Femtosecond lasers for sub-surface tissue cutting Chris B. Schaffer

Message Using a tightly-focused femtosecond laser, it is possible to produce an micrometer-scale incision in the bulk of a tissue without affecting the overlying surface

How sharp is our scalpel? Minimum cut size is smaller than a single cell Maximal depth is around 1 mm Cut rates could be around 1 cm/s

Nonlinear absorption Tight focusing of femtosecond pulses produces high intensity in the focal volume

Nonlinear absorption High intensity leads to nonlinear absorption

Nonlinear absorption Energy is deposited into a microscopic volume located in the bulk of the material

Nonlinear absorption This energy deposition can lead to permanent structural changes in the bulk of the glass

Can even cut inside a piece of glass Sub-surface damage in a glass sample C. B. Schaffer, et al., Appl. Phys. Lett 84, 1441 (2004)

In vivo cortical cutting Urethane anesthetized rat with craniotomy for optical access to the brain Intravenous injection of fluorescent dye with two-photon excited fluorescence microscopy to visualize vasculature Translate animal at 10 µm/s while irradiating with –1-kHz train of 0.5 to 7-µJ energy, 50-fs duration, 800-nm wavelength laser pulses –Focused at 0.95 NA at multiple depths between 100 and 700 µm beneath the brain surface. Collaborative work with Ted Schwartz, Weill Cornell, Neurological Surgery

In vivo fluorescent angiography during cut

In vivo fluorescent angiography during cut

Post-mortem of cut

Post-mortem of cut

Demonstrated capabilities and limits Cuts up to 700 µm deep achievable in brain –We’ll likely reach the 1.1-mm theoretical limit (in brain) Cuts size ranges from sub-micrometer to 10’s of micrometers, depending on laser energy It is difficult to cut directly underneath large blood vessels

Microvascular lesioning Can selectively target any vessel within the top 0.7 mm of cortex C. Schaffer, et al., PLoS Biology 4, e22 (2006) N. Nishimura, et al., Nature Methods 3, 99 (2006)

Surface arteriole occlusion C. Schaffer, et al., PLoS Biology 4, e22 (2006)

Flow change after surface arteriole occlusion C. Schaffer, et al., PLoS Biology 4, e22 (2006)

Single-cell surgery Cutting the lateral dendrite in the Mauthner cell of a zebrafish Collaboration with Joe Fetcho, Cornell Neurobiology

Acknowledgments Funding: Ellison Medical Foundation American Heart Association American Society of Laser Medicine and Surgery Photonics Technologies Assistantship Program Cornell Ithaca/Weill seed grant