Chemically expanded graphite-based ultra-high molecular weight polyethylene nanocomposites with enhanced mechanical properties

Chemically expanded graphite (CEG) has recently been identified as promising reinforcement for polymer composites with the ability for commercial up-scaling. In this work, silane and polydopamine functionalized CEG were successfully synthesized and employed to prepare ultra-high molecular weight polyethylene (UHMWPE) composites with an enhanced interfa- cial compatibility. Characterisation of the functionalized CEG indicated a significant oxygen reduction, which gave rise to a restoration of the graphitic structure. The polydopamine functionalized CEG showed an enhanced exfoliation and dispersion in organic solvents and the polymer matrix with respect to the non-modified CEG. The silane functionalized CEG provided a higher affinity towards the matrix with polymer chains covering the CEG sheets on the fracture surfaces. The addition of functionalized CEG enhanced the mechanical prop- erties of the matrix with an increase in micro-hardness of up to 25% and storage modulus up to 58%. Furthermore, the hydrophobicity of the composites was significantly enhanced with an increase in water contact angle from 98.6◦ for the pure polymer to 119◦ for 5 wt% silane functionalized CEG. Preliminary wear experiments indicated the potential of the composites for tribological applications with a decrease in wear rate of up to 99% under water lubricated conditions.publishe

Neurobehavioral Effects of Occupational Exposure to Organic Solvents among Pharmaceutical Laboratory Workers in Iran

Background: Workers exposed to organic solvents are at risk of developing chronic central nervous system disorders. The aim of this cross-sectional study was to investigate the neurobehavioral effects of occupational exposure to organic solvents among pharmaceutical laboratory workers. Methods: The study groups consisted of 78 laboratory workers as the exposed group and 98 office workers as unexposed controls. The subjects were studied with the World Health Organization neurobehavioral core test battery (WHO-NCTB) by running Simple Reaction Time (SRT), Benton Visual Retention Test (BVRT) and Purdue Pegboard tests. Results: The SRT and BVRT test scores were poorer among the laboratory workers. However, no significant differences were found between the two groups for the Purdue Pegboard Test. Conclusions: The results of this study suggest that occupational exposure to organic solvents could induce a neurobehavioral deficiency in pharmaceutical laboratory workers. Therefore, objective neurobehavioral tests should be used for assessing the relation between exposure and effect and also as a guide for establishing standards in the control of workplace exposure

A scientific perspective on reducing ski-snow friction to improve performance in Olympic Cross-Country Skiing, the Biathlon and Nordic Combined

Of the medals awarded at the 2022 Winter Olympics in Beijing, 24% were for events involving cross-country skiing, the biathlon and Nordic combined. Although much research has focused on physiological and biomechanical characteristics that determine success in these sports, considerably less is yet known about the resistive forces. Here, we specifically describe what is presently known about ski-snow friction, one of the major resistive forces. Today, elite ski races take place on natural and/or machine-made snow. Prior to each race, several pairs of skis with different grinding and waxing of the base are tested against one another with respect to key parameters, such as how rapidly and for how long the ski glides, which is dependent on ski-snow friction. This friction arises from a combination of factors, including compaction, plowing, adhesion, viscous drag, and water bridging, as well as contaminants and dirt on the surface of and within the snow. In this context the stiffness of the ski, shape of its camber, and material composition and topography of the base exert a major influence. An understanding of the interactions between these factors, in combination with information concerning the temperature and humidity of both the air and snow, as well as the nature of the snow, provides a basis for designing specific strategies to minimize ski-snow friction. In conclusion, although performance on "narrow skis" has improved considerably in recent decades, future insights into how best to reduce ski-snow friction offer great promise for even further advances

Neurobehavioral Effects of Occupational Exposure to Organic Solvents among Pharmaceutical Laboratory Workers in Iran

Background: Workers exposed to organic solvents are at risk of developing chronic central nervous system disorders. The aim of this cross-sectional study was to investigate the neurobehavioral effects of occupational exposure to organic solvents among pharmaceutical laboratory workers. Methods: The study groups consisted of 78 laboratory workers as the exposed group and 98 office workers as unexposed controls. The subjects were studied with the World Health Organization neurobehavioral core test battery (WHO-NCTB) by running Simple Reaction Time (SRT), Benton Visual Retention Test (BVRT) and Purdue Pegboard tests. Results: The SRT and BVRT test scores were poorer among the laboratory workers. However, no significant differences were found between the two groups for the Purdue Pegboard Test. Conclusions: The results of this study suggest that occupational exposure to organic solvents could induce a neurobehavioral deficiency in pharmaceutical laboratory workers. Therefore, objective neurobehavioral tests should be used for assessing the relation between exposure and effect and also as a guide for establishing standards in the control of workplace exposure

