Preparation, characterization, and in vitro evaluation of nanostructured chitosan/apatite and chitosan/Si-doped apatite composites

Chitosan/apatite (CHI/Ap) composites are attracting great attention as biomaterials for bone repair and regeneration procedures. The reason is their unique set of properties: bioactivity and osteoconductivity provided by Ap and resorbability supplied by CHI among others. Thus, in this study, CHI/Ap and CHI/Si-doped Ap composites were prepared and characterized. Particle size, surface area, in vitro physiological stability, enzymatic biodegradation, and bioactivity were evaluated. Unimodal particle size distribution was obtained for composites with high CHI/Ap ratios while bimodal distribution was present in composites with low CHI/Ap ratio. Physiological stability decreased with Si doping and with the CHI content. Acetylation degree and molecular weight of CHI did not affect in vitro stability. Rate of enzymatic degradation increased with the CHI content in composites. Si-doped Ap composites also showed increased degradation with respect to non-doped ones. The bioactivity of the composites was evidenced by the deposition on their surface of a calcium phosphate layer with Ap morphology after immersion in simulated body fluid. Both, biodegradation and bioactivity were dependent on the molecular weight of the polymeric CHI matrix. These results suggest that the CHI/Ap composites obtained are promising materials for bone regeneration applications.     

Enhancement of magnetic losses in hybrid polymer composites with MnZn-ferrite and conductive fillers

Polymer composites (PCs) with a polyurethane (PU) matrix filled with magnetic filler (MnZn ferrite) and hybrid polymer composites (HPCs) consisting of this magnetic filler and various types of conductive fillers (carbon black, carbon fibers, aluminum powder, polypyrrole) are prepared. The matrix structure of a HPC is formed (i) by a polymer filled with conductive filler, which forms the skeleton of an infinite cluster, and (ii) by ferrite particles that are larger than conductive particles. Thus, an HPC represents an ensemble of ferrite particles each of which is surrounded by a conductive medium and can be considered as a “core–shell” structure. The development of a core–shell structure is evidenced by the lower electric percolation threshold in an HPC compared with that in PU filled with conductive filler. Magnetic and dielectric spectra of PCs and HPCs are studied in the frequency range from 1 MHz to 10 GHz. Hybrid systems exhibit a considerable enhancement of magnetic losses compared with PCs. The enhancement of magnetic losses in HPCs is due to the conduction currents that are induced in the conductive shell by a microwave magnetic field.     

Use of Weibull distribution statistics in assessing long term compatibility of propellants with polymeric materials

The long term compatibility of propellants with polymers may be evaluated by statistical means. The Weibull distribution function was used in an effort to provid a more accurate means of estimating the effect of aging of the inert material in contact with the propellant.This method was applied to several systems exhibiting different degrees of compatibility. Exposure at 140°F of the RTV 680 rubber with M30 propellant in the XM735 projectile displayed no apparent adverse effects. Distribution analysis supported the conclusion that the RTV 680/M30 system is compatible at ambient temperatures. Another silicone displayed an initial decline in mechanical properties followed by a period of stability when stored with M30 at elevated temperatures over a period of 12 months.A fair amount of incompatibility was displayed by 30% glass filled nylon which had been exposed to a double base propellant WC870 for an extended time. The Weibull distribution plots indicate that the propellant exerts a damaging effect on both Nylon 12 materials, particularly at elevated temperatures.Thermal aging may contribute to the ultimate failure of a polymer, as well as direct contact with an energetic. This is illustrated in the case of the M205 non-metallic cartridge case used in the projectile of a 152mm round, with M26E1 propellant. Although it is difficult to separate the effect of these variables upon the lifetime of the system, Weibull statistics provide some measure of prediction.     

