The millirobot is getting more and more attention from researchers because of its small size and less intrusiveness in narrow-enclosed space. Compared to other propulsion methods including light, temperature, humidity and ultrasound, the magnetic field always means enhanced penetrability, controllability and compatibility which make the magnetic millirobot have a wide spectrum of applications and potential in microfactories, micromanipulation and biomedical fields. Currently, as the development of novel materials, advanced fabrications and innovative structures, magnetic millirobots with a certain degree of environmental adaptability have been proposed for diverse tasks. However, under the constraints of energy consumption and narrow space, the environmental adaptability of millirobot to unstructured conditions and unpredicted targets is still limited. Moreover, the current applications put forward higher requirements for the millirobot's interaction with circumstances and targets. Therefore, the study on magnetic millirobots with environmental adaptability is desired, which can greatly promote them towards practical applications. In this thesis, we introduce the design, fabrication and control of magnetic millirobots which can adaptively interact with environment including harsh conditions or diverse targets.

To enhance the locomotion ability of magnetic millirobot on a wet surface with obstacles, we propose a starfish inspired soft millirobot. Different from the simple imitation of locomotion mode in the previous literature, we introduce the micro tube feet structures of starfish into the robot design. The magnetization measurement and friction test indicate that the microstructures of tube feet can strengthen the driving performance of millirobot, reduce the motion resistance from the ground, and enhance the obstacle-climbing ability. Moreover, benefitting from the radial symmetry shape of the starfish, the soft millirobot can achieve omnidirectional movement under the actuation of magnetic field. The successful locomotion demonstrations, including moving with “S” trajectory, adapting to wet surface and gravel surface, overcoming obstacles, indicate the environmental adaptability of the starfish inspired soft millirobot in harsh conditions.

Besides the harsh conditions with wet surfaces and obstacles, some circumstances are unpredicted and unstructured. To tackle these challenges, we report the concept of milli-scale celluar robot (mCEBOT) achieved by the heterogeneous assembly of master and slave units. Under the actuation of magnetic field, the proposed mCEBOT units can not only selectively assemble (e.g., end-by-end and side-by-side) into diverse morphologies corresponding to the unstructured environments, but also configure multi-modes motion behaviors (e.g., slipping, rolling, walking and climbing) based on the on-site task requirements. We demonstrate its adaptive mobility from narrow space to high barrier to wetting surface, and its potential applications in hanging target taking and environment exploration. The concept of mCEBOT offers new opportunities for modular robot design, and will shed light on the realization of flexible, adaptive and functionalized robot for broad spectrum of applications at small-scale.

Despite the reconfigurable mCEBOT showing great adaptability to unstructured conditions than ever before, the dimension and structure of monomer units are still unchangeable. Moreover, the interaction between robots and diverse targets is still defective. To further enhance the environmental adaptability, we introduce a minimalist approach to construct millirobots on-site by coating composited agglutinate magnetic spray, which is arbitrarily expandable and without a fixed form. Our approach enables a variety of one-dimensional (1D), 2D, or 3D targets to be covered with a thin magnetically drivable film (~100 to 250 micrometers in thickness). The film is thin enough to preserve the original size, morphology, and structure of the objects while providing actuation of up to hundreds of times its own weight. Under the actuation of a magnetic field, our millirobots are able to demonstrate a range of locomotive abilities: crawling, walking, and rolling. Moreover, we can reprogram and disintegrate the magnetic film on our millirobots on demand. We leverage these abilities to demonstrate biomedical applications, including catheter navigation and drug delivery.

In conclusion, we innovate in the design, fabrication and control of magnetic millirobots to overcome the challenges from environmental interactions including unstructured conditions and unpredicted targets. These works represent a remarkable advance in the magnetic millirobots, which will shed light on the realization of environmentally adaptable robots for a broad spectrum of applications at small scale.