Adrian M. Goodman

Regional variation in the mechanical properties of cortical bone from the porcine femur

Despite the widespread use of porcine bone as a substitute for human bone in the development of surgical technique and the use of fixation devices, relatively few studies have reported on the mechanical behaviour of porcine long bones. Regional variation in the mechanical properties of cortical bone from porcine femora was investigated using three-point bending and cutting tests. Results were related to measurements of bone architecture and composition and Rutherford backscattering spectrometry (RBS) was used to calculate the calcium to phosphorus ratio. There was significant, but limited, regional variation in the strength of the femur with bone from the distal, posterior quadrant (241.4 ± 10.43 MPa) being significantly stronger than that of the lateral quadrant (162.3 ± 17.96 MPa). Cortical bone was also anisotropic; samples cut transverse to the bones axis were around six times tougher than those cut parallel to the axis (p<0.05). This corresponded with a significant negative correlation between the Youngs modulus and toughness when cut along the longitudinal axis. RBS analysis of cortical bone samples gave a Ca:P ratio of 1.37 ± 0.035, somewhat lower than that reported for cortical bone of adult human femora. These results indicate that the mechanical properties of cortical bone show significant, but limited, variation around the porcine femur and that this should be taken into consideration when sampling and choosing an appropriate animal model for orthopaedic biomechanics research.

A mechanical study of retting in glyphosate treated flax stems (Linum usitatissimum)

The process of retting (the dissociation of the fibre bundles from the central stele by the action of microbes) in two varieties of flax (Linum usitatissimum; cvs. Laura and Escalina) was investigated by studying the morphology and mechanics of plants after treatment with a translocated herbicide, glyphosate. The mechanical changes in the stems were measured on a weekly basis, by carrying out a series of mechanical peel and tear tests on the stem tissue of mature plants. There was a pronounced drop in the moisture content of the stem 14 days after application of the herbicide, from a moisture content of ~60 to 10%. This was consistent with the onset of senescence and subsequent dehydration of the plant tissues. The dehydration of the stem tissues corresponded with an increase in the work required to peel the fibre bundles from the secondary phloem tissue, from 212±7.9 to 539±22 J m−2 (P<0.001). However, 27 days after application of the herbicide there was a more gradual but significant drop in the work required to peel the stem, by ~45% to a mean work to peel of 297±19.8 J m−2. This is thought to be a result of the retting process. This study indicates that peel tests can be used to measure mechanical changes in the interface between the fibre bundles (primary phloem tissue) and the secondary phloem tissue. It enables the progression of retting to be monitored and allows comparisons to be made to determine the optimum harvest time for flax.

Morphology and biomechanics of the nests of the Common Blackbird Turdus merula

Capsule Common blackbirds select different materials, with varying biomechanical properties, to construct different parts of their nest. Aims This study tested the hypothesis that outer components of a nest have a more structural role and so are stronger than materials used to line the cup. Methods Blackbird nests were measured prior to being dismantled to isolate structural components which were tested for mechanical strength and rigidity. Results Outer nest wall materials were significantly thicker, stronger and more rigid than materials in the inner structural wall or the cup lining. In the vertical plane materials used in the structural wall did not differ. By contrast, lining materials from the bottom of the nest cup were significantly thicker, stronger and more rigid than materials from the top of the cup. Conclusion Blackbirds use different materials in nest construction roles suited to their properties and so may be able to recognize the structural properties of these materials. Materials on the outside of the nest may have a key structural role during construction.

A specific case in the classification of woods by FTIR and chemometric: discrimination of Fagales from Malpighiales

Fourier transform infrared (FTIR) spectroscopic data was used to classify wood samples from nine species within the Fagales and Malpighiales using a range of multivariate statistical methods. Taxonomic classification of the family Fagaceae and Betulaceae from Angiosperm Phylogenetic System Classification (APG II System) was successfully performed using supervised pattern recognition techniques. A methodology for wood sample discrimination was developed using both sapwood and heartwood samples. Ten and eight biomarkers emerged from the dataset to discriminate order and family, respectively. In the species studied FTIR in combination with multivariate analysis highlighted significant chemical differences in hemicelluloses, cellulose and guaiacyl (lignin) and shows promise as a suitable approach for wood sample classification.

