Hierarchical levels of organization of the Brazil nut mesocarp

Aiming to understand Nature´s strategies that inspire new composite materials, the hierarchical levels of organization of the Brazil nut (Bertholletia excelsa) mesocarp were investigated. Optical microscopy, scanning electron microscopy (SEM), microtomography (MicroCT) and small-angle X-ray scattering (SAXS) were used to deeply describe the cellular and fibrillary levels of organization. The mesocarp is the middle layer of the fruit which has developed several strategies to avoid its opening and protect its seed. Fibers have a different orientation in the three layers of the mesocarp, what reduces the anisotropy of the structure. Sclereids cells with thick cell walls fill the spaces between the fibers resembling a foam-filled structural composite. The mesocarp has several tubular channels and fractured surfaces which may work as sites for crack trapping and increase toughness. The thick and lignified cell wall of sclereids and fibers and the weak interface between cells can promote a longer and tortuous intercellular crack path. Additionally, fibers with high strength and stiffness due to microfibrils oriented along the main cell axis (µ = 0° to 17°) were identified in the innermost layer of the mesocarp. Such an understanding of each hierarchical level can inspire the development of new cellular composites with improved mechanical behaviorDFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berli

Influence of the clay content and the polysulfone molar mass on nanocomposite membrane properties

AbstractPolysulfone/MMT nanocomposite membranes were prepared by a congruence of the wet-phase inversion and the solution dispersion techniques. Different clay contents and two kinds of polysulfone were used in order to investigate the changes in the nanocomposite structure as well as in the thermal and mechanical properties. The increase in the basal spacing with the clay content increase was revealed by SAXRD. TEM images depicted the presence of hybrid morphology and SEM images showed that the clay particles were trapped inside the cross-section pores. By increasing the clay content and polysulfone molar mass, the onset temperature of decomposition was increased and the mass loss was decreased. From DTA studies, it was observed that PSf P-1700 low clay content membranes had higher values of enthalpies and the enthalpy values of PSf P-3500 membranes did not present a regular behavior. Also in the tensile tests, the increase of the clay content up to 4.0mass% promoted the increase of elongation at break and tensile strength

Polymer Nanocomposites for Hydrogen Storage

Hydrogen is considered to be a clean, economical and safe renewable energy source that would be ideal to replace fossil fuels, because it is light, highly abundant and its oxidation product (water) is environmentally benign. However, hydrogen is easy to burn (the chemical energy per mass of hydrogen is at least three times larger than that of other chemical fuels), which has the risk of fire and explosion. The problems of transportation and storage restrict the application of hydrogen energy, which has become a key factor in the development and utilization of hydrogen energy. This gas adsorbs at solid surfaces depending on the applied pressure and temperature. For storage purposes in mobile applications, the adsorption of hydrogen has been studied mainly on carbon species, but light and reasonably cheap materials of high surface area should prove to be attractive as well. Porous material is a very promising hydrogen storage material, which stores the gas in the form of molecules at low temperatures and compresses hydrogen into the holes effectively. The purpose of this work was to develop a hybrid porous materials consisting of sulfonated polyetherimide matrix with aluminum nanoparticles and faujasite type zeolite. Dilute solutions were first prepared under stirring at room temperature and the solutions were dried under vacuum. The hybrids were analyzed by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and hydrogen sorption measurements. The addition of aluminum decreased the glass transition temperature of the hybrids when compared to the sulfonated polymer and the TEM images showed that simply physically mixture occurred between polymer and metallic nanoparticles. Hydrogen sorption tests showed an increase in the amount of hydrogen in the presence of zeolite.CNPq (Brazilian Counsel of Technological and Scientific Development)FAPESP (Sao Paulo Research Foundation)Univ Fed Sao Carlos, Dept Mat Engn, Sao Carlos, SP, BrazilUniv Fed Pelotas, Ctr Technol Dev, Pelotas, RS, BrazilUniv Fed Sao Paulo, Inst Sci & Technol, Sao Jose Dos Campos, SP, BrazilUniv Fed Sao Paulo, Inst Sci & Technol, Sao Jose Dos Campos, SP, BrazilCNPq: 159187/2014-1FAPESP: 2013/23586-0Web of Scienc

