a). Describe how collagen fibrils are formed from tropocollagen macromolecules.
Throughout the extracellular matrix and in the connective tissue, collagen is the largest insoluble fibrous protein. The collagen molecules combine together to form long, thin, similarly organized fibrils. Multiple subunits of tropocollagen molecules form collagen fibrils by lysyl oxidase, this enzyme links hydroxylysine with the lysine residues, and through covalent cross-linking (aldol reaction) multiple fibrils of collagen develop into fibres of collagen. The tropocollagen subunits in the extracellular spaces of tissues spontaneously get self-assembled, with frequently spaced ends, into even greater arrays. Additional fibril assembly is driven by fibroblasts which deposit completely formed fibrils from fibridepositors. Within the fibrillar collagens the subunits are staggered by about 67 nm to neighbouring molecules (Raspanti et al., 2018). The five subunits are arranged making a cross-sectional portion, called the overlap. Another portion is made up of four subunit molecules called the gap. These portions of the gap and overlap regions are maintained as microfibrils, which are assembled into fibrillates.
b). Explain where mineral forms within the collagen fibrils and why.
Bone is a fascinating structured biomaterial with two main constituents, a soft protein form of collagen and a much stiffer mineral from apatite. The molecules of collagen assemble into fibrils during bone formation, which are mineralised by the formation of apatite crystals. The mineral forms within the fibrils but also on the surface of the fibrils in collagen gap regions. With its c-axes parallel to the axes of the collagen molecule, the crystals within the fibrils expand. In crystallography, this alignment in a polycrystalline sample is "fibre texture," and it occurs in both cortical bone and cancellous bone and trabecular bone (Nair et al., 2013).
e). Suggest how organization of the collagen fibrils could be used to make bone a tough material.
Collagen is the most abundant protein on Earth, a fibrous structural protein with excellent mechanical properties, and an interesting example of a biological nanomaterial of hierarchy. Collagen consists of molecules of tropocollagen (TC), with lengths of 280 nm and diameters of approximately 1.5 nm, resulting in an aspect ratio of about 190. Collagen comprises of a synchronized sequence of extremely long strands of tropocollagen composed of collagen fibrils. Conceptual and computational modelling indicates that this normal nature of collagen fibrils significantly increases toughness and gives great dissipation of energy during curvature, thereby making a durable and resilient material (Buehler, 2006).
a). Briefly schematise x-ray generation and physics.
b). What is the SNR? Why is it important?
SNR is the signal-to-noise ratio, which is the ratio of the frequency of an electrical or other information carrying signal to that of unwanted interference. SNR ratio is essential since our central goal in interaction is on signal, but it's been impacted by certain noise signal throughout transmitting. There is need to have the same transmitted signal at the receiving end, in order to achieve this noise should be minimized and SNR plays an important role here. So, SNR ratio means optimizing the delivery of a message moves along a clear noise - free channel, such that the receiver can decode the intended meaning clearly (Wojciechowski et al., 2018).
c). What is BMD? Which technique is used to measure it and what are the main results?
Bone mineral density or bone density, is the mineral content of bone in bone tissue. The definition is of mineral mass per bone volume, although it is medically measured on imaging by proxy according to optical density per square centimeter of bone surface. The dual energy X-ray absorptiometry is the most commonly used method for calculating the bone mineral density. In order to quantify the mineral content present in bone and therefore density, this harnesses the high strength of bone calcium to absorbing X-rays to determine the relative quantities of bone and other soft tissue (Sheu, & Diamond, 2016).
d). What is Computed Tomography? Briefly describe the process of projections acquisition and image reconstruction.
A CT (computed tomography) scan, is an imaging technique used in diagnostics that uses machine-processed variations of multiple X-ray scans collected from the different angles to create a cross-sectional image of particular parts of a scanning body, allowing doctors to see through the sample without cutting. The signals obtained are processed in computer to make cross-sectional images of the body. These slices or the images obtained are called tomographic images, which contains information which is accurate than the standard x-rays. The images are then successively stacked together and a 3-D image of the patient is obtained. This technique is used to identify tumours or any abnormality in the body (Ardeshirpour et al., 2016).
e). How high-resolution micro-CT is currently used in the micromechanical characterisation of bone? Please comment on associated techniques used to quantify bone mechanical properties.
CT technique currently used for quantitative measurements of the structure of bone and can be used mathematically to quantify the strength of bone. The high-resolution CT technologies will provide clinically valuable knowledge by enhancing our perception of muscle strength and assessing the potential of an antifracture from osteoporosis and other metabolic bone disorders. New technologies such as the HR-pQCT now allow in vivo images to be acquired at distal sites with an isotropic voxel size in very short amount of time. New methodological approaches can acquire direct estimates of mechanical properties and important information concerning the bone topology, as well as parameters of length and alignment (Burghardt, Link & Majumdar, 2011).
Ardeshirpour, F., McCarn, K. E., McKinney, A. M., Odland, R. M., Yueh, B., & Hilger, P. A. (2016). Computed tomography scan does not correlate with patient experience of nasal obstruction. The Laryngoscope, 126(4), 820-825.
Buehler, M. J. (2006). Nature designs tough collagen: Explaining the nanostructure of collagen fibrils. PNAS, 103(33) 12285-12290; https://doi.org/10.1073/pnas.0603216103
Burghardt, A. J., Link, T. M., & Majumdar, S. (2011). High-resolution computed tomography for clinical imaging of bone microarchitecture. Clinical Orthopaedics and Related Research, 469(8), 2179–2193. https://doi.org/10.1007/s11999-010-1766-x
Nair, A., Gautieri, A., Chang, S. et al. Molecular mechanics of mineralized collagen fibrils in bone. National Community 4, 1724(2013). https://doi.org/10.1038/ncomms2720
Raspanti, M., Reguzzoni, M., Protasoni, M., & Basso, P. (2018). Not only tendons: The other architecture of collagen fibrils. International Journal of Biological Macromolecules, 107, 1668-1674.
Sheu, A., & Diamond, T. (2016). Bone mineral density: testing for osteoporosis. Australian Prescriber, 39(2), 35–39. https://doi.org/10.18773/austprescr.2016.020
Wojciechowski, S., Maruda, R. W., Krolczyk, G. M., & Niesłony, P. (2018). Application of signal to noise ratio and grey relational analysis to minimize forces and vibrations during precise ball end milling. Precision Engineering, 51, 582-596.
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