Cytotoxic and Genotoxic Effects of Composite Resins on Cultured Human Gingival Fibroblasts

The aim of the study was to evaluate the cytotoxic and genotoxic potential of five commercially available dental composite resins (CRs), investigating the effect of their quantifiable bisphenol-A-glycidyl-methacrylate (Bis-GMA) and/or triethylene glycol dimethacrylate (TEGDMA) release. Experiments were performed using the method of soaking extracts, which were derived from the immersion of the following CRs in the culture medium: Clearfil-Majesty-ES-2, GrandioSO, and Enamel-plus-HRi (Bis-GMA-based); Enamel-BioFunction and VenusDiamond (Bis-GMA-free). Human Gingival Fibroblasts (hGDFs) were employed as the cellular model to mimic in vitro the oral cavity milieu, where CRs simultaneously release various components. Cell metabolic activity, oxidative stress, and genotoxicity were used as cellular outcomes. Results showed that only VenusDiamond and Enamel-plus-HRi significantly affected the hGDF cell metabolic activity. In accordance with this, although no CR-derived extract induced a significantly detectable oxidative stress, only VenusDiamond and Enamel-plus-HRi induced significant genotoxicity. Our findings showed, for the CRs employed, a cytotoxic and genotoxic potential that did not seem to depend only on the actual Bis-GMA or TEGDMA content. Enamel-BioFunction appeared optimal in terms of cytotoxicity, and similar findings were observed for Clearfil-Majesty-ES-2 despite their different Bis-GMA/TEGDMA release patterns. This suggested that simply excluding one specific monomer from the CR formulation might not steadily turn out as a successful approach for improving their biocompatibility.     

Modulation of genotoxicity of azathioprine by intracellular glutathione in hepatocytes

Summary The role of intracellular glutathione (GSH) against the genotoxicity of azathioprine (AZA) was examined by the use of rat hepatocytes and alkaline and neutral elution techniques. Treatment of hepatocytes with AZA for 3 h induced DNA fragmentation in alkaline conditions but not in neutral conditions. A dose-dependent increase in DNA single-strand breaks was observed with the treatment of AZA ranging from 0.3 mM to 1.0 mM with concomitant cytotoxicity. However, neither 6-mercaptopurine, which is a major metabolite of AZA, nor 6-mercaptopurine riboside, an active form of the former, induced the DNA damage at the same concentrations. Moreover, the elution rate of DNA fragmentation, even at low dose of AZA that is not cytotoxic, significantly increased in the presence of buthionine sulfoximine, which is a selective inhibitor of-glutamylcysteine synthetase; i.e., depletion of GSH in hepatocytes enhanced the DNA damage by AZA. Thus, AZA has been proved to be genotoxic, and the genotoxicity is likely to be protected by GSH present in hepatocytes, suggesting that GSH depletion potentiates the carcinogenic effect of AZA.Abbreviations AZA azathioprine - GSH glutathione - 6-MP 6-mercaptopurine - SDS sodium dodecyl sulfate - BSO buthionine sulfoximine     

Biological activity of plant extract isolated from Papaver rhoeas on human lymfoblastoid cell line

Varied medicinal plants are known as a source of natural phytochemicals with antioxidant activities that can protect organisms from oxidative stress and from various chronic diseases. Papaver rhoeas has a long history of medicinal usage, especially for ailments in adults and children. The possible cytotoxicity, genotoxicity and potential antioxidant effect of plant extract isolated from flowers of Papaver rhoeas was investigated in human lymfoblastoid cell line (TK6). Antioxidant activity of this extract was determined using the DPPH assay. The plant extract exhibited dose dependent free radical scavenging ability. The growth activity assay was used for determination of cytotoxicity. To assess potential genotoxicity the comet assay was used. The lower extract concentrations (0.25 and 0.5 mg/ml) neither exerted cytotoxic, nor genotoxic effects in TK6 cells but they stimulated cell proliferation. The concentration 25 mg/ml scavenged almost 85% of DPPH free radical. On the other hand, this concentration had strong cytotoxic and genotoxic effect on TK6 cells. The balance between beneficial and harmful effects should be always considered when choosing the effective dose.     

