Force-adjustable parallel-occlusion grasper

Abstract

Background: During laparoscopic surgery, the operating surgeon grasps sections of the gastrointestinal tract (GIT), including delicate structures, with long (270 mm) 5 mm diameter graspers. These grasping instruments increase the risk of iatrogenic damage due to crushing of the grasped tissue. This risk is increased significantly by diseases such as bacterial peritonitis and inflammatory bowel disease and reduced but not abolished by using parallel-closing laparoscopic instruments. This study describes the design and laboratory testing of fully developed and tested smart graspers capable of reducing the grasping force used for inflamed tissues and hollow viscera.

Materials and methods: In an ISO 13485-certified mechanical laboratory and CAD machine workshop, the authors have designed, developed, and evaluated a smart gasper capable of exerting a preselected uniform grasping force on the gastrointestinal tract and other structures/ tissues, through a mechanism incorporated in the handle of the instrument. This enables the control and graded reduction of the grasping force by the incorporation of a compression spring. The authors named the new instrument the force-adjustable parallel-occlusion grasper (FA-POG) because, in addition to applying a uniform force on the grasped bowel/tissue, it also enables the surgeon to select the force before grasping, depending on its physical condition, and pathological state.

Results: FA-POG differs from traditional pinch-occlusion grasper in two respects: it exerts a uniform force on the grasped tissue/bowel and enables the operating surgeon to select and apply a predetermined uniform grasping force, ranging from 1 to 5 N, depending on the pathological condition of the bowel/structure. The ISO 13485-certified and fully developed prototype has been subjected to various grasping in-vitro tests using freshly harvested porcine small-bowel segments obtained from a local abattoir, using Instron tensiometry.

Conclusions: The authors designed and α/β tested a parallel-occlusion gasper that enables the operating surgeon to select the force before grasping. This grasper design consists of end-effectors jaws with a 4-bar linkage mechanism for wide, uniform parallel-occlusion force, surpassing traditional scissor-type laparoscopic graspers. It incorporates a force-level controller knob, based on a spring-loaded mechanism, enabling surgeon-preselected grip force to prevent excessive grasping. The authors validated the design experimentally using porcine small-bowel segments, optimizing teeth for maximum grip friction to minimize slippage.

Graphical abstract

Figure 1

Force-adjustable parallel-occlusion graspers; (A) open position, (B) closed jaws.

Figure 2

Schematic representation of scissor-type laparoscopic graspers. The small circles represent a pivoting connection between the blue rigid elements. (A) single jaw action scissor laparoscopic grasper, (B) double jaw action scissor laparoscopic grasper.

Figure 3

(A) schematic representation of force distribution in single action pinch laparoscopic grasper; (B) 4-bar parallel mechanism which produces uniform force throughout the length.

Figure 4

Schematic representation of parallel laparoscopic graspers; (A) Parallel-occlusion double jaw action laparoscopic grasper; (B) Parallel-occlusion single jaw action laparoscopic grasper.

Figure 5

The three components of the single jaw action smart force-adjustable parallel-occlusion grasper.

Figure 6

Cross-section CAD view of FA-POG End-Effectors Jaws mechanism. Pin joints ABCD defines the 4-bar linkage of this mechanism.

Figure 7

CAD of FA-POG force-control knob; (A) control to rotate between the three levels: min, mid, and max. (B) cross-section view of control knob incorporating spring.

Figure 8

Picture sequence of the occlusion force testing and measurements at their different controller levels of FA-POG.

Figure 9

FA-POG upper jaw closing/opening force; red dotted line shows the working range of jaw extension.

Figure 10

Experimental setup for performing slippage force testing; (A) Instron 5564 dual columns where one of small-bowel segment is grasped by the FA-POG and the other end is connected, inside yellow box (B) shows how the small-bowel segment is held, with one end being clamped and other end grasped by the upper jaw of FA-POG.

Figure 11

Slippage force testing results; vertical axis of each graph shows pull force measured and horizontal axis represent the position movement of vertical head of Instron where one each of FA-POG is attached. Experiments were repeated for three trails at each configuration.