Infrared low-level laser therapy enhances proliferation and viability in murine osteoblasts in vitro

Infrared low-level laser therapy (LLLT) has shown great promise in promoting cell proliferation and viability, making it a valuable tool in regenerative medicine. This study investigated how the interval between sessions shapes the response to 970 nm LLLT in murine osteoblast cultures by delivering three 10 J/cm² sessions separated by 24-48 h and measuring proliferation, reactive oxygen species (ROS), cytotoxicity, and apoptosis, with the goal of informing protocol design for bone regeneration.

Two osteoblast cultures were used, one control and the other LLL-treated group. The latter consisted of three irradiation sessions (10 J/cm² each) applied at 24, 48, and 96 h.

The experimental results showed a significant increase in cell proliferation after two and three sessions (p < 0.05), while ROS levels progressively accumulated, peaking after the third session (p < 0.001). Cell viability remained above 90% in both groups during the first 48 h; however, a slight but significant reduction was observed in the LLLT group at 96 h. Apoptosis levels were lower in LLLT-treated cells during early phases (24-48 h), suggesting a transient cytoprotective effect that diminished after the third session. These findings indicate that infrared LLLT promotes cell proliferation without inducing cytotoxicity or programmed cell death.

The results demonstrate that applying three infrared LLLT sessions of 10 J/cm² applied at 24, 48, and 96 h promotes osteoblastic proliferation and viability without inducing cytotoxicity or apoptosis. The proposed protocol, defined by energy dose and irradiation timing, provides a safe and effective strategy for bone tissue engineering.