Influence of Zirconia and Organic Additives on Mechanical and Electrochemical Properties of Silica Sol-Gel Coatings

This paper presents the result of the investigation of organically modified silica (ORMOSIL)-zirconia coatings used to enhance their protective properties, namely corrosion and scratch resistance. Two different materials, i.e., SiO₂/ZrO₂ and SiO₂/GPTMS/ZrO₂, were synthesized, measured, and analyzed to find the difference in the used organosilane precursor (dimethyldiethoxysilane and (3-glycidoxypropyl)trimethoxysilane, respectively). SiO₂/ZrO₂ coatings showed higher hardness than SiO₂/GPTMS/ZrO₂. Moreover, the value of polarization resistance (R_p) for SiO₂/GPTMS/ZrO₂ coated 316L steel relative to the uncoated one was obtained. It was nearly 84 times higher. The coating delamination was observed with load 16N. Additionally, the corrosion mitigation for 316L coated by SiO₂/GPTMS/ZrO₂ was observed even after extended exposure to corrosion agents.     

Assessment of genotoxicity and cytotoxicity of standardized aqueous extract from leaves of Erythroxylum cuneatum in human HepG2 and WRL68 cells line

ObjectiveTo investigate the cytotoxicity and the genotoxicity of standardized aqueous of dry leaves of Erythroxylum cuneatum (E. cuneatum) in human HepG2 and WRL68 cells.MethodsThe cytotoxicity of E. cuneatum extract was evaluated by both MTS and LDH assays. Genotoxicity study on E. cuneatum extract was assessed by the single cell gel electrophoresis (comet assay). The protective effect of E. cuneatum against menadione-induced cytotoxicity was also investigated.ResultsResults from this study showed that E. cuneatum extract exhibited cytotoxic activities towards the cells with IC₅₀ value of (125±12) and (125±14) μg/mL for HepG2 and WRL68 cells respectively, after 72 h incubation period as determined by MTS assay. LDH leakage was detected at (251±19) and (199.5±12.0) μg/mL for HepG2 and WRL68 respectively. Genotoxicity study results showed that treatment with E. cuneatum up to 1 mg/mL did not cause obvious DNA damage in WRL68 and HepG2 cells. Addition of E. cunaetum did not show significant protection towards menadione in WRL68 and HepG2 Cells.ConclusionsE. cuneatum standardized aqueous extract might be developed in order to establish new pharmacological possibilities for its application.     

Impact of Sandblasting on Morphology,Structure and Conductivity of Zirconia Dental Ceramics Material

Over the last decade, zirconia (ZrO₂)-based ceramic materials have become more applicable to modern dental medicine due to the sustained development of diverse computer-aided design/computer-aided manufacturing (CAD/CAM) systems. However, before the cementation and clinical application, the freshly prepared zirconia material (e.g., crowns) has to be processed by sandblasting in the dental laboratory. In this work, the impact of the sandblasting on the zirconia is monitored as changes in morphology (i.e., grains and cracks), and the presence of impurities might result in a poor adhesive bonding with cement. The sandblasting is conducted by using Al₂O₃ powder (25, 50, 110 and 125 µm) under various amounts of air-abrasion pressure (0.1, 0.2, 0.4 and 0.6 MPa). There has been much interest in both the determination of the impact of the sandblasting on the zirconia phase transformations and conductivity. Morphology changes are observed by using Scanning Electron Microscope (SEM), the conductivity is measured by Impedance Spectroscopy (IS), and the phase transformation is observed by using Powder X-Ray Diffraction (PXRD). The results imply that even the application of the lowest amount of air-abrasion pressure and the smallest Al₂O₃ powder size yields a morphology change, a phase transformation and a material contamination.     

