Microcavitation and spot size dependence for damage of artificially pigmented hTERT-RPE1 cells

Abstract

We performed measurements to validate damage threshold trends in minimum visible lesion (MVL) studies as a function of spot size for nanosecond laser pulses. At threshold levels, nanosecond pulses produce microcavitation bubbles that expand and collapse around individual melanosomes. This microcavitation process damages the membranes of retinal pigment epithelium (RPE) cells. A spot size study on retinal explants 1 found cell damage fluence (energy/area) thresholds were independent of spot size when microcavitation caused the damage, contradicting past in vivo retinal spot size experiments. 2 3 4 The explant study (ex vivo) used a top-hat beam profile, whereas the in vivo studies used Gaussian beams. The difference in spot size trends for damage in vivo versus ex vivo may be attributed to the optics of the eye but this has not been validated. In this study, we exposed artificially pigmented human RPE cells (hTERT-RPE1)-in vitro-to 7 ns pulsed irradiation from a Ti:Sa TSA-02 regenerative amplifier (1055 nm) with beam diameters of 44, 86, and 273 µm (Gaussian beam profiles). We detected the microcavitation event with strobe illumination and time-resolved imaging. We used the fluorescent indicator dye calcein-AM, with excitation by an Argon laser (488 nm), to assess cell damage. Our current results follow trends found in the in vivo studies.

Laser vaccine adjuvants

“…120,121 Once these localized temperature spikes significantly exceed 100 °C, the result will be microcavitation or explosive vaporization of the water in and around the target chromophore. [122][123][124] This phase transition can cause significant damage to the tissue. Laser pulse durations in the nanosecond range with pulse powers in the kW or MW range like the CV, Q-Nd:YAG, and Q-Nd:YVO 4 lasers, contain sufficient energy to induce significant temperature perturbations at the subcellular level (microhyperthermia), resulting in cellular stress from heat shock.…”