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In this study we investigate the rate-dependency of the mechanical behaviour of semilunar heart valves under biaxial deformation, from quasi-static to physiological loading rates. This work extends and complements our previous undertaking, where the rate-dependency in the mechanical behaviour of semilunar valve specimens was documented in sub-physiological rate domains (Acta Biomater. 2019; https://doi.org/10.1016/j.actbio.2019.02.008). For the first time we demonstrate herein that the stress-stretch curves obtained from specimens under physiological rates too are markedly different to those at sufficiently lower rates and at quasi-static conditions. The results importantly underline that the mechanical behaviour of semilunar heart valves is rate dependent, and the physiological mechanical behaviour of the valves may not be correctly obtained via material characterisation tests at arbitrary low deformation rates. Presented results in this work provide an inclusive dataset for material characterisation and modelling of semilunar heart valves across a 10,000 fold deformation rate, both under equi-biaxial and 1:3 ratio deformation rates. The important application of these results is to inform the development of appropriate mechanical testing protocols, as well as devising new models, for suitable determination of the rate-dependent constitutive mechanical behaviour of the semilunar valves.
Assuntos
Valva Aórtica , Estresse MecânicoRESUMO
A new anisotropic viscoelastic model is developed for application to the aortic valve (AV). The directional dependency in the mechanical properties of the valve, arising from the predominantly circumferential alignment of collagen fibres, is accounted for in the form of transverse isotropy. The rate dependency of the valve's mechanical behaviour is considered to stem from the viscous (η) dissipative effects of the AV matrix, and is incorporated as an explicit function of the deformation rate ([Formula: see text]). Model (material) parameters were determined from uniaxial tensile deformation tests of porcine AV specimens at various deformation rates, by fitting the model to each experimental dataset. It is shown that the model provides an excellent fit to the experimental data across all different rates and satisfies the condition of strict local convexity. Based on the fitting results, a nonlinear relationship between η and [Formula: see text] is established, highlighting a 'shear-thinning' behaviour for the AV with increase in the deformation rate. Using the model and these outcomes, the stress-deformation curves of the AV tissue under physiological deformation rates in both the circumferential and radial directions are predicted and presented. To verify the predictive capabilities of the model, the stress-deformation curves of AV specimens at an intermediate deformation rate were estimated and validated against the experimental data at that rate, showing an excellent agreement. While the model is primarily developed for application to the AV, it may be applied without the loss of generality to other collagenous soft tissues possessing a similar structure, with a single preferred direction of embedded collagen fibres.
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Se determinó el efecto de la temperatura sobre la tasa de aclaramiento (TA), ingestión (TI) y consumo especifico de oxígeno (CEO) en individuos de Argopecten purpuratus (Lamarck, 1891) de distintos grupos de tallas. Las pruebas de TA y TI se realizaron a una concentración de Chaetoceros calcitrans de aproximadamente 1x10(6) cel.mL-1, se evaluaron dos temperaturas 17 y 22°C y se conformaron diferentes grupos de tallas promedio de 7.6 ± 0.265, 4.9 ± 0.058 y 3.7 ± 0.173 cm. En las pruebas de CEO los grupos de tallas promedio fueron 8.1 ± 0.351, 5.6 ± 0.058 y 4.3 ± 0.100 cm. Los resultados muestran un efecto significativo de la temperatura en la TA (L.h-1) y TI (cel.h-1 x 10(5)) sobre los individuos de mayor tamaño (7.6 ± 0.265 cm), observándose a 22°C un incremento promedio, respecto a 17°C, de hasta 250% para TA y 48% para TI. Además, se observó una relación directa del tamaño corporal con las TA y TI en ambas temperaturas. Se registró el efecto de la temperatura de 22°C sobre CEO en todos los grupos evaluados, con un incremento de 239.8, 165.3 y 183.4% para individuos de tallas de 8.1 ± 0.351, 5.6 ± 0.058 y 4.3 ± 0.100 respectivamente. Asimismo, los resultados muestran una relación indirecta del tamaño corporal con la CEO, en ambas temperaturas evaluadas.
