Microrobot configured to move in a viscous material

Abstract

A microrobot configured to move in a viscous material, in particular in an organ of a subject such as a brain, the microrobot having a propulsion structure including a head portion, a rear portion and a deformable portion connecting the head portion and the rear portion. The deformable portion is deformable in elongation/contraction along a main axis connecting the head portion and the rear portion. The head portion includes at its surface at least one propulsion cilium, one end of the at least one propulsion cilium being attached to the head portion and the other end of the at least one propulsion cilium being a free end configured to move freely in the viscous material. The propulsion structure further comprises a motor configured to actuate sequentially elongation/contraction cycles of the deformable portion.

1 . A microrobot configured to move in a viscous material, in particular in an organ of a subject such as a brain, the microrobot having a propulsion structure comprising a head portion, a rear portion and a deformable portion connecting the head portion and the rear portion, the deformable portion being deformable in elongation/contraction along a main axis connecting the head portion and the rear portion, wherein the head portion comprises at its surface at least one propulsion cilium, one end of the at least one propulsion cilium being attached to the head portion and the other end of the at least one propulsion cilium being a free end configured to move freely in the viscous material, wherein the propulsion structure further comprises an actuator configured to actuate sequentially elongation/contraction cycles of the deformable portion. 
     
     
         2 . The microrobot according to  claim 1 , wherein, for each elongation/contraction cycle of the deformable portion actuated by the actuator, the path of the free end of the at least one propulsion cilium in the viscous material in the contraction phase of the deformable portion is different from the path of the free end of the at least one propulsion cilium in the viscous material in the elongation phase of the deformable portion. 
     
     
         3 . The microrobot according to  claim 1 , wherein the at least one propulsion cilium comprises a cilium body having an asymmetric cross section taken transversely to a longitudinal axis of the cilium body. 
     
     
         4 . The microrobot according to  claim 1 , wherein the at least one propulsion cilium comprises a cilium body and an enlarged end portion forming the free end of the at least one propulsion cilium, wherein the cross-sectional area of the enlarged end portion taken transversely to a longitudinal axis of the cilium body is less than the cross-sectional area of the enlarged end portion in at least one plane parallel to the longitudinal axis of the cilium body. 
     
     
         5 . The microrobot according to  claim 1 , wherein the deformable portion comprises a bellows member having a front end attached to the head portion and a rear end attached to the rear portion. 
     
     
         6 . The microrobot according to  claim 5 , wherein the ratio of the thickness of the peak and valley portions of the peripheral wall of the bellows member to the thickness of the junction portions between two successive peak and valley portions of the peripheral wall of the bellows member is higher than 2, preferably higher than 5, more preferably higher than 10. 
     
     
         7 . The microrobot according to  claim 1 , wherein the front portion comprises a plurality of propulsion cilia arranged on the front portion in a helical configuration so as to cause a rotational movement of the microrobot about the main axis when it moves forward. 
     
     
         8 . The microrobot according to  claim 1 , wherein the rear portion comprises at its surface at least one propulsion cilium similar to, or different from, the at least one propulsion cilium of the head portion. 
     
     
         9 . The microrobot according to  claim 1 , wherein the deformable portion comprises a spring member having a front end attached to the head portion and a rear end attached to the rear portion. 
     
     
         10 . The microrobot according to  claim 9 , wherein the spring member comprises at least three legs arranged helically relative to one another. 
     
     
         11 . The microrobot according to  claim 1 , comprising at least two propulsion structures positioned in a row, wherein the actuators of the propulsion structures are configured to actuate elongation/contraction cycles of the deformable portions of the propulsion structures in predefined sequences so as to generate a non-reciprocal motion of the microrobot in the viscous material. 
     
     
         12 . The microrobot according to  claim 1 , wherein the actuator comprises a piezoelectric transducer. 
     
     
         13 . The microrobot according to  claim 1 , wherein the actuator comprises a pump, in particular an electroosmotic pump. 
     
     
         14 . The microrobot according to  claim 1 , wherein the actuator comprises an electromagnetic transducer including a combination of an electromagnetic coil attached at one end of the deformable portion and a magnet attached at the other end of the deformable portion. 
     
     
         15 . The microrobot according to  claim 1 , wherein the actuator comprises a photoreactive material included in the deformable portion, where the photoreactive material is configured to retract or extend under the effect of light, and a luminous source provided in the vicinity of the deformable portion, in particular by a fiber optic. 
     
     
         16 . The microrobot according to  claim 1 , wherein the deformable portion is made of a polymer having a Young's modulus between 0.1 and 10 GPa, preferably between 0.5 and 2 GPa. 
     
     
         17 . The microrobot according to  claim 1 , wherein the at least one propulsion cilium is made of the same material as the deformable portion. 
     
     
         18 . The microrobot according to  claim 1 , wherein the microrobot is configured to move in a fluidic material at low Reynolds number, with a Reynolds number Re between 10 −5  and 10 −1 .