Applications of Nanomaterials in Multifunctional Polymer Nanocomposites

Copyright © 2016 Bin Li et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Incorporating functional nanomaterials into polymers is an effective approach to achieving enhanced performances and creating new functionalities for the lightweight material applications. The resulting polymer nanocomposites benefit from advantages of both polymer matrix and nanoreinforcement phase

Association of SERPIND1 expression with grade, stage and presence of metastasis in breast cancer

71-82The role of SERPIND1 gene in the development of breast cancer is completely unknown. The aim of the present study was to assess the expression of SERPIND1 in patients suffering from breast malignancies. Tumoural specimens and non-tumoural adjacent tissues were collected from 31 patients who were pathologically confirmed for breast cancer. Furthermore, 43 fasting venous blood samples were collected from the breast cancer patients as well as from the healthy volunteers as control group. The SERPIND1 mRNA expression levels were assessed using the q-RT PCR while the plasma levels of SERPIND1 protein were detected using ELISA. The SERPIND1 relative expression levels were compared with the clinicopathological factors. The expression of the SERPIND1 was significantly higher at both mRNA and protein levels in breast cancer patients compared to the control groups. Moreover, the relative expression of the SERPIND1 showed a significant positive correlation with cancer grade, stage and presence of metastasis (PSERPIND1 may be a metastasis-enhancer factor in breast cancer and a strong predictive marker for distinguishing patients with poor prognosis

Evaluation of squamous cell carcinoma antigen 1 expression in oral squamous cell carcinoma (tumor cells and peritumoral T-lymphocytes) and verrucous carcinoma and comparison with normal oral mucosa

Background: Squamous cell carcinoma antigen (SCCA) is used as a prognostic marker for recurrence of squamous cell carcinoma in various sites, including head and neck. Studies suggest that its high serum levels are correlated to some clinical features, such as nodal metastasis. However, it is still unknown if high SCCA in patients with SCCA tissue expression in tumor cells are related to peripheral T-lymphocytes. Therefore, we did this study to evaluate SCCA expression in squamous cell carcinoma and verrucous carcinoma and to compare it with normal oral mucosa, also investigating the correlation between serum-based and tissue-based antigen levels. Methodology: In this study, the immunohistochemistry (IHC) technique was used to determine the SCCA1 expression pattern in 81 specimens divided into 3 groups, including oral squamous cell carcinoma, verrucous carcinoma, and normal oral mucosa. Serum-based and tissue-based antigen levels of 20 oral squamous cell carcinoma cases were compared by the western blot assay. SCCA expression was also evaluated and compared in both tumor cells and peripheral T-lymphocytes by the immunofluorescence assay. Results: Our results showed that the SCCA levels in SCC specimens were significantly lower than in verrucous carcinoma and normal and hyperplastic oral mucosa specimens. We found no correlation between the IHC expression of SCCA and serum levels. SCCA was well expressed in both tumor cells and peripheral T-lymphocytes. Conclusion: Decreasing SCCA in SCC specimens suggested that SCC tumor cells may affect more than the serum levels of SCCA in some patients. In addition, expression of SCCA in peripheral T-lymphocytes showed that both tumor cells and T-lymphocytes may cause serum SCCA.&nbsp

Investigation of wear and wear particles from a UHMWPE/multi-walled carbon nanotube nanocomposite for total joint replacements

Ultra high molecular weight polyethylene (UHMWPE) has been extensively used as a bearing surface in joint prostheses. However, wear debris generated from this material has been associated with osteolysis and implant loosening. Alternative materials, such as polymer composites, have been investigated due to their exceptional mechanical properties. The goal of the present work was to investigate the wear rate, size and volume distributions, bioactivity and biocompatibility of the wear debris generated from a UHMWPE/Multi-walled carbon nanotube (MWCNT) nanocomposite material compared with conventional UHMWPE. The results showed that the addition of MWCNTs led to a significant reduction in wear rate. Specific biological activity and functional biological activity predictions showed that wear particles from the UHMWPE/MWCNT nanocomposite had a reduced osteolytic potential compared to those produced from the conventional polyethylene. In addition, clinically relevant UHMWPE/MWCNT wear particles did not show any adverse effects on the L929 fibroblast cell viability at any of the concentrations tested over time. These findings suggest that UHMWPE/MWCNT nanocomposites represent an attractive alternative for orthopaedic applications

