Objective Uniaxial Identification of Transition Points in Non-Linear Materials: Sample Application to Porcine Coronary Arteries and the Dependency of Their Pre- and Post-Transitional Moduli with Position

This study aimed to develop an objective method for the elastic characterisation of pre- and post-transitional moduli of left anterior descending (LAD) porcine coronary arteries. Methods Eight coronary arteries were divided into proximal, middle and distal test specimens. Specimens underwent uniaxial extension up to 3 mm. Force–displacement measurements were used to determine the induced true stress and stretch for each specimen. A local maximum of the stretch-true stress data was used to identify a transition point. Pre- and post-transitional moduli were calculated up to and from this point, respectively. Results The mean pre-transitional moduli for all specimens was 0.76 MPa, as compared to 4.86 MPa for the post-transitional moduli. However, proximal post-transitional moduli were significantly greater than that of middle and distal test specimens (p < 0.05). Conclusion Post-transitional uniaxial properties of the LAD are dependent on location along the artery. Further, it is feasible to objectively identify a transition point between pre- and post-transitional moduli

Viscoelastic properties of human and bovine articular cartilage : a comparison of frequency-dependent trends

Acknowledgments The authors would like to thank Spencer C. Barnes and Hamid Sadeghi for assistance during experimentation. We would also like to thank patients donating tissue and the surgeons collecting these. Funding The equipment used in this study was funded by Arthritis Research UK (Grant number H0671). We are grateful to Arthritis Research UK for the award of a PhD studentship to Anna A. Cederlund (Grant number 19971). Arthritis Research UK had no role in the design of the study and collection, analysis and interpretation of data and in writing the manuscript.Peer reviewedPublisher PD

Variation in viscoelastic properties of bovine articular cartilage below, up to and above healthy gait-relevant loading frequencies

The aim of this study was to determine the variation in viscoelastic properties of femoral head bovine articular cartilage, on-bone, over five orders of magnitude of loading frequency. These frequencies ranged from below, up to and above healthy gait-relevant frequencies, using<1, 1–5 and 10 Hz, respectively. Dynamic mechanical analysis was used to measure storage and loss stiffness. A maximum compressive force of 36 N was applied through a chamfered-end, 5.2-mm-diameter, indenter. This induced a maximum nominal stress of 1.7 MPa. The ratio of storage to loss stiffness increased from near parity (2.5) at low frequencies to 11.4 at 10 Hz. This was the result of a significant logarithmic increase (p < 0.05) in storage stiffness with frequency, from 367 N/mm (0.001 Hz) up to 1460 N/mm (10 Hz). In contrast, the loss stiffness remained approximately constant. In conclusion, viscoelastic properties of articular cartilage measured at frequencies below those of gait activities are poor predictors of its relevant dynamic mechanical behaviour

Multiscale three-dimensional surface reconstruction and surface roughness of porcine left anterior descending coronary arteries

The aim of this study was to investigate the multiscale surface roughness characteristics of coronary arteries, to aid in the development of novel biomaterials and bioinspired medical devices. Porcine left anterior descending coronary arteries were dissected ex vivo, and specimens were chemically fixed and dehydrated for testing. Surface roughness was calculated from three-dimensional reconstructed surface images obtained by optical, scanning electron and atomic force microscopy, ranging in magnification from 10× to 5500×. Circumferential surface roughness decreased with magnification, and microscopy type was found to influence surface roughness values. Longitudinal surface roughness was not affected by magnification or microscopy types within the parameters of this study. This study found that coronary arteries exhibit multiscale characteristics. It also highlights the importance of ensuring consistent microscopy parameters to provide comparable surface roughness values

Vulnerability to urban flooding assessed based on spatial demographic, socio-economic and infrastructure inequalities

Urban flooding is a priority in natural risk management and mitigation because it is the most frequent natural disaster in densely urbanised environments. This research explores flood vulnerability in cities by developing an index that can be easily implemented across the world. Our methodology is based on the arrangement of a series variables into three different classes (demography, socioeconomics and infrastructure) and the determination of their spatial variability through a Principal Component Analysis (PCA). We tested the proposed approach in the city of Santander (Spain) where a vulnerability index map was generated based on the combination of the proposed classes. The analysis show that we can reduce complexity from an initially identified 159 relevant variables to 16 representative and impactful variables in terms of spatial variance. Classification of the variables into three different classes made it possible to quantify the main causes of vulnerability to flooding across space. We produce a flood risk map by integrating our findings with a flood hazard map for the same area. This flood risk map gives urban planners detailed information about the most affected areas and allows them to design measures that mitigate the severity and effects of floods optimising available resources

Analysis of hydration and subchondral bone density on the viscoelastic properties of bovine articular cartilage.

Funding JC is currently funded by an Engineering and Physical Sciences Research Council scholarship (EP/N509590/1). We are also grateful to Arthritis Research UK for the award of a PhD studentship to Anna A. Cederlund (Grant number 19971). The materials and testing equipment used in this study was funded by an Arthritis Research UK grant (H0671). The Engineering and Physical Sciences Research Council and Arthritis Research UK (now part of Versus Arthritis) had no role in the design of the study and collection, analysis and interpretation of data and in writing the manuscript.Peer reviewedPublisher PD

Dynamic Viscoelasticity and Surface Properties of Porcine Left Anterior Descending Coronary Arteries

The aim of this study was, for the first time, to measure and compare quantitatively the viscoelastic properties and surface roughness of coronary arteries. Porcine left anterior descending coronary arteries were dissected ex vivo. Viscoelastic properties were measured longitudinally using dynamic mechanical analysis, for a range of frequencies from 0.5 to 10 Hz. Surface roughness was calculated following three-dimensional reconstructed of surface images obtained using an optical microscope. Storage modulus ranged from 14.47 to 25.82 MPa, and was found to be frequency-dependent, decreasing as the frequency increased. Storage was greater than the loss modulus, with the latter found to be frequency-independent with a mean value of 2.10 ± 0.33 MPa. The circumferential surface roughness was significantly greater (p < 0.05) than the longitudinal surface roughness, ranging from 0.73 to 2.83 and 0.35 to 0.92 µm, respectively. However, if surface roughness values were corrected for shrinkage during processing, circumferential and longitudinal surface roughness were not significantly different (1.04 ± 0.47, 0.89 ± 0.27 µm, respectively; p > 0.05). No correlation was found between the viscoelastic properties and surface roughness. It is feasible to quantitatively measure the viscoelastic properties of coronary arteries and the roughness of their endothelial surface

Towards Additive Manufacture of Functional, Spline-Based Morphometric Models of Healthy and Diseased Coronary Arteries:In Vitro Proof-of-Concept Using a Porcine Template

The aim of this study is to assess the additive manufacture of morphometric models of healthy and diseased coronary arteries. Using a dissected porcine coronary artery, a model was developed with the use of computer aided engineering, with splines used to design arteries in health and disease. The model was altered to demonstrate four cases of stenosis displaying varying severity, based on published morphometric data available. Both an Objet Eden 250 printer and a Solidscape 3Z Pro printer were used in this analysis. A wax printed model was set into a flexible thermoplastic and was valuable for experimental testing with helical flow patterns observed in healthy models, dominating the distal LAD (left anterior descending) and left circumflex arteries. Recirculation zones were detected in all models, but were visibly larger in the stenosed cases. Resin models provide useful analytical tools for understanding the spatial relationships of blood vessels, and could be applied to preoperative planning techniques, but were not suitable for physical testing. In conclusion, it is feasible to develop blood vessel models enabling experimental work; further, through additive manufacture of bio-compatible materials, there is the possibility of manufacturing customized replacement arteries