A new picosecond laser (Impulse+, Irisiome, France) with bursts of ultrashort pulses was recently proposed for tattoo removal to enhance efficiency and patient tolerance. This study aims to analyse the optical properties of tissues and cells of the skin subject to laser irradiation with or without black ink pigments. Results show that black tattoo ink alone is not cytotoxic for dermis cells but it can induce particular cells’ reactions up to death with laser irradiation. These results are promising and help understanding picosecond laser process for tattoo removal.

Using a picosecond laser that delivers bursts of ultrashort pulses may improve thermal effects and limit side effects, compared to a sub-nanosecond laser. This study aims to analyse how the temperature increases on agar with or without black ink and on human skin. Results showed that large beams, and so long macropulses, present higher peaks of temperature than the small ones, as well as when fluencies and frequencies increase. Besides, higher thermal loading occurred with the nanosecond pulses. These results may explain why picosecond laser induces less side effects than sub-nanosecond laser.

Background: Q-Switched laser in nano- or pico-second regime are actually the gold standard for tattoo removal. Despite the selective feature, the delivered power is important and these lasers have shown their limitations in term of efficiency, pain and side effects. We propose a new approach to avoid the energy levels used today. The objective of this study was to assess the tolerance and the efficacy of a laser delivering ultrafast burst of pulses for tattoo removal. Methods: A preclinical followed by a phase 1-2 prospective studies were performed on ex-vivo skin explants and on healthy subjects with black tattoos, respectively, using an ultrafast burst of pulses laser (35 ps, 4 MHz, 1064 nm) with cumulative fluencies of 2.5 to 50 J/cm². Efficacy was assessed on standardized pictures by two independent physicians. Pain during treatment was evaluated using a visual analogical scale. Histological examinations were performed immediately after the laser session and at two months. Findings: In the preclinical study, the treated explants presented no clinical sign of suffering. Histological analysis showed no damage in epidermis, dermis or hypodermis. In the first in man proof-of-concept study, 10 patients from skin type II to IV were included. The fluences of 10 and 50 J/cm2 have reduced the intensity of the pigment in 6 patients with a better decrease at 50 J/cm2. The average pain ranged from 0.4 to 2.75/10 depending on the fluences. Side effects were mild and only at the highest fluencies. Interpretation: We report here for the first time, the use of a new way to deliver the energy into the skin by emitting a burst of pulses to sum up the energy and decreasing the unwanted heating of the tissues. Our results show that such a technique provides very good tolerance and promising efficacy for removing tattoos. Clinical Trial Number: NCT03386760 Funding Statement: This study was supported by Irisiome©, France. Declaration of Interests: RR and RD are employees of Irisiome© company Ethics Approval Statement: IRB status: Accepted: 60-17 (Ile de France VI); ANSM (French Agency for Medicine Security) approval: Id-RCB : 2017-A02216-47