Vibration-assisted slicing of soft tissue for biopsy procedures

Skin cancer represents one of the most common forms of cancer in the U.S. This and other skin disorders can be effectively diagnosed by performing a punch biopsy to obtain full-thickness skin specimens. Their quality depends on the forces exerted by the punch cannula during the cutting process. The reduction of these forces is critical in the extraction of high quality tissue samples from the patient. During skin biopsy, the biopsy punch (BP) is advanced into the lesion while it is rotated alternately clockwise and counterclockwise generating, therefore, a rotary vibrational motion. No previous studies analyzed whether this motion is effective in soft tissue cutting and if it could be improved. In this study, the BP procedure is investigated in detail. First, the steady cutting motion of the BP is analyzed. Then, the superimposition of several vibrational motions onto the rotary motion of the BP is investigated. Analytical models, based on a fracture mechanics approach, are adopted to predict the cutting forces. Experimental studies are performed on phantom tissue, usually adopted in medical investigations. The results demonstrate that the application of rotary vibrational motions determines the increase of the force and penetration depth necessary to fracture soft tissue, while the implementation of axial vibrations can lead to 30% decrease of the axial force. The outcome of this study can benefit several clinical procedures in which a cannula device is used to cut and collect soft tissue samples.