Robotic massage cleared neutrophils and induced muscle regeneration

Skeletal muscle injury can limit daily activities. Now research has pointed regenerative muscle fiber formation and maturation are critical for functional repair. Immune cells can facilitate skeletal muscle regeneration by clearing damaged muscle fibers. They secrete specific cytokines and growth factors that modulate the sequence of satellite cell activation and differentiation. This, in turn, instructs neighboring stromal cells to participate in extracellular matrix  remodeling and angiogenesis. Stimulating these immune cells is an emerging therapeutic strategy.

Massage or mechanical stimulation has been reported to attenuate inflammatory responses and promote skeletal muscle repair. However, manual therapy can be masked by therapists’ touch and empathy, and thus it is difficult to separate mechanical from neurological effect. After all, many internet gurus proclaim that manual therapy just affects the brain.

Engineers from Harvard developed a robotic device equipped with real-time force control and ultrasound imaging for tissue strain analysis. They worked with biologists; they tested different compressive forces to injured tibialis anterior  muscle in mice.

They found that cyclic compressive loading within a specific range of forces substantially improves functional recovery of severely injured muscle in mice. Application of different forces reduced interstitial fibrosis and damaged muscle fibers. However, blood perfusion slowly recovered in the injured limbs, with no impact of mechanical loading.

They found that mechano-treated muscles exhibited a significant reduction in neutrophils after 3 days. The authors hypothesised that the therapy flushed out tissue cytokines from the injured tissue. After an injury, neutrophils play a crucial initial role in clearing dead cells and debris, but their long-term presence can impede muscle regeneration. In addition, mechanical treatment was found to increase cells expressing MyoD, a myogenic regulator.

Mechanical treatment reduces muscle damage by clearing neutrophil populations and neutrophil-mediated factors, which otherwise may impede myogenesis.