Avaliação de próteses de Si3N4/diamante por ressonância magnética

Mestrado em Materiais e Dispositivos BiomédicosA Ressonância Magnética (RM) é uma modalidade imagiológica que tem permitido grandes avanços na área do diagnóstico médico. Tem vindo a ser cada vez mais utilizada para avaliação pós-operatória em variadas situações. No entanto, existem alguns obstáculos à obtenção de imagens de qualidade. Esses obstáculos são, muitas vezes, provocados pela presença de material cirúrgico, como é caso das próteses da anca, que devido às suas características, dão origem a artefactos de suscetibilidade magnética que prejudicam a qualidade da imagem. O desenvolvimento de novos materiais tem demonstrado vantagens no que respeita aos artefactos provocados por estes em exames imagiológicos. Os cerâmicos de nitreto de silício (Si3N4) revestidos por diamante nanocristalino obtido por deposição química em fase vapor (CVD), desenvolvido nos laboratórios do Centro de Investigação em Materiais Cerâmicos e Compósitos (CICECO) da Universidade de Aveiro, é um novo material candidato à utilização em próteses articulares, nomeadamente na cabeça do fémur em próteses da anca. Estes cerâmicos apresentam excelentes características de resistência ao desgaste e de biocompatibilidade. Um estudo prévio com Tomografia Computorizada (TC) apresentou bons resultados com diminuição dos artefactos metálicos. Não são conhecidos estudos que avaliem o seu comportamento no contexto da RM. O presente trabalho teve como objetivo avaliar o comportamento imagiológico deste novo material, Si3N4 revestido a nanodiamante, em RM e compará-lo com materiais atualmente comercializados. Para tal, utilizou-se um fantoma com características que não colocam em causa a segurança na realização dos testes no ambiente de RM. Foram utilizadas amostras de cabeças do fémur de próteses da anca de diferentes materiais nomeadamente Cobalto-Crómio, Oxinium, Zirconia-Toughened Alumina, Nitreto de Silício e Nitreto de Silício revestido com diamante. As imagens foram adquiridas em condições similares em dois equipamentos de RM, um de 3T no Instituto de Ciências Nucleares Aplicadas à Saúde (ICNAS) e outro de 1,5T no Centro de Tomografia Computorizada de Aveiro (CENTAC), procedendo-se posteriormente à análise das imagens, quantificação de artefactos e à comparação dos artefactos causados pelos diferentes materiais. Os resultados alcançados no contexto do presente estudo permitem evidenciar propriedades imagiológicas promissoras dos cerâmicos Si3N4/diamante, uma vez que os artefactos produzidos por estes cerâmicos são reduzidos quando comparados com os originados por outros materiais atualmente utilizados no fabrico deste tipo de próteses.Magnetic resonance imaging (MRI) is an imaging modality that has allowed major advances in medical diagnostics. It has been increasingly used for postoperative evaluation in different situations. However, there are some obstacles to obtain quality images. These obstacles are often caused by the presence of surgical material, as it is the case of hip prostheses. Hip prostheses characteristics give rise to magnetic susceptibility artifacts that affects image quality. The development of new materials has shown advantages regarding artifacts in diagnostic imaging. Ceramic Silicon Nitride (Si3N4) coated nanocrystalline diamond obtained by Chemical Vapor Deposition (CVD) developed in CICECO – Centre for Research in Ceramics and Composites Materials at the University of Aveiro is a new candidate to be used in joint prostheses, namely in hip prostheses of femur head. This ceramics material has excellent characteristics of wear resistance and biocompatibility. A previous study with CT showed good results since metal artifacts were reduced. Yet, no previous studies assessing Si3N4 coated nanocrystalline diamond behavior in MRI are found. This study is aimed at evaluating the imaging performance of this new material, Si3N4 coated nanocrystalline diamond in MRI, and comparing it with materials currently marketed. For this purpose, a phantom which does not jeopardize safety in testing MRI was used. Samples of hip prostheses femoral heads made of different materials, namely Cobalt-Chromium (CC), Oxinium (OX), Zirconia-Toughened Alumina (ZTA), Silicon Nitride (NS) and Silicon Nitride coated with diamond (NSD) were used. Images were acquired in two MRI equipments under similar conditions, a 3T at the Institute of Nuclear Sciences Applied to Health (ICNAS) and a 1.5T at the Centre of Computed Tomography of Aveiro (CENTAC). Images analysis, artifacts quantification and comparison of artifacts caused by different materials were performed. The results obtained in this study show promising imaging properties of Si3N4/diamond. The artifacts produced by this material are reduced when compared to those generated by other materials currently used in hip prostheses manufacture

