Image-based meshing is opening up exciting new possibilities for the application of computational continuum mechanics methods (finite-element and computational fluid dynamics) to a wide range of biomechanical and biomedical problems that were previously intractable owing to the difficulty in obtaining suitably realistic models. Innovative surface and volume mesh generation techniques have recently been developed, which convert three-dimensional imaging data, as obtained from magnetic resonance imaging, computed tomography, micro-CT and ultrasound, for example, directly into meshes suitable for use in physics-based simulations. These techniques have several key advantages, including the ability to robustly generate meshes for topologies of arbitrary complexity (such as bioscaffolds or composite micro-architectures) and with any number of constituent materials (multi-part modelling), providing meshes in which the geometric accuracy of mesh domains is only dependent on the image accuracy (image-based accuracy) and the ability for certain problems to model material inhomogeneity by assigning the properties based on image signal strength. Commonly used mesh generation techniques will be compared with the proposed enhanced volumetric marching cubes (EVoMaCs) approach and some issues specific to simulations based on threedimensional image data will be discussed. A number of case studies will be presented to illustrate how these techniques can be used effectively across a wide range of problems from characterization of micro-scaffolds through to head impact modelling.

Nest-building orangutans must daily build safe and comfortable nest structures in the forest canopy and do this quickly and effectively using the branches that surround them. This study aimed to investigate the mechanical design and architecture of orangutan nests and determine the degree of technical sophistication used in their construction. We measured the whole nest compliance and the thickness of the branches used and recorded the ways in which the branches were fractured. Branch samples were also collected from the nests and subjected to three-point bending tests to determine their mechanical properties. We demonstrated that the center of the nest is more compliant than the edges; this may add extra comfort and safety to the structure. During construction orangutans use the fact that branches only break half-way across in "greenstick" fracture to weave the main nest structure. They choose thicker branches with greater rigidity and strength to build the main structure in this way. They then detach thinner branches by following greenstick fracture with a twisting action to make the lining. These results suggest that orangutans exhibit a degree of technical knowledge and choice in the construction of nests.biomechanics | intelligence | great apes | wood

The tropical arboreal environment is a mechanically complex and varied habitat. Arboreal inhabitants must adapt to changes in the compliance and stability of supports when moving around trees. Because the orangutan is the largest habitual arboreal inhabitant, it is unusually susceptible to branch compliance and stability and therefore represents a unique animal model to help investigate how animals cope with the mechanical heterogeneity of the tropical canopy. The aim of this study was to investigate how changes in compliance and time of oscillation of branches are related to easily observable traits of arboreal supports. This should help predict how supports react mechanically to the weight and mass of a moving orangutan, and suggest how orangutans themselves predict branch properties. We measured the compliance and time of oscillation of branches from 11 tree species frequented by orangutans in the rainforest of Sumatra. Branches were pulled at several points along their length using a force balance at the end of a stiff rope, and the local diameter of the branch and the distance to its base and tip were measured. Compliance was negatively associated with both local diameter and length to the tip of the branch, and positively, if weakly, associated with length from the trunk. However, branch diameter not only predicted compliance best, but would also be easiest for an orangutan to observe. In contrast, oscillation times of branches were largely unaffected by local diameter, and only significantly increased at diameters below 2 cm. The results of this study validate previous field research, which related locomotory modes to local branch diameter, while suggesting how arboreal animals themselves sense their mechanical environment.

Living tree branches are almost impossible to snap. Some show ''greenstick fracture'', breaking halfway across before splitting along their length, while others simply buckle. In this study we investigated the bending failure of coppice branches of three temperate angiosperm trees: ash, Fraxinus excelsior; hazel, Corylus avellana; and white willow, Salix alba. We carried out bending tests, and made a series of observations on the structure, density and tensile and compressive strength of their wood to understand the pattern of failure. The three species showed contrasting behaviour; willow buckled whereas ash showed clean greenstick fracture and hazel a more diffuse greenstick fracture. These differences could be related to their wood properties. Willow buckled because its light wood had very low transverse compressive strength, particularly tangentially and was crushed by transverse stresses. Though the other species yielded in longitudinal compression on the concave side, they ultimately failed in tension on the convex side when bent because their higher density wood resisted transverse compression better. However, the crack was diverted down the midline because of the low tangential tensile strength of their wood. Differences in fracture between ash and hazel are related to fine-scale differences in their wood anatomy and mechanics.

Napier and Walker's (1967) locomotor category of vertical clinging and leaping (VC&L) is one of the most familiar in primatology, and tarsiers are probably the most morphologically specialized of its membership. However, the link between vertical clinging and leaping remains unelucidated. We attempt to do so by reanalysis of Crompton's 1985 and 1986 field observations of locomotion and habitat use in Tarsius bancanus, using loglinear modeling. Loglinear modeling is better suited to the categorical variables used in many field studies than more traditional statistics, such as ANOVA, developed for continuous variables. We show that climbing, as well as leaping, is one of the predominant forms of locomotion, and that all other things being equal, tarsiers tend to take off from, and land on, similar sized supports, which suggests that the following findings are not likely to be a result of substrate availability alone. Small body size lead to a prediction that tarsiers should leap down but climb up: this was not sustained: rather leaps tend to be level, and climbing accounts for more height loss than randomly expected. However, a prediction that to avoid energy loss to the substrate, the tarsiers should show a preference for large diameter supports for takeoff when leaping longer distances was supported, although tarsiers do not avoid moderately compliant supports. The prediction from ballistic principles that the longest leaps should start from high-angled supports was only weakly sustained, but low-angled supports Int J Primatol (2010) 31:958-979 tend to be strongly associated with short leaps, suggesting that such supports do not facilitate 45°takeoff trajectories. However, tarsiers displayed a preference for landing on medium-sized supports when leaping long distances, suggesting a preference for balancing the need for stability with minimizing musculoskeletal shock.