This case study describes work by Gafford et al. (2014). The team developed a deployable atraumatic grasper with on-board pressure sensing, allowing a surgeon to grasp and manipulate soft tissue during minimally-invasive pancreatic surgery.
Due to the size limitations imposed by minimally-invasive surgery, current laparoscopic tools used to retract or manipulate delicate tissues are morphologically simple in nature, with fulcrum-based, rigid, steel components incapable of sufficiently distributing forces. This often leads to tissue damage and inadvertent perforation of thin-walled, high-pressure vessels including the superior mesenteric artery and vein (SMA, SMV), and the portal vein, as shown in the figure below. Any amount of intraoperative bleeding can block the surgeon’s view of the workspace, greatly complicating an already taxing procedure. If the hemorrhage is not controlled in a timely manner, the surgeon may be forced to convert the procedure to an open surgery to prevent the patient bleeding to death.
The team's solution consists of SDM fingers (fabricated using closed-top molding to allow the grasper to fit through a 15mm laparoscopic port) attached to a latching mechanism which holds the fingers in the "grasping" position. The fingers can be released by turning the handle of the device, allowing quick release. The fingers contain Takktile pressure sensors which alert the surgeon when too much pressure is being exerted. An overview of the device is shown in the image below.
The use of soft, compliant materials in making the fingers helps to ensure that the grasper will not cause trauma to the pancreas or surrounding vessels. The use of SDM allowed the team to embed pressure sensors, steel structural elements, and cables inside the fingers to improve functionality.
To converge on a finger design appropriate for a pancreatic grasping application, the team prototyped several variations on the morphology of the finger, as described here. After testing different lengths and stiffnesses of finger segments and connecting links, a 3-joint finger with proportionally decreasing joint stiffnesses was chosen. Force and transmission ratio were estimated using an analytical model, the results of which were validated via bench testing.