Slow-release fluoride devices: a literature review

Although the prevalence of caries has decreased dramatically over the past decades, it has become a polarised disease, with most of subjects presenting low caries levels and few individuals accounting for most of the caries affected surfaces. Thus it become evident for the need of clinical approaches directed at these high-risk patients, in order to overcome problems related to compliance and low attendance at dental care centres. Slow-release fluoride devices were developed based on the inverse relationship existing between intra-oral fluoride levels and dental caries experience. The two main types of slow-release devices - copolymer membrane type and glass bead - are addressed in the present review. A substantial number of studies have demonstrated that these devices are effective in raising intra-oral F concentrations at levels able to reduce enamel solubility, resulting in a caries-protective effect. Studies in animals and humans demonstrated that the use of these devices was able to also protect the occlusal surfaces, not normally protected by conventional fluoride regimens. However, retention rates have been shown to be the main problem related to these devices and still requires further improvements. Although the results of these studies are very promising, further randomised clinical trials are needed in order to validate the use of these devices in clinical practice. The concept of continuously providing low levels of intra-oral fluoride has great potential for caries prevention in high caries-risk groups

Conteúdo de flúor em leites UHT disponíveis comercialmente em Bauru, Brasil

OBJECTIVES: The aims of the present study were to evaluate the fluoride (F) concentrations in whole, defatted and chocolate milks commercially available in Brazil and to estimate the daily F intake from these sources. MATERIAL AND METHODS: F concentrations were determined for 23 brands of milks, after HMDS-facilitated diffusion, using a F ion-specific electrode. Possible F ingestion per kg body weight was estimated, based on suggested volumes of formula consumption, for infants aging 1 to 12 months. RESULTS: F concentrations ranged from 0.02 to 1.6 µg/mL F for all brands analyzed. Whole and defatted milks had the lowest F concentrations, ranging from 0.02 to 0.07 µg/mL. With respect to chocolate milks, three brands had F concentrations above 0.5 µg/mL. Some brands of chocolate milks exceeded the dose regarded as the threshold level for the development of dental fluorosis, without taking into account other sources of fluoride intake. CONCLUSION: The high fluoride concentrations found in some brands of chocolate milks in the present study indicate that many products may be important contributors to the total fluoride intake, reinforcing the need of assaying fluoride content of foods and beverages consumed by small children.OBJETIVOS: Os objetivos do presente estudo foram avaliar as concentrações de flúor (F) em leites integrais, desnatados e achocolatados disponíveis comercialmente no Brasil e estimar a ingestão diária de F a partir destas fontes. MATERIAL E MÉTODOS: as concentrações de F foram determinadas em 23 marcas de leite, após difusão facilitada por HMDS, usando um eletrodo íon-específico para F. A ingestão provável de F por Kg de peso corporal foi estimada, baseando-se em volumes sugeridos de consumo de fórmulas infantis, para crianças entre 1 e 12 meses de idade. RESULTADOS: As concentrações de F variaram entre 0,02 e 1,6 µg/mL para todas as marcas analisadas. Os leites integrais e desnatados apresentaram as menores concentrações de F, variando entre 0,02 e 0,07 µg/mL. Com relação aos leites achocolatados, três marcas apresentaram concentrações de F acima de 0,5 µg/mL. Algumas marcas de leites achocolatados excederam a dose de flúor reconhecida como o limite máximo de exposição a fim de se evitar o desenvolvimento da fluorose dentária, sem se considerar outras fontes de ingestão de F. CONCLUSÃO: As altas concentrações de F encontradas em algumas marcas de leites achocolatados no presente estudo indicam que muitos produtos podem contribuir significativamente para a ingestão total de F, reforçando a necessidade de se avaliar o conteúdo de F em alimentos e bebidas consumidos por crianças pequenas

Fluoride concentrations in industrialized beverages consumed by children in the city of Bauru, Brazil

The increasing consumption of juices, soft drinks and teas among children has increased significantly fluoride ingestion at the age range of risk for development of dental fluorosis. Objective: The purpose of this study was to evaluate fluoride concentrations in some brands of industrialized beverages consumed by children in the city of Bauru, SP, Brazil. Material and Methods: 98 brands of beverages were analyzed, divided into 3 lots, comprising 36, 32 and 30 brands, respectively, for the first, second and third lots. Fluoride concentrations were determined by HMDS-facilitated diffusion, using a fluoride ion-specific electrode (Orion 9409). Results: Fluoride concentrations ranged between 0.04 and 1.76 µg F/mL. It was observed a wide variation in fluoride concentrations among the different brands, as well as the different lots of the same brand. There was no information on fluoride concentrations on the labels of any product. Conclusions: Some of the products analyzed could contribute significantly to the total fluoride intake and, thus, be important risk factors for development of dental fluorosis, which indicates the need of controlling the production of these beverages with respect to fluoride concentration

Effects of polyphosphates and fluoride on hydroxyapatite dissolution:A pH-stat investigation

