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Title: Towards real-time imaging of strain in soft tissue
Author: Lee, Z. S.
ISNI:       0000 0004 7231 0147
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2018
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The study of deformation and strain in soft tissues has always been important in the biomechanics field because it is part of understanding the mechanism on how human body perceives the external or environmental stimulation and also the main cause of superficial injuries or torn soft tissues. In addition, it is particularly challenging to investigate the strain behaviour of the soft tissue undergoing sliding interaction experimentally in real-time due to the limitations of the available measuring equipment. As such, this research introduced a range of high-speed imaging techniques to aim at developing and working towards real-time imaging of deformation and strain in soft tissue. The imaging techniques used were 3D-digital image correlation (3D-DIC), optical coherence tomography (OCT) and confocal tomography. 3D-DIC was used to find the surface strain profiles of the human skin and also to measure the apparent contact area of the finger pads on a glass plate. OCT was able to measure the roughness profile and the real-toapparent contact area ratio of the finger pads. Confocal microscopy was used to determine the orientation of the tissue fibres in the porcine aorta before and after the damage was inflicted. Confocal microscopy was not used on the human skin because there were high risks in using this imaging technique on the human skin in vivo tests. The frictional and the strain behaviour of the finger pad during a sliding interaction with a smooth glass plate are relatable because the normal load has shown to have a linear relationship with the average strain of the contact area in this study. In general, the predominant friction mechanism of the finger pad was adhesion and the edge of the contact area has higher surface strain values than the middle region. It was found that the apparent contact area has a power-law relationship with the normal load and a linear relationship with the shear force during sliding. The roughness profile of the finger pad was influence by the normal load and the sliding state of the finger pad as well. It was found that the moist finger pad had a moisture level similar to the dry finger pad after the acclimatisation period even though the frictional behaviours of the two finger pads were different, highlighting the importance of documentation of water application method. A batch of homogenous silicone hemi-spheres with different stiffness was manufactured to simulate finger pads. Some silicone hemi-spheres have similar frictional behaviours as the finger pads and the predominant friction mechanism was still adhesion. Also, the dynamic coefficients of friction of the silicone hemi-spheres were directly proportional (with a negative gradient) to the stiffness of the silicone hemi-spheres. However, the silicone hemi-spheres experienced much higher surface strain than the finger pad during sliding, which is caused by the adhesion hysteresis effect. In addition, it could also due to the homogenous properties, size and geometry, and the surface roughness of the silicone hemi-spheres. Furthermore, a theoretical strain model was used successfully to predict the strain distribution pattern of a silicone hemi-sphere. A study on the forearm skin showed that the surface strain and morphological change of human skin are relatable even when performing simple movements. A study on the porcine aorta tissue fibres found that the damage done on the porcine aorta might have permanently deformed the tissue fibres. It was unsure how the orientation of the tissue fibres changes during the damage application because the confocal microscopy was not able to monitor the tissue fibres orientation in real-time, hence, highlighting the importance of real-time imaging.
Supervisor: Lewis, Roger ; Carré, Matt Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available