Various Types Of Modification Research Articles

MODIFICATION OF POLYMERS IN JOINT ARTHROPLASTY

The review describes the known and most common modifications to various polymers in surgical applications. A short history of the plastics used as sliding materials in endoprostheses is presented. The unsuccessful attempts of using materials in joint alloplastic, such as PMMA, POM, PTFE and PEEK, as well as their modifications, were analyzed. Many polymers with excellent sliding properties cannot be used in joint arthroplasty due to allergic, toxicological reactions or technological problems. Attention was focused on PE-UHMW polyethylene, and also its modifications that increase its wear resistance and mechanical strength. The paper summarizes the wear rates of polyethylene subjected to various types of modification, such as plastic working, crosslinking, or carbon fiber reinforcement. The latest trends for improving polyethylene are also described. Modification of polymers in joint arthroplasty. A significant advance would be to obtain PEEK that is suitable for use in arthroplasty without negative consequences. An important direction of development in the area of sliding biomaterials may also concern materials obtained by incremental methods (3D printing).

Вплив комплексного модифікування на структуру й властивості жароміцного нікелевого сплаву

In this work, a study of the influence of complex modification of the ZhS3DK-VІ nickel-based heat-resistant super alloy was conducted. The modification was performed out according to different technological schemes: with highly dispersed titanium carbonitrides Ti[Ti(C,N)] particles, with Ti [Ti(C,N)]+CoAl2O4 and Ti[Ti(C,N)]+CoAl2O4+Ni-Y complex that made it possible to investigate the specifics of the influence of the volume modifier Ti[Ti(C,N)] separately, and its complex effect with surface modifierCoAl2O4 and rare earth metals (with Ni-Y master alloy use) in the macro- and microstructure of a heat-resistant nickel alloy. It was shown that the use of modifiers allows for significant refining of macrograins, and the greatest effect was obtained with Ti[Ti(C,N)]+CoAl2O4 and Ti[Ti(C,N)]+Ni-Y+CoAl2O4complexes. Microstructure study allows to show that the value of interdendritic distances in both the case of modification with Ti[Ti(C,N)] and Ti[Ti(C,N)]+Ni-Y+CoAl2O4 complexes essignificantly decreased, from 100…130 μm to 80...120 μm, which is the result of many nuclei formation during crystallization in the volume of the alloy and with highly intense heat transfer from the melt by CoAl2Omodified ceramic mould after melt pouring. Based on the results of the influence of various types of modification on the microstructure of the alloy under study, it was established that modification according to all schemes allows obtaining carbides of smaller sizes, but grown sizes of carbonitrides was observed. Globular particles of carbide and carbonitrides are evenly located along the cross-section of the samples under study. In all cases of modification, a decrease in the value of the shrinkage microporosity was observed. The mechanical properties of the specimens after standard heat treatment shows, that modification with complexes under study allows provide mechanical properties that meet the specification requirements. The best complex of alloy mechanical properties at room temperature, fracture toughness and stress-rupture strength provides with Ti[Ti(C,N)]+Ni-Y+CoAl2O4 modifiers complex.

WAYS TO MANAGE THE QUALITY OF NANOCRETE

"This article presents an integrated approach to the design of the concrete composition, which contains a combination of various types of modification of the concrete mixture by introducing a hyperplasticizer based on polycarboxylate ether, as well as reinforcing fibers (anisotropic additive), activation of aggregates, binders and mixing water. It is shown how the reinforcement of concrete cement stone with fibers reduces the formation of shrinkage cracks and increases its frost resistance, and polycarboxylate nanoparticles significantly reduce the amount of water used and the drying time of the material, making the steam treatment stage optional. The article presents the mechanism of action of the hyperplasticizer, the test results of samples-beams and samples-cubes at the age of 28 days, as well as the result. As a result of the action, polycarboxylate particles are adsorbed on the surface of cement grains, repel each other and set the cement mortar in motion. With the help of this approach, a condition is created for the formation of a cement stone nanostructure of various functional actions with the help of nanoparticles already at the initial stage of mixing."

Effectiveness of Silanization and Plasma Treatment in the Improvement of Selected Flax Fibers' Properties.

