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Contributions to Soft Microrobotics : Advanced Kinematics Based on Digital Manufacturing of Active Materials and Pneumatic Actuation for Endoscopy

par Decroly, Gilles
Président du jury Nonclercq, Antoine
Promoteur Delchambre, Alain
Co-Promoteur Lambert, Pierre
Publication Non publié, 2022-09-08

Thèse de doctorat

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Résumé :

This thesis studies soft microrobotics actuation solutions for the generation of complex motions in thecontext of medical and endoscopic applications. Flexible endoscopy requires flexible and steerable toolsto perform medical interventions through the natural orifices. It could benefit from soft and dexterousactuators with multiple degrees of freedom to ensure patient safety while navigating tortuous pathways.To this end, the rise of soft actuation, using stimuli-responsive materials of similar softness as biologicaltissues opens new opportunities. This thesis investigates the potential of three soft actuation solutionsto generate complex deformations (deformations beyond pure elongation, compression, shear, twist orbending) while assessing their potential in terms of miniaturization, safety, and mechanical capabilitiesfor future use in medical applications. Firstly, a 6mm diameter pneumatic actuator for endoscopyis designed, implemented, and characterized. It bends in every direction and incorporates a workingchannel. A vacuum centrifugal overmolding method capable of producing small geometries with a varietyof silicones is described, and meter-long actuators are extruded industrially. The actuator achievesbending of more than 180° and curvatures of up to 0.1mm–1. The exerted force remains below 100mN,and with no rigid parts in the design, it limits the risks of damage to surrounding tissues. The responsetime below 300 ms is not limiting for medical applications. An 85 cm long steerable catheter carryingan optical fiber is demonstrated in a bronchial tree phantom. To generate more complex motions,and further from the medical application, a voxel-based approach is proposed from the literaturereview. This methodology is based on the decomposition of complex motions into active buildingblocks, called voxels, each able of a given basic kinematic. Designs are presented to build these voxelsusing only an active isotropically expansive or compressive material, reinforced adequately by a passive(or less expansive) material. This approach is first implemented using heat actuated Phase-ChangeMaterial–Elastomer Composite (PCMEC)-based expansive actuators. Centimetric kirigami-inspiredpaper reinforced voxels are modeled, built and characterized. All basic kinematics can be obtained.Additionally, a manufacturing method to use different fluid–elastomer combinations without alteringthe quality of the samples is proposed. This allows PCMEC to be used safely in contact with humanbodies, by using fluids with a low boiling point (as low as 34°C). The voxel-based methodology is thenimplemented at the micrometer scale using shrinking pNIPAM hydrogel-based actuators. A digitalfabrication method (two-photon polymerization) is adapted to build patterned structures in a one-stepprocess. Voxels able of bending, compression, and twisting are built and assembled. The influence ofthe exposure dose and temperature on the pNIPAM actuation strain is characterized. Curvature up to10 mm–1 is measured. Even if far from any application, the demonstrated structures would be difficultto achieve at this scale with another strategy, and the versatility of the voxel-based approach makes itadaptable to a large variety of motions. This thesis is supervised by prof. Alain Delchambre in theBEAMS department and prof. Pierre Lambert in the TIPs department.