AbstractObjectivesThis study investigated the immediate and sustained effect of sodium trimetaphosphate (TMP) and sodium hexametaphosphate (HMP) associated or not with fluoride (F) on hydroxyapatite (HA) dissolution using an erosion-like model, considering as well as the influence of salivary coating.DesignBaseline dissolution rates were determined for HA discs using a pH-stat system. In the first set of experiments, HA discs were treated with 1100μgF/mL, 1% or 8% of HMP, 1% or 8% of TMP and 1100μgF/mL associated with 1% or 8% of HMP or TMP, totaling 9 groups (n=8). In a second phase, HA discs were kept in pooled human saliva at 37°C for 2h before treatment with deionised water and 1100μgF/mL associated with 1% or 8% of HMP or TMP, totaling 5 groups (n=8). The post-treatment dissolution rate was determined from three consecutive 30-min assays. Data were analysed using 2 and 3-way ANOVA followed by Fisher and Holm–Sidak methods, respectively (α=0.05).ResultsAll test solutions promoted reduction in HA dissolution rate when compared to baseline control in the first post-treatment run (p<0.001). However, a synergistic effect was only observed between fluoride and 1% HMP. Moreover, the duration of inhibitory effect was greater when 8% HMP and 1 or 8% HMP associated with F were assessed (p<0.001). The presence of salivary coating led to higher protection for all groups when compared to discs without coating (p<0.001).ConclusionThe reduction of HA dissolution rate, as well as the duration of this effect were influenced by fluoride, type and concentration of phosphate salt and the presence of a salivary coating

Enamel subsurface caries-like lesions induced in human teeth by different solutions : a TMR analysis

This study assessed the effectiveness of models for developing subsurface caries lesions in vitro and verified mineral changes by transverse microradiography (TMR). Enamel blocks from permanent (n=5) and deciduous teeth (n=5) were submitted to lesion induction by immersion in demineralizing solutions during 96 h, followed by pH cycles of demineralization (de) and remineralization (re) for 10 days. Two de-/re solutions were tested. Demineralizing solution “A” was composed by 2.2 mM CaCl2, 2.2 mM KH2PO4, 0.05 M acetic acid, with pH 4.4 adjusted by 1 M KOH. Demineralizing solution “B” was composed by 2.2 mM CaCl2, 2.2 mM NaH2PO4, 0.05 M acetic acid and 0.25 ppmF, with pH 4.5 adjusted by 1M KOH. Solution “A” produced cavitated lesions in permanent teeth, whereas solution “B” led to subsurface lesions in deciduous teeth. Solution “B” was then tested in enamel blocks from permanent teeth (n=5) and subsurface lesions were obtained, so that solution “B” was employed for both substrates, and the blocks were treated with slurries of a fluoride dentifrice (1450 ppm F, as NaF, n=5) or a fluoride-free dentifrice (n=5). Solution “B” produced subsurface lesions in permanent and primary teeth of an average (±SD) depth of 88.4μm (±14.3) and 89.3μm (±15.8), respectively. TMR analysis demonstrated that lesions treated with fluoride-free dentifrice had significantly greater mineral loss. This study concluded that solution “B” developed subsurface lesions after pH cycling, and that mineral changes were successfully assessed by TMR.Este estudo avaliou a efetividade de modelos para o desenvolvimento de lesões de cárie subsuperficiais in vitro e verificou alterações minerais por microradiografia transversal (TMR). Blocos de esmalte de dentes permanentes (n = 5) e decíduos (n = 5) foram submetidos à indução de lesão por imersão em soluções desmineralizadoras durante 96h, seguido de ciclos de pH de desmineralização e remineralização por 10 dias. Duas soluções des-/re foram testadas. A solução desmineralizadora “A” foi composta por 2,2 mM de CaCl2, 2,2 mM de KH2PO4, 0,05 M de ácido acético, com pH de 4,4 ajustado por 1 M de KOH. A solução desmineralizadora “B” foi composta por 2,2 mM de CaCl2, 2,2 mM de NaH2PO4, 0,05 M de ácido acético e 0,25 ppmF, com pH de 4,5 ajustado por 1 M de KOH. A solução “A” produziu lesões cavitadas em dentes permanentes, enquanto a solução “B” apresentou lesões subsuperficiais em dentes decíduos. Portanto, a solução “B” foi posteriormente usada em blocos de esmalte de dentes permanentes (n = 5) e lesões subsuperficiais foram obtidas. Portanto, a solução “B” foi empregada para ambos os substratos, sendo metade deles tratada com dentifrício fluoretado e a outra metade com dentifrício livre de flúor. A solução “B” produziu lesões subsuperficiais de cárie com profundidade de 88.4μm (14.3) em dentes permanentes e com 89.3 μm (15.8) em dentes decíduos e TMR demonstrou que lesões tratadas com dentifrício sem flúor tiveram maior perda mineral. Este estudo concluiu que a solução “B” desenvolveu lesões subsuperficiais após o ciclo de pH e as alterações minerais foram avaliadas com sucesso por TMR