The study investigated the effectiveness of the combination of chemical and physical methods of natural fibers’ modification. The long flax fibers were subjected to various types of modification. These were silanization, plasma modification and a combination of these methods. For the silanization process, two types of silanes were used: amino- and vinylsilane. The application of structurally different compounds allowed us to acquire knowledge about the effect of the modifier structure on its properties. Various properties of flax fibers were investigated, comparing the results before and after different modification processes. The flammability of prepared samples were tested by pyrolysis combustion flow calorimeter (PCFC). In the effect of the natural fibers’ modifications, flammability was reduced even by 30%. The thermal stability of modified fibers increased. The FTIR tests of the gases released during thermal degradation of the tested fibers allowed us to determine the important compounds and prove a lower degree of flax-fiber decomposition after modification. Flax fibers were also tested to evaluate their physical properties (linear mass, average diameter, aspect ratio and hygroscopicity). Changes in surface morphology were observed by scanning electron microscope (SEM). The properties of natural fibers improved significantly, thus contributing to an increase in their suitability for the use in composites.

Charge reversible hyaluronic acid-modified dendrimer-based nanoparticles for siMDR-1 and doxorubicin co-delivery

Dendrimer-based nanoparticles have shown promising applications in delivery of small interference RNA (siRNA) to downregulate proteins that contribute to multidrug resistance (MDR). Various types of modification can further enhance the anti-tumor efficacy of dendrimer-based nanoparticles. In this study, generation 4 polyamodoamine (PAMAM) was conjugated with PEG2k-DOPE. The PAMAM-PEG2k-DOPE co-polymer, together with mPEG2k-DOPE, was formulated into mixed dendrimer micelles (MDMs) that can complex siRNA through the cationic PAMAM moieties and encapsulate hydrophobic drug in the micellar lipid cores. DOPE-conjugated hyaluronic acid (HA) was coated on the surface of MDMs to shield the exposed positive charge on PAMAM and to increase the cellular association with CD44+ cancer cells. The HA-modified MDMs could form stable complexes with siRNA, prevent RNase-mediated siRNA degradation and maintain its integrity. Cellular association and cytotoxicity of HA-modified MDMs were investigated in A2780 ADR, MDA-MB-231 and HCT 116 cell lines. The HA-modified MDMs alleviated the toxicity from cationic charge, increase the cancer cell specificity and enhance the cancer cell killing effect in CD44+ cell line.

Modification of Oligopeptides on Aspartic Acid or Lysine Residues by Solid-Phase Synthesis through On-Resin Side-Chain Conjugation

On-resin side-chain conjugations of various moieties to oligo­peptides were performed through an orthogonal protecting protocol using side-chain-protecting groups for aspartic acid or lysine that could be selectively removed on-resin. Various types of modification, such as PEGylation, biotinylation, glycosylation, or fluorophore-labeling of peptides, were realized by using this strategy. The formation of ester, amide, hydrazide, and thiourea bonds was accomplished through the on-resin conjugation. Our work provides an improved and convenient solid-phase synthetic protocol for the modification of oligopeptides on their aspartic acid or lysine residues. This is a universal and practical method that is expected to increase the potential application of peptide-related drugs.

A technical review on epoxy-clay nanocomposites: Structure, properties, and their applications in fiber reinforced composites

Abstract The review presents a survey of the literature on structure–property relationships in epoxy-clay nanocomposites. Herein, various pivotal parameters affecting structures and properties of the nanocomposites including various types of modification as well as a vast range of available dispersion techniques were discussed. Opportunities and challenges in regards to potential applications of nanoclay in multi-scale composites have been also addressed. The multi-scale composites containing nanoclays have been reviewed in terms of mechanical properties in both out-of-plane and in-plane directions, and compared with those containing carbon based nanofillers. In this regards, the improving mechanisms in mechanical properties of both epoxy-clay nanocomposites and nanoclay filled fiber reinforced composites were also discussed.

Mutagenic consequences of cytosine alterations site-specifically embedded in the human genome.

