Flexure-based mecano-optical multi-degree-of-freedom transducers dedicated to medical force sensing instruments

This thesis develops novel multi-degrees-of-freedom flexure-based force sensors by exploiting white light interferometry. Fabry-Pérot interferometry measurement has nanometric accuracy which yields sub milli-Newton force sensing accuracy. Such force sensing accuracy can be advantageously utilisized for medical applications. Using these techniques, this thesis develops the first monolithically fabricated medical instrument having submillimetric diameter, a peeling hook used to treat epiretinal membranes in the eye. The thesis describes the concepts, design, simulation, fabrication and characterization of this type of instrument. The results of this thesis pave the way for new techniques in Minimally Invasive Surgery (MIS).

The study starts with systematization of sensor manufacturing, which is followed by catalogue of proposed sensor topologies. These structures are then dimensioned using Finite Element Analysis (FEA), with emphasis on two medical applications: biopsy needles and intraocular surgery.

Selected designs were manufactured and characterized on a motorized test bench with automatic and repetitive measurement. Sensor calibration methods were developed and tested and characterization methods were also evaluated. Manufacturing and measurement error were also described.

The test results showed a significant reduction of sensor calibration error in the selected workspace, as compared to industry solutions.

The tool developed in this thesis is an epiretinal membrane peeling hook for minimally invasive intraocular surgery. It was fabricated using Electro Discharge Machining (EDM), and was at the limit of the feature size of this method.

The novel methods developed in this thesis open new horizons for designing submillimetric tools having complex kinematic force sensing and thereby significantly advance delicate surgical procedures.