Cancellous bone and theropod dinosaur locomotion. Part I—an examination of cancellous bone architecture in the hindlimb bones of theropods

This paper is the first of a three-part series that investigates the architecture of cancellous (‘spongy’) bone in the main hindlimb bones of theropod dinosaurs, and uses cancellous bone architectural patterns to infer locomotor biomechanics in extinct non-avian species. Cancellous bone is widely known to be highly sensitive to its mechanical environment, and has previously been used to infer locomotor biomechanics in extinct tetrapod vertebrates, especially primates. Despite great promise, cancellous bone architecture has remained little utilized for investigating locomotion in many other extinct vertebrate groups, such as dinosaurs. Documentation and quantification of architectural patterns across a whole bone, and across multiple bones, can provide much information on cancellous bone architectural patterns and variation across species. Additionally, this also lends itself to analysis of the musculoskeletal biomechanical factors involved in a direct, mechanistic fashion. On this premise, computed tomographic and image analysis techniques were used to describe and analyse the three-dimensional architecture of cancellous bone in the main hindlimb bones of theropod dinosaurs for the first time. A comprehensive survey across many extant and extinct species is produced, identifying several patterns of similarity and contrast between groups. For instance, more stemward non-avian theropods (e.g. ceratosaurs and tyrannosaurids) exhibit cancellous bone architectures more comparable to that present in humans, whereas species more closely related to birds (e.g. paravians) exhibit architectural patterns bearing greater similarity to those of extant birds. Many of the observed patterns may be linked to particular aspects of locomotor biomechanics, such as the degree of hip or knee flexion during stance and gait. A further important observation is the abundance of markedly oblique trabeculae in the diaphyses of the femur and tibia of birds, which in large species produces spiralling patterns along the endosteal surface. Not only do these observations provide new insight into theropod anatomy and behaviour, they also provide the foundation for mechanistic testing of locomotor hypotheses via musculoskeletal biomechanical modelling

Characterising variability and regional correlations of microstructure and mechanical competence of human tibial trabecular bone: An in-vivo HR-pQCT study.

OBJECTIVE: Quantifying spatial distribution of trabecular bone mechanical competence and microstructure is important for early diagnosis of skeletal disorders and potential risk of fracture. The objective of this study was to determine a spatial distribution of trabecular mechanical and morphological properties in human distal tibia and examine the contribution of regional variability of trabecular microarchitecture to mechanical competence. METHODS: A total of 340 representative volume elements at five anatomic regions of trabecular bone - anterior, posterior, lateral, medial and centre - from ten white European-origin postmenopausal women were studied. Region-specific trabecular parameters such as trabecular volume fraction, trabecular thickness, trabecular number, trabecular surface area, trabecular separation, plate-like structure fraction and finite element analysis of trabecular stiffness were determined based on in-vivo high resolution peripheral quantitative computed tomographic (HR-pQCT) images of distal tibiae from ten postmenopausal women. Mean values were compared using analysis of variance. The correlations between morphological parameters and stiffness were calculated. RESULTS: Significant regional variation in trabecular microarchitecture of the human distal tibia was observed (0.001 ≤ p ≤ 0.05), with up to 106% differences between lowest (central and anterior) and highest (medial and posterior) regions. Higher proportion of plate-like trabecular morphology (63% and 53%) was found in medial and posterior regions in the distal tibia. Stiffness estimated from finite element models also differed significantly (0.001 ≤ p ≤ 0.05), with stiffness being 4.5 times higher in the highest (medial) than lowest (central) regions. The bone volume fraction was the strongest correlate of stiffness in all regions. CONCLUSION: A novel finding of this study is the fact that significant regional variation of stiffness derived from two-phased FEA model with individual trabecula representation correlated highly to regional morphology obtained from in-vivo HR-pQCT images at the distal tibia. The correlations between regional morphological parameters and mechanical competence of trabecular bone were consistent at all regions studied, with regional BV/TV showing the highest correlation. The method developed for regional analysis of trabecular mechanical competence may offer a better insight into the relationship between mechanical behaviour and microstructure of bone. The findings provide evidence needed to further justify a larger-cohort feasibility study for early detection of bone degenerative diseases: examining regional variations in mechanical competence and trabecular specifications may allow better understanding of fracture risks in addition to others contributing factors

