc onto PFA film was investigated. The results showed that the degree of grafting increases with increasing the irradiation dose. The grafted [PFA-COOH] film was chemically modified by reaction with aniline to produce modified [PFA-CO-NH-ph] film, followed by sulphonation reaction to introduce sulfonic acid (SO₃H) groups to get other modified [PFA-CO-NH-ph-SO₃H] film. The chemical structures of the grafted and modified films were identified by FT-IR, XRD, and SEM. It is of particular interest to measure the electrical conductivity of grafted and modified membranes as a function of degree of grafting. It was found that the conductivity of the grafted films increases with increasing the degree of grafting, however a slightly increase in conductivity was observed in [PFA-CO-NH-ph-SO₃H] sample. The electrical conductivity property of the modified PFA membranes suggests their possible use for fuel cell applications.     

Long-Term Evaluation of Poly(lactic acid) (PLA) Implants in a Horse: An Experimental Pilot Study

In horses, there is an increasing interest in developing long-lasting drug formulations, with biopolymers as viable carrier alternatives in addition to their use as scaffolds, suture threads, screws, pins, and plates for orthopedic surgeries. This communication focuses on the prolonged biocompatibility and biodegradation of PLA, prepared by hot pressing at 180 °C. Six samples were implanted subcutaneously on the lateral surface of the neck of one horse. The polymers remained implanted for 24 to 57 weeks. Physical examination, plasma fibrinogen, and the mechanical nociceptive threshold (MNT) were performed. After 24, 28, 34, 38, and 57 weeks, the materials were removed for histochemical analysis using hematoxylin-eosin and scanning electron microscopy (SEM). There were no essential clinical changes. MNT decreased after the implantation procedure, returning to normal after 48 h. A foreign body response was observed by histopathologic evaluation up to 38 weeks. At 57 weeks, no polymer or fibrotic capsules were identified. SEM showed surface roughness suggesting a biodegradation process, with an increase in the median pore diameter. As in the histopathological evaluation, it was not possible to detect the polymer 57 weeks after implantation. PLA showed biocompatible degradation and these findings may contribute to future research in the biomedical area.     

Catalytic synthesis of nitrogen-containing heterocycles (a review)

The process of the catalytic synthesis of a number of nitrogenous heterocyclic compounds based on the utilization of reactions involving the amination of oxygen-containing heterocycles, the dehydration cyclization of amino alcohols, the deamination of di- and polyamines, and the intermolecular dehydration cyclization of glycols with diamines have been considered.     

Methanolysis of poly(lactic acid) (PLA) catalyzed by ionic liquids

Poly(lactic acid) (PLA) was depolymerized by methanol in the presence of a novel catalyst: ionic liquids. It was found that the purification method of the main products in the methanolysis catalyzed by ionic liquids was simpler than that of traditional compounds, such as sulfuric acid. Qualitative analysis indicated that the main product in the methanolysis process was methyl lactate. The influences of experimental parameters, such as the amount of ionic liquids, methanolysis time, reaction temperature, and dosages of methanol on the conversion of PLA, yield of methyl lactate were investigated. Under the optimum conditions, using ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim][Ac]) as catalyst, results showed that the ionic liquid could be reused up to 6 times without apparent decrease in the conversion of PLA and yield of methyl lactate. The kinetics of the reaction was also investigated. The results indicated that the methanolysis of PLA was a first-order kinetic reaction with activation energy of 38.29 kJ/mol. In addition, a possible catalysis mechanism of the methanolysis of PLA was proposed.     

Synthesis and characterization of polylactic acid (PLA) using a solid acid catalyst system in the polycondensation method

In this study, synthesis of poly(l(+) lactic acid) was carried out by using an acid catalyst. Neat chlorosulfonic acid reacts with cellulose to give cellulose sulfuric acid in which sulfuric acid is immobilized on the cellulose surface via bond formation. Cellulose sulfuric acid was used as a catalyst in a quantity of 1.0 wt.% calculated on the monomer. Polycondensation was carried out over a period of 24 h. The resulting poly(l(+) lactic acid) was characterized by Fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC) thermogravimetric analysis (TGA), ¹H and ¹³C nuclear magnetic resonance (NMR), and gel permeation chromatography. The molecular weight of poly(l-lactic acid) reached as high as 14,875.     

