The goal of the current experiment is to explore the influence of combined and/or single applications of red and near infrared (NIR) photobiomodulation (PBM) at different wavelengths, energy densities and times on cell viability, population doubling time (PDT), and apoptosis of in vitro cultures of human bone marrow-derived mesenchymal stem cells (hBM-MSCs) and h adipose-derived stem cells (hASCs). Both in vitro hBM-MSCs and hASCs were irradiated with 36 protocols using two different laser types (helium‑neon [He-Ne] and diodes), four different laser wavelengths (HeNe laser, 630 nm, 810 nm, 630 + 810 nm); three different energy densities (0.6 J/cm, 1.2 J/cm, 2.4 J/cm); and three different PBM times (1, 2, and 3). One-way ANOVA analysis showed that PBM with the 630 nm red laser significantly stimulated cellular viability of both hBM-MSCs and hASCs. The 630 nm red laser significantly decreased PDT of hBM-MSCs. One-way ANOVA demonstrated that the 630 + 810 laser significantly stimulated cellular viability, and significantly decreased PDT and apoptosis of hBM-MSCs and hASCs. Two-way ANOVA analysis showed that PBM with the 630 nm red laser and 630 + 810 nm laser significantly stimulated cellular viability of hASCs compared to the control hASCs, and experimental and control hBM-MSCs. Our study demonstrated that PBM with the combined 630 + 810 nm lasers significantly stimulated cell viability, and significantly decreased PDT and apoptosis of hBM-MSCs and hASCs in vitro. We reported new in vitro evidence where PBM administered at 630 nm (one and two times, 0.6 and 1.2 J/cm) and 630 + 810 nm (three times, 2.4 J/cm) significantly increased hASC cell viability compared to its control and the PBM-treated hBM-MSC groups. 2 2 2 2 2
