Frederic Bourgeois

Femtosecond laser nanoaxotomy properties and their effect on axonal recovery in C. elegans

We present a study characterizing the properties of femtosecond laser nanosurgery applied to individual axons in live Caenorhabditis elegans (C. elegans) using nano-Joule laser pulses at 1 kHz repetition rate. Emphasis is placed on the characterization of the damage threshold, the extent of damage, and the statistical rates of axonal recovery as a function of laser parameters. The ablation threshold decreases with increasing number of pulses applied during nanoaxotomy. This dependency suggests the existence of an incubation effect. In terms of extent of damage, the energy per pulse is found to be a more critical parameter than the number of pulses. Axonal recovery improves when surgery is performed using a large number of low energy pulses.

Ultrafast laser nanosurgery in microfluidics for genome-wide screenings

The use of ultrafast laser pulses in surgery has allowed for unprecedented precision with minimal collateral damage to surrounding tissues. For these reasons, ultrafast laser nanosurgery, as an injury model, has gained tremendous momentum in experimental biology ranging from in vitro manipulations of subcellular structures to in vivo studies in whole living organisms. For example, femtosecond laser nanosurgery on such model organism as the nematode Caenorhabditis elegans has opened new opportunities for in vivo nerve regeneration studies. Meanwhile, the development of novel microfluidic devices has brought the control in experimental environment to the level required for precise nanosurgery in various animal models. Merging microfluidics and laser nanosurgery has recently improved the specificities and increased the speed of laser surgeries enabling fast genome-wide screenings that can more readily decode the genetic map of various biological processes.

Ultrasound measurements of cavitation bubble radius for femtosecond laser-induced breakdown in water

A recently developed ultrasound technique is evaluated by measuring the behavior of a cavitation bubble that is induced in water by a femtosecond laser pulse. The passive acoustic emission during optical breakdown is used to estimate the location of the cavitation bubbles origin. In turn, the position of the bubble wall is defined based on the active ultrasonic pulse-echo signal. The results suggest that the developed ultrasound technique can be used for quantitative measurements of femtosecond laser-induced microbubbles.

Quantitative ultrasound method to detect and monitor laser-induced cavitation bubbles

An ultrasound technique to measure the spatial and temporal behavior of the laser-induced cavitation bubble is introduced. The cavitation bubbles were formed in water and in gels using a nanosecond pulsed Nd:YAG laser operating at 532 nm. A focused, single-element, 25-MHz ultrasound transducer was employed both to detect the acoustic emission generated by plasma expansion and to acoustically probe the bubble at different stages of its evolution. The arrival time of the passive acoustic emission was used to estimate the location of the cavitation bubbles origin and the time of flight of the ultrasound pulse-echo signal was used to define its spatial extent. The results of ultrasound estimations of the bubble size were compared and found to be in agreement with both the direct optical measurements of the stationary bubble and the theoretical estimates of bubble dynamics derived from the well-known Rayleigh model of a cavity collapse. The results of this study indicate that the proposed quantitative ultrasound technique, capable of detecting and accurately measuring laser-induced cavitation bubbles in water and in a tissue-like medium, could be used in various biomedical and clinical applications.

Ultrasound characterization of cavitation microbubbles produced by femtosecond laser pulses

An ultrasound-based technique capable of detection and spatio-temporal characterization of microbubbles induced in water by femtosecond laser is reported. A highly focused single-element ultrasound transducer was used both to detect passive acoustic emission of the microbubbles and to probe the microbubbles at different stage of their evolution. The location of origin and wall of the microbubble was assessed from temporal characteristics of the passive acoustic emissions and of the pulse-echo signals. The radius of the microbubble was estimated as the distance between the origin of the bubble and its wall. The ultrasound characterization of microbubbles induced by femtosecond pulses agreed well with theoretical predictions based on the well-known Rayleigh-based model of bubble behavior in liquid. The results of this study demonstrate that femtosecond laser-induced microbubbles with typical sizes of several tens of micrometers can be characterized by the developed ultrasound technique.

Femtosecond laser nanosurgery in microfluidic devices and its emerging role in nerve regeneration studies

Fs-laser nanosurgery as a precise injury tool has opened new frontiers in achieving a thorough understanding of nerve regeneration in model organisms. Using microfluidic devices we can now perform high-throughput genetic/pharmacological screenings in Caenorhabditis elegans.

Development of ultrasound technique to detect and characterize laser-induced microbubbles

An ultrasound-based method to detect and characterize the laser-induced microbubbles was developed. This method is based on temporal measurement of passive acoustic emission from cavity during laser-tissue interaction and simultaneous active pulse-echo ultrasound probing of the cavitation bubble. These measurements were used to estimate the location of the nanosecond laser induced cavity and to monitor the spatial and temporal behavior of the microbubble. The measurements agreed with estimates derived from a well-known Rayleigh model of the cavity collapse. Overall, the studies indicate that the developed ultrasound technique can be used to detect and accurately measure laser-induced microbubbles in tissue.

Femtosecond Laser Nano-Surgery for Nerve Regeneration Studies

Ultrashort laser pulses are increasingly being used to ablate subcellular structures inside living cells and multi-cellular organisms. We have recently demonstrated the feasibility of nano-axotomy in the nematode Caenorhabditis elegans (C. elegans) and observed nerve regeneration of the severed axons. Neural regeneration process can be impaired by the amount of collateral damage. Such damage is due to expansion of the thermoelastic stress-induced cavitation bubbles and the shock-waves expanding beyond the focal volume of the laser beam. This study presents a systematic characterization of the extent of damage in C. elegans created by 100-fs pulses at 1-kHz repetition rate with energies varying from 2-nJ to 20-nJ per pulse and the total number of pulses ranging from 1 to 1000. The minimum energy required for ablation greatly depends on the total number of pulses used. While a single shot of 21-nJ of energy can severe an axon, the threshold drops to as low as 3.8-nJ for 1000 pulses