PLAM system-mediated optimization of 808 nm low-level laser power density for enhanced bioactivity in human umbilical cord mesenchymal stem cells

Low-level laser therapy (LLLT) has significant potential in regenerative medicine for enhancing mesenchymal stem cells (MSCs) function. However, the optimal irradiation parameters, particularly power density, remain unclear. In this study, we developed an automated Precision Laser Adjustment and Motion (PLAM) system to investigate the effects of an 808 nm power-adjustable laser on human umbilical cord mesenchymal stem cells (HUMSCs). The laser was applied at power densities ranging from 10 to 500 mW/cm², with a constant energy density of 4 J/cm². Under these irradiation conditions, the biological responses showed clear power-dependence, with optimal effects observed at 100 and 250 mW/cm², consistent with the Arndt-Schulz law. Specifically, the 250 mW/cm² irradiation significantly accelerated cell migration at 24 hours and achieved the highest cell viability at 48 hours (P < 0.01). Notably, the 100 mW/cm² protocol demonstrated superior biosafety, maintaining sustained ATP production (p < 0.001 at 24 hours; p < 0.01 at 48 hours) and moderate reactive oxygen species (ROS) levels (p < 0.0001), making it reliable for long-term stem cells expansion. Real-time temperature monitoring showed ΔT ≤1 °C, ruling out thermal damage. The results emphasize the importance of optimizing power density in LLLT and identify 100 mW/cm² as the optimal balance between therapeutic efficacy and safety. Furthermore, the PLAM system simplifies the irradiation procedure, reduces operational errors, and enhances experimental repeatability. These findings provide a scientific basis for standardizing LLLT parameters in regenerative medicine and introduce the PLAM automated experimental platform for future photobiomodulation research.