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Title:Probing the effect of microstructure on water diffusion in engineered or biological materials with MRI
Author(s):Lu, Jiaxi
Director of Research:Georgiadis, John G.
Doctoral Committee Chair(s):Georgiadis, John G.
Doctoral Committee Member(s):Aluru, Narayana R.; Sutton, Bradley P.; Bahl, Gaurav
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Magnetic Resonance Imaging (MRI)
Polyethylene Glycol Diacrylate (PEG-DA) Hydrogel
Carbon Nanotube (CNT)
Measurement
Diffusivity
Myofiber
Anisotropic diffusion
Abstract:Water diffusion within skeletal muscles is a complex mass transport process due to the presence of barriers at multiple scales and the anisotropic structure of muscles. Magnetic Resonance Imaging (MRI) is an effective non-invasive technology for studying water transport in biological or engineered systems, and has been increasingly used to probe water diffusion in muscle. Because of the disparity between the length scales over which diffusion operates and MRI spatial resolution, the use of model systems is required in order to develop the methodology for deriving quantitative information from MRI data. Some engineered materials and systems share certain structural or functional characteristic with skeletal muscles and therefore can be used as model systems. For example, certain hydrogels that can change size shape or mechanical properties in response to solvent concentration have been used to fabricate artificial muscles. Bundles of aligned carbon nanotubes (CNTs) can be used to mimic the effect of the organization of myofibrils on water transport. Finally, the extraction of mass transfer properties from MRI data requires the integration of the underlying mass diffusion process with MRI imaging physics. In this thesis, the diffusion-weighted MRI protocol is used to probe water diffusion inside a swelling Polyethylene Glycol Diacrylate (PEG-DA) hydrogel and in the interstitial water-filled spaces in a bundle of aligned CNTs. Additionally, the diffusion-weighted MRI signal resulting from transversely anisotropic myofibers is simulated. The technical deliverables include: (1) A relationship between local water diffusivity and water concentration for PEG-DA hydrogel, which can be used to describe hydrogel actuator dynamics; (2) Water diffusivity parallel and perpendicular to the CNT orientation, which can be employed in the characterization of the intertube space; (3) Development of a two-compartment model for mass transfer in myofiber, which can account for anisotropic water diffusion in skeletal muscle. In general, sub-voxel modeling and numerical simulation can facilitate the exploration of microscale structure using MRI when the structure is characterized by short range order. The reported experiments on these engineered materials not only contribute to the development of MRI methods for probing skeletal muscle, but also help advance their own intrinsic applications and understand the limitation of MRI for probing such materials.
Issue Date:2013-05-24
URI:http://hdl.handle.net/2142/44251
Rights Information:Copyright 2013 Jiaxi Lu
Date Available in IDEALS:2013-05-24
Date Deposited:2013-05


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