22 research outputs found
Cellulose Filaments for Responsive and Functional Materials
Cellulosic filaments, found in plants, are crucial structural elements for their
survival and are a great source of inspiration to obtain new functional materials.
The work performed out in this thesis aimed for the isolation, physical
characterization, study of the morphology and shape, as well as the mechanical
behaviour of cellulosic filaments obtained from the leaves of Agapanthus
africanus and Ornithogalum thyrsoides and from the filaments that form the
ribbons existing on the awns of the Erodium plants. These cellulosic filaments
and filament networks were chosen due to the fundamental role that they play in
the plant kingdom and their ability to change shape in the presence of an external
stimuli. The study of the chosen systems served as an inspiration for the
preparation and production of new membranes formed by non-woven networks
of micro/nano filaments. A prototype, which allows for the selective removal of oil
micro droplets from aqueous emulsions, was developed.
This dissertation begins with a general introduction, based on two review
papers, which the author of this thesis is the first author, in which the main
concepts used in the following chapters are addressed and interconnected. The
original part of the work is in chapters II, III and IV.
In chapter II, the study of microfilaments from the leaves tracheary of two
plants, Agapanthus africanus and Ornithogalum thyrsoides, is made. These microfilaments belong to plants of the same order and have identical shapes (left
helices), chemical composition and skeletons, but different mechanical
properties. For the first time, micrometric droplets of a nematic liquid crystal were
used as sensors to reveal the morphology of the filaments. In order to obtain
quantitative characteristics on the surface of the microfilaments, photos of the
textures of pierced droplets were obtained by Polarized Optical Microscopy
(POM). These textures were compared with simulated optical microphotographs
obtained by numerical modelling for the nematic droplets. Homeotropic anchoring
at the air, and different anchoring conditions, at the interfaces with the filaments
were considered for the nematic structure. This study allowed the establishment
of relationships between the physical properties/morphology of the filaments and
to determine their interactions with other filaments and with the environment.
In chapter III, cellulosic networks existing on dead tissues of the Erodium
awns were isolated and characterized. An interesting feature of these cellulosic
networks is that they form ribbons that change reversibly the shape in the
presence of moisture. When dried these ribbons are right-handed helices, that
uncoil remaining taut, in the presence of moisture. The work performed allowed
the preparation of helical ribbons that can change the shape from right- to lefthanded
helices in the presence of moisture. The behaviour observed was
explained using computational simulations, considering filaments that contract
and expand asymmetrically. Birefringent transparent ribbons were also isolated.
The asymmetric arrangement of cellulosic fibres allows the material to be
stimuli-responsive without the use of complicated lithography and intricate
deposition techniques, making it suitable for a diverse range of applications, such
as the production of intelligent textiles and environmental friendly micro
components.
In chapter IV, non-woven membranes obtained from cellulosic materials
and cellulose nanocrystals were prepared and characterized. Different patterns
were designed using the screenprinting technique. The adhesion between the
different types of cellulosic fibres was promoted through a heat treatment. The
non-woven membranes produced allowed the development of a prototype that
selectively removes oil droplets from aqueous emulsions with an efficiency of
approximately 80%.
Throughout this thesis (chapters II and III), the complexity of the systems
increases. The work begins by studying the morphology of a filament and its
mechanical behaviour in the presence of other filaments. After a much more complex system, in which anisotropic filament networks, produced by the
Erodium plant were addressed. The stimuli-responsive behaviour of these
anisotropic networks was investigated after being released by the plant. Based
on the understanding of the systems formed by cellulosic filaments, studied in
chapters II and III, functional non-woven membranes were produced, printed, and
characterized. The non-woven membranes led to the development of a prototype,
which allows the selective removal of micro droplets of oil form aqueous
emulsions.
At the end, a summary of the main scientific results and future work
including a technological application, which was developed in the framework of
this thesis, are presented.Os filamentos celulósicos, existentes nas plantas, são elementos
estruturais cruciais para a sua sobrevivência e fontes de inspiração para a
obtenção de novos materiais funcionais.
O trabalho realizado nesta tese visou o isolamento, caracterização física,
estudo da morfologia e forma, assim como do comportamento mecânico de
filamentos celulósicos obtidos a partir das folhas das plantas Agapanthus
africanus e Ornithogalum thyrsoides e de filamentos que formam fitas existentes
nas hastes da planta Erodium. Estes filamentos e redes de filamentos celulósicos
foram escolhidos devido ao papel fundamental que desempenham no reino
vegetal e à resposta que podem apresentar na presença de estímulos externos.
O estudo dos sistemas escolhidos serviu de inspiração para a preparação e
fabrico de novas membranas formadas por redes não tecidas de filamentos
micro/nanométricos e o desenvolvimento de um protótipo, que permite a
remoção seletiva de microgotas de óleo de emulsões aquosas.
Inicia-se com uma introdução de caracter geral, baseada em dois artigos
de revisão, dos quais a autora desta tese é primeira autora, na qual se abordam
e interligam os conceitos principais, que são utilizados nos capítulos seguintes.
