Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedi... more Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedical applications due to its small size, intrinsic optical properties, large specific surface area, and easy to functionalize. To fully exploit nano-GO properties, a reproducible method for its production is of utmost importance. Herein we report, the study of the sequential fracture of GO sheets onto nano-GO with controllable lateral width, by a simple, and reproducible method based on a mechanism that we describe as a confined hot spot atomic fragmentation/reduction of GO promoted by ultrasonication. The chemical and structural changes on GO structure during the breakage were monitored by XPS, FTIR, Raman and HRTEM. We found that GO sheets starts breaking from the defects region and in a second phase through the disruption of carbon bonds while still maintaining crystalline carbon domains. The breaking of GO is accompanied by its own reduction, essentially by the elimination of carboxylic and carbonyl functional groups. Photoluminescence and photothermal studies using this nano-GO are also presented highlighting the potential of this nanomaterial as a unique imaging/therapy platform. N owadays, one of the most prompt methods to prepare graphene oxide (GO) or reduced graphene oxide (rGO) is through the wet chemical exfoliation of graphite. This approach has the advantage of large scale production, procedure simplicity, high efficiency and low cost 1 . The exfoliation of graphite in solution occurs through extensive intercalation of oxygen moieties on the aromatic structure. This increases the interplanar carbon distance and consequently weakening the interactions between adjacent carbon planes 2 .
ABSTRACT Abstract Numerous carbon nanostructures have been investigated in the last years due to ... more ABSTRACT Abstract Numerous carbon nanostructures have been investigated in the last years due to their excellent mechanical properties. In this work, the effect of the addition of graphene oxide (GO) nanoparticles to UHMWPE and the optimal %wt GO addition were investigated. UHMWPE/GO nanocomposites with different GO wt% contents were prepared and their mechanical, thermal, structural and wettability properties were investigated and compared with virgin UHMWPE. The results showed that the thermal stability, oxidative resistance, mechanical properties and wettability properties of UHMWPE were enhanced due to the addition of GO. UHMWPE/GO materials prepared with up to 0.5 wt% GO exhibited improved characteristics compared to virgin UHMWPE and nanocomposites prepared with higher GO contents.
Hafnium has been suggested as an interesting candidate for orthopaedic applications due to its go... more Hafnium has been suggested as an interesting candidate for orthopaedic applications due to its good biocompatibility and osteogenesis. However, there is a need to further investigate its resistance to wear and corrosion in biological environments if hafnium is to be considered for such applications. The corrosion and tribocorrosion behaviour of hafnium and commercially pure titanium in simulated body fluids were investigated using electrochemical techniques. A ball-on-plate configuration tribometer and a three electrode electrochemical cell were integrated to investigate the tribocorrosion performance of the studied materials. In addition, the effect of micro-motions on the corrosion resistance of the material was also studied. Cyclic polarisation scans, open circuit potential measurements and potentiostatic tests were performed in 0.9% NaCl solution and 25% bovine calf serum solution in order to assess the effect of organic species on the corrosion behaviour of the metal.The result...
This work explores the preparation of three-dimensional graphene oxide macroscopic structures, sh... more This work explores the preparation of three-dimensional graphene oxide macroscopic structures, shaped by self-assembling single graphene oxide (3DGO) sheets with control of its surface chemistry by combining with nitrogen functional groups (3DGON), or with nitrogen and sulphur functional groups (3DGOSN), and their application in the removal of mercury (Hg(II)) from aqueous solutions. The chemical structure of the materials was assessed by using different characterization techniques: SEM, XPS and BET. Adsorption studies conducted in Hg(II) contaminated ultra-pure water reveal the enhanced ability of 3DGON for the adsorption of this metal, when compared to the other GO foams. A small dose of 3DGON (10mgL(-1)) allows to remove up to 96% of Hg(II) after 24h of contact time, leading to a residual concentration in solution close to the guideline value for drinking water (1μgL(-1)). The ability of this material to adsorb Hg (II) was evaluated relatively to different experimental parameters such as pH, sorbent dose, time and effect on different competing metal ions. Real application was also evaluated by testing its performance in two different natural matrices, river and sea water, with very promising results.