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear un derstanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5–7 vast areas of the tropics remain understudied.8–11 In the American tropics, Amazonia stands out as the world’s most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepre sented in biodiversity databases.13–15 To worsen this situation, human-induced modifications16,17 may elim inate pieces of the Amazon’s biodiversity puzzle before we can use them to understand how ecological com munities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple or ganism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region’s vulnerability to environmental change. 15%–18% of the most ne glected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lostinfo:eu-repo/semantics/publishedVersio

Geographic patterns of tree dispersal modes in Amazonia and their ecological correlates

Aim: To investigate the geographic patterns and ecological correlates in the geographic distribution of the most common tree dispersal modes in Amazonia (endozoochory, synzoochory, anemochory and hydrochory). We examined if the proportional abundance of these dispersal modes could be explained by the availability of dispersal agents (disperser-availability hypothesis) and/or the availability of resources for constructing zoochorous fruits (resource-availability hypothesis). Time period: Tree-inventory plots established between 1934 and 2019. Major taxa studied: Trees with a diameter at breast height (DBH) ≥ 9.55 cm. Location: Amazonia, here defined as the lowland rain forests of the Amazon River basin and the Guiana Shield. Methods: We assigned dispersal modes to a total of 5433 species and morphospecies within 1877 tree-inventory plots across terra-firme, seasonally flooded, and permanently flooded forests. We investigated geographic patterns in the proportional abundance of dispersal modes. We performed an abundance-weighted mean pairwise distance (MPD) test and fit generalized linear models (GLMs) to explain the geographic distribution of dispersal modes. Results: Anemochory was significantly, positively associated with mean annual wind speed, and hydrochory was significantly higher in flooded forests. Dispersal modes did not consistently show significant associations with the availability of resources for constructing zoochorous fruits. A lower dissimilarity in dispersal modes, resulting from a higher dominance of endozoochory, occurred in terra-firme forests (excluding podzols) compared to flooded forests. Main conclusions: The disperser-availability hypothesis was well supported for abiotic dispersal modes (anemochory and hydrochory). The availability of resources for constructing zoochorous fruits seems an unlikely explanation for the distribution of dispersal modes in Amazonia. The association between frugivores and the proportional abundance of zoochory requires further research, as tree recruitment not only depends on dispersal vectors but also on conditions that favour or limit seedling recruitment across forest types

Geography and ecology shape the phylogenetic composition of Amazonian tree communities

Aim: Amazonia hosts more tree species from numerous evolutionary lineages, both young and ancient, than any other biogeographic region. Previous studies have shown that tree lineages colonized multiple edaphic environments and dispersed widely across Amazonia, leading to a hypothesis, which we test, that lineages should not be strongly associated with either geographic regions or edaphic forest types. Location: Amazonia. Taxon: Angiosperms (Magnoliids; Monocots; Eudicots). Methods: Data for the abundance of 5082 tree species in 1989 plots were combined with a mega-phylogeny. We applied evolutionary ordination to assess how phylogenetic composition varies across Amazonia. We used variation partitioning and Moran\u27s eigenvector maps (MEM) to test and quantify the separate and joint contributions of spatial and environmental variables to explain the phylogenetic composition of plots. We tested the indicator value of lineages for geographic regions and edaphic forest types and mapped associations onto the phylogeny. Results: In the terra firme and várzea forest types, the phylogenetic composition varies by geographic region, but the igapó and white-sand forest types retain a unique evolutionary signature regardless of region. Overall, we find that soil chemistry, climate and topography explain 24% of the variation in phylogenetic composition, with 79% of that variation being spatially structured (R$^{2}$ = 19% overall for combined spatial/environmental effects). The phylogenetic composition also shows substantial spatial patterns not related to the environmental variables we quantified (R$^{2}$ = 28%). A greater number of lineages were significant indicators of geographic regions than forest types. Main Conclusion: Numerous tree lineages, including some ancient ones (>66 Ma), show strong associations with geographic regions and edaphic forest types of Amazonia. This shows that specialization in specific edaphic environments has played a long-standing role in the evolutionary assembly of Amazonian forests. Furthermore, many lineages, even those that have dispersed across Amazonia, dominate within a specific region, likely because of phylogenetically conserved niches for environmental conditions that are prevalent within regions