The Effects of Mechanical Stimulation on the Morphology and Mechanics of Maize Roots Grown in an Aerated Nutrient Solution

The effects of local mechanical stimulation on local root growth was investigated in maize (Zea mays L.) growing in an aerated nutrient solution. The morphology and mechanical properties of primary nodal roots were compared between those that underwent a program of flexing and those that received no mechanical stimulation. Local mechanical stimulation had limited effects on the morphology of maize nodal roots; there was no significant effect of flexing on the diameter of primary nodal roots when compared with untreated roots. However, there were significant differences in root mass between treatments; there was a large decrease of 43% in the fresh and 41% in the dry mass of the fine roots in the flexed roots compared with the untreated roots. Surprisingly, there was only a small effect on the mass of the primary nodal roots: only at the fifth node was there a significant increase of 15% in the dry mass of flexed roots compared to those that received no mechanical stimulation. The effects of root flexure on the mechanical properties of the roots were more dramatic. Roots at both nodes 4 and 5 were significantly more rigid, stronger, and composed of a stiffer material than those that received no mechanical stimulation. After flexing, the primary nodal roots at the fifth node showed increases of 75% in the rigidity, 60% in the bending strength, and 70% in the bending modulus of the flexed roots compared to unstimulated roots. This study shows that the thigmomorphogenetic response, at least in maize roots, can be localized even down to individual roots and not just to regions of the root system.

Application of chemometric analysis to infrared spectroscopy for the identification of wood origin

In this study, the chemical characteristics of wood are used for plant taxonomic classification based on the current Angiosperm Phylogeny Group classification (APG III System) for the division, class and subclass of woody plants. Infrared spectra contain information about the molecular structure and intermolecular interactions among the components in wood, but the understanding of this information requires multivariate techniques for the analysis of highly dense data sets. This article is written with the purposes of specifying the chemical differences among taxonomic groups and predicting the taxa of unknown samples with a mathematical model. Principal component analysis, t test, stepwise discriminant analysis and linear discriminant analysis were some of the multivariate techniques chosen. A procedure to determine the division, class, subclass and order of unknown samples was built with promising implications for future applications of Fourier transform infrared spectroscopy in wood taxonomy classification.

Construction patterns of birds’ nests provide insight into nest-building behaviours

Previous studies have suggested that birds and mammals select materials needed for nest building based on their thermal or structural properties, although the amounts or properties of the materials used have been recorded for only a very small number of species. Some of the behaviours underlying the construction of nests can be indirectly determined by careful deconstruction of the structure and measurement of the biomechanical properties of the materials used. Here we examined this idea in an investigation of Bullfinch (Pyrrhula pyrrhula) nests as a model for open-nesting songbird species that construct a “twig” nest, and tested the hypothesis that materials in different parts of nests serve different functions. The quantities of materials present in the nest base, sides and cup were recorded before structural analysis. Structural analysis showed that the base of the outer nests were composed of significantly thicker, stronger and more rigid materials compared to the side walls, which in turn were significantly thicker, stronger and more rigid than materials used in the cup. These results suggest that the placement of particular materials in nests may not be random, but further work is required to determine if the final structure of a nest accurately reflects the construction process.

Geographical effects on the mass and dimensions of finch (Fringillidae, Passeriformes) and thrush (Turdidae, Passeriformes) nests

Birds’ nests exhibit a considerable amount of plasticity in their size and construction. Indeed, several studies have shown that geographical location can affect this plasticity because local climatic conditions appear to affect nest-construction behaviours. This study examined nests collected in the UK and housed either at the University of Lincoln or at the British National Nest Reference Collection at the Hunterian Museum, University of Glasgow. Our aim was to increase the species diversity and the sample sizes for each species, over and above published studies. Mass and linear dimensions were recorded from nests of five finch species and two thrush species together with longitude and latitude for the nest site locations. An effect of species was shown for all finch nest dimensions measured but only for particular thrush dimensions. Latitude (range from 50.4 to 57.8°N) had no effect on nest measurements taken for thrush or finch species. However, while longitude (range from 6.8°W to 1.1°E) had no effect on thrush nests, it had a significant effect on the nest mass of finches, with nests constructed in the west being lighter in mass than those from the east. Previous studies examining the effects of latitude have used nests collected from different locations and built in a single year, which suggests that climatic conditions will be broadly comparable between locations. We found that museum collections have nests from a range of years and this rather limits their value in studies trying to ascertain the effects of location. Across different years there may be many unknown factors contributing to the patterns observed. We suggest that any future studies of the effects of climate on nest construction will have to rely on materials especially collected rather than using museum collections.

Regional variation in the flexural properties of the equine hoof wall

The equine hoof wall is a hard, keratinous structure that transmits forces generated when the hoof connects the ground to the skeleton of the horse. During locomotion the hoof capsule is known to deform, resulting in an inward curvature of the dorsal wall and expansion of the heels. However, while researchers have studied the tensile and compressive properties, there is a lack of data on the flexural properties of the hoof wall in different locations around the hoof capsule. In this study, the flexural properties and hydration status of the hoof wall were investigated in two orthogonal directions, in different locations around the hoof capsule. The hoof was divided into three regions: the dorsal-most aspect (toe), the medial and lateral regions (quarters) and the heels caudally. Beams were cut both perpendicular (transverse) and parallel (longitudinal) to the orientation of the tubules. Differences in the mechanical properties were then investigated using three-point bending tests. There were considerable differences in the flexural properties around the hoof capsule; transverse beams from the heel were 45% more compliant than those from the toe region. This corresponded with changes in the hydration of the hoof wall; beams from the heel region were more hydrated (28.2 ^ 0.60%) than those from the toe (24.2 ^ 0.44%; P , 0.01). Regional variation in the water content is thought to help explain differences in the flexural properties. Mechanical data are further discussed in relation to variation in the structure and loading of the hoof wall.

