Modeling thermal cross-talk and cooling kinetics in clustered melanosomes after nanosecond laser heating

Abstract

Abstract Selective photothermal confinement is commonly evaluated using the thermal relaxation time (TRT) of individual absorbers, but ultrastructural studies have shown that epidermal melanosomes are organized in clustered arrangements that may alter post-pulse cooling. Here, we modeled thermal cross-talk and cooling kinetics in three-dimensional clusters of ellipsoidal melanosome units after 532-nm, 10-ns laser heating. Sixteen cluster models were constructed from four melanosome size distributions and four inter-melanosome gap distributions, with 20 units per model. Clustered cooling was compared with isolated-unit cooling under the same optical energy-deposition and thermal-diffusion formulation, and with a conventional cylindrical TRT calculation. During post-pulse cooling, the unit with the largest maximum thermal cross-talk value showed a clustered-minus-isolated temperature difference of 16.76 °C. At the 50% cooling level, the largest clustered-minus-isolated delay occurred in a 700 × 350 nm unit in M09, where clustering increased the 50% cooling time by 35.61 ns, corresponding to a 54.4% increase relative to the isolated-unit 50% cooling time. These results indicate that melanosome clustering can prolong post-pulse cooling in a geometry-dependent manner through neighbor-derived thermal cross-talk.