Metal-on-Polyethylene (MoP) is the bearing combination most commonly used in total joint replacem... more Metal-on-Polyethylene (MoP) is the bearing combination most commonly used in total joint replacements. However, the degradative oxidation behaviour of ultra high molecular weight polyethylene (UHMWPE) results in increased wear and wear debris, which contributes to the development of aseptic loosening and eventually to the failure of the implant. In order to address this issue, investigations have focused on the development of novel materials with improved characteristics. Recently, graphene oxide (GO) has generated great interest as reinforcement for polymer matrices due to its excellent mechanical properties. The aim of this study was to investigate the possibilities of UHMWPE/GO nanocomposites for their use in joint implants. UHMWPE/GO nanocomposites with different wt% GO content, up to 2 wt%, were manufactured under optimised conditions using a ball milling technique. Thermal, mechanical and structural characterisation of the UHMWPE/GO nanocomposites and conventional UHMWPE were ...
Ultra high molecular weight polyethylene (UHMWPE) has been extensively used as a bearing surface ... more 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.
We tested the hypothesis that the degree of conversion of a light-cured dental composite relates ... more We tested the hypothesis that the degree of conversion of a light-cured dental composite relates to the calculated (s × mW cm−2 = mJ cm−2) rather than to the irradiance value (mW cm−2) of the light source. Two light-curable composite resins were cured with three different light irradiance values over different curing times. The specimens tested were 2, 4 or 6 mm thick, and the degree of conversion values were measured with Raman spectroscopy on the top and the bottom surfaces of the specimens. The highest conversion value of one of the materials was just below 60%, while the maximal conversion value of the other material was just below 65%. That difference in conversion values could be related to differences in monomer systems used in the two composites. By considering light energy per square centimeter (J cm−2) rather than light irradiance (mW cm−2), we found that equivalent energy values gave similar conversion values for a certain sample thickness. From these findings, we conclude that our experimental results support our hypothesis.
The hypothesis that low light intensity and long but sufficient curing time can produce composite... more The hypothesis that low light intensity and long but sufficient curing time can produce composites with volumetric shrinkage, degree of conversion (DC%) and Young's modulus (E-modulus) comparable to those of high light intensity cured composite was tested, when the contraction strain and heat generation were lower with low light intensity curing. Dental composites (Z100 and Z250, 3M ESPE) were investigated. Specimens were cured with light intensities of 200, 450 and 800 mW/cm(2) for 140, 60 and 35 s from a distance of 7 mm. Strain-gages were used for contraction strain measurements. DC% was measured at the top and the bottom of 4 mm thick samples using FT-Raman spectroscopy. Volumetric polymerization shrinkage was determined using a water displacement method. E-modulus was determined in tension on composite specimens. The results were analyzed using ANOVA and Duncan's multiple range tests and regular t-test. Polymerization stress level decreased significantly (p<0.05) when cured with 200 mW/cm(2) rather than with 800 mW/cm(2). Temperature rises were significantly different (p<0.05) for different composites and light intensity values. Reduction in light intensity did not decrease the DC% values significantly at the top surfaces. The most dramatic differences existed between top and bottom surfaces (p<0.05) rather than among curing groups. Measured E-modulus and volumetric shrinkage values were not significantly different (p>0.05) between different light intensity groups. DC%, E-modulus and the volumetric shrinkage values in cured composites were not affected by low light intensity, however, the contraction strain and polymerization's exotherm were decreased. Thus our results support the proposed hypothesis.
We tested the hypothesis that the degree of conversion of a light-cured dental composite relates ... more We tested the hypothesis that the degree of conversion of a light-cured dental composite relates to the calculated (s x mW cm-2 = mJ cm-2) rather than to the irradiance value (mW cm-2) of the light source. Two light-curable composite resins were cured with three different light irradiance values over different curing times. The specimens tested were 2, 4 or 6 mm thick, and the degree of conversion values were measured with Raman spectroscopy on the top and the bottom surfaces of the specimens. The highest conversion value of one of the materials was just below 60%, while the maximal conversion value of the other material was just below 65%. That difference in conversion values could be related to differences in monomer systems used in the two composites. By considering light energy per square centimeter (J cm-2) rather than light irradiance (mW cm-2), we found that equivalent energy values gave similar conversion values for a certain sample thickness. From these findings, we conclude that our experimental results support our hypothesis.