Stereoblock poly(lactic acid): synthesis via solid-state polycondensation of a stereocomplexed mixture of poly(L-lactic acid) and poly(D-lactic acid)

Stereoblock poly(lactic acid) consisting of D- and L-lactate stereosequences can be successfully synthesized by solid-state polycondensation of a 1:1 mixture of poly(L-lactic acid) and poly(D-lactic acid). In the first step, melt-polycondensation of L- and D-lactic acids is conducted to synthesize poly(L-lactic acid) and poly(D-lactic acid) with a medium-molecular-weight, respectively. In the next step, these poly(L-lactic acid) and poly(D-lactic acid) are melt-blended in 1:1 ratio to allow formation of their stereocomplex. In the last step, this melt-blend is subjected to solid-state polycondensation at temperature where the dehydrative condensation is allowed to promote chain extension in the amorphous phase with the stereocomplex crystals preserved. Finally, stereoblock poly(lactic acid) having high-molecular-weight is obtained. The stereoblock poly(lactic acid) synthesized by this way shows a higher melting temperature in consequence of the controlled block lengths and the resulting higher-molecular-weight. The product characterization as well as the optimization of the polymerization conditions is described. Changes in M(w) of stereoblock poly(lactic acid) (sb-PLA) as a function of the reaction time.     

A review on TiO2 nanotubes: synthesis strategies,modifications, and applications

Journal of Solid State Electrochemistry - In the field of nanotechnology, titanium dioxide nanotubes (TiO2 NTs) are one of the most valued inventions. They were discovered in 1996, and have since...     

生物可降解聚乳酸的改性及其应用研究进展

综述了近年来国内外关于生物可降解材料聚乳酸(PLA)通过共聚、共混、增塑和复合等方法得到聚乳酸改性材料的研究进展,以及对其在生物医学领域、纺织领域和包装领域中的应用作了广泛而深入的总结和评述,并预示了聚乳酸材料的研究开发前景。     

1,3,4-Thiadiazines: Methods of synthesis and reactivity (review)

The synthetic methods for 1,3,4-thiadiazines and their intramolecular rearrangement reactions are reviewed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 435–448, April, 1991.     

alpha-L-ribo-configured locked nucleic acid (alpha-L-LNA): synthesis and properties

The syntheses of monomeric nucleosides and 3'-O-phosphoramidite building blocks en route to alpha-L-ribo-configured locked nucleic acids (alpha-L-LNA), composed entirely of alpha-L-LNA monomers (alpha-L-ribo configuration) or of a mixture of alpha-L-LNA and DNA monomers (beta-D-ribo configuration), are described and the alpha-L-LNA oligomers are studied. Bicyclic 5-methylcytosin-1-yl and adenine-9-yl nucleoside derivatives have been prepared and the phosphoramidite approach has been used for the automated oligomerization leading to alpha-L-LNA oligomers. Binding studies revealed very efficient recognition of single-stranded DNA and RNA target oligonucleotide strands. Thus, stereoirregular alpha-L-LNA 11-mers containing a mixture of alpha-L-LNA monomers and DNA monomers ("mix-mer alpha-L-LNA") were shown to display DeltaT(m) values of +1 to +3 degrees C per modification toward DNA and +4 to +5 degrees C toward RNA when compared with the corresponding unmodified DNA x DNA and DNA x RNA reference duplexes. The corresponding DeltaT(m) values per modification for the stereoregular fully modified alpha-L-LNA were determined to be +4 degrees C (against DNA) and +5 degrees C (against RNA). 11-Mer alpha-L-LNAs (mix-mer alpha- L-LNA or fully modified alpha- L-LNA) were shown in vitro to be significantly stabilized toward 3'-exonucleolytic degradation. A duplex formed between RNA and either mix-mer alpha-L-LNA or fully modified alpha-L-LNA induced in vitro Escherichia coli RNase H-mediated cleavage, albeit very slow, of the RNA targets at high enzyme concentrations.     

Migration of oligomers from a food contact biopolymer based on polylactic acid (PLA) and polyester

Analytical and Bioanalytical Chemistry - Polylactic acid (PLA) is a biopolymer commonly used in food packaging due to its good characteristics, similar to PET. To evaluate the safety of this...     

聚乳酸组织工程支架材料

综述了生物活性因子固定化的聚乳酸-聚氨基酸衍生物共聚物和通过亲-疏水性设计的众多聚乳酸-聚氧化乙烯（PLA-PEO）共聚物的研究进展。展现了其在组织工程材料,药物控释体系和其他生物医用材料中的广泛应用前景。     

Chemically imaging the interaction of acetylated nanocrystalline cellulose (NCC) with a polylactic acid (PLA) polymer matrix

The non-covalent interaction of acetylated nanocrystalline cellulose (AC-NCC) with polylactic acid (PLA) in a composite blend has been studied at the micron scale by synchrotron Fourier transform infrared (FTIR) microspectroscopy. Microtomed sections of AC-NCC in PLA showed strong, localized carbonyl stretching (νC=O) absorbance characteristic of the cellulose acetylation, and this was observed on the surface of larger aggregated AC-NCC particles. A shift in the νC=O IR absorption peak of AC-NCC in PLA, relative to unblended AC-NCC was observed, which is indicative of an intermolecular interaction between AC-NCC and PLA matrix. Acetylation can therefore potentially improve the performance of the composite by enabling linkages between carbonyl groups, helping to establish a good stress transfer between the fiber and the matrix. This could in turn lead to a material with high yield elastic modulus. This is the first reported chemical imaging of acetylated nanocrystalline cellulose-based composite materials using synchrotron FTIR microspectroscopy.     