Geography and ecology shape the phylogenetic composition of Amazonian tree communities

AimAmazonia hosts more tree species from numerous evolutionary lineages, both young and ancient, than any other biogeographic region. Previous studies have shown that tree lineages colonized multiple edaphic environments and dispersed widely across Amazonia, leading to a hypothesis, which we test, that lineages should not be strongly associated with either geographic regions or edaphic forest types.LocationAmazonia.TaxonAngiosperms (Magnoliids; Monocots; Eudicots).MethodsData for the abundance of 5082 tree species in 1989 plots were combined with a mega-phylogeny. We applied evolutionary ordination to assess how phylogenetic composition varies across Amazonia. We used variation partitioning and Moran's eigenvector maps (MEM) to test and quantify the separate and joint contributions of spatial and environmental variables to explain the phylogenetic composition of plots. We tested the indicator value of lineages for geographic regions and edaphic forest types and mapped associations onto the phylogeny.ResultsIn the terra firme and várzea forest types, the phylogenetic composition varies by geographic region, but the igapó and white-sand forest types retain a unique evolutionary signature regardless of region. Overall, we find that soil chemistry, climate and topography explain 24% of the variation in phylogenetic composition, with 79% of that variation being spatially structured (R2 = 19% overall for combined spatial/environmental effects). The phylogenetic composition also shows substantial spatial patterns not related to the environmental variables we quantified (R2 = 28%). A greater number of lineages were significant indicators of geographic regions than forest types.Main ConclusionNumerous tree lineages, including some ancient ones (>66 Ma), show strong associations with geographic regions and edaphic forest types of Amazonia. This shows that specialization in specific edaphic environments has played a long-standing role in the evolutionary assembly of Amazonian forests. Furthermore, many lineages, even those that have dispersed across Amazonia, dominate within a specific region, likely because of phylogenetically conserved niches for environmental conditions that are prevalent within regions

Mapping density, diversity and species-richness of the Amazon tree flora

Using 2.046 botanically-inventoried tree plots across the largest tropical forest on Earth, we mapped tree species-diversity and tree species-richness at 0.1-degree resolution, and investigated drivers for diversity and richness. Using only location, stratified by forest type, as predictor, our spatial model, to the best of our knowledge, provides the most accurate map of tree diversity in Amazonia to date, explaining approximately 70% of the tree diversity and species-richness. Large soil-forest combinations determine a significant percentage of the variation in tree species-richness and tree alpha-diversity in Amazonian forest-plots. We suggest that the size and fragmentation of these systems drive their large-scale diversity patterns and hence local diversity. A model not using location but cumulative water deficit, tree density, and temperature seasonality explains 47% of the tree species-richness in the terra-firme forest in Amazonia. Over large areas across Amazonia, residuals of this relationship are small and poorly spatially structured, suggesting that much of the residual variation may be local. The Guyana Shield area has consistently negative residuals, showing that this area has lower tree species-richness than expected by our models. We provide extensive plot meta-data, including tree density, tree alpha-diversity and tree species-richness results and gridded maps at 0.1-degree resolution

Consistent patterns of common species across tropical tree communities

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1,2,3,4,5,6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees.Publisher PDFPeer reviewe