Clinical observations suggest that some composite resins are more often linked to post-operative ... more Clinical observations suggest that some composite resins are more often linked to post-operative sensitivity than others. These differences may relate to differences in modulus of elasticity and polymerization rates among materials. The aim of this study was to identify viscoelastic behavior of two light curable composites and determine whether significant differences in viscoelastic behavior exist between the two materials when light cured at each of three different irradiance values.Two composites (Z100 and Z250 by 3M ESPE) were evaluated. Six specimens per composite and irradiance value (250, 500 and 850 mW/cm2) were made. The curing times were chosen to produce a fixed energy value of 30 J/cm2 independent of irradiation value. Dynamic mechanical thermal analysis (DMTA) was performed in single cantilever clamped mode.There were significant differences in transition temperatures between the two materials and the three frequencies at their glass transition temperatures, while significant differences did not exist at the lower transitions. The glass transition of Z250 was lower and narrower than that of Z100. Z250 exhibited lower storage modulus values. The irradiance values did not affect any of the transition temperatures significantly.The lower and more distinct Tg of Z250 suggests that Z250 cures more efficiently than Z100. The lower storage modulus of Z250 suggests that Z250 develops less stress in the tooth than Z100 during curing if shrinkage is the same for the two materials. The findings suggest that the material chosen, rather than irradiance, determines the stress level developed during light curing.
It was hypothesized that by standardizing variables such as light sources, filler types and fille... more It was hypothesized that by standardizing variables such as light sources, filler types and filler surface treatment, it should be possible to use Beer–Lambert's law to predict light absorption in visible light-cured dental composites.Mixture of 50 wt% bisGMA and 50 wt% TEGDMA to which a photo-initiator (0.35 wt% champhorquinone) and a co-initiator (0.7 wt% of dimethylaminoethylmethacrylate) was prepared. Three different filler types (HBB, SBB and KU) were added to that mixture in eight different volume percentage. Filler particles were either silane surface treated or not. Specimens were made with thicknesses of 1–5 mm. Total number of 1200 specimens were made for this study. Light transmission was obtained for halogen source and laser lights, which made the number of observations 2400. The absorbance values of the different materials were analyzed in Matlab with respect to the differences in filler fraction and sample thickness.The obtained results revealed that of the two light sources, more light was absorbed by the composite when the laser light was used. Among different filler types, the HBB filler absorbed most light and the KU filler the least. There were significant differences (p<0.05) in light absorption between all three filler types.By comparing the modeled surfaces generated by Matlab for different materials it was possible to determine how different variables such as filler type, filler surface treatment and light source affect light attenuation. The characteristic of incident light affected the light absorbance, meaning that not only the composite's composition needs to be considered in light absorption studies of dental composites.
Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedi... more Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedical applications due to its small size, intrinsic optical properties, large specific surface area, and easy to functionalize. To fully exploit nano-GO properties, a reproducible method for its production is of utmost importance. Herein we report, the study of the sequential fracture of GO sheets onto nano-GO with controllable lateral width, by a simple, and reproducible method based on a mechanism that we describe as a confined hot spot atomic fragmentation/reduction of GO promoted by ultrasonication. The chemical and structural changes on GO structure during the breakage were monitored by XPS, FTIR, Raman and HRTEM. We found that GO sheets starts breaking from the defects region and in a second phase through the disruption of carbon bonds while still maintaining crystalline carbon domains. The breaking of GO is accompanied by its own reduction, essentially by the elimination of carboxylic and carbonyl functional groups. Photoluminescence and photothermal studies using this nano-GO are also presented highlighting the potential of this nanomaterial as a unique imaging/therapy platform. N owadays, one of the most prompt methods to prepare graphene oxide (GO) or reduced graphene oxide (rGO) is through the wet chemical exfoliation of graphite. This approach has the advantage of large scale production, procedure simplicity, high efficiency and low cost 1 . The exfoliation of graphite in solution occurs through extensive intercalation of oxygen moieties on the aromatic structure. This increases the interplanar carbon distance and consequently weakening the interactions between adjacent carbon planes 2 .
The goal of this paper is to emphasis and presents briefly the nanotechnology science and its pot... more The goal of this paper is to emphasis and presents briefly the nanotechnology science and its potential impact on the automotive industry in order to improve the production of recent models with an optimization of the safety performance and a reduction in the environmental impacts, mainly pollutant emissions. Nanomaterials can be applied in car bodies as light weight constructions without compromising the stiffness and crash resistance, which means less material and less fuel consumption. This paper outlines the progress of nanotechnology applications into the safety features of more recent vehicle models and fuel efficiency, but also emphasis the importance of sustainable development on the application of these technologies and life cycle analysis of the considered materials, in order to meet the society trends and customers demands to improve ecology, safety and comfort.
Graphene is a two-dimensional new allotrope of carbon, which is stimulating great curiosity due t... more 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.
Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedi... more Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedical applications due to its small size, intrinsic optical properties, large specific surface area, and easy to functionalize. To fully exploit nano-GO properties, a reproducible method for its production is of utmost importance. Herein we report, the study of the sequential fracture of GO sheets onto nano-GO with controllable lateral width, by a simple, and reproducible method based on a mechanism that we describe as a confined hot spot atomic fragmentation/reduction of GO promoted by ultrasonication. The chemical and structural changes on GO structure during the breakage were monitored by XPS, FTIR, Raman and HRTEM. We found that GO sheets starts breaking from the defects region and in a second phase through the disruption of carbon bonds while still maintaining crystalline carbon domains. The breaking of GO is accompanied by its own reduction, essentially by the elimination of carboxylic and carbonyl functional groups. Photoluminescence and photothermal studies using this nano-GO are also presented highlighting the potential of this nanomaterial as a unique imaging/therapy platform. N owadays, one of the most prompt methods to prepare graphene oxide (GO) or reduced graphene oxide (rGO) is through the wet chemical exfoliation of graphite. This approach has the advantage of large scale production, procedure simplicity, high efficiency and low cost 1 . The exfoliation of graphite in solution occurs through extensive intercalation of oxygen moieties on the aromatic structure. This increases the interplanar carbon distance and consequently weakening the interactions between adjacent carbon planes 2 .
ABSTRACT Abstract Numerous carbon nanostructures have been investigated in the last years due to ... more ABSTRACT Abstract Numerous carbon nanostructures have been investigated in the last years due to their excellent mechanical properties. In this work, the effect of the addition of graphene oxide (GO) nanoparticles to UHMWPE and the optimal %wt GO addition were investigated. UHMWPE/GO nanocomposites with different GO wt% contents were prepared and their mechanical, thermal, structural and wettability properties were investigated and compared with virgin UHMWPE. The results showed that the thermal stability, oxidative resistance, mechanical properties and wettability properties of UHMWPE were enhanced due to the addition of GO. UHMWPE/GO materials prepared with up to 0.5 wt% GO exhibited improved characteristics compared to virgin UHMWPE and nanocomposites prepared with higher GO contents.
Hafnium has been suggested as an interesting candidate for orthopaedic applications due to its go... more Hafnium has been suggested as an interesting candidate for orthopaedic applications due to its good biocompatibility and osteogenesis. However, there is a need to further investigate its resistance to wear and corrosion in biological environments if hafnium is to be considered for such applications. The corrosion and tribocorrosion behaviour of hafnium and commercially pure titanium in simulated body fluids were investigated using electrochemical techniques. A ball-on-plate configuration tribometer and a three electrode electrochemical cell were integrated to investigate the tribocorrosion performance of the studied materials. In addition, the effect of micro-motions on the corrosion resistance of the material was also studied. Cyclic polarisation scans, open circuit potential measurements and potentiostatic tests were performed in 0.9% NaCl solution and 25% bovine calf serum solution in order to assess the effect of organic species on the corrosion behaviour of the metal.The result...
This work explores the preparation of three-dimensional graphene oxide macroscopic structures, sh... more This work explores the preparation of three-dimensional graphene oxide macroscopic structures, shaped by self-assembling single graphene oxide (3DGO) sheets with control of its surface chemistry by combining with nitrogen functional groups (3DGON), or with nitrogen and sulphur functional groups (3DGOSN), and their application in the removal of mercury (Hg(II)) from aqueous solutions. The chemical structure of the materials was assessed by using different characterization techniques: SEM, XPS and BET. Adsorption studies conducted in Hg(II) contaminated ultra-pure water reveal the enhanced ability of 3DGON for the adsorption of this metal, when compared to the other GO foams. A small dose of 3DGON (10mgL(-1)) allows to remove up to 96% of Hg(II) after 24h of contact time, leading to a residual concentration in solution close to the guideline value for drinking water (1μgL(-1)). The ability of this material to adsorb Hg (II) was evaluated relatively to different experimental parameters such as pH, sorbent dose, time and effect on different competing metal ions. Real application was also evaluated by testing its performance in two different natural matrices, river and sea water, with very promising results.