Growth Temperature and Salinity Impact Fatty Acid Composition and Degree of Unsaturation in Peanut-Nodulating Rhizobia

Growth and survival of bacteria depend on homeostasis of membrane lipids, and the capacity to adjust lipid composition to adapt to various environmental stresses. Membrane fluidity is regulated in part by the ratio of unsaturated to saturated fatty acids present in membrane lipids. Here, we studied the effects of high growth temperature and salinity (NaCl) stress, separately or in combination, on fatty acids composition and de novo synthesis in two peanut-nodulating Bradyrhizobium strains (fast-growing TAL1000 and slow-growing SEMIA6144). Both strains contained the fatty acids palmitic, stearic, and cis-vaccenic + oleic. TAL1000 also contained eicosatrienoic acid and cyclopropane fatty acid. The most striking change, in both strains, was a decreased percentage of cis-vaccenic + oleic (≥80% for TAL1000), and an associated increase in saturated fatty acids, under high growth temperature or combined conditions. Cyclopropane fatty acid was significantly increased in TAL1000 under the above conditions. De novo synthesis of fatty acids was shifted to the synthesis of a higher proportion of saturated fatty acids under all tested conditions, but to a lesser degree for SEMIA6144 compared to TAL1000. The major adaptive response of these rhizobial strains to increased temperature and salinity was an altered degree of fatty acid unsaturation, to maintain the normal physical state of membrane lipids.     

Investigation of Bemethyl Biotransformation Pathways by Combination of LC–MS/HRMS and In Silico Methods

Bemethyl is an actoprotector, an antihypoxant, and a moderate psychostimulant. Even though the therapeutic effectiveness of bemethyl is well documented, there is a gap in knowledge regarding its metabolic products and their quantitative and qualitative characteristics. Since 2018, bemethyl is included to the Monitoring Program of the World Anti-Doping Agency, which highlights the challenge of identifying its urinary metabolites. The objective of the study was to investigate the biotransformation pathways of bemethyl using a combination of liquid chromatography-high-resolution mass spectrometry and in silico studies. Metabolites were analyzed in a 24 h rat urine collected after oral administration of bemethyl at a single dose of 330 mg/kg. The urine samples were prepared for analysis by a procedure developed in the present work and analyzed by high performance liquid chromatography–tandem mass spectrometry. For the first time, nine metabolites of bemethyl with six molecular formulas were identified in rat urine. The most abundant metabolite was a benzimidazole–acetylcysteine conjugate; this biotransformation pathway is associated with the detoxification of xenobiotics. The BioTransformer and GLORY computational tools were used to predict bemethyl metabolites in silico. The molecular docking of bemethyl and its derivatives to the binding site of glutathione S-transferase has revealed the mechanism of bemethyl conjugation with glutathione. The findings will help to understand the pharmacokinetics and pharmacodynamics of actoprotectors and to improve antihypoxant and adaptogenic therapy.     

Detection of paralytic shellfish toxins by a solid-phase inhibition immunoassay using a microsphere-flow cytometry system

Paralytic shellfish poisoning is a toxic syndrome described in humans following the ingestion of seafood contaminated with saxitoxin and/or its derivatives. The presence of these toxins in shellfish is considered an important health threat and their levels in seafood destined to human consumption are regulated in many countries, as well as the levels of other chemically unrelated toxins. We studied the feasibility of immunodetection of saxitoxin and its analogs using a solid-phase microsphere assay coupled to flow cytometry detection in a Luminex 200 system. The technique consists of a competition assay where the toxins in solution compete with bead-bound saxitoxin for binding to an antigonyautoxin 2/3 monoclonal antibody (GT-13A). The assay allowed the detection of saxitoxin both in buffer and mussel extracts in the range of 2.2-19.7 ng/mL (IC(20)-IC(80)). Moreover, the assay cross-reactivity with other toxins of the group is similar to previously published immunoassays, with adequate detection of most analogs except N-1 hydroxy analogs. The recovery rate of the assay for saxitoxin was close to 100%. This microsphere-based immunoassay is suitable to be used as a screening method, detecting saxitoxin from 260 to 2360 μg/kg. This microsphere/flow cytometry system provided similar sensitivities to previously published immunoassays and provides a solid background for the development of easy, flexible multiplexing of toxin detection in one sample.