MODELING, DESIGN, AND FABRICATION OