Near-infrared photobiomodulation stimulates viability and cartilage matrix synthesis in human chondrocytes

Photobiomodulation (PBM) within red to near-infrared spectrum has been proposed as a method to restore articular cartilage injuries, due to its ability to modulate effectively chondrocyte activity, namely viability, proliferation and extracellular matrix synthesis. This in vitro study aimed to determine the most appropriate PBM dosage on human chondrocytes. Firstly, human chondrocytes were stimulated daily or every other day with light-emitting diodes (LEDs) at wavelengths of 600-940 nm and power densities of 4-17 mW/cm², in continuous or pulsed mode for up to 4 min with temperature monitored during stimulation. After 3 days, the PBM most effective protocols enhancing metabolic activity and proliferation were further applied for seven days to assess their effect on cartilage protein production using immunocytochemistry, western blot, and alcian blue staining. Near-infrared LEDs (850 and 940 nm) at power densities of 4-17 mW/cm², in continuous or pulsed mode, significantly increased normalized chondrocyte metabolic activity, regardless of the periodicity or operation mode applied. A dose-dependent response was demonstrated, with variations among the PBM parameters. Particularly, PBM with 17 mW/cm² at 940 nm consistently promoted collagen type II, aggrecan, and glycosaminoglycans deposition in the chondrocyte matrix, while preserving their normal phenotype in monolayer cultures. Stimulation with LEDs did not cause a significant temperature increase. Herein, stimulation with near-infrared LEDs effectively increased the viability and secretion of cartilage proteins in human chondrocytes. This approach holds promise as a non-invasive therapeutic modality for articular cartilage repair in future preclinical and clinical research.