Fabrication and In Vitro Characterization of Novel Hydroxyapatite Scaffolds 3D Printed Using Polyvinyl Alcohol as a Thermoplastic Binder

This paper presents a proof-of-concept study on the biocolonization of 3D-printed hydroxyapatite scaffolds with mesenchymal stem cells (MSCs). Three-dimensional (3D) printed biomimetic bone structure made of calcium deficient hydroxyapatite (CDHA) intended as a future bone graft was made from newly developed composite material for FDM printing. The biopolymer polyvinyl alcohol serves in this material as a thermoplastic binder for 3D molding of the printed object with a passive function and is completely removed during sintering. The study presents the material, the process of fused deposition modeling (FDM) of CDHA scaffolds, and its post-processing at three temperatures (1200, 1300, and 1400 °C), as well it evaluates the cytotoxicity and biocompatibility of scaffolds with MTT and LDH release assays after 14 days. The study also includes a morphological evaluation of cellular colonization with scanning electron microscopy (SEM) in two different filament orientations (rectilinear and gyroid). The results of the MTT assay showed that the tested material was not toxic, and cells were preserved in both orientations, with most cells present on the material fired at 1300 °C. Results of the LDH release assay showed a slight increase in LDH leakage from all samples. Visual evaluation of SEM confirmed the ideal post-processing temperature of the 3D-printed FDM framework for samples fired at 1300 °C and 1400 °C, with a porosity of 0.3 mm between filaments. In conclusion, the presented fabrication and colonization of CDHA scaffolds have great potential to be used in the tissue engineering of bones.     

Linear DNA plasmid pPK2 of Pichia kluyveri: distinction between cytoplasmic and mitochondrial linear plasmids in yeasts

The linear plasmids frequently found in plants and filamentous fungi are associated with mitochondria or chloroplasts. In contrast, all the linear plasmids known in yeasts are cytoplasmic elements. From a strain of the yeast Pichia kluyveri, we have isolated a new linear plasmid, pPK2, which was found to be associated with mitochondria. This 7·1 kilobase pairs‐long DNA contained only two genes, which code for DNA and RNA polymerases, as judged from their nucleotide sequences translated by a mitochondrial genetic code. When we examined several recently isolated yeast plasmids for their subcellular localization, we found that two linear plasmids, pPH1 from Pichia heedii, as well as pPK1 from another strain of P. kluyveri, were also localized in mitochondria. These plasmids are the first examples of mitochondria‐associated linear plasmids in yeast. All other linear plasmids we examined were of cytoplasmic origin. Whilst the cytoplasmic type linear plasmids were efficiently eliminated by ultraviolet irradiation of host cells, the mitochondria‐associated plasmids were highly resistant. The mitochondrial pPK2 plasmid was rapidly lost by treatment of the host cells with ethidum bromide. Copyright © 1999 John Wiley & Sons, Ltd.     

Phenolic Compounds in Virgin Olive Oils: Fractionation by Solid Phase Extraction and Antioxidant Activity Assessment

The polar fraction of virgin olive oil was separated into two main parts (A and B) using solid phase extraction. Analysis of individual components by RP-HPLC indicated that the part (A) contained only simple phenols and phenolic acids. Part (B) had a complex nature. The two parts tested for their antioxidant activity showed relatively high protection factors in safflower oil stored at 80°C. Part B was found to contribute more than part A to the stability of the oil. The antioxidant activity of both fractions was related to their content of total polyphenols and o-diphenols. Acidic and alkaline hydrolysis showed significant quantitative changes in the HPLC profiles indicating the presence of ether and ester bonds while high-performance anion exchange chromatography of sugars after hydrolysis gave evidence for the presence of only traces of glycosides. A first attempt to identify a characteristic chromatographic peak of part B by HPLC fractionation and mass spectrometry showed the presence of an ester of tyrosol most probably with a dicarboxylic acid. © 1997 SCI.     

