1. Hamlyn Centre for Robotic Surgery, Imperial College London, London, SW7 2AZ, UK
2. Ansaldo STS, Genova 16100, Italy, E-mail: matte.pinna@gmail.com
3. Department of Biophysical and Electronic Engineering, University of Genova, Genova 16145, Italy, E-mails: ciardelli@dibe.unige.it, carlo@dibe.unige.it