Research Papers

Experimental Techniques for Studying Poroelasticity in Brain Phantom Gels Under High Flow Microinfusion

[+] Author and Article Information
O. Ivanchenko, N. Sindhwani, A. Linninger

Laboratory of Product and Process Design, University of Illinois at Chicago, Chicago, IL 60607

J Biomech Eng 132(5), 051008 (Mar 29, 2010) (8 pages) doi:10.1115/1.4001164 History: Received November 18, 2009; Revised January 27, 2010; Posted February 02, 2010; Published March 29, 2010

Convection enhanced delivery is an attractive option for the treatment of several neurodegenerative diseases such as Parkinson, Alzheimer, and brain tumors. However, the occurrence of a backflow is a major problem impeding the widespread use of this technique. In this paper, we analyze experimentally the force impact of high flow microinfusion on the deformable gel matrix. To investigate these fluid structure interactions, two optical methods are reported. First, gel stresses during microinfusion were visualized through a linear polariscope. Second, the displacement field was tracked using 400 nm nanobeads as space markers. The corresponding strain and porosity fields were calculated from the experimental observations. Finally, experimental data were used to validate a computational model for fluid flow and deformation in soft porous media. Our studies demonstrate experimentally, the distribution and magnitude of stress and displacement fields near the catheter tip. The effect of fluid traction on porosity and hydraulic conductivity is analyzed. The increase in fluid content in the catheter vicinity enhances the gel hydraulic conductivity. Our computational model takes into account the changes in porosity and hydraulic conductivity. The simulations agree with experimental findings. The experiments quantified solid matrix deformation, due to fluid infusion. Maximum deformations occur in areas of relatively large fluid velocities leading to volumetric strain of the matrix, causing changes in hydraulic conductivity and porosity close to the catheter tip. The gradual expansion of this region with increased porosity leads to decreased hydraulic resistance that may also create an alternative pathway for fluid flow.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Comparison of backflow with normal spread. Infusion with single port catheter at 2.0 μl/min (a) without backflow and (b) with extensive backflow upwards along the catheter shaft.

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Figure 2

Linear polariscope for stress visualization in a gel sample. The equipment consists of a collimated light source, a polarizer, an agarose gel sample chamber, and a second polarizer called the analyzer. The polarized light from the polarizer decomposes into two component waves along the principle stresses in the gel sample. The light then passes through the analyzer; the camera records the resultant isoclinics pattern.

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Figure 3

Schematic and experimental setup for tracking nanobeads seeded in agarose gels during infusion

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Figure 4

The space correlation between two interrogation windows (left) yields the displacement vector. Individual nanobeads are represented as circles. To obtain the displacement vector, cross-correlation procedure is executed by maximizing a correlation function (right). Here, coordinates sx and sy correspond to the displacement vector components along the x and y axis.

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Figure 5

The polariscope is held in the dark field mode. The gray box shows the outline of the catheter through which fluid was infused from right to left, as indicated by the arrow: frame (a) before infusion, no isoclinic pattern; (b) infusion begins at high flow rate 5 μl/min, isoclinic fringes start to develop and is seen as a white field; (c) infusion continues and isoclinic fringe pattern can be observed more clearly.

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Figure 6

The crude digital images at two different time frames to compute space correlation. Water was infused from right to left through the catheter at a rate of 5 μl/min.

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Figure 7

Space correlation showing the displacement field obtained. Frame (a) U vertical displacement field, X derivative; (b) V horizontal displacement field, Y derivative; and (c) total displacement magnitude field, m=U2+V2. Maximum displacement magnitude was m=7 μm.

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Figure 8

Strain and porosity fields in vicinity of the catheter tip. Frames (a) and (b): α and β strain fields in X and Y directions. The (c) volumetric strain and the (d) porosity field.

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Figure 9

In microinfusion experiment, the experimental scaled hydraulic conductivity, K/K0 shown here, increased up to 40% close to the tip

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Figure 10

Computational mesh: (a) showing the whole domain; (b) showing catheter tip and mesh density near the catheter tip

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Figure 11

Computational results. Frames (a) and (b): α and β strain fields, bottom: (c) volumetric strain and (d) the porosity fields coupled by Eq. 3.

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Figure 12

Computational results showing scaled hydraulic conductivity caused by infusion. The maximum of up to 40% increase was calculated close to the tip.

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Figure 13

Comparison between computational and experimental strains. (a) α strain along a vertical line at the catheter tip. The profiles match well. (b) β strain along a horizontal line at the catheter tip. The profiles follow a similar trend, but agree poorly in terms of actual values.



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