• soft
• sensori
• chirurgia
• flop
• sensors
• robotics
• surgery
• Stiff

Recently, attention has been focused to minimize the invasiveness of existing minimally invasive surgery (MIS) approaches: one example is the development of continuum-like and soft robots that can bend, extend, contract at any point along their length. This provides them with capabilities well beyond those of their rigid-link counterparts, thus allowing to perform whole arm manipulation.
One recent approach to soft and modular systems is represented by the on-going EU project STIFF-FLOP (www.stiff-flop.eu). The STIFF-FLOP arm is not fabricated by rigid structures, but soft ones showing advanced manipulation capabilities for surgical applications, with multiple degrees of freedom (DOFs), and ability of multi-bending.
Ideally, the entire robotic structure should safely move with contact and bend detection and the embedded sensors should not interfere with the movements: the use of small sensors, both soft and stretchable, which remain functional when deformed, becomes necessary.
For the aforementioned reasons, we introduce a small, low-cost, soft and stretchable sensor composed of a silicone rubber (EcoFlex0030, SmoothOn), integrating a conductive liquid channel filled with biocompatible Sodium Chloride (NaCl) solution. By stretching the sensor the cross-section of the channel deforms, thus leading to a change in electrical resistance. The functionality of the sensor has been proved through testing: changes in electrical resistance are measured as a function of the applied strain.
The advantage of using silicone rubber is its mechanical durability and high flexibility, non-toxicity, chemical stability and low cost.
Furthermore, liquid conductors eliminate the need for rigid electronics and preserve the natural elasticity of the sensor, and the NaCl solution fulfills the need for a biocompatible liquid.
Differently from existing solutions that are not truly stretchable and biocompatible, the contribution of this work is an effort for improving the current soft sensors technologies through the demonstration that NaCl filled channel rubbers represent a valid solution for measuring deformations in flexible surgical instrumentation.