Metal-on-Polyethylene (MoP) is the bearing combination most commonly used in total joint replacem... more Metal-on-Polyethylene (MoP) is the bearing combination most commonly used in total joint replacements. However, the degradative oxidation behaviour of ultra high molecular weight polyethylene (UHMWPE) results in increased wear and wear debris, which contributes to the development of aseptic loosening and eventually to the failure of the implant. In order to address this issue, investigations have focused on the development of novel materials with improved characteristics. Recently, graphene oxide (GO) has generated great interest as reinforcement for polymer matrices due to its excellent mechanical properties. The aim of this study was to investigate the possibilities of UHMWPE/GO nanocomposites for their use in joint implants. UHMWPE/GO nanocomposites with different wt% GO content, up to 2 wt%, were manufactured under optimised conditions using a ball milling technique. Thermal, mechanical and structural characterisation of the UHMWPE/GO nanocomposites and conventional UHMWPE were ...
Ultra high molecular weight polyethylene (UHMWPE) has been extensively used as a bearing surface ... more 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.
We tested the hypothesis that the degree of conversion of a light-cured dental composite relates ... more We tested the hypothesis that the degree of conversion of a light-cured dental composite relates to the calculated (s × mW cm−2 = mJ cm−2) rather than to the irradiance value (mW cm−2) of the light source. Two light-curable composite resins were cured with three different light irradiance values over different curing times. The specimens tested were 2, 4 or 6 mm thick, and the degree of conversion values were measured with Raman spectroscopy on the top and the bottom surfaces of the specimens. The highest conversion value of one of the materials was just below 60%, while the maximal conversion value of the other material was just below 65%. That difference in conversion values could be related to differences in monomer systems used in the two composites. By considering light energy per square centimeter (J cm−2) rather than light irradiance (mW cm−2), we found that equivalent energy values gave similar conversion values for a certain sample thickness. From these findings, we conclude that our experimental results support our hypothesis.
The hypothesis that low light intensity and long but sufficient curing time can produce composite... more The hypothesis that low light intensity and long but sufficient curing time can produce composites with volumetric shrinkage, degree of conversion (DC%) and Young&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s modulus (E-modulus) comparable to those of high light intensity cured composite was tested, when the contraction strain and heat generation were lower with low light intensity curing. Dental composites (Z100 and Z250, 3M ESPE) were investigated. Specimens were cured with light intensities of 200, 450 and 800 mW/cm(2) for 140, 60 and 35 s from a distance of 7 mm. Strain-gages were used for contraction strain measurements. DC% was measured at the top and the bottom of 4 mm thick samples using FT-Raman spectroscopy. Volumetric polymerization shrinkage was determined using a water displacement method. E-modulus was determined in tension on composite specimens. The results were analyzed using ANOVA and Duncan&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s multiple range tests and regular t-test. Polymerization stress level decreased significantly (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05) when cured with 200 mW/cm(2) rather than with 800 mW/cm(2). Temperature rises were significantly different (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05) for different composites and light intensity values. Reduction in light intensity did not decrease the DC% values significantly at the top surfaces. The most dramatic differences existed between top and bottom surfaces (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05) rather than among curing groups. Measured E-modulus and volumetric shrinkage values were not significantly different (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;0.05) between different light intensity groups. DC%, E-modulus and the volumetric shrinkage values in cured composites were not affected by low light intensity, however, the contraction strain and polymerization&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s exotherm were decreased. Thus our results support the proposed hypothesis.
We tested the hypothesis that the degree of conversion of a light-cured dental composite relates ... more We tested the hypothesis that the degree of conversion of a light-cured dental composite relates to the calculated (s x mW cm-2 = mJ cm-2) rather than to the irradiance value (mW cm-2) of the light source. Two light-curable composite resins were cured with three different light irradiance values over different curing times. The specimens tested were 2, 4 or 6 mm thick, and the degree of conversion values were measured with Raman spectroscopy on the top and the bottom surfaces of the specimens. The highest conversion value of one of the materials was just below 60%, while the maximal conversion value of the other material was just below 65%. That difference in conversion values could be related to differences in monomer systems used in the two composites. By considering light energy per square centimeter (J cm-2) rather than light irradiance (mW cm-2), we found that equivalent energy values gave similar conversion values for a certain sample thickness. From these findings, we conclude that our experimental results support our hypothesis.