Effect of Titanium and Zirconium Oxide Microparticles on Pro-Inflammatory Response in Human Macrophages under Induced Sterile Inflammation: An In Vitro Study

The wear-debris particles released by shearing forces during dental implant insertion may contribute to inflammatory reactions or osteolysis associated with peri-implantitis by stimulating inflammasome-activation. The study aim was to examine cytotoxic and pro-inflammatory effects of titanium (TiO₂) and zirconia (ZrO₂) particles in macrophages regarding their nature/particle concentration over time under sterile lipopolysaccharide (LPS) inflammation. Macrophages were exposed to TiO₂ and ZrO₂ particles (≤5 µm) in cell culture. Dental glass was used as inert control and LPS (1 μg/mL) was used to promote sterile inflammation. Cytotoxicity was determined using MTT assays and cytokine expression of TNF-α, IL-1β and IL-6 was evaluated by qRT-PCR. Data were analyzed using Student’s t-test and ANOVA (p ≤ 0.05). Cytotoxicity was significantly increased when exposed to higher concentrations of glass, TiO₂ and ZrO₂ (≥10⁷ particles/mL) compared to controls (p ≤ 0.05). Macrophages challenged with TiO₂ particles expressed up to ≈3.5-fold higher upregulation than ZrO₂ from 12 to 48 h. However, when exposed to LPS, TiO₂ and ZrO₂ particle-induced pro-inflammatory gene expression was further enhanced (p ≤ 0.05). Our data suggest that ZrO₂ particles produce less toxicity/inflammatory cytokine production than TiO₂. The present study shows that the biological reactivity of TiO₂ and ZrO₂ depends on the type and concentration of particles in a time-dependent manner.     

Sintering Behavior,Thermal Expansion,and Environmental Impacts Accompanying Materials of the Al2O3/ZrO2 System Fabricated via Slip Casting

This work focuses on research on obtaining and characterizing Al₂O₃/ZrO₂ materials formed via slip casting method. The main emphasis in the research was placed on environmental aspects and those related to the practical use of ceramic materials. The goal was to analyze the environmental loads associated with the manufacturing of Al₂O₃/ZrO₂ composites, as well as to determine the coefficient of thermal expansion of the obtained materials, classified as technical ceramics. This parameter is crucial in terms of their practical applications in high-temperature working conditions, e.g., as parts of industrial machines. The study reports on the four series of Al₂O₃/ZrO₂ materials differing in the volume content of ZrO₂. The sintering process was preceded by thermogravimetric measurements. The fabricated and sintered materials were characterized by dilatometric study, scanning electron microscopy, X-ray diffraction, and stereological analysis. Further, life cycle assessment was supplied. Based on dilatometric tests, it was observed that Al₂O₃/ZrO₂ composites show a higher coefficient of thermal expansion than that resulting from the content of individual phases. The results of the life cycle analysis showed that the environmental loads (carbon footprint) resulting from the acquisition and processing of raw materials necessary for the production of sinters from Al₂O₃ and ZrO₂ are comparable to those associated with the production of plastic products such as polypropylene or polyvinyl chloride.     

Anatase Forming Treatment without Surface Morphological Alteration of Dental Implant

The osseointegration of titanium implants is allowed by the TiO₂ layer that covers the implants. Titania can exist in amorphous form or in three different crystalline conformations: anatase, rutile and brookite. Few studies have characterized TiO₂ covering the surface of dental implants from the crystalline point of view. The aim of the present study was to characterize the evolution of the TiO₂ layer following different surface treatments from a crystallographic point of view. Commercially pure titanium and Ti-6Al-4V implants subjected to different surface treatments were analyzed by Raman spectroscopy to evaluate the crystalline conformation of titania. The surface treatments evaluated were: machining, sandblasting, sandblasting and etching and sandblasting, etching and anodization. The anodizing treatment evaluated in this study allowed to obtain anatase on commercially pure titanium implants without altering the morphological characteristics of the surface.     

