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Technical Briefs

Changes in the Tangent Modulus of Rabbit Septal and Auricular Cartilage Following Electromechanical Reshaping

[+] Author and Article Information
Amanda Lim

Department of Biomedical Engineering, The Beckman Laser Institute and Medical Clinic,  University of California, Irvine, Irvine, CA 92697adlim@alumni.uci.edu

Dmitry E. Protsenko

The Beckman Laser Institute and Medical Clinic,  University of California, Irvine, 1002 Health Sciences Road, Irvine, CA 92612dprotsen@uci.edu

Brian J. F. Wong

Department of Otolaryngology, Head and Neck Surgery and Department of Biomedical Engineering, The Beckman Laser Institute and Medical Clinic,  University of California, Irvine, 1002 Health Sciences Road, Irvine, CA 92612bjwong@uci.edu

J Biomech Eng 133(9), 094502 (Oct 04, 2011) (5 pages) doi:10.1115/1.4004916 History: Received January 27, 2011; Accepted August 17, 2011; Published October 04, 2011; Online October 04, 2011

Transforming decades’ old methodology, electromechanical reshaping (EMR) may someday replace traditionally destructive surgical techniques with a less invasive means of cartilage reshaping for reconstructive and esthetic facial surgery. Electromechanical reshaping is essentially accomplished through the application of voltage to a mechanically deformed cartilage specimen. While the capacity of the method for effective reshaping has been consistently shown, its associated effects on cartilage mechanical properties are not fully comprehended. To begin to explore the mechanical effect of EMR on cartilage, the tangent moduli of EMR-treated rabbit septal and auricular cartilage were calculated and compared to matched control values. Between the two main EMR parameters, voltage and application time, the former was varied from 2–8 V and the latter held constant at 2 min for septal cartilage, 3 min for auricular cartilage. Flat platinum electrodes were used to apply voltage, maintaining the flatness of the specimens for more precise mechanical testing through a uniaxial tension test of constant strain rate 0.01 mm/s. Above 2 V, both septal and auricular cartilage demonstrated a slight reduction in stiffness, quantified by the tangent modulus. A thermal effect was observed above 5 V, a newly identified EMR application threshold to avoid the dangers associated with thermoforming cartilage. Optimizing EMR application parameters and understanding various side effects bridge the gap between EMR laboratory research and clinical use, and the knowledge acquired through this mechanical study may be one additional support for that bridge.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Two types of EMR jigs with corresponding reshaped specimens. (a) Schematic of semicylindrical surface electrode jig with sandwiched cartilage (b) Schematic of right angle nonconducting jig with two 3 needle electrode arrays (c)–(d) Pre-EMR rabbit septal samples (e)–(f) EMR-reshaped samples corresponding to each jig after 30 min (e), or 10 min (f). (Black scale bar indicates 1 cm.)

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Figure 2

Scheme of experiment: Two samples of cartilage each were harvested from (a) a dissected rabbit ear in the region indicated with black dashed lines or from (b) rabbit septal cartilage with mucosa and perichondrium removed. (White double arrow lines indicate 1 cm.) (c) Voltage was applied to each sample through flat platinum electrodes. (d) Samples were rehydrated in PBS for 15 min. (e) Each sample was placed between grips of mechanical testing device, and a tensile force was applied.

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Figure 3

Typical strain-stress curve with specified linear region indicated with markers (O)

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Figure 4

Current profiles over time for auricular and septal samples. (a) Current at higher voltages corresponds to the left scale. (b) Current at 2V corresponds to the right scale.

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Figure 5

(a) Maximum current for septal samples (n = 5), EMR application time = two min and auricular samples (n = 5), EMR application time = three min. (b) Maximum change in temperature for septal and auricular samples (n = 2 to 4 for each data point). Error bars indicate ± standard error.

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Figure 6

Cartilage tangent moduli plotted as average ± standard error. * indicates p < 0.001 in a two-sample t-test with control data. (a) Septal data, EMR application time = two min, with n ≥ 9 for each voltage value, and n = 52 compiled control values. (b) Auricular data, EMR application time = three min, with n ≥ 11 for each voltage value, and n = 75 compiled control values. Moduli above 5 and 4 V were omitted due to excessive temperature elevation during EMR.

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