Non-rigid cutting characteristics and separation mechanisms of soft muscle tissue under waterjet impact.

Muscle tissue is most frequently cut or separated in surgery. Waterjet as an emerging non-rigid cutting method is newly introduced into soft tissue dissection which shows a great potential in soft muscle cutting for low-trauma surgery. However, the cutting mechanisms of muscle material to waterjet impact remain unknown. This study reports the cutting responses of muscle tissue to waterjet impact. Waterjet morphology, depths of cut, cutting surface morphology and deformation of muscles were experimentally investigated using a computer-controlled waterjet machine. The mechanical properties of muscles were also measured to explore the property-processing relation. The conversion relationship between kinetic energy of waterjet and potential energy of muscle damage was established based on energy balance theory. Based on the experimental investigation and fracture mechanism analysis, the critical and the reasonable waterjet separation pressures for the muscles were respectively 0.8-1.1 MPa and 1.4-2.0 MPa for balancing separation efficiency and surrounding tissue protection. It was also found the muscle depth of cut under waterjet impact significantly increased with the impact pressure, but rapidly reduced with the increase in impact angle and transverse speed. In addition, a new phenomenon of swelling effect of the muscles was discovered in waterjet impact, which heavily affects the depths of cut. The proper stand-off distance was determined considering the muscle swelling effect and initial segment of waterjet. This research first provides practical insights into the process selection and quality control for waterjet cutting of soft muscles, advancing the clinical application of waterjet to muscle separation.