The Surgical Technology Group in the Department of Surgery (University of Dundee) is involved in several areas of research related to the engineering aspects of laparoscopic surgery. This includes design of surgical instruments, development of novel imaging methods and measurement of surgical performance. In addition, many projects have been undertaken to study tissue-instrument interaction, which is essential in novel instrument design and surgical simulator development.

Surgical training is also an area of interest, the Surgical Skills Unit runs several specialist courses and undertakes related research. Current teaching methods involve the use of synthetic and animal tissue to simulate human organs in the operative field. Whilst this is a cheap and effective training method, there is a lack of realistic tissue reactivity. The obvious successor to these methods is a computer-based surgical simulator, where the anatomy can be faithfully reproduced and the tissues deform in a realistic fashion. For simulated tissues to behave in a biomechanically authentic manner it is important to have information on the elasticity of organs.

With this in mind, it was decided to investigate ways of measuring and mathematically modelling the mechanical factors involved during laparoscopic surgical interactions. Mechanical indentation tests have been carried out to test surface compliance of ex-vivo animal organs such as liver and spleen under different conditions. Since laparoscopic surgical interactions with these tissues will be on a very small scale, our studies have been limited to small strains. In later studies the puncture force of the surface layer of solid organs was investigated.

The mathematical modelling of solid organ surface deformation has been carried out in collaboration with the Mathematics Departments of Dundee and Strathclyde Universities. We have found that an incompressible non-linear elastic material of the type introduced by Fung is a promising model for solid organ tissue under compression by a rigid probe. Initially, the best-fit parameters were obtained using an indentor that was large with respect to the thickness of the tissue tested. These parameters were then used to attempt to satisfy the model equations when a much smaller probe is used (a more physically realistic situation). There is no exact closed-form solution for this system of equations i.e. they are very difficult to solve. The equations themselves are highly non-linear, and since we assume that the tissue in question is incompressible, this means that a very complex internal constraint has to hold everywhere in the material. Solving the boundary value problem numerically is extremely complicated, indeed there appears to be no one best method for solving boundary value problems in non-linear elasticity (a rapidly growing area of active research).

In order to validate the mathematical models of animal solid organs, novel instrumentation was developed that could be used during open surgery to measure surface compliance of human tissues in-vivo. Initial studies showed that biomechanical measurements taken from animal tissues were similar to those from human tissues and that subtle alterations in tissue’s state could be detected. This instrumentation is also being used to measure compliance of normal and pathological breast tissue in patients undergoing mastectomy and it is intended to extend this trial further.

Finally, we are currently involved in an European project (Minimal Invasive Surgical Simulator - MISSIMU) whose aim is to produce a computer-based simulator for surgical training in Laparoscopic Cholecystectomy. This has involved the alteration of current surgical instruments to sense the mechanical response of soft tissue during dissection. Force sensing graspers and scissors have been produced, and will be used in theatre to extend our database of tissue properties.