Magnetic resonance studies of fluid transport in porous systems and medical devices

Abstract

This research describes the application of nuclear magnetic resonance (NMR) techniques for non-invasive investigation of fluid transport and hydrodynamics in porous systems and medical devices. NMR microscopy is used to obtain information about internal structures and transport properties in porous materials and opaque systems. Controlling dispersion within restricted pore spaces is of importance in a variety of applications including soil consolidation and dewatering and electromigration of solutes. NMR pulsed gradient stimulated echo (PGSTE) techniques combined with electroosmotic flow (EOF) are used to study diffusion and dispersion coefficients in model glass bead packs. The results show that significant EOF-induced backflow can cause structural changes and alter the flow. Understanding the transport of liquids in porous materials during the application of electrical field holds promise for solving problems involving the delivery of binding agents to infill the pore space in rigid cement-based structures via electroosmosis. NMR PGSTE techniques and micro-CT scan imaging were used to study fluid transport and structural changes in a hydrating cement paste in a closed cell. It is shown that EOF in closed cement paste samples caused a significant increase in macroscopic void volume compared to closed samples with no flow. Needleless connectors (NCs) are commonly used medical devices with complicated internal design that leads to flow complexity that may cause undesirable bacterial deposition and biofilm formation. Magnetic resonance imaging (MRI) is applied to acquire spatial velocity maps of fluid flow at various positions within the devices. MRI velocimetry is demonstrated as an effective method to quantify flow patterns and fluid dynamic dependence on structural features of NCs. Alginate and alginate-based materials find an increasing interest in environmental engineering as adsorbents for heavy metal recovery from aqueous solutions. A Ca 2+ and Cu 2+ containing fluid flow through calcium-based alginate gel has been visualized using NMR velocimetry. NMR indicated velocity changes in gel capillaries caused by ion exchange processes and followed gel structural changes. NMR microscopy is shown as an effective method to describe fluid transport and internal structural features in opaque porous systems and medical devices.