Clinical observations suggest that some composite resins are more often linked to post-operative ... more Clinical observations suggest that some composite resins are more often linked to post-operative sensitivity than others. These differences may relate to differences in modulus of elasticity and polymerization rates among materials. The aim of this study was to identify viscoelastic behavior of two light curable composites and determine whether significant differences in viscoelastic behavior exist between the two materials when light cured at each of three different irradiance values.Two composites (Z100 and Z250 by 3M ESPE) were evaluated. Six specimens per composite and irradiance value (250, 500 and 850 mW/cm2) were made. The curing times were chosen to produce a fixed energy value of 30 J/cm2 independent of irradiation value. Dynamic mechanical thermal analysis (DMTA) was performed in single cantilever clamped mode.There were significant differences in transition temperatures between the two materials and the three frequencies at their glass transition temperatures, while significant differences did not exist at the lower transitions. The glass transition of Z250 was lower and narrower than that of Z100. Z250 exhibited lower storage modulus values. The irradiance values did not affect any of the transition temperatures significantly.The lower and more distinct Tg of Z250 suggests that Z250 cures more efficiently than Z100. The lower storage modulus of Z250 suggests that Z250 develops less stress in the tooth than Z100 during curing if shrinkage is the same for the two materials. The findings suggest that the material chosen, rather than irradiance, determines the stress level developed during light curing.
It was hypothesized that by standardizing variables such as light sources, filler types and fille... more It was hypothesized that by standardizing variables such as light sources, filler types and filler surface treatment, it should be possible to use Beer–Lambert's law to predict light absorption in visible light-cured dental composites.Mixture of 50 wt% bisGMA and 50 wt% TEGDMA to which a photo-initiator (0.35 wt% champhorquinone) and a co-initiator (0.7 wt% of dimethylaminoethylmethacrylate) was prepared. Three different filler types (HBB, SBB and KU) were added to that mixture in eight different volume percentage. Filler particles were either silane surface treated or not. Specimens were made with thicknesses of 1–5 mm. Total number of 1200 specimens were made for this study. Light transmission was obtained for halogen source and laser lights, which made the number of observations 2400. The absorbance values of the different materials were analyzed in Matlab with respect to the differences in filler fraction and sample thickness.The obtained results revealed that of the two light sources, more light was absorbed by the composite when the laser light was used. Among different filler types, the HBB filler absorbed most light and the KU filler the least. There were significant differences (p<0.05) in light absorption between all three filler types.By comparing the modeled surfaces generated by Matlab for different materials it was possible to determine how different variables such as filler type, filler surface treatment and light source affect light attenuation. The characteristic of incident light affected the light absorbance, meaning that not only the composite's composition needs to be considered in light absorption studies of dental composites.
Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedi... more Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedical applications due to its small size, intrinsic optical properties, large specific surface area, and easy to functionalize. To fully exploit nano-GO properties, a reproducible method for its production is of utmost importance. Herein we report, the study of the sequential fracture of GO sheets onto nano-GO with controllable lateral width, by a simple, and reproducible method based on a mechanism that we describe as a confined hot spot atomic fragmentation/reduction of GO promoted by ultrasonication. The chemical and structural changes on GO structure during the breakage were monitored by XPS, FTIR, Raman and HRTEM. We found that GO sheets starts breaking from the defects region and in a second phase through the disruption of carbon bonds while still maintaining crystalline carbon domains. The breaking of GO is accompanied by its own reduction, essentially by the elimination of carboxylic and carbonyl functional groups. Photoluminescence and photothermal studies using this nano-GO are also presented highlighting the potential of this nanomaterial as a unique imaging/therapy platform. N owadays, one of the most prompt methods to prepare graphene oxide (GO) or reduced graphene oxide (rGO) is through the wet chemical exfoliation of graphite. This approach has the advantage of large scale production, procedure simplicity, high efficiency and low cost 1 . The exfoliation of graphite in solution occurs through extensive intercalation of oxygen moieties on the aromatic structure. This increases the interplanar carbon distance and consequently weakening the interactions between adjacent carbon planes 2 .
The goal of this paper is to emphasis and presents briefly the nanotechnology science and its pot... more The goal of this paper is to emphasis and presents briefly the nanotechnology science and its potential impact on the automotive industry in order to improve the production of recent models with an optimization of the safety performance and a reduction in the environmental impacts, mainly pollutant emissions. Nanomaterials can be applied in car bodies as light weight constructions without compromising the stiffness and crash resistance, which means less material and less fuel consumption. This paper outlines the progress of nanotechnology applications into the safety features of more recent vehicle models and fuel efficiency, but also emphasis the importance of sustainable development on the application of these technologies and life cycle analysis of the considered materials, in order to meet the society trends and customers demands to improve ecology, safety and comfort.
Graphene is a two-dimensional new allotrope of carbon, which is stimulating great curiosity due t... more 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.
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Papers by Nazanin Emami