Birds use structural properties when selecting materials for different parts of their nests

AbstractBird nests can have various roles but all act as the location for incubation, so at least have to serve to hold and support the incubating bird and its clutch of eggs. Nest construction is species specific and the use of materials varies between different parts of the nest. At present we know very little about the role that these materials play in the structural characteristics of the nest. This study examined materials from deconstructed nests from four species of thrush (Turdidae) and two species of finch (Fringillidae) that all constructed nests made of woody stems. It was hypothesised that structural properties would vary within the different regions of a nest, with thicker and stronger materials being found in parts of the nest needing the most support. Secondly, it was predicted that structural properties would vary little between nests of members of the same family, but would be quite different between nests of different families. Nests were deconstructed to quantify the materials used in the cup lining, and the upper and lower parts of the outer nest. The 20 thickest pieces of material were selected from each nest part and for each piece, and their diameter and mass quantified. Each piece was then subjected to a three-point bending test using an Instron universal testing machine to determine its rigidity and bending strength. Placement of materials in the nest was non-random in all species. The materials used in the outer part of the nest were thicker, stronger and stiffer than those materials found in the cup lining. The extent to which these structural properties varied between families depended on where the material was taken from the nest. Both strength and rigidity strongly positively correlated with the diameter of the piece of material. We hypothesise that birds are not directly aware of the structural properties of the material per se but rather assess diameter and mass of the material when they pick it up by the bill. Using this information they decide on whether the piece is suitable for that appropriate stage of nest construction.ZusammenfassungVögel nutzen Struktureigenschaften bei der Materialauswahl für verschiedene Nestbereiche. Vogelnester können vielfältige Funktionen erfüllen, aber alle dienen als Ort der Bebrütung und müssen so zumindest groß und stabil genug für den brütenden Vogel und das Gelege sein. Die Nestbauweise ist artspezifisch, und die Materialverwendung unterscheidet sich zwischen den einzelnen Nestbereichen. Derzeit wissen wir nur sehr wenig über die Bedeutung, welche diese Materialien für die strukturellen Eigenschaften des Nestes haben. In dieser Studie wurden Materialien aus zerlegten Nestern von vier Drossel- (Turdidae) und zwei Finkenarten (Fringillidae) untersucht, die alle Nester aus holzigen Stängeln bauen. Unsere Hypothese besagte, dass sich die strukturellen Eigenschaften verschiedener Nestbereiche dahingehend unterscheiden sollten, dass sich dickeres und stabileres Material in den Nestteilen befindet, welche die größte Stabilität brauchen. Zweitens gingen wir von der Erwartung aus, dass sich die strukturellen Eigenschaften zwischen Mitgliedern derselben Vogelfamilie nur wenig unterscheiden, von Familie zu Familie jedoch sehr verschieden sein sollten. Die Nester wurden zerlegt, um die Materialmengen zu quantifizieren, die für die Auspolsterung der Nestmulde sowie für die oberen und unteren Bereiche des äußeren Nests verwendet wurden. Aus jedem Nestbereich wählten wir die 20 dicksten Materialteile aus und bestimmten für jedes davon Durchmesser und Masse. Dann wurde jedes Stück einem 3-Punkt-Biegeversuch mit einer Instron-Universalprüfmaschine unterzogen, um dessen Starrheit und Biegefestigkeit zu ermitteln. Die Anordnung der Materialien im Nest war bei allen Arten nicht zufallsverteilt. Die im äußeren Nestbereich verbauten Materialien waren dicker, stabiler und starrer als die Polstermaterialien in der Nestmulde. Das Ausmaß, zu dem diese Struktureigenschaften sich zwischen den Familien unterschieden, hing vom Nestbereich ab, aus dem das Material entnommen wurde. Sowohl Stabilität als auch Starrheit zeigten eine starke positive Korrelation mit dem Durchmesser des Materialteiles. Wir stellen die Hypothese auf, dass sich die Vögel der strukturellen Eigenschaften des Materials nicht per se bewusst sind, sondern stattdessen eher Durchmesser und Masse des Materials erfassen, wenn sie es mit dem Schnabel aufnehmen. Anhand dieser Informationen entscheiden sie dann, ob dieses Stück für die betreffende Phase des Nestbaus geeignet ist.