Wear Behavior of Conventionally and Directly Aged Maraging 18Ni-300 Steel Produced by Laser Powder Bed Fusion

This study aims to explore the wear performance of maraging 18Ni-300 steel, fabricated via laser powder bed fusion (LPBF). The building direction dependence of wear resistance was investigated with various wear loads and in terms of ball-on-disk wear tests. The effect of direct aging heat treatment, i.e., aging without solution heat treatment, on the wear performance was investigated by comparing the wear rates of directly aged samples, followed by solution heat treatment. The effect of counterpart material on the wear performance of the maraging steel was studied using two counterpart materials of bearing steel and ZrO₂ balls. When the bearing steel ball was used as the counterpart material, both the as-built and heat-treated maraging steel produced by the LPBF showed pronounced building direction dependence on their wear performance when the applied wear load was sufficiently high. However, when the ZrO₂ ball was used as the counterpart material, isotropic wear resistance was reported. The maraging steel produced by the LPBF demonstrated excellent wear resistance, particularly when it was aging heat-treated and the counterpart material was ZrO₂. The directly aged sample showed wear performance almost the same as the sample solution heat-treated and then aged, indicating that direct aging can be used as an alternative post heat treatment for tribological applications of the maraging steels produced by LPBF.     

Difference between Toxicities of Iron Oxide Magnetic Nanoparticles with Various Surface-Functional Groups against Human Normal Fibroblasts and Fibrosarcoma Cells

Recently, many nanomedical studies have been focused on magnetic nanoparticles (MNPs) because MNPs possess attractive properties for potential uses in imaging, drug delivery, and theranostics. MNPs must have optimized size as well as functionalized surface for such applications. However, careful cytotoxicity and genotoxicity assessments to ensure the biocompatibility and biosafety of MNPs are essential. In this study, Fe₃O₄ MNPs of different sizes (approximately 10 and 100–150 nm) were prepared with different functional groups, hydroxyl (–OH) and amine (–NH₂) groups, by coating their surfaces with tetraethyl orthosilicate (TEOS), 3-aminopropyltrimethoxysilane (APTMS) or TEOS/APTMS. Differential cellular responses to those surface-functionalized MNPs were investigated in normal fibroblasts vs. fibrosarcoma cells. Following the characterization of MNP properties according to size, surface charge and functional groups, cellular responses to MNPs in normal fibroblasts and fibrosarcoma cells were determined by quantifying metabolic activity, membrane integrity, and DNA stability. While all MNPs induced just about 5% or less cytotoxicity and genotoxicity in fibrosarcoma cells at lower than 500 μg/mL, APTMS-coated MNPs resulted in greater than 10% toxicity against normal cells. Particularly, the genotoxicity of MNPs was dependent on their dose, size and surface charge, showing that positively charged (APTMS- or TEOS/APTMS-coated) MNPs induced appreciable DNA aberrations irrespective of cell type. Resultantly, smaller and positively charged (APTMS-coated) MNPs led to more severe toxicity in normal cells than their cancer counterparts. Although it was difficult to fully differentiate cellular responses to various MNPs between normal fibroblasts and their cancer counterparts, normal cells were shown to be more vulnerable to internalized MNPs than cancer cells. Our results suggest that functional groups and sizes of MNPs are critical determinants of degrees of cytotoxicity and genotoxicity, and potential mechanisms of toxicity.     

Modified Titanium Surface-Mediated Effects on Human Bone Marrow Stromal Cell Response