Cyanamides in heterodiene synthesis (review)

The published data on the participation of cyanamides in heterodiene synthesis as dienophophiles were organized and generalized.Institute of Industrial Chemistry, Ural Branch, Russian Academy of Sciences, Perm'614600. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 115–1162, September, 1994. Original article submitted March 28, 1994.     

Catalytic synthesis of dihydrofurans (review)

Various methods for the preparation of 2,3-dihydrofuran, 2,5-dihydrofuran, 2-methylenetetrahydrofuran, and their alkyl and aryl derivatives are examined. The most promising method for the preparation of 2,3-dihydrofuran is the conversion of 1,4-butanediol on cobalt catalysts. 2,5-Dihydrofuran is obtained by dehydration of 2-butene-1,4-diol on Al₂O₃, cobalt-containing and other catalysts, while 2-methylenetetrahydrofuran is obtained by dehydrohalogenation of tetrahydrofurfuryl halides. The various methods for the isomerization of 2,5-dihydrofuran to 2,3-dihydrofuran are discussed. Examples of the application of dihydrofurans in organic synthesis are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1299–1311, October, 1982.     

2-Cyanoacrylates as reagents in heteroatomic synthesis (a review)

Several types of addition reactions to the CC bond of alkyl 2-cyanoacrylates, CH₂C(CN)COOR ( 1 ), are considered. The first examples deal with addition of CH-Acids (p K _a less than 13) and of H₂S in the presence of catalytic amounts of strong amines, also of mercaptans, thiocarboxylic, and thiophosphoric acids. P-Sulfenylchlorides and acidic phosphites add irreversibly at 20°C to form addition products in accordance with the distribution of charges in 1 . HCl reversibly adds to 1 and to the acid chloride CH₂C(CN)COCl ( 2 ). Alcohols and H₂O also add reversibly to the acid CH₂C(CN)COOH ( 3 ) and to esters of 1 to transform 1 and 3 into polymers. Triethylsilane in the presence of CF₃COOH ( 4 ) reduces the CC bond of 1 and 3 to the corresponding saturated derivatives. The second set of examples involves reactions of 1 with P-III compounds in the presence or absence of 4 . Ph₃P as well as other weak nucleophiles reversibly add to 1 in the absence of 4 to cause instant polymerization. However, 4 protonates an initially formed zwitter-ion in the reaction of 1 with Ph₃P,(EtO)₂PCl,Ph₂PCl and thiourea to afford stable addition products. IR spectroscopy reveals the formation of H-complexes of 4 with the CN and COOR groups of 1 , which stimulates the addition of the weak nucleophile (o-C₆H₄O₂)PCl to the CC bond of 1 . This reagent does not react with 1 in the absence of 4 . Strong nucleophiles, Alk₃P, and (Et₂N)₃P in excess irreversibly add at 20°C to 1 to form zwitterions, which specifically react with PhNCO to give stable products. 1,3,2-Dioxaphospholes react with 1 either to form spirophosphoranes or 2-cyano-3-phosphoranylpropionates.     

Stereocomplex Mediated Gelation of PEG-(PLA)2 and PEG-(PLA)8 Block Copolymers

Stereocomplex mediated hydrogels have been prepared by mixing solutions of polymers of opposite chirality of either PEG-(PLA)₂ triblock copolymers or PEG-(PLA)₈ star block copolymers. The critical gel concentrations of the mixed enantiomer solutions were considerably lower compared to polymer solutions containing only the single enantiomer. Moreover, gel-sol transition temperatures were increased and gel regions were expanded due to stereocomplexation. Rheology measurements showed that stereocomplexed hydrogels based on PEG-(PLA)₈ have higher storage moduli compared to those based on PEG-(PLA)₂. Stereocomplexed hydrogels prepared from 13 wt% PEG-(PLA)₂ solutions in PBS showed a storage modulus of 0.9 kPa at 37 °C, while at similar conditions stereocomplexed hydrogels of PEG-(PLA)₈ showed a storage modulus of 1.9 kPa at 10 wt%.