Effects of Pulse Length and Energy on Collateral Damage in Embryonic Chick Calvarial Bone using the 980-nm Diode and 775-nm Femtosecond System

Methods: The calvarial bone was dissected from 3-week-old chick embryos and placed in modified Fitton-Jackson media (GIBCO BRL). Samples were irradiated using a 980 nm diode laser and a 775 nm femtosecond laser. Immediately after ablation, samples were stained using either Trypan Blue or Live/Dead kit (Molecular probes) to measure the width of dead cells surrounding the incisions. Samples were stained for alkaline phosphatase activity to assess enzymatic thermal denaturation.

Results: With a treatment energy of 7W using the 980 nm laser with two pulses each 0.1s in duration and separated by 0.2s an average of 120 +/- 10 mm in loss of cellular activity was measured. Loss of cellular viability and of alkaline phosphatase activity increased with increasing pulse energy while pulse length was maintained constant. Decreasing the pulse length to 0.01s and hence increasing the frequency of pulses significantly reduced collateral damage. In comparison, the femtosecond laser with a 150 X 10^-15s pulse length reduced collateral damage to an average of 9 +/- 2 mm. The average damage obtained by scalpel cuts was 25 +/- 6 mm.

Conclusion: The clinician should reduce the power and pulse length during tissue cutting to minimize collateral damage. (Funded by Photonics Research of Ontario fund # 419387).