Surface modification of titanium implants is used to enhance osseointegration. The study objective was to evaluate five modified titanium surfaces in terms of cytocompatibility and pro-osteogenic/pro-angiogenic properties for human mesenchymal stromal cells: amorphous microporous silica (AMS), bone morphogenetic protein-2 immobilized on AMS (AMS + BMP), bio-active glass (BAG) and two titanium coatings with different porosity (T1; T2). Four surfaces served as controls: uncoated Ti (Ti), Ti functionalized with BMP-2 (Ti + BMP), Ti surface with a thickened titanium oxide layer (TiO₂) and a tissue culture polystyrene surface (TCPS). The proliferation of eGFP-fLuc (enhanced green fluorescence protein-firefly luciferase) transfected cells was tracked non-invasively by fluorescence microscopy and bio-luminescence imaging. The implant surface-mediated effects on cell differentiation potential was tracked by determination of osteogenic and angiogenic parameters [alkaline phosphatase (ALP); osteocalcin (OC); osteoprotegerin (OPG); vascular endothelial growth factor-A (VEGF-A)]. Unrestrained cell proliferation was observed on (un)functionalized Ti and AMS surfaces, whereas BAG and porous titanium coatings T1 and T2 did not support cell proliferation. An important pro-osteogenic and pro-angiogenic potential of the AMS + BMP surface was observed. In contrast, coating the Ti surface with BMP did not affect the osteogenic differentiation of the progenitor cells. A significantly slower BMP-2 release from AMS compared to Ti supports these findings. In the unfunctionalized state, Ti was found to be superior to AMS in terms of OPG and VEGF-A production. AMS is suggested to be a promising implant coating material for bioactive agents delivery.     

Greater Osseointegration Potential with Nanostructured Surfaces on TiZr: Accelerated vs. Real-Time Ageing

Surface chemistry and nanotopography of dental implants can have a substantial impact on osseointegration. The aim of this investigation was to evaluate the effects of surface chemistry and nanotopography on the osseointegration of titanium-zirconium (TiZr; Roxolid^®) discs, using a biomechanical pull-out model in rabbits. Two discs each were placed in both the right and left tibiae of 16 rabbits. Five groups of sandblasted acid etched (SLA) discs were tested: (1) hydrophobic without nanostructures (dry/micro) (n = 13); (2) hydrophobic with nanostructures, accelerated aged (dry/nano/AA) (n = 12); (3) hydrophilic without nanostructures (wet/micro) (n = 13); (4) hydrophilic with nanostructures, accelerated aged (wet/nano/AA; SLActive^®) (n = 13); (5) hydrophilic with nanostructures, real-time aged (wet/nano/RTA). The animals were sacrificed after four weeks and the biomechanical pull-out force required to remove the discs was evaluated. Adjusted mean pull-out force was greatest for group wet/nano/RTA (64.5 ± 17.7 N) and lowest for group dry/micro (33.8 ± 10.7 N). Multivariate mixed model analysis showed that the pull-out force was significantly greater for all other disc types compared to the dry/micro group. Surface chemistry and topography both had a significant effect on pull-out force (p < 0.0001 for both), but the effect of the interaction between chemistry and topography was not significant (p = 0.1056). The introduction of nanostructures on the TiZr surface significantly increases osseointegration. The introduction of hydrophilicity to the TiZr implant surface significantly increases the capacity for osseointegration, irrespective of the presence or absence of nanotopography.     

Initial Bacterial Adhesion on Different Yttria-Stabilized Tetragonal Zirconia Implant Surfaces in Vitro

Bacterial adhesion to implant biomaterials constitutes a virulence factor leading to biofilm formation, infection and treatment failure. The aim of this study was to examine the initial bacterial adhesion on different implant materials in vitro. Four implant biomaterials were incubated with Enterococcus faecalis, Staphylococcus aureus and Candida albicans for 2 h: 3 mol % yttria-stabilized tetragonal zirconia polycrystal surface (B1a), B1a with zirconium oxide (ZrO₂) coating (B2a), B1a with zirconia-based composite coating (B1b) and B1a with zirconia-based composite and ZrO₂ coatings (B2b). Bovine enamel slabs (BES) served as control. The adherent microorganisms were quantified and visualized using scanning electron microscopy (SEM); DAPI and live/dead staining. The lowest bacterial count of E. faecalis was detected on BES and the highest on B1a. The fewest vital C. albicans strains (42.22%) were detected on B2a surfaces, while most E. faecalis and S. aureus strains (approximately 80%) were vital overall. Compared to BES; coated and uncoated zirconia substrata exhibited no anti-adhesive properties. Further improvement of the material surface characteristics is essential.     

