Browsing by Author "Rodrigues, Alexandra"
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- Competitiveness of chitosan-based implantsPublication . Oliveira, Nuno Guitian; Pinto, Luís F. V.; Reis, Luís; Rodrigues, AlexandraBiomaterials have been extensively developed and applied in medical devices. Among these materials, bioabsorbable polymers have attracted special attention for orthopedic applications where a transient existence of an implant can provide better results, when compared with permanent implants. Chitosan, a natural biopolymer, has generated enormous interest due to its various advantages such as biocompatibility, biodegradability and osteoconductive properties. In this paper, an assessment of the potential of a developed innovative production process of 3D solid and dense chitosan-based products for biomedical applications is performed and presented. Therefore, it starts with a brief explanation of the technology, highlighting its main features. Then, several potential applications and their markets were identified and assessed. After choosing a primary application and market, its potential as well as its uncertainties and risks were identified. A business model suggesting how to materialize the value from the application was sketched. After that, a brief description of the market as well as the identification of the main competitors and their distinctive features was made. The supply chain analysis and the go-to-market strategy were the following steps. In the end, a final recommendation based on the assessment of the information was prepared.
- Improving indoor air quality in a higher-education institution through biophilic solutionsPublication . Idália da Gomes, Maria; Joanaz De Melo, Ana Maria Garcia Henriques Barreiros; Pinto, Iola; Rodrigues, AlexandraSchools are vital infrastructures where students acquire essential skills and foster social values. Indoor air quality (IAQ) is of paramount importance in schools, given that students spend a considerable amount of time indoors. This study examines the influence of a natural green structure (NGS) on IAQ in an Eco-Campus classroom. The IAQ of a classroom with an NGS was compared to that of an adjacent classroom without an NGS. The thermal conditions were monitored, including air temperature (T) and relative humidity (RH), as well as indoor pollutants, including carbon dioxide (CO2), volatile organic compounds (VOCs), and particulate matter (PM2.5 and PM10). The findings indicated a substantial improvement in indoor air quality in the classroom where the green structure was installed. This study lends support to the incorporation of biophilic solutions as sustainable approaches to fostering healthier learning environments, which in turn can lead to improvements in student performance and well-being.
- Influence of strain rate on the mechanical behavior of dry and hydrated chitosan-based dense materials for bioabsorbable implant applicationsPublication . Figueiredo, Lígia; Gregório, Afonso V. L.; Rodrigues, Alexandra; Rosa, P.A.R.Chitosan has generated enormous interest in the scientific community because of its distinctive biological and physicochemical properties, which allow new advanced structures and applications. Porous chitosan scaffolds have been extensively studied and explored in bone generation, however it is still a challenge to obtain bio-absorbable orthopedic implants that involves pure 3D dense chitosan geometries due to the inherent difficulties in producing and shaping such structures. In this work, chitosan was blended with 10% glycerol and 10% glycerol + 10% biphasic mixture of calcium phosphate (70% hydroxyapatite with 30% beta-tricalcium phosphate) to produce dense chitosan-based blocks, which were then shaped into rods. The introduction of plasticizer aimed to improve the materials ductility while the ceramic particles were used to increase stiffness and strength. The mechanical behavior of the two chitosan-based compositions was evaluated by uniaxial compression tests using a customized split-Hopkinson pressure bar (SHPB). The specimens were analysed in quasi-static conditions (less than 0.1 s(-1)) and medium strain rate conditions (200-800 s(-1)), both in dry state and in different hydrated conditions, in the latter case to approximate the in vivo implant conditions. The results showed promising results for the intended application. The chitosan blends present excellent ductility with an elastic perfect-plastic behavior in quasi-static conditions, with yield stresses around 40 MPa for the dry state, with a decay for 3 MPa after 48h hydration. An empirical model was proposed to describe the flow stress curves, with a good agreement with the experimental data, allowing future modelling of this material behavior.
- Mechanical properties of stent-graft materialsPublication . Santos, Isa C. T.; Rodrigues, Alexandra; Figueiredo, Lígia; Rocha, Luís A.; Tavares, João Manuel R. S.An aneurysm is a localized blood-filled dilatation of an artery whose consequences can be deadly. One of its current treatments is endovascular aneurysm repair, a minimally invasive procedure in which an endoprosthesis, called a stent-graft, is placed transluminally to prevent wall rupture. Early stent-grafts were custom designed for the patient through the assembling of off-the-shelf components by the operating surgeon. However, nowadays, stent-grafts have become a commercial product. The existing endoprostheses differ in several aspects, such as shape design and materials, but they have in common a metallic scaffold with a polymeric covering membrane. This article aims to gather relevant information for those who wish to understand the principles of stent-grafts and even to develop new devices. Hence, a stent-graft classification based on different characteristics is presented and the desired features for an ideal device are pointed out. Additionally, the materials currently in use to fabricate this type of endoprosthesis are reviewed and new materials are suggested.
- Processing and characterization of 3D dense chitosan pieces, for orthopedic applications, by adding plasticizersPublication . Figueiredo, Lígia; Moura, Carla; Pinto, Luís F. V.; Ferreira, Frederico Castelo; Rodrigues, AlexandraIn this work, plasticizer agents were incorporated in a chitosan based formulation, as a strategy to improve the fragile structure of chitosan based-materials. Three different plasticizers: ethylene glycol, glycerol and sorbitol, were blended with chitosan to prepare 3D dense chitosan specimens. The properties of the obtained structures were assessed for mechanical, microstructural, physical and biocompatibility behavior. The results obtained revealed that from the different specimens prepared, the blend of chitosan with glycerol has superior mechanical properties and good biological behavior, making this chitosan based formulation a good candidate to improve robust chitosan structures for the construction of bioabsorbable orthopedic implants.
