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TECHNICAL BRIEFS

Altered Multiaxial Mechanical Properties of the Porcine Anterior Lens Capsule Cultured in High Glucose

[+] Author and Article Information
R. M. Pedrigi, E. Staff, G. David, S. Glenn

Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843-3120

J. D. Humphrey1

Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843-3120jhumphrey@tamu.edu

1

Corresponding author.

J Biomech Eng 129(1), 121-125 (Jul 26, 2006) (5 pages) doi:10.1115/1.2401192 History: Received March 21, 2006; Revised July 26, 2006

Hyperglycemia can alter the mechanical properties of tissues through the formation of advanced glycation endproducts in matrix proteins that have long half-lives. We used a custom experimental system and subdomain finite element method to quantify alterations in the regional multiaxial mechanical properties of porcine lens capsules that were cultured for 8 or 14 weeks in high glucose versus control media. Findings revealed that high glucose significantly stiffened the capsules in both the circumferential and the meridional directions, but it did not affect the known regional variations in anisotropy. Such information could be important in the design of both improved clinical procedures and intraocular implants for diabetic patients.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figure 4

Results from the subdomain inverse finite element estimation of the best-fit parameters in the Fung strain energy function w for the 14week control and 14week high glucose cultured lens capsules. Panel a shows the ratio of c1 to c2 and panel b shows c (N/mm). The change in c1∕c2 from the pole (set D) towards the equator (sets C and E) indicates a regional anisotropy. In a comparison of control versus high glucose lens capsules, this regional anisotropy does not appear to be affected by the process of glycation, as does the overall stiffness of the capsule indicated by the statistically larger c-value (Fig. 4) in the high glucose cultured capsules. Error bars represent standard error.

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Figure 1

Schematic drawing of the lens capsule showing the insertion site for the needle (to distend the capsule at multiple pressures from 5to35mmHg), the three overlapping sets of five microspheres needed for both strain calculation and inverse finite element estimation of material properties, the y-suture on which set D was centered, and two axes representing those of the charge coupled device video cameras used to obtain the three-dimensional coordinates of each marker at a given pressure

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Figure 2

Summary of pressure-strain data for set D in the meridional direction of all 40 lens capsules (note that circumferential data were similar for set D and therefore not shown). Data are shown as mean ± standard error, except for controls (for clarity), which had similar standard errors. A t test revealed that high-glucose capsules were significantly stiffer (p<0.05) than corresponding cultured controls, but the 14- and the 8-week data were not statistically different (high glucose or controls). Strains were calculated relative to the cut, stress-free configuration.

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Figure 3

Panels a and b show pressure-strain data for sets C and D, respectively, for the 14week high-glucose cultured lens capsules in both the meridional and circumferential directions. Note that, consistent with Heistand (9), the circumferential direction “becomes” stiffer than the meridional as one moves from the pole (set D) towards the equator, thus suggesting a regional anisotropy. Strains were calculated relative to the intact, unloaded configuration. Error bars represent standard error.

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