Design strategies for optical tactile sensors in minimally invasive surgery

The possibility to provide a sensing feedback during endoscopic interventions can significantly improve the perception of the endoscopist of the pressures applied to the inner tissues of the patient. Current sensing technologies are still too big and often present significant dead zones to be applied to flexible endoscopes. The development of sensing technologies with high spatial resolution aimed to sense normal pressures applied to the non-planar external surface of an endoscope is still an open challenge. Flexibility, sterilization, robustness and magnetic resonance compatibility are also common challenges for electronic sensors. Optical sensors can potentially fulfil these important requirements. In this thesis three different optical sensing strategies are explored as prove of concept to expand the capabilities of current optical sensor designs. All the three approaches propose alternative methods to (i) reduce the number of optical channels, (ii) detect pressures perpendicular to the endoscope surface, (iii) enhance the spatial resolution, (iv) be fabricated through a simple and scalable manufacturing process. The sensitivity of all the three designs widely stretches over the range of pressures [0−30kPa] usually applied during endoscopic interventions. All the three designs lend themselves to biocompatibility, sterilisation and magnetic resonance compatibility. The first design proposes an array sensor based on lab-made soft channels integrated on a rigid substrate. Its drawbacks, such as lack of flexibility and limited sensing area, are addressed by the second design presenting a flexible sensing skin able to detect pressures in any point of its surface. Fluorescence was employed to enhance the signal-to-noise ratio from ∼ 22 of the first design to ∼ 117, so reaching an improvement of over 5 times. In the third design, the use of quantum dots was preferred respect to fluorescent dyes, because of their better photostability and photoefficiency. It was proved that the quantum dots based sensor can enhance the signal-to-noise ratio up to ∼ 280, so 2.5 times respect to the sensor based on fluorescent dyes. The third design also offers a sensitivity up to 3 times better respect to the first two designs, with a value of 0.020kPa−1. The piezoelectric effect of the quantum dots integrated in a polymer waveguide, allowed to simultaneously detect a pressure and provide information regarding its application point along the waveguide. This third design offers promising characteristics for the development of a sensing skin able to measure pressures applied during endoscopic interventions and it is worthy to be further investigated in future studies.