- Rankings de sustentabilidade no ensino superior: o uso do UI Greenmetric no Politécnico de LisboaPublication . Manteigas, Vítor; Silva, Maria João; Rodrigues, Alexandra; Seabra, Fernando; Monteiro, Ana; Romão Dias de Mendonça David, Maria Alexandra; Silvestre, Cláudia; Oliveira, Heitor; Raposo, Ana; Escudeiro, Maria JoãoO Politécnico de Lisboa (IPL), instituição de ensino superior constituída por oito Unidades Orgânicas (UO), distribuídas por cinco campi e pelas instalações dos Serviços da Presidência, conta com uma comunidade académica de cerca de quinze mil estudantes, docentes e não docente, definiu a sustentabilidade ambiental como um dos seus eixos estratégicos e assumiu um compromisso com a comunidade académica, no cumprimento da Agenda 2030 da Organização das Nações Unidas. Com o objetivo de melhorar as práticas na área da sustentabilidade, o IPL tem vindo a participar no UI GreenMetric World University Ranking, um ranking internacional de Instituições de Ensino Superior (IES), que atualmente faz uso de 39 indicadores distribuídos por 6 categorias, nomeadamente: (i) campus e infraestruturas; (ii) energia e alterações climáticas; (iii) resíduos; (iv) água; (v) transportes; e (vi) educação e investigação. Em 2023, e com base nas pontuações em cada uma das categorias, o IPL atingiu a posição 553 de entre um total de 1183 IES oriundas de 84 países. Das múltiplas categorias avaliadas, “resíduos” teve o melhor resultado, com uma pontuação de 1575 em 1800 possíveis (87,50%). Em situação contrária, “campus e infraestruturas” obteve uma pontuação de 550 em 1500 (36,67%), havendo, por isso, uma margem significativa de melhoria associada a esta categoria. Para as restantes categorias, os resultados registaram-se entre os 50% (água) e os 65,28% (transportes e educação e investigação). O resultado alcançado decorreu do trabalho colaborativo e concertado das UO, alicerçado numa visão holística e numa gestão estratégica, associada às múltiplas dimensões da sustentabilidade e com particular enfoque naquilo que tem vindo a ser feito no âmbito dos programas Eco-Escolas e EcoCampus, como sejam, por exemplo: (i) a água, com a distribuição de garrafas reutilizáveis e a promoção do consumo da água de rede pública de abastecimento; (ii) a alimentação, com a realização de eventos de democracia participativa, workshops sobre alimentação saudável e sustentável e a disponibilização de ementas com impacte ambiental reduzido; (iii) a biodiversidade e os espaços verdes, com a plantação de espécies arbóreas, assim como a construção e instalação nos campi, de hotéis de insetos; (iv) a educação, usando os campi como “laboratórios vivos” e com o uso de unidades curriculares para a abordagem às questões da sustentabilidade; (v) a mobilidade, com a promoção do uso da bicicleta pela comunidade académica; e (vi) os resíduos, com a promoção da compostagem e a instalação de ecopontos para a deposição e recolha seletiva de vários fluxos específicos Em conclusão, salienta-se o resultado obtido pelo IPL no UI GreenMetric, figurando na primeira metade da seriação das IES participantes neste ranking. Na comunicação proposta será apresentada a metodologia que garantiu a sistematização da informação necessária para a participação no ranking, assim como serão apresentadas algumas das práticas de sustentabilidade que viabilizaram o desempenho alcançado no UI GreenMetric 2023. Serão igualmente abordados os desafios para o futuro, tendo em conta o objetivo de melhorar as práticas na área da sustentabilidade no IPL.
- Strategy to improve the mechanical properties of bioabsorbable materials based on chitosan for orthopedic fixation applicationsPublication . Figueiredo, Lígia; Fonseca, Rita; Pinto, Luís F. V.; Ferreira, Frederico Castelo; Almeida, Amélia; Rodrigues, AlexandraBioabsorbable polymeric fixation devices have been used as an alternative to metallic implants in orthopedics, preventing the stress shielding effect and avoiding a second surgery for implant removal. However, several problems are still associated with current bioabsorbable implants, including the limited mechanical stiffness and strength, and the adverse tissue reactions generated. To minimize or even eliminate the problems associated with these implants, strategies have been developed to synthesize new implant materials based on chitosan. To overcome the brittle behavior of most 3D chitosan-based structures, glycerol and sorbitol were blended to chitosan and the effect of these plasticizers in the produced specimens was analyzed by flexural tests, Berkovich tests, scanning electron microscopy (SEM) and micro-CT analyzes. The improvement of the mechanical properties was also tested by adding ceramics, namely hydroxyapatite powder and biphasic mixtures of hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP). In the plasticizers group, the best combination of the measured properties was obtained for chitosan with 10% glycerol (flexural strength of 53.8 MPa and indentation hardness of 19.4 kgf/mm(2)), while in the ceramics group the best mechanical behavior was obtained for chitosan with 10% HA+beta-TCP powder (flexural strength of 67.5 MPa and indentation hardness 28.2 kgf/mm(2)). All the tested material compositions were dense and homogeneous, fundamental condition for a good implant performance. These are encouraging results, which support the continued development of chitosan-based materials for orthopedic fixation applications.