The effect of temperature on the clearance rate (CR), ingestion rate (IR) and specific oxygen consumption (SOC) in individuals of Argopecten purpuratus at different size groups were determined. The CR and IR tests were performed at a concentration of approximately 1x10(6) cel.mlL-1 of Chaetoceros calcitrans, two temperatures 17 and 22 °C were evaluated and different groups of average size were formed of 7.6 ± 0.265, and 0.058 ± 4.9 3.7 ± 0.173 cm. In SOC test the average size groups were 8.1 ± 0.351, 0.058 ± 5.6 and 4.3 ± 0.100 cm. The results show a significant effect of temperature in CR (Lh-1) and IR (cel.h-1 x 10(5)) on the larger individuals (7.6 ± 0.265 cm), it was observed at 22 °C an average increase, about 17 °C, up to 250% to CR and 48% to IR. In addition, a direct relationship of body size with CR and IR in both temperatures was observed. The effect of temperature at 22 ° C on SOC in all groups was evaluated, with an increase of 239.8, 165.3 and 183.4% for size individuals of 8.1 ± 0.351, 0.058 ± 5.6 and 4.3 ± 0.100 respectively. Furthermore, in both evaluated temperatures, the results show an indirect relationship of body size with the SOC.
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RESUMO: O objetivo do trabalho foi avaliar a influência de diferentes composições de substratos no crescimento inicial de Campomanesia xanthocarpa, bem como avaliar índices fisiológicos. O trabalho foi desenvolvido em Dourados-MS, no período de janeiro a outubro de 2008. Foi estudada a Campomanesia xanthocarpa sob cinco diferentes substratos (LVd/A/O= Latossolo Vermelho distroférrico+areia grossa lavada+Organosuper® (5:4:1 v/v); LVd/A/C= Latossolo Vermelho distroférrico+areia grossa lavada+cama-de-frango (5:4:1 v/v); LVd/A/O2= Latossolo Vermelho distroférrico+areia grossa lavada+Organosuper® (7:2:1 v/v); LVd/A/C2= Latossolo Vermelho distroférrico+areia grossa lavada+cama-de-frango (7:2:1 v/v); LVd/A= Latossolo Vermelho distroférrico+areia grossa lavada (6:4 v/v)), em vasos de 7 dm3, e mantidos em ambiente protegido com 100% de luminosidade. O substrato composto por Latossolo Vermelho distroférrico + areia grossa lavada proporcionou maior diâmetro de caule (8,29 mm), massa seca de raiz, caule e folhas (6,98; 4,49 e 9,06 g/planta, respectivamente) e aumento nos índices fisiológicos nas avaliações finais, indicando que este substrato pode ser utilizado no desenvolvimento de Campomanesia xanthocarpa.
ABSTRACT: The objective of this study was to evaluate the influence of different compositions of substrates on the initial growth of Campomanesia xanthocarpa and to evaluate the physiological rate. The study was conduct in the city of Dourados - state of Mato Grosso do Sul, Brazil, in the period from January to October 2008. The Campomanesia xanthocarpa was studying under five different substrates (LVd/A/O= Oxisol+coarse sand+Organosuper® (5:4:1 v/v); LVd/A/C= Oxisol+ coarse sand+ chicken manure (5:4:1 v/v); LVd/A/O2= Oxisol+ coarse sand+Organosuper® (7:2:1 v/v); LVd/A/C2= Oxisol+ coarse sand+chicken manure (7:2:1 v/v); LVd/A= Oxisol+ coarse sand (6:4 v/v)) in 7 dm3 pots and kept in a protected environment with 100% brightness. The substrate consisting of Oxisol + coarse sand provided greater stem diameter (8.29 mm), dry weight of the root, stem and leaf (6.98, 4.49 and 9.06 g / plant, respectively) and increased the physiological indices in the final evaluations, which indicates that this substrate can be used in the development of Campomanesia xanthocarpa.
