| Minimally invasive surgical (MIS) techniques provide many patient benefits and are becoming preferred for a number of common procedures. However, poor tactile sensation from the tools used in these techniques, including surgical robots, can lead to inadvertent damage to tissues from excess stress application. In addition, lack of feedback from surgical simulators to surgical trainees regarding safe handling of tissues provides potentially inadequate training. Little is known about the types of stresses that can be applied safely to in vivo tissues during surgery and the local effects of surgical grasping. This work provides a systematic characterization of the grasper-tissue interface in MIS. It includes measurements of visual changes and stress profiles resulting from surgical grasping and introduces quantified relationships between tissue damage and stress at the cellular level. Using the porcine model, stresses typical to MIS were applied to in vivo organs using a motorized endoscopic grasper. Acute indicators of tissue damage including cellular death, vascular injury, and inflammation were measured using histological and image analysis techniques. Mixed-effects models of results indicate that stress magnitude, but not duration, can be used to predict tissue injury. Finite element analysis was used to identify approximate stress distributions experienced by the tissues between the grasper jaws. Correlations between damage measured from experimental studies and tissue models at the 5--10 millimeter scale further validate the ability to predict damage from stress magnitude. However, the correlation between computational and experimental results was less reliable at the submillimeter scale. Finally, an 'atraumatic' grasper design was evaluated using computational techniques. The results presented here provide a better understanding of the effects of grasping at surgically relevant parameters. They can be expanded upon and potentially used to design safer instruments and more accurate simulators. For example, it may be possible for researchers to create 'smart' surgical devices that guide surgeons to manipulate tissues with minimal resulting damage. Grasper designs that eliminate or reduce high tissue stresses may also aid in the development of better MIS tools. In addition, surgical simulators could be altered to reflect more realistic tissue responses and to evaluate trainees' tissue handling skills. |
