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Research Papers

Effects of Collagenase Type II on Vitreous Humor—An In Situ Rheological Study

[+] Author and Article Information
Aysan Rangchian

Department of Bioengineering,
Complex Fluid and Interfacial Physics
Laboratory,
University of California Los Angeles,
Los Angeles, CA 90095-1597
e-mail: aysanrangchian@ucla.edu

Anibal Francone

Retina Division,
Stein Eye Institute,
University of California Los Angeles,
Los Angeles, CA 90095
e-mail: anibalfrancone@live.com.ar

Matthew Farajzadeh

Retina Division,
Stein Eye Institute,
University of California Los Angeles,
Los Angeles, CA 90095
e-mail: matt.farajz@gmail.com

Helia Hosseini

Department of Mechanical and
Aerospace Engineering,
University of California Los Angeles,
Tehran University of Medical Sciences,
Tehran 1416753955, Iran
e-mail: hosseini.helia.md@gmail.com

Kelly Connelly

Department of Mechanical and
Aerospace Engineering,
University of California Los Angeles,
Los Angeles, CA 90095
e-mail: kellyconnelly12@gmail.com

Jean-Pierre Hubschman

Retina Division,
Stein Eye Institute,
University of California Los Angeles,
Los Angeles, CA 90095
e-mail: hubschman@jsei.ucla.edu

H. Pirouz Kavehpour

Department of Mechanical and
Aerospace Engineering,
University of California Los Angeles,
Los Angeles, CA 90095;
Department of Bioengineering,
University of California Los Angeles,
Los Angeles, CA 90095
e-mail: pirouz@seas.ucla.edu

1Corresponding author.

Manuscript received October 29, 2018; final manuscript received March 26, 2019; published online May 6, 2019. Assoc. Editor: Thao (Vicky) Nguyen.

J Biomech Eng 141(8), 081007 (May 06, 2019) (6 pages) Paper No: BIO-18-1468; doi: 10.1115/1.4043358 History: Received October 29, 2018; Revised March 26, 2019

The purpose of this study is to quantify the impact of enzyme activity on the vitreous humor structure over time to understand the mechanical characteristics of the vitreous humor gel. Changes in the mechanical behavior of the vitreous occur due to many reasons including aging, which may lead to many vitreoretinal diseases. The degeneration process of the vitreous has been studied; however, in situ experimental procedures to validate the existing hypotheses are limited. We examined thirty-eight porcine eyes using in situ rheological creep tests to measure the mechanical properties of the vitreous humor of the eyes prior to, 1 h and 24 h after the intravitreal injection. Eyes in one group were injected with collagenase type II solution and eyes in the control group were injected with phosphate buffered saline solution (PBS) with calcium and magnesium chloride. Prior to the injection, viscosity and creep compliance intercept values between both groups were not statistically different. At 1 h and 24 h after the injection, vitreous properties in the eyes from the first group showed a statistically significant increase in the J intercept values (representing the inverse of elasticity) compared to the control group. In addition, 1 h and 24 h after the injection, vitreous viscosity was lower in the eyes from the first group than in the eyes from the control group. These findings are a foundation for future studies on the effectiveness of intravitreal drugs that modify the mechanical properties of the vitreous humor.

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Figures

Grahic Jump Location
Fig. 1

(a) The mounting block with a half sphere cut out (13 mm radius), which was 3D printed to keep the eye in place and prevent unnecessary movements, (b) the location of the incision is consistent for all of the specimens, the eye is secured in the 3D printed mounting block and the block is taped to the surface of the rheometer, and (c) the rough surface of the probe is fully inserted in a porcine eye with minimal interaction with retina or sclera

Grahic Jump Location
Fig. 2

Schematic of the eye during the in situ rheological test probe toward center. The roughened end of the probe has a 0.86 mm radius. We insert 10 mm of the probe into the eye. This ensures that the roughened part is fully in the vitreous and the angle is toward the center of the vitreous.

Grahic Jump Location
Fig. 3

(a) Graphical representation of a creep test where a constant shear stress (τ) is applied to the sample for a constant period of time (t), during the experiment, (b) representation of a typical theoretical creep curve, which shows the creep compliance over time. Js at t = 0 s shows the intercept of the steady-state region of the sample with the y-axis indicating the elasticity of the sample. In addition, the slope of the steady-state part of the graph is inverse of the viscosity (μ) of the sample in the steady-state.

Grahic Jump Location
Fig. 4

Examples of the creep compliance curve for one eye from each group (indicated with collagenase or control) before the injection (t =0), and 24 h after the injection (t =24)

Grahic Jump Location
Fig. 5

Comparison of compliance intercept values for the porcine eyes injected with PBS, collagenase and no injection over time, standard deviation of the values are shown with the bars. The differences between the collagenase injected eyes at 1 h compared to the values of the same time from the PBS injected eyes are statistically significant (with the mean values of 0.326 compared to 0.161). The same holds for the difference between the groups at 24 h (with the mean values of 0.715 for group 1 and 0.207 for group 2). The eyes in group 1 show significant increases from t = 0 to t = 1, and t = 1 to t = 24. This does not hold for the eyes in group 2.

Grahic Jump Location
Fig. 6

Comparison of viscosity values for the porcine eyes injected with PBS versus collagenase over time, standard deviation of the values are shown with the bars. The differences between the collagenase injected eyes at 1 h compared to the values of the same time from the PBS injected eyes are statistically significant (with the mean values of 10.1 × 103 compared to 18.8 × 103). The same holds for the difference between the groups at 24 h (with the mean values of 6.96 × 103 for group 1 and 14.2 × 103 for group 2). The eyes in group 1 show significant increases from t = 0 to t = 1, and t = 1 to t = 24. This does not hold for the eyes in group 2.

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