Wavelength-dependent collagen fragmentation during mid-IR laser ablation

Area of Science:

• Biomedical Engineering
• Laser Physics
• Biochemistry

Background:

• Mid-infrared free-electron lasers (FELs) are effective in surgery, precisely removing soft tissue with minimal collateral damage.
• The wavelength-dependence of this collateral damage is linked to protein structural integrity loss, but the molecular basis remains unclear.

Purpose of the Study:

• To investigate the molecular mechanism of wavelength-dependent collateral damage during mid-infrared FEL ablation.
• To identify specific molecular transitions responsible for tissue damage at different wavelengths.

Main Methods:

• Ablation of porcine corneas using a free-electron laser tuned to 2.77 µm (targeting water) and 6.45 µm (targeting protein).
• Characterization of ejected debris using gel electrophoresis, Fourier transform infrared spectroscopy, micro-Raman, and 13C-NMR spectroscopy.

Main Results:

• High-fluence ablation at 6.45 µm resulted in protein fragmentation and the appearance of nitrile and alkyne species.
• Ablation at 2.77 µm did not produce these specific molecular changes.
• The observed molecular changes are consistent with the scission of collagen protein backbone N-alkylamide bonds.

Conclusions:

• Scission of collagen N-alkylamide bonds is the likely molecular transition responsible for wavelength-dependent collateral damage in mid-infrared laser ablation.
• Understanding this specific molecular mechanism is crucial for optimizing laser parameters and minimizing tissue damage in surgical applications.