title: Wavelength-dependent collagen fragmentation during mid-IR laser ablation.
abstract: Mid-infrared free-electron lasers have proven adept in surgical applications. When tuned to wavelengths between 6 and 7 microm, 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 nonvolatile debris ejected during ablation. Porcine corneas were ablated with a free-electron laser tuned to 2.77 or 6.45 microm-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 Fourier transform infrared spectroscopy, micro-Raman and 13C-NMR spectroscopy. We find that high-fluence (240 J/cm2) ablation at 6.45 microm, but not at 2.77 microm, 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 toward understanding the observed wavelength-dependence of collateral damage in mid-infrared laser ablation.
authors.affiliation: Department of Physics & Astronomy and Vanderbilt Institute for Integrative Biosystem Research & Education, Vanderbilt University, Nashville, Tennessee, USA.
authors.forename: Yaowu
authors.initials: Y
authors.lastname: Xiao
authors.forename: Mingsheng
authors.initials: M
authors.lastname: Guo
authors.forename: Kevin
authors.initials: K
authors.lastname: Parker
authors.forename: M Shane
authors.initials: MS
authors.lastname: Hutson
mesh_terms: D000818:Animals; D003094:Collagen / Q000032:analysis / Q000737:chemistry* / Q000528:radiation effects*; D003315:Cornea / Q000737:chemistry* / Q000528:radiation effects* / Q000601:surgery; D004307:Dose-Response Relationship, Radiation; D066298:In Vitro Techniques; D007259:Infrared Rays; D053685:Laser Therapy; D010446:Peptide Fragments / Q000032:analysis / Q000737:chemistry / Q000528:radiation effects; D011829:Radiation Dosage; D013552:Swine
chemical_list: D010446:Peptide Fragments; D003094:Collagen