Bioceramic materials emitting infrared radiation for musculoskeletal pain relief

While shorter wavelength IR-A or IR-B (near infrared) penetrates deep into the skin and can cause tissue damage, long wavelength IR-C (mid and far infrared) is completely absorbed in the epidermal layers (see Fig. 1). In several studies, IR-C light (far infrared) showed positive therapeutic effects in deep tissue layers that were not accessible to direct radiation (see Fig. 1): The authors describe an energy transfer through pathways other than direct radiation and propose water as a dynamic biomolecule and possible transmitter of energy [2].

Based on the current findings, the biological effects of IR-C on MSK disorders can be divided into three categories as indicated in Figure 2. Infrared radiation can relieve pain by increasing NO levels and reducing oxidative stress and inflammatory mediators.

1. Oxidative damage: Oxidative stress is defined as an excess production of reactive oxygen species (ROS) that can lead to oxidative damage to cells. Oxidative stress can cause tissue damage and inflammation, which in turn can alter nociception via stimulation of sensory neurons and lead to hyperalgesia. Indeed, in studies, IR radiation has been shown to decrease oxidative stress and relieve pain and inflammation at the muscular level [2].

2. Vasodilation: IR radiation can upregulate endothelial nitric oxide synthase (eNOS), increasing the bioavailability of nitroxide (NO). NO has a relaxing, vasodilator effect on vessels, as well as other beneficial effects on the body, such as inhibiting platelet aggregation and preventing leukocyte adhesion. It promotes muscle repair. Via inhibiting the migration of inflammatory cells, it may protect muscle from damage and inflammatory responses. An antinociceptive effect via hyperpolarization of nociceptors is discussed [2].

3. Anti-inflammatory action: Inflammation can increase the pain response via sensitization of sensory nerves. During inflammation or tissue injury, damaged cells and immune cells release inflammatory mediators. Increased serum levels of IL-6 and IL-8 lead to hyperalgesia, fatigue, and pain. TNF-α can promote sensitization of nociceptors, leading to chronic pain and muscle fatigue. IR-C radiation inhibits the expression of inflammatory cytokines [2].

_{Acknowledgements: The authors thank Paula Fontanilla, PhD, for critically reviewing the manuscript for scientific content.}

_{Conflict of interest: B. Giannakopoulos and M. Amessou are employees of Sanofi.}

_{Disclosure: Medical writing and publication funded by Sanofi.}