IntroductionCytosine residues in CpG dinucleotides often undergo various types of modification, such as methylation, deamination, and halogenation. These types of modifications can be pro-mutagenic and can contribute to the formation of mutational hotspots in cells. To analyze mutations induced by DNA modifications in the human genome, we recently developed a system for tracing DNA adducts in targeted mutagenesis (TATAM). In this system, a modified/damaged base is site-specifically introduced into intron 4 of thymidine kinase genes in human lymphoblastoid cells. To further the understanding of the mutagenesis of cytosine modification, we directly introduced different types of altered cytosine residues into the genome and investigated their genomic consequences using the TATAM system.FindingsIn the genome, the pairing of thymine and 5-bromouracil with guanine, resulting from the deamination of 5-methylcytosine and 5-bromocytosine, respectively, was highly pro-mutagenic compared with the pairing of uracil with guanine, resulting from the deamination of cytosine residues.ConclusionsThe deamination of 5-methylcytosine and 5-bromocytosine rather than that of normal cytosine dramatically enhances the mutagenic potential in the human genome.

Monocyte/macrophage response to β2-microglobulin modified with advanced glycation end products

We recently found that acidic beta 2-microglobulin (beta 2m), a major isoform of beta 2m in amyloid fibrils of patients with dialysis-related amyloidosis (DRA), contained early Amadori products and advanced glycation end products (AGEs) formed nonenzymatically between sugar and protein. Further analysis revealed that acidic beta 2m induces monocyte chemotaxis and macrophage secretion of bone-resorbing cytokines, suggesting the involvement of acidic beta 2m in the pathogenesis of DRA. Acidic beta 2m, however, is a mixture of heterogeneous molecular adducts due to various types of modification. In the present study, we investigated the modification responsible for the biological activity of acidic beta 2m toward monocytes/macrophages. The presence of a fair amount of beta 2m species with deamidation was detected in acidic beta 2m isolated from urine of non-diabetic long-term hemodialysis patients, but deamidated beta 2m had no biological activity. In contrast, normal beta 2m acquired the activity upon incubation with glucose in vitro. Among the glycated beta 2m, the pigmented and fluorescent beta 2m that formed after a long incubation period, that is, AGE-modified beta 2m, exhibited biological activity, whereas beta 2m modified with Amadori products, major Maillard products in acidic beta 2m, had no such activity. These findings suggest that AGEs, although only a minor constituent of acidic beta 2m, are responsible for monocyte chemotaxis and macrophage secretion of cytokines, implicating the contribution of AGEs to bone and joint destruction in DRA.

Toxicological Studies on the Metabolism of the Insecticides Pyrethroids and Rotenoids

The metabolism of trans- and cis-permethrin are studied in rat, cow and insects. The studies utilized eight 14C-permethrin preparations. Permethrin isomers are rapidly metabolized both hydrolytically and oxidatively. The ester hydrolysis are rapid with trans- than with cis-permethrin from all species. There are species-dependent differences in the preferred sites for hydroxylation of the permethrin isomers and in the conjugation reactions of the metabolites. The parent compound, free metabolites and their conjugates are quickly eliminated from mammals. Decamethrin metabolism in rat is on analogy wtih the metabolism of [IR, cis] permethrin. The cleavage of the decamethrin ester group leads to release of cyanide which is converted mainly to thiocyanate and a small amount of 2-iminothiazolidine-4-carboxylic acid. Allethrin, tetramethrin, resmethrin and furamethrin are included in β-cyclodextrin (CD) in 1:2 molar ratio. The included pyrethroids are stabilized for photodecomposition. The CD inclusion retardes th photochemical attack of the acid moiety for allethrin and of the alcohol moiety for resmethrin. Cochromatographic comparison of the synthetic compounds with the eight metabolites of rotenone confirmed the stereochemical configurations for the metabolites. 2-O-Demethylation is established as a new detoxification mechanism. All the four stereoisomers of natural rotenone and its O-demethyl derivatives are synthesized by the reaction of rotenone and d-epirotenone with one to three equivalents of boron tribromide followed by recyclization of the E-ring. The structure-biological activity relationships of 63 rotenone derivatives including 40 new ones are studied. High potency appears to be associated with the presence of ABCD ring system with the cis-6aβ, 12aβ-B/C ring juncture as in rotenone. Various types of modification of this juncture result in the diminished potency.

Structural modifications in membrane glycoproteins during the erythrocyte life-span.

Erythrocyte membrane glycoproteins undergo various types of modification during the life of the cell in the circulation; when only sialic acid is removed, the younger red cells can be repaired in the liver and return to the circulation. Otherwise, when an autolytic mechanism removing a sialopeptide becomes active as a consequence of the metabolic impairment of the cell, the erythrocyte is probably trapped by the hemocatheretic organs and destroyed.