Magnetic Resonance Imaging (MRI) of Water Diffusion in 2-Hydroxyethyl Methacrylate (HEMA) Gels
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0930-JJ04-05
Magnetic Resonance Imaging (MRI) of Water Diffusion in 2-Hydroxyethyl Methacrylate (HEMA) Gels Guy Raguin1, Cibele V. Falkenberg1, Shaurya Prakash1, Heather R. FitzHenry1, Glennys Mensing1, Luisa Ciobanu2, John G. Georgiadis1,3, and Mark A. Shannon1 1 Mechanical Engineering, University of Illnois at Urbana-Champaign, 1206 West Green Street, 140MEB, MC-244, Urbana, IL, 61801 2 Beckman Institute for Advanced Science and Technology, University of Illnois at UrbanaChampaign, Biomedical Imaging Center, 2100 S Goodwin Ave, Urbana, IL, 61801 3 Beckman Institute for Advanced Science and Technology, 405 North Mathews Avenue, Urbana, IL, 61801
ABSTRACT A fundamental study focusing on correlating the local water self-diffusion coefficient to the local free water content in 2-hydroxyethyl methacrylate (HEMA) gels was conducted. HEMA gels were synthesized with different nominal water content (50% to 90%). MRI measurements of local diffusion coefficient distribution and local water content profiles were conducted on a 600 MHz scanner. The local water content was measured via two spin-echo images with sufficiently long repetition time (TR) to eliminate T1-weighting and two values for the echo time (TE) in order to account for T2-weighting. The local diffusion coefficient was determined using a standard pulsed-field gradient spin-echo sequence. The measured local water content and diffusion coefficient data were compared with several single-parameter diffusion models for interstitial diffusion in the hydrogel (Makie-Meares, Stokes-Einstein, and Brownian motion around overlapping spheres).
INTRODUCTION Hydrogels are complex materials composed of tangled molecular networks incorporating large amounts of water and therefore constitute excellent hydration agents. Water organizes in various states, such as free, bound, and interfacial [1], and it plays a significant role in determining the transport properties of hydrogels. It is also known that the specific hydrogel synthesis procedure, characterized by the specific polymerization methodology, curing temperature, and cross-linker content, affects gel microstructure, and can even create spatial inhomogeneities within the gel [2], both in terms of pore structure and water content. The objective of this study is to establish a relationship between the local gel pore structure and the local water self-diffusion coefficient in uniform bulk samples of a hydrogel. We chose Magnetic Resonance Imaging (MRI) as the means of accomplishing this. Prior studies have used MRI to extract the diffusion coefficient of water into hydrogels by curve-fitting the relative water concentration profiles obtained from MRI measurements during sorption [3]. Here, we opt for independent measurements of the self-
diffusion coefficient and water content, as a first step towards probing the interstitial space of a class of hydrogels.
EXPERIMENTAL DETAILS Gel preparation The gels under study were prepared in 2 ml capacity transparent glass vials with PTFE caps (OD = 1.15 cm and height = 3.5 cm) from
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