Hormonomic Changes Driving the Negative Impact of Broomrape on Plant Host Interactions with Arbuscular Mycorrhizal Fungi

Belowground interactions of plants with other organisms in the rhizosphere rely on extensive small-molecule communication. Chemical signals released from host plant roots ensure the development of beneficial arbuscular mycorrhizal (AM) fungi which in turn modulate host plant growth and stress tolerance. However, parasitic plants have adopted the capacity to sense the same signaling molecules and to trigger their own seed germination in the immediate vicinity of host roots. The contribution of AM fungi and parasitic plants to the regulation of phytohormone levels in host plant roots and root exudates remains largely obscure. Here, we studied the hormonome in the model system comprising tobacco as a host plant, Phelipanche spp. as a holoparasitic plant, and the AM fungus Rhizophagus irregularis. Co-cultivation of tobacco with broomrape and AM fungi alone or in combination led to characteristic changes in the levels of endogenous and exuded abscisic acid, indole-3-acetic acid, cytokinins, salicylic acid, and orobanchol-type strigolactones. The hormonal content in exudates of broomrape-infested mycorrhizal roots resembled that in exudates of infested non-mycorrhizal roots and differed from that observed in exudates of non-infested mycorrhizal roots. Moreover, we observed a significant reduction in AM colonization of infested tobacco plants, pointing to a dominant role of the holoparasite within the tripartite system.     

Experimental analysis of the influence of imposed displacements at the base of a cooling tower on its buckling stability

The results of an experimental investigation into the effect of displacements of the base of a model cooling tower on its buckling stability are presented. The displacement of the cooling tower base was imposed according to the formula: u_v = Δ_vcos 2β, where Δ_v represents the amplitude of the vertical displacements and β is the circumferential coordinate. An additional axisymmetric load was applied to the upper ring and the shell. The results were compared with findings for a shell without any base deformations. These investigations showed an insignificant influence of the imposed displacements at the tower base on its stability. Recommendations for design practice concerning the influence of base displacements on the cooling tower shell stability are included.     

Antioxidant activity of extracts obtained by different isolation procedures from some aromatic herbs grown in Lithuania

An increasing demand for natural additives has shifted the attention from synthetic to natural antioxidants. The present work examines the potential of some aromatic herbs grown in Lithuania as a source of natural antioxidants: marjoram (Majorana hortensis Moench), catnip (Nepeta cataria L), oregano (Origanum vulgare L), lavender (Lavandula angustifolia Mill), thyme (Thymus vulgaris L), hyssop (Hyssopus officinalis L), anise hyssop (Lophantus anisatus Benth), and sage (Salvia officinalis L). Dried herb samples were submitted to extraction with supercritical CO₂, acetone or methanol/water and hydrodistillation. Deodorised herb samples (after removal of essential oil) were also extracted with acetone. The antioxidant activity of these extracts, essential oils and dried deodorised aqueous extracts was assessed by the β-carotene bleaching test (diffusion and spectrophotometric methods). The highest yields of extracts were obtained using polar solvents. Thyme and sage acetone oleoresins showed high antioxidant activity in the tests performed and were regarded as the most promising sources. © 1998 SCI.     

A new role-switching mechanism optimizing the coexistence of?bluetooth and Wi-Fi networks

Unlicensed ISM band is used by various wireless technologies. Therefore, issues related to ensuring the required efficiency and quality of operation of coexisting networks become essential. The paper addresses the problem of mutual interferences between IEEE 802.11b transmitters (commercially named Wi-Fi) and Bluetooth (BT) devices. An optimization approach to modeling the topology of BT scatternets is introduced, resulting in more efficient utilization of ISM environment consisting of BT and Wi-Fi networks. To achieve it, the Integer Linear Programming approach has been proposed. Example results presented in the paper illustrate significant benefits of using the proposed modeling strategy.     

Synthesis and characterization of Cr2AlC ceramics prepared by spark plasma sintering

The investigation of bulk Cr₂AlC ceramic fabricated by Spark Plasma Sintering (SPS) from coarse powders (CAC10) and fine powders (NCAC10) in the temperature range of 1100-1400 °C was carried out. The XRD results indicate that Cr₂AlC, as major phase, always appears with minor and trace amount of Cr₇C₃ and Cr₂Al respectively in both NCAC10 and CAC10 samples and the amounts of later two phases decrease with increase in temperature. However, the Cr₂AlC phase content in NCAC10 is higher than that of CAC10 sintered at the same temperature. The micrographs of back-scattered SEM show that grains with smaller size and pores with fewer amounts appear in SPSed NCAC10 in comparison to that of CAC10. As consequence, the higher hardness (5.6 GPa) of NCAC10 than that (3.9 GPa) of CAC10 was obtained. The patterns of XRD, microstructure and hardness of samples HPed at 1400 °C for the same composition were also presented for comparison.