New Coating Technique of Ceramic Implants with Different Glass Solder Matrices for Improved Osseointegration-Mechanical Investigations

Ceramics are a very popular material in dental implant technology due to their tribological properties, their biocompatibility and their esthetic appearance. However, their natural surface structure lacks the ability of proper osseointegration, which constitutes a crucial process for the stability and, thus, the functionality of a bone implant. We investigated the application of a glass solder matrix in three configurations—consisting mainly of SiO₂, Al₂O₃, K₂O and Na₂O to TZP-A ceramic specimens. The corresponding adhesive strength and surface roughness of the coatings on ceramic specimens have been analyzed. Thereby, high adhesive strength (70.3 ± 7.9 MPa) was found for the three different coatings. The obtained roughness (R_z) amounted to 18.24 ± 2.48 µm in average, with significant differences between the glass solder configurations. Furthermore, one configuration was also tested after additional etching which did not lead to significant increase of surface roughness (19.37 ± 1.04 µm) or adhesive strength (57.2 ± 5.8 MPa). In conclusion, coating with glass solder matrix seems to be a promising surface modification technique that may enable direct insertion of ceramic implants in dental and orthopaedic surgery.     

The role of anaemia in oxidative and genotoxic damage in transfused β-thalassaemic patients

Objectives: Redox imbalance and genotoxic damage are commonly observed in β thalassaemic patients. The aim of this study was to assess the role of anaemia in oxidative and genotoxic damage in regularly transfused thalassaemic patients, undergoing iron chelation therapy.

Methods: We studied the relationships of haematological, biochemical and clinical parameters with oxidative (reactive oxygen species and 8-oxo-7,8-dihydro-2′-deoxyguanosine) and genotoxic biomarkers (Comet assay and cytokinesis-block micronucleus test) in blood samples from 105 patients. To reduce the early effect of redox-active iron, samples were collected when pharmacokinetics of the iron chelators ensured their maximum effectiveness. The transfusion regimen, cardiac and hepatic magnetic resonance imaging T2* were evaluated to characterize the patient cohort. Labile plasma iron (LPI) was also assayed.

Results: Haemoglobin level had a significant effect on ROS, %DNA in the tail and micronuclei-micronucleated cell frequency (p?<?0.05). Higher Hb values reduced redox imbalance. LPI, detectable in 50.5% of patients, was related to the number of apoptotic and necrotic lymphocytes (p?=?0.03), demonstrating the cytotoxic effect of iron.

Discussion: The results highlight that an adequate transfusion regimen is essential to limit oxidative and genotoxic damage in β-thalassemic patients undergoing chelation therapy.

Conclusion: Owing to the higher risk of cancer in the thalassaemic cohorts, specific genotoxicity/oxidative biomarkers should be monitored in order to ameliorate and formulate more personalized disease management.     

Evaluation of antioxidant,in vitro cytotoxicity of micropropagated and naturally grown plants of Leptadenia reticulata (Retz.) Wight & Arn.-an endangered medicinal plant

ObjectiveTo evaluate the antioxidant and anti proliferative potential of different solvent extract of micropropagated and naturally grown plants of Leptadenia reticulata against various cancer cell lines.MethodsIn this study different extract were tested for cytotoxicity against human breast adenocarcinoma cell line MCF-7, human colon adenocarcinoma grade II cell line HT-29 and non cancer skeletal muscle cell line L6 through 3-(4, 5–dimethyl thiazol–2–yl)–5–diphenyl tetrazolium bromide assay. The total antioxidant potential was estimated by three different antioxidant model diphenylpicrylhydrazyl free radical scavenging activity, H₂O₂ scavenging activity and FeCl₃ reducing activity.ResultsThe ethyl acetate extract of both naturally grown plant and tissue cultured plant exhibited significant cytotoxicity with IC₅₀ values of 21 µg/mL, 26 µg/mL and 22 µg/mL; 20 µg/mL, 30 µg/mL and 18 µg/mL respectively against three cell lines. The diphenylpicrylhydrazyl free radical scavenging activity was found to be highest with IC₅₀ value of 267.13 µg/mL in ethyl acetate extract. The methanolic extract exhibited moderate antioxidant activity with IC₅₀ value of 510.15 µg/mL. A highly positive correlation was observed between the antioxidant potential and cytotoxic activity of the plant.ConclusionsThe strong cytotoxicity of ethyl acetate extract revealed anti carcinogenic potential of the plant which supports its traditional use as medicine. The present investigation is new to literature till date and will provide better scientific basis for future pharmacological, in vivo studies and novel source of pure bioactive compounds having anti cancer properties in this plant.     

