In vitro mechanical fatigue behavior of poly-ε-caprolactone macroporous scaffolds for cartilage tissue engineering: Influence of pore filling by a poly(vinyl alcohol) gel

Polymeric scaffolds used in regenerative therapies are implanted in the damaged tissue and subjected to repeated loading cycles. In the case of articular cartilage engineering, an implanted scaffold is typically subjected to long term dynamic compression. The evolution of the mechanical properties of the scaffold during bioresorption has been deeply studied in the past, but the possibility of failure due to mechanical fatigue has not been properly addressed. Nevertheless, the macroporous scaffold is susceptible to failure after repeated loading-unloading cycles. In this work fatigue studies of polycaprolactone scaffolds were carried by subjecting the scaffold to repeated compression cycles in conditions simulating the scaffold implanted in the articular cartilage. The behaviour of the polycaprolactone sponge with the pores filled with a poly(vinyl alcohol) gel simulating the new formed tissue within the pores was compared with that of the material immersed in water. Results were analyzed with Morrow’s criteria for failure and accurate fittings are obtained just up to 200 loading cycles. It is also shown that the presence of poly(vinyl alcohol) increases the elastic modulus of the scaffolds, the effect being more pronounced with increasing the number of freeze/thawing cycles.

A high order model for piezoelectric rods: an asymptotic approach

Preprint submitted to International Journal of Solids and Structures. ISSN 0020-7683

Structural analysis of the timber structure of Ica Cathedral, Peru

Dissertação de mestrado em Structural Analysis of Monuments and Historical Constructions

Simulação numérica do comportamento ao impacto de componentes para calçado de segurança

Dissertação de mestrado integrado em Engenharia Mecânica

Desenvolvimento de modelos numéricos e análise experimental de subestruturas soldadas de transformadores de potência, sujeitas a forças de curto-circuito em regime transitório

Dissertação de mestrado integrado em Engenharia Mecânica

Nonlinear behavior of gelatin networks reveals a hierarchical structure

We investigate the strain hardening behavior of various gelatin networks-namely physical gelatin gel, chemically cross-linked gelatin gel, and a hybrid gel made of a combination of the former two-under large shear deformations using the pre-stress, strain ramp, and large amplitude oscillations shear protocols. Further, the internal structures of physical gelatin gels and chemically cross-linked gelatin gels were characterized by small angle neutron scattering (SANS) to enable their internal structures to be correlated with their nonlinear rheology. The Kratky plots of SANS data demonstrate the presence of small cross-linked aggregates within the chemically cross-linked network whereas, in the physical gelatin gels, a relatively homogeneous structure is observed. Through model fitting to the scattering data, we were able to obtain structural parameters, such as the correlation length (ξ), the cross-sectional polymer chain radius (Rc) and the fractal dimension (df) of the gel networks. The fractal dimension df obtained from the SANS data of the physical and chemically cross-linked gels is 1.31 and 1.53, respectively. These values are in excellent agreement with the ones obtained from a generalized nonlinear elastic theory that has been used to fit the stress-strain curves. The chemical cross-linking that generates coils and aggregates hinders the free stretching of the triple helix bundles in the physical gels.

Retroanálise de parâmetros geomecânicos baseada em algoritmos de otimização

Dissertação de mestrado integrado em Engenharia Civil

Biomaterials for cartilage tissue engineering under mechanical stimulus

Tese de Doutoramento em Ciências (Especialidade de Física)

Seismic behavior of concrete block masonry buildings

Tese de Doutoramento em Engenharia Civil

Influência do tipo de adesivo no comportamento de elementos de betão reforçados com laminados de CFRP de acordo com a técnica NSM

Dissertação de mestrado integrado em Engenharia Civil

Synthesis of new peptide derivatives that self-assemble into nanostructured hydrogels for biomedical applications

Tese de Doutoramento em Ciências (área de especialização em Química)

Poly(ester-urethane) scaffolds: effect of structure on properties and osteogenic activity of stem cells

The present study aimed to investigate the effect of structure (design and porosity) on the matrix stiffness and osteogenic activity of stem cells cultured on poly(ester-urethane) (PEU) scaffolds. Different three-dimensional (3D) forms of scaffold were prepared from lysine-based PEU using traditional salt-leaching and advanced bioplotting techniques. The resulting scaffolds were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), mercury porosimetry and mechanical testing. The scaffolds had various pore sizes with different designs, and all were thermally stable up to 300â °C. In vitrotests, carried out using rat bone marrow stem cells (BMSCs) for bone tissue engineering, demonstrated better viability and higher cell proliferation on bioplotted scaffolds compared to salt-leached ones, most probably due to their larger and interconnected pores and stiffer nature, as shown by higher compressive moduli, which were measured by compression testing. Similarly, SEM, von Kossa staining and EDX analyses indicated higher amounts of calcium deposition on bioplotted scaffolds during cell culture. It was concluded that the design with larger interconnected porosity and stiffness has an effect on the osteogenic activity of the stem cells.

A perda precoce do diâmetro luminal após angioplastia coronária e sua influência no fenômeno da reestenose

OBJETIVO: Analisar a perda do diâmetro luminal mínimo (DLM) nos primeiros 15min após angioplastia coronária por balão (AC), quantificando sua influência na reestenose coronária. MÉTODOS: Foram estudadas, prospectivamente, 86 AC em 86 pacientes. Os pacientes foram divididos em dois subgrupos de acordo com a presença ou ausência de reestenose; o 1º grupo compreendendo as 31 lesões com reestenose e o 2º, as 55 lesões sem reestenose. RESULTADOS: A análise univariada mostrou que a relação balão/artéria foi menor no grupo com reestenose (0,92±0,01 vs 1,00±0,11, P= .003). O grupo com reestenose apresentou maior recolhimento elástico absoluto e relativo no 1°min (0,79±0,54 vs 0,68±0,59mm; P= 0,007 e 32,04±14,27 vs 22,15±16,65%; P= 0,006.) e no controle angiográfico do 15°min (1,25±0,59 vs 0,90±0,65mm, P= 0,017 e 46,75±15,69 vs 29,18±17,84%, P<0,00001) do que o grupo sem reestenose. O DLM no 1°min foi menor no grupo com reestenose (2,15±0,42 vs 2,43±0,58mm; P=0,022). O grupo com reestenose apresentou uma maior perda precoce no DLM (0,46±0,34 vs 0,22±0,35mm, P= 0,004). Este decréscimo na luz do vaso determinou que o DLM do 15°min fosse ainda menor no grupo com reestenose (1,69±0,48 vs 2,20±0,61; P= 0,0001). Da análise multivariada, entretanto, identificou-se apenas a relação balão/artéria e o DLM do 15°min como os dois fatores independentes mais relacionados à reestenose. CONCLUSÃO: O recolhimento elástico e a perda do DLM ao longo dos 15min são fatores diretamente relacionados à reestenose. Entretanto, a análise multivariada mostrou que a relação balão/artéria e o DLM de 15min são os dois fatores independentes mais fortemente preditores de reestenose.

Fluência no betão desde as primeiras idades: um estudo experimental

Dissertação de mestrado integrado em Engenharia Civil

Development of multifunctional coatings deposited on polymers based sensors for biomedical applications

Tese de Doutoramento (Programa Doutoral em Engenharia de Materiais)