Thermal, mechanical and chemical analysis of poly(vinyl alcohol) multifilament and braided yarns

Poly(vinyl alcohol) (PVA) in multifilament and braided yarns (BY) forms presents great potential for the design of numerous applications. However, such solutions fail to accomplish their requirements if the chemical and thermomechanical behaviour is not sufficiently known. Hence, a comprehensive characterisation of PVA multifilament and three BY architectures (6, 8, and 10 yarns) was performed involving the application of several techniques to evaluate the morphological, chem- ical, thermal, and mechanical features of those structures. Scanning electron microscopy (SEM) was used to reveal structural and morphological information. Differential thermal analysis (DTA) pointed out the glass transition temperature of PVA at 76 °C and the corresponding crystalline melt- ing point at 210 °C. PVA BY exhibited higher tensile strength under monotonic quasi-static loading in comparison to their multifilament forms. Creep tests demonstrated that 6BY structures present the most deformable behaviour, while 8BY structures are the least deformable. Relaxation tests showed that 8BY architecture presents a more expressive variation of tensile stress, while 10BY of- fered the least. Dynamic mechanical analysis (DMA) revealed storage and loss moduli curves with similar transition peaks for the tested structures, except for the 10BY. Storage modulus is always four to six times higher than the loss modulus.This work was funded by European Regional Development funds (FEDER) through the Competitiveness and Internationalization Operational Program (POCI)—COMPETE andby Na-tional Funds through Portuguese Fundação para a Ciência e Tecnologia (FCT) under the project UID/EMS/50022/2020, UID/EEA/04436/2019 andUID/ CTM/00264/2019. Andrea Zille acknowledges financial support of the FCT through the project PTDC/CTM-TEX/28295/2017,and Nuno Dourado acknowledges financial support of the FCT through the project PTDC/EME-SIS/28225/2017. M.F.S.M. de Moura acknowledges the ‘Laboratório Associado de Energia, Transportes e Aeronáutica’ (LAETA) for the financial support

Comportamento viscoelástico de fibras de álcool polivinílico reforçadas com cristais de hidroxiapatite para aplicações biomédicas: estudo do efeito da arquitetura das fibras na resposta mecânica

Dissertação de mestrado integrado em Engenharia BiomédicaA área ortopédica, principalmente a da fixação e tratamento de fraturas é, sem dúvida, um mercado em crescimento. As técnicas cirúrgicas evoluíram para responder a padrões de fratura complexos, como as fraturas diafisárias multifragmentares (cominutivas) que afetam imensos pacientes. Hoje em dia, esta área movimenta muito dinheiro e tem um impacto muito relevante na saúde humana, sendo um grande tema científico e uma oportunidade comercial entre investigadores e cirurgiões. Nesta dissertação apresenta-se um estudo de caracterização de compósitos de álcool polivinílico (PVA) com hidroxiapatite (HAp), na forma de entrançados, a fim de compreender a influência destes cristais de HAp no comportamento mecânico e viscoelástico daquelas estruturas. A microscopia eletrónica de varrimento (SEM) mostrou a formação de uma camada uniforme de HAp na superfície dos entrançados e a espectroscopia de energia dispersiva de raios X (EDS) indicou uma razão atómica de cálcio/fósforo semelhante à do osso natural. A análise termogravimétrica (TGA) demonstrou que a temperatura de perda de massa (degradação) máxima diminuiu ligeiramente com a adição de HAp. A análise térmica diferencial (DTA) e a análise mecânica dinâmica (DMA) mostraram que a incorporação de HAp nos entrançados de PVA levou a um incremento da temperatura de transição vítrea (Tg). A espectroscopia de infravermelho com transformada de Fourier (FTIR) confirmou que os picos dos entrançados compostos por PVA/HAp combinaram bem com os padrões de PVA e HAp standard. Nos ensaios à tração monotónicos, os entrançados de PVA/HAp exibiram melhores propriedades mecânicas gerais. Os ensaios de fluência e de relaxação indicaram que a adição de HAp foi vantajosa nas arquiteturas compósito de oito fios entrançados (8BY) e seis fios entrançados (6BY). A aplicação das arquiteturas compósito de PVA/HAp pode ser adequada como um sistema de fixação fibroso, oferecendo bom desempenho mecânico e propriedades biológicas potencialmente melhoradas, que complementam o cuidado standard para aplicações ósseas, tais como a área de tratamento de fraturas, especialmente as multifragmentares. Um trabalho que ainda continua.The orthopaedic field, particularly fracture fixation and healing, is undoubtedly a growing market. Surgical techniques have evolved to respond to complex fracture patterns, such as multifragmentary (comminuted) diaphyseal fractures affecting many patients. Nowadays, it is moving plenty of money worldwide and has a very relevant impact on human health, being a great scientific topic and a commercial opportunity among researchers and surgeons. Composites of poly (vinyl alcohol) (PVA) with hydroxyapatite (HAp) in the form of braids were studied in order to understand the influence of these HAp crystals on mechanical and viscoelastic behaviour. Scanning electron microscopy (SEM) showed the formation of a uniform layer of HAp on the surface of the braids, and energy-dispersive X-ray spectroscopy (EDS) indicated a calcium/phosphorus atomic ratio similar to natural bone. The thermogravimetric analysis (TGA) demonstrated that the maximum loss mass (degradation) temperature decreased slightly with the addition of HAp. Differential thermal analysis (DTA) and dynamical mechanical analysis (DMA) showed that the incorporation of HAp onto PVA braids led to an increment of glass transition temperature (Tg). Fourier-transform infrared (FTIR) spectroscopy confirmed that the peaks from PVA/HAp composite braids matched well with standard PVA and HAp patterns. In monotonic tensile tests, PVA/HAp braids exhibited better overall mechanical properties. Creep and relaxation tests indicated that the addition of HAp was advantageous in the eight braided yarn (8BY) and six braided yarn (6BY) composite architectures. The application of PVA/HAp composite architectures can be suitable as a fibrous fixation system by offering good mechanical performance and potentially improved biological properties that complement the standard care for bone applications such as fracture healing field, especially multifragmentary ones. A work that still goes on.This work was supported by the FCT -- Foundation for Science and Technology, through the project with the reference PTDC/EME-SIS/28225/2017, entitled “Development of an innovative composite system for comminuted bone fractures stabilisation”, with the acronym “BoFraPla”, through the Competitiveness and Internationalisation Operational Program and the Lisbon Regional Operational Programme, supported by the FEDER