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Biophys. J. BioFAST: First Published May 19, 2006. doi:10.1529/biophysj.106.084616
© 2006 by the Biophysical Society.

A more recent version of this article appeared on August 15, 2006.
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PHOTOBIOPHYSICS

Wavelength-dependent collagen fragmentation during mid-IR laser ablation

Yaowu Xiao 1, Mingsheng Guo 2, Kevin Parker 3 and M. Shane Hutson 1*

1 Vanderbilt University
2 Fisk University
3 Duke University

* To whom correspondence should be addressed. E-mail: shane.hutson{at}vanderbilt.edu.

Submitted on March 8, 2006
Revised on April 20, 2006
Accepted on 9 May 2006


  Abstract
Mid-IR free-electron lasers have proven adept in surgical applications. When tuned to wavelengths between 6-7 µm, such lasers remove defined volumes of soft tissue with very little collateral damage. Previous attempts to explain the wavelength-dependence of collateral damage have invoked a wavelength-dependent loss of protein structural integrity. However, the molecular nature of this structural failure has been heretofore ill-defined. In this report, we evaluate several candidates for the relevant transition by analyzing the non-volatile debris ejected during ablation. Porcine corneas were ablated with a free-electron laser tuned to 2.77 or 6.45 µm - wavelengths with matched absorption coefficients for hydrated corneas that respectively target either tissue water or protein. The debris ejected during these ablations was characterized via gel electrophoresis, as well as FTIR, micro-Raman and 13C-NMR spectroscopy. We find that high-fluence (240 J/cm2) ablation at 6.45 µm, but not at 2.77 µm, leads to protein fragmentation accompanied by the accumulation of nitrile and alkyne species. The candidate transition most consistent with these observations is scission of the collagen protein backbone at N-alkylamide bonds. Identifying this transition is a key step towards understanding the observed wavelength-dependence of collateral damage in mid-IR laser ablation.

Key Words: 13C-NMR, FTIR, Raman spectroscopy, amide vibration, electrophoresis, free-electron laser




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A. Zavalin, D. L. Hachey, M. Sundaramoorthy, S. Banerjee, S. Morgan, L. Feldman, N. Tolk, and D. W. Piston
Kinetics of a Collagen-Like Polypeptide Fragmentation after Mid-IR Free-Electron Laser Ablation
Biophys. J., August 1, 2008; 95(3): 1371 - 1381.
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Y. Xiao, M. Guo, P. Zhang, G. Shanmugam, P. L. Polavarapu, and M. S. Hutson
Wavelength-Dependent Conformational Changes in Collagen after Mid-Infrared Laser Ablation of Cornea
Biophys. J., February 15, 2008; 94(4): 1359 - 1366.
[Abstract] [Full Text] [PDF]


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Copyright © 2006 by the Biophysical Society.