Ethanol-enhanced cytotoxicity of alkylating agents

BACKGROUND: Although ethanol itself is not genotoxic, chronic alcohol consumption increases the risk of neoplastic disease. The mechanism by which ethanol exerts a cocarcinogenic effect is not well established, and the aim of this study was to determine whether exposure to ethanol increased the cytotoxicity of known carcinogens. METHODS: To assess cell survival, the ability of Chinese hamster A10 cells, which express alcohol dehydrogenase, to form colonies was determined after exposure to ethanol and other substances, including both genotoxicants and non-DNA-reactive cytotoxic agents. RESULTS: 1-Methyl-3-nitro-1-nitrosoguanidine (MNNG) is an alkylating agent that forms covalent bonds with DNA. The cytotoxicity of MNNG at concentrations of 0.17 to 0.68 microM was markedly enhanced when cells were also treated with 50 mM ethanol. When combined with 0.34 microM MNNG, concentrations of ethanol as low as 2 mM exacerbated the toxicity of this alkylating agent. When these experiments were repeated in the presence of 4-methylpyrazole, an inhibitor of alcohol dehydrogenase, pretreatment with ethanol did not affect the toxicity of MNNG. When ethanol treatment was combined with exposure to other carcinogens, as well as agents that do not directly damage DNA, the cytotoxicity of the DNA-reactive agents 4-nitroquinoline-N-oxide, mitomycin C, and 6-chloro-9-(3-[2-chloroethyl]aminopropylamino)-2-methoxyacridine was modestly enhanced, and that of a second alkylating agent, ethyl methanesulfonate, was markedly increased. CONCLUSIONS: The results are consistent with impairment of DNA repair processes, particularly base excision repair, by acetaldehyde, as a mechanism by which ethanol increases the genotoxicity of certain genotoxic agents.     

Tensile and Compressive Responses of Ceramic and Metallic Nanoparticle Reinforced Mg Composites

In the present study, room temperature mechanical properties of pure magnesium, Mg/ZrO₂ and Mg/(ZrO₂ + Cu) composites with various compositions are investigated. Results revealed that the use of hybrid (ZrO₂ + Cu) reinforcements in Mg led to enhanced mechanical properties when compared to that of single reinforcement (ZrO₂). Marginal reduction in mechanical properties of Mg/ZrO₂ composites were observed mainly due to clustering of ZrO₂ particles in Mg matrix and lack of matrix grain refinement. Addition of hybrid reinforcements led to grain size reduction and uniform distribution of hybrid reinforcements, globally and locally, in the hybrid composites. Macro- and micro- hardness, tensile strengths and compressive strengths were all significantly increased in the hybrid composites. With respect to unreinforced magnesium, failure strain was almost unchanged under tensile loading while it was reduced under compressive loading for both Mg/ZrO₂ and Mg/(ZrO₂ + Cu) composites.     

The ZrO2 Formation in ZrB2/SiC Composite Irradiated by Laser

In order to clearly understand the details of ZrO₂ formation during ablation, high intensity continuous laser was chosen to irradiate ZrB₂/SiC. The results reveal that there are two different modes of ZrO₂ formation depending on whether liquid SiO₂ is present. When liquid SiO₂ is present, ZrO₂ generated by the oxidation of ZrB₂ is firstly dissolved into SiO₂. Then, ZrO₂ will precipitate again, the temperature will decrease and the SiO₂ will evaporate. Otherwise, the ZrB₂ will be oxidized to ZrO₂ directly.