A parte original do trabalho reparte-se pelos capítulos II, III e IV. No capítulo II é feito o estudo de microfilamentos existentes nos sistemas
vasculares das folhas de duas plantas, Agaphantus africanus e Ornithogalum
thyrsoides. Estes microfilamentos pertencem a plantas da mesma ordem e
possuem formas (hélices esquerdas), composições químicas e esqueletos
idênticos, mas apresentam propriedades mecânicas distintas. Pela primeira vez
foram utilizadas gotas micrométricas de um cristal líquido nemático como
sensores da morfologia dos filamentos isolados. De modo a obter características
quantitativas sobre a superfície dos microfilamentos, fotos de texturas obtidas
por microscopia com luz polarizada foram comparadas com microfotografias
óticas simuladas a partir de modelação numérica de um meio contínuo das
estruturas das gotas nemáticas, com ancoragem homeotrópica na superfície
com o ar suspensas nos microfilamentos com diferentes ancoragens. O estudo
realizado permitiu estabelecer relações entre as propriedades físicas/morfologia
dos filamentos e determinar as suas interações com outros filamentos e com o
meio ambiente.
No capítulo III foram isoladas e caracterizadas redes celulósicas existentes
nas hastes de tecidos mortos da planta Erodium. Uma característica interessante
destas redes celulósicas é a de formarem fitas que mudam reversivelmente de
conformação na presença de humidade. Quando secas estas fitas são hélices
direitas, que na presença de humidade desenrolam para fitas esticadas, sem
torção nem flexão. Este trabalho permitiu induzir uma inversão de quiralidade
nas fitas que foi explicada pelo uso de simulações computacionais considerando
que as fitas contraem e esticam de modo assimétrico. Fitas birrefringentes
transparentes também foram isoladas. A disposição assimétrica das fibras
celulósicas permite a resposta do material não envolvendo o uso de técnicas
complicadas de litografia nem de deposição, podendo ser aplicado, por exemplo,
no fabrico de têxteis inteligentes e de microcomponentes amigos do ambiente.
No capítulo IV foram preparadas e caracterizadas membranas não tecidas
obtidas a partir de soluções de derivados celulósicos e de celulose nano
cristalina. Foram desenhadas diferentes geometrias pela utilização da técnica de
“screenprinting” e promovida a adesão entre os diferentes tipos de fibras
celulósicas através de tratamento térmico. As membranas não tecidas
produzidas permitiram o desenvolvimento de um protótipo que remove, de forma
seletiva, microgotas de óleo de emulsões aquosas com uma eficiência de cerca
de 80%. Ao longo desta tese (capítulo II e III), a complexidade dos sistemas
estudados aumenta, isto é, começa-se por estudar a morfologia de um filamento
e o seu comportamento mecânico na presença de outros filamentos, para depois
se passar para um sistema muito mais complexo em que redes anisotrópicas de
filamentos, impressas pela planta Erodium, permitem a resposta a estímulos
externos da estrutura formada, mesmo após esta ter abandonado a planta.
Tendo por base a compreensão dos sistemas formados por filamentos
celulósicos, estudados nos capítulos II e III, foram produzidas, impressas e
caracterizadas, no laboratório, membranas funcionais tecidas de filamentos
micro/nano celulósicos. As membranas não tecidas originaram o
desenvolvimento de um protótipo, que permite a remoção seletiva de micro gotas
de óleo existentes em emulsões aquosas.
No final é apresentado um sumário dos principais resultados científicos e
perspetivas de avanço tecnológico alcançadas por este trabalho
A Systematic Review and Meta-Analysis of the Incidence of Injury in Professional Female Soccer
The epidemiology of injury in male professional football is well documented and has been used as a basis to monitor injury trends and implement injury prevention strategies. There are no systematic reviews that have investigated injury incidence in women’s professional football. Therefore, the extent of injury burden in women’s professional football remains unknown. PURPOSE: The primary aim of this study was to calculate an overall incidence rate of injury in senior female professional soccer. The secondary aims were to provide an incidence rate for training and match play. METHODS: PubMed, Discover, EBSCO, Embase and ScienceDirect electronic databases were searched from inception to September 2018. Two reviewers independently assessed study quality using the Strengthening the Reporting of Observational Studies in Epidemiology statement using a 22-item STROBE checklist. Seven prospective studies (n=1137 professional players) were combined in a pooled analysis of injury incidence using a mixed effects model. Heterogeneity was evaluated using the Cochrane Q statistic and I2. RESULTS: The epidemiological incidence proportion over one season was 0.62 (95% CI 0.59 - 0.64). Mean total incidence of injury was 3.15 (95% CI 1.54 - 4.75) injuries per 1000 hours. The mean incidence of injury during match play was 10.72 (95% CI 9.11 - 12.33) and during training was 2.21 (95% CI 0.96 - 3.45). Data analysis found a significant level of heterogeneity (total Incidence, X2 = 16.57 P < 0.05; I2 = 63.8%) and during subsequent sub group analyses in those studies reviewed (match incidence, X2 = 76.4 (d.f. = 7), P <0.05; I2 = 90.8%, training incidence, X2 = 16.97 (d.f. = 7), P < 0.05; I2 = 58.8%). Appraisal of the study methodologies revealed inconsistency in the use of injury terminology, data collection procedures and calculation of exposure by researchers. Such inconsistencies likely contribute to the large variance in the incidence and prevalence of injury reported. CONCLUSIONS: The estimated risk of sustaining at least one injury over one football season is 62%. Continued reporting of heterogeneous results in population samples limits meaningful comparison of studies. Standardising the criteria used to attribute injury and activity coupled with more accurate methods of calculating exposure will overcome such limitations