Mechanisms of laser activation of chondrocytes in osteoarthritis healing

Lasers offer new possibilities in the treatment of such widespread diseases as osteoarthritis, with both direct and indirect effects on cell metabolism. Cyclic hydrostatic pressure is one of the main natural stimuli of cartilage chondrocytes. The present work shows that hydrostatic stimulation with magnitudes of up to 20 MPa can be realized locally through infrared impact on the neighboring media of chondrocytes. We compare indirect (thermomechanical, λ = 1560 nm) and direct (photo-modulation, λ1 = 1560 nm, λ2 = 670 nm) laser effects on the synthetic activity of chondrocytes in cultures within a 1 min exposure time limit, to study separately the photo-modulation and thermomechanical components of laser impact. The chondrocyte activity was monitored by immunohistochemical analysis in normoxic and hypoxic conditions. Collagen II and proteoglycan accumulation increased significantly (up to 70%) after a pulsed thermomechanical laser impact. Thermomechanical laser irradiation showed the more pronounced stimulation in both normoxic and hypoxic conditions, while the effect of photo-modulation was inhibited by oxygen concentration increase. Theoretical calculations of the laser-induced temperature and stress fields show that the spreading of the stress field with a maximum at 19.2 MPa is approximately three times greater than that of appreciable (>1 °C) heating. Thus, thermomechanical infrared stimulation of chondrocytes can be a perspective method for the restoration of hyaline-type cartilage.