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Design Innovation

A Gimbal-Mounted Pressurization Chamber for Macroscopic and Microscopic Assessment of Ocular Tissues

[+] Author and Article Information
Joseph T. Keyes

Graduate Interdisciplinary Program in Biomedical Engineering,  The University of Arizona, Tucson, AZ 85721

Dongmei Yan, Jacob H. Rader

The Department of Aerospace and Mechanical Engineering,  The University of Arizona, Tucson, AZ 85721

Urs Utzinger

Graduate Interdisciplinary Program in Biomedical Engineering,  The University of Arizona, Tucson, AZ 85721; BIO5 Institute for Biocollaborative Research,  The University of Arizona, Tucson, AZ 85721; Department of Biomedical Engineering,  The University of Arizona, Tucson, AZ 85721

Jonathan P. Vande Geest1

Graduate Interdisciplinary Program in Biomedical Engineering,  The University of Arizona, Tucson, AZ 85721; The Department of Aerospace and Mechanical Engineering,  The University of Arizona, Tucson, AZ 85721; BIO5 Institute for Biocollaborative Research,  The University of Arizona, Tucson, AZ 85721; Department of Biomedical Engineering,  The University of Arizona, Tucson, AZ 85721 e-mail: jpv1@email.arizona.edu

1

Corresponding author.

J Biomech Eng 133(9), 095001 (Oct 11, 2011) (7 pages) doi:10.1115/1.4004921 History: Received July 18, 2011; Accepted August 08, 2011; Published October 11, 2011; Online October 11, 2011

The biomechanical model of glaucoma considers intraocular pressure-related stress and resultant strain on load bearing connective tissues of the optic nerve and surrounding peripapillary sclera as one major causative influence that effects cellular, vascular, and axonal components of the optic nerve. By this reasoning, the quantification of variations in the microstructural architecture and macromechanical response of scleral shells in glaucomatous compared to healthy populations provides an insight into any variations that exist between patient populations. While scleral shells have been tested mechanically in planar and pressure-inflation scenarios the link between the macroscopic biomechanical response and the underlying microstructure has not been determined to date. A potential roadblock to determining how the microstructure changes based on pressure is the ability to mount the spherical scleral shells in a method that does not induce unwanted stresses to the samples (for instance, in the flattening of the spherical specimens), and then capturing macroscopic and microscopic changes under pressure. Often what is done is a macroscopic test followed by sample fixation and then imaging to determine microstructural organization. We introduce a novel device and method, which allows spherical samples to be pressurized and macroscopic and microstructural behavior quantified on fully hydrated ocular specimens. The samples are pressurized and a series of markers on the surface of the sclera imaged from several different perspectives and reconstructed between pressure points to allow for mapping of nonhomogenous strain. Pictures are taken from different perspectives through the use of mounting the pressurization scheme in a gimbal that allows for positioning the sample in several different spherical coordinate system configurations. This ability to move the sclera in space about the center of the globe, coupled with an upright multiphoton microscope, allows for collecting collagen, and elastin signal in a rapid automated fashion so the entire globe can be imaged.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Overall pressurization scheme for the sclera: (A) isometric cutaway view, (B) shows a side cutaway view of the mount, (C) demonstrates the ability to test different sizes scleras, (D) is the sclera, (E) is the inflow hole, (F) is the fluid exit hole, (G) is the mounting ring touching the sclera, and (H) is the mounting plate for the sclera. Scale bar is 10 mm.

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Figure 2

Movement scheme of the gimbal: Panel (A) the assembled motion component scheme with the rotation axes, (C) is the mounted sclera, (D) is the axis for motorized rotation about the optical axis (equatorial), (E) is the manual rotation axis for installation of the sprocket for axis (D), and (F) is the motorized axis for lateral rotation (meridional). Note that as rotation occurs about (F), the (D) axis is rotated about (F), as well. Panel (B) is an isometric exploded view of the mounting scheme to the motion components. (C) is the sclera and (D) is the centerline for rotation about the optical axis.

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Figure 3

Assembly of the sclera into the device: (A) sclera before clamping, (B) sclera after clamping, (C) attaching the sprocket for optical axis rotation, and (D) ready system for testing

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Figure 4

View from underneath the device showing the design scheme for maintaining proper tension on the optical axis rotation sprocket/pulley system: (A) optical axis rotation sprocket with the red arrow indicating the lateral movement induced by rotation from the lateral rotation motor, (B) pulley, (C) pulley drive from the optical axis rotation motor, and (D) tension sprocket. The arrows here indicate lateral movements that occur with lateral movement of (A). This is to keep constant tension on the belt. Tension is applied with the spring shown in (G) with the arrow indicating force (F) is the lateral rotation motor.

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Figure 5

Comparisons of the renders from the solid modeling of the design (A): Overall and (C): bath hidden from underneath, (B) side-view through the macroscopic observation window, and (D) the device under the microscope. Scale bar is 25 mm.

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Figure 6

(A) A side-view of a sample through the bath window with applied markers to monitor macroscopic strain, (B) thresholded image, and (C) a top-down view of marker placement. Scale bar is 5 mm for panels A and B.

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Figure 7

Result of moving points manually: (A) a three-dimensional reconstruction of points (vertical axis is in pixels, other axes show the rotational angle), (B) equatorial strain, (C) demonstrates how two points were moved. This image is rotated computationally about the optical axis four times to capture three-dimensional points and (D) meridional strain.

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Figure 8

Result of testing a single piece of latex glove: (A) top-down view of the markers (units are the angle of rotation), (B) equatorial strain, (C) isometric view of the points (units in pixels), and (D) meridional strain

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Figure 9

Macroscopic strain results of a porcine scleral shell from 5 to 30 mm Hg. (A) 3D view of displacement field (vertical axis is in pixels), (B) equatorial strain, (C) first principal strain, and (D) meridional strain.

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Figure 10

Multiphoton (SHG) image of the LC (13 multiphoton imaging regions). (A) LC at 5 mm Hg, (B) LC at 30 mm Hg. The bottom insets show a specific pore and how it changes in aspect ratio.

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Figure 11

Digital image correlation analysis (DIC): (A) section of the LC at 5 mm Hg with blue markers from the DIC program, (B) the same region at 30 mm Hg, but without markers, and (C) the first principal strain as quantified from DIC

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Figure 12

A region of the temporal PS (meridional angle = 5 deg) at 5 mm Hg (A) and 30 mm Hg (B). Red in this image is SHG (collagen) while green is elastin (2PEF). Scale bar is 100 μ m.

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