Modelling of non-linear elastic tissues for surgical simulation

Abstract

Realistic modelling of the interaction between surgical instruments and human organs has been recognised as a key requirement in the development of high-fidelity surgical simulators. Primarily due to computational considerations, most of the past real-time surgical simulation research has assumed linear elastic behaviour for modelling tissues, even though human soft tissues generally possess non-linear properties. For a non-linear model, the well-known Poynting effect developed during shearing of the tissue results in normal forces not seen in a linear elastic model. Using constitutive equations of non-linear tissue models together with experiments, we show that the Poynting effect results in differences in force magnitude larger than the absolute human perception threshold for force discrimination in some tissues (e.g. myocardial tissues) but not in others (e.g. brain tissue simulants).

Keywords:

• haptics
• hyperelasticity
• Poynting effect
• non-linear elasticity
• soft tissue mechanics
• surgical simulation

Acknowledgements

This research was supported by NSF Grant No. EIA-0312551, NIH Grant No. R01-EB002004 and a Link Foundation Fellowship. The authors would like to thank Dr Jack C. Roberts, Dr Andrew M. Lennon and Andrew C. Merkle from the Applied Physics Laboratory, Johns Hopkins University for providing us with the Sylgard gel samples. The authors would also like to acknowledge the help from Matthew Moses (Johns Hopkins University) in conducting the experiments using Sylgard gel.