Graphene oxide modified with PMMA via ATRP as a reinforcement filler

Graphene is a two-dimensional new allotrope of carbon, which is stimulating great curiosity due to its superior mechanical, electrical, thermal and optical properties. Particularly attractive is the availability of bulk quantities of graphene (G) which can be easily processed by chemical exfoliation, yielding graphene oxide (GO). The resultant oxygenated graphene sheets covered with hydroxyl, epoxy and carboxyl groups offer tremendous opportunities for further functionalization opening plenty of opportunities for the preparation of advanced composite materials. In this work poly(methyl methacrylate) (PMMA) chains have been grafted from the GO surface via atom transfer radical polymerization (ATRP), yielding a nanocomposite which was soluble in chloroform. The surface of the PMMA grafted GO (GPMMA) was characterized by AFM, HRTEM, Raman, FTIR and contact angle. The interest of these novel nanocomposites lies in their potential to be homogenously dispersed in polymeric dense matrices and to promote good interfacial adhesion, of particular relevance in stress transfer to the fillers. PMMA composite films were prepared using different percentages of GPMMA and pristine GO. Mechanical analysis of the resulting films showed that loadings as low as 1% (w/w) of GPMMA are effective reinforcing agents, yielding tougher films than pure PMMA films and even than composite films of PMMA prepared with GO. In fact, addition of 1% (w/w) of GPMMA fillers led to a significant improvement of the elongation at break, yielding a much more ductile and therefore tougher material. Thermal analysis showed an increase of the thermal stability properties of these films providing evidence that strong interfacial interactions between PMMA and GPMMA are achieved. In addition, AFM analysis, in friction force mode, is demonstrated to be an effective tool to analyse the surface filler distribution on polymer matrices

Variables affecting stress development and resin conversion in light-cured dental composites

The general aim of this dissertation was to identify and investigate factors that can be used to minimize stress development in light cured dental resins without compromising the conversion level of the polymer. Modulus of elasticity, polymerization contraction strain, degree of conversion and shrinkage of light-cure dental composites were determined after curing with three different light power densities where total irradiated energy (J/cm2) kept constant. FT-Raman spectroscopy was employed to determine the degree of conversion. The cure kinetic of light cured resins was studied by use of photocalorimetry (photo-DSC). Dynamic mechanical thermal (DMTA) analysis was used to investigate how different light curing methods affected glass transition and tangent delta of light curable dental resins when the temperature changed from 0 to 200°C. Optical properties of dental composites were studied. Three different filler types, two different surface treatments and eight different filler fractions per filler type and surface treatment were investigated. Light transmission was measured for the different composite compositions at sample thicknesses of 1 to 5 mm by use of a universal power meter. As long as the total light energy remained the same, the modulus of elasticity remained constant for each composite, even though the power density differed. Composite thickness, irradiance time, composition of the light cure composite and irradiation value had significant impact on degree of conversion. The irradiance value did not significantly affect on the transition temperature value. Initiator, co-initiators and light irradiance value had all significant impact on cure behavior. Different filler types and filler surface treatments had significant effects on light absorption. In general, light absorption increased linearly with filler fraction and sample thickness of the cured composites. Conclusion: Low rather than high light irradiance values decrease stress levels in composites, and comparable conversion levels are reached as long as the total light energy value remains the same for low versus high irradiance. By increasing the composite thickness above 2 mm but not exceeding 6 mm, energy levels exceeding 30 J are needed to achieve acceptable levels of degree of conversion. Different irradiance values do not affect the final Tg of tested composites as long as the total light energy remains the same. By using appropriate photo initiator/co-initiator combination and soft-start curing it is possible to achieve slow curing and high DC within a 40 s. As expected, different filler particle properties have significant effects on light absorption during curing making it important to consider these differences when one tries to develop a general light curing strategy for light curable dental resins.Godkänd; 2004; 20061030 (haneit