Understanding nonlinear vibration behaviours in high-power ultrasonic surgical devices

Ultrasonic surgical devices are increasingly used in oral, craniofacial and maxillofacial surgery to cut mineralized tissue, offering the surgeon high accuracy with minimal risk to nerve and vessel tissue. Power ultrasonic devices operate in resonance, requiring their length to be a half-wavelength or multiple-half-wavelength. For bone surgery, devices based on a half-wavelength have seen considerable success, but longer multiple-half-wavelength endoscopic devices have recently been proposed to widen the range of surgeries. To provide context for these developments, some examples of surgical procedures and the associated designs of ultrasonic cutting tips are presented. However, multiple-half-wavelength components, typical of endoscopic devices, have greater potential to exhibit nonlinear dynamic behaviours that have a highly detrimental effect on device performance. Through experimental characterization of the dynamic behaviour of endoscopic devices, it is demonstrated how geometrical features influence nonlinear dynamic responses. Period doubling, a known route to chaotic behaviour, is shown to be significantly influenced by the cutting tip shape, whereas the cutting tip has only a limited effect on Duffing-like responses, particularly the shape of the hysteresis curve, which is important for device stability. These findings underpin design, aiming to pave the way for a new generation of ultrasonic endoscopic surgical devices

Calcified Algae for Tissue Engineering.

This book presents the latest advances in marine structures and related biomaterials for applications in both soft- and hard-tissue engineering, as well as controlled drug delivery

A Novel Ceramic Precursor Route for the Direct Production of Hierarchically Structured Titanium Alloy Foams

Titanium alloys find extensive use in the biomedical field, including applications in the form of a porous structure as a scaffold material for bone repair. Scaffold materials have demanding mechanical and biocompatibility requirements, which vary depending on the orthopaedic application. These requirements are determined by both the porous macrostructure of the foams and the strut wall microstructure. Therefore techniques are needed to characterise these structural features and relate them to the mechanical and physical properties. In this thesis new methods were developed to both manufacture titanium alloy foams and characterise them. Non- destructive X-ray micro-computed tomography (μCT) methods were employed to characterise the pore and interconnect size. The pore and interconnect size dominates the flow properties (permeability) of open-foam structures. Thus, μCT data was meshed and computational fluid dynamics analysis was performed to predict permeability. Direct finite element modelling, continuum micromechanics and analytical models of the foam were employed to characterise the elasto-plastic deformation behaviour. Pore anisotropy was quantified and related to the yield stress anisotropy, allowing identification of initial pore collapse. These results were validated against experimental measurements. Finally, the conventional production method of porous titanium is achieved through a costly multi-step powder metallurgical (PM) route. A new, potentially low cost, method was developed to produce porous titanium with properties similar or better than the existing titanium foam from a ceramic precursor via an electrochemical route. Two steps were involved: (1) preparing the ceramic precursor foam via a gel-casting route; and (2) reducing the oxide electrochemically via the FFC (Fray, Farthing and Chen) Cambridge process. The results of this preliminary study are very promising, with the foams produced via this method demonstrating mechanical and physical properties comparable to conventionally manufactured foams

3D Printing StarPoreⓇ for Bone Tissue Engineering

Since the advent of Tissue Engineering (TE) in the late 1980’s, significant progress has been made within the biomedical landscape. A recently established branch within TE is biofabrication, a field that aims to automate the fabrication of biologically functional materials through the use of additive manufacturing or three-dimensional (3D) printing, among other techniques. Additive manufacturing offers fine control over part porosity, with the capacity to match the complex internal architecture of human bone. Coupled with clinical 3D scanning techniques, 3D printing has the capacity to generate implants that accurately match defected areas. However, due to the limited number of regulatory approved devices for human implantation and high cost of sophisticated powder bed fusion printers, the printing techniques are restricted. To be compatible with regulatory requirements, this work aims to utilise a widely accessible and regulatory approved device, high-density polyethylene (HDPE) to generate bone substitutes. HDPE in the form of StarPore® supplied by industry collaborator Anatomics Pty Ltd, a three-pronged star or trilobal shape, is an established material approved by both the Federal Drug Administration (FDA) in the United States of America and the Therapeutic Goods Administration (TGA) in Australia as a bone substitute for human implantation

The effect of boundary conditions and architecture on the response of cancellous bone

The investigation presented herein was performed to determine the effect of boundary conditions and architectural parameters on the mechanical properties of bovine cancellous bone. 124 cylindrical cancellous samples (7.5 mm height) were harvested from a total of 9 bovine humeri. Mechanical properties of these samples were determined using compression tests performed at three, quasi-static strain rates, namely: 10−3 , 10−2 and 10−1 s −1 .The specimen conditions investigated were standard specimens (with marrow, 10 mm diameter), defatted specimens (without marrow, 10 mm diameter), structurally confined specimens (with marrow and a confining collar, 10 mm diameter) and bone confined specimens (with marrow, 20 mm and 28 mm diameters). Each specimen was scanned using a µCT scanner (Phoenix, voxel size 80 µm, 70 kV, 350 µA, acquisition time of 500 ms per image). The images were used to determine the architectural parameters for each specimen, which were calculated using algorithms developed during the study. These algorithms were validated against existing software (BoneJ) which is available to calculate cancellous bone architectural parameters. The results of the compression testing showed little dependence of mechanical properties on strain rate. The results of the defatted and structurally confined specimens showed a decrease in scatter with the elimination and reduction, respectively, of flow of the marrow within the trabecular network. This suggests that although marrow does not strengthen bone at quasi-static strain rates, the flow of marrow disrupts the trabecular network. The bone confinement results showed significantly increased mechanical strength of the inner 10 mm core compared to the whole sample. Apparent modulus was found to be 58% and 60% higher in the central core of the sample for 20 mm and 28 mm samples respectively. This suggests that doubling the diameter effectively removes the edge effects, with any additional diameter increase having no effect. Inner core yield strength was 58% higher in the 20 mm samples, and roughly 96% higher in the 28 mm samples compared to full specimen yield strength. This suggested that post-yield behaviour requires a further increase in overall diameter to sufficiently remove the edge effects due to the boundary condition. University of Cape Town Department of Mechanical Engineering The results of the architectural parameters suggested a linear correlation between the mechanical properties and parameters bone volume versus total volume and trabecular number. An exponential relationship was found to exist between the mechanical properties and mean trabecular separation. No correlation was found between mechanical properties and mean trabecular thickness. It was also concluded that specimen condition affects the relationship between mechanical properties and architectural parameters. Therefore, to effectively predict the response of cancellous bone, specimen condition should be used in conjunction with at least two architectural parameters, preferably bone volume versus total volume and mean trabecular separation

On the Mechanical Properties of Microfibre-Based 3D Chitinous Scaffolds from Selected Verongiida Sponges

Skeletal constructs of diverse marine sponges remain to be a sustainable source of biocompatible porous biopolymer-based 3D scaffolds for tissue engineering and technology, especially structures isolated from cultivated demosponges, which belong to the Verongiida order, due to the renewability of their chitinous, fibre-containing architecture focused attention. These chitinous scaffolds have already shown excellent and promising results in biomimetics and tissue engineering with respect to their broad diversity of cells. However, the mechanical features of these constructs have been poorly studied before. For the first time, the elastic moduli characterising the chitinous samples have been determined. Moreover, nanoindentation of the selected bromotyrosine-containing as well as pigment-free chitinous scaffolds isolated from selected verongiids was used in the study for comparative purposes. It was shown that the removal of bromotyrosines from chitin scaffolds results in a reduced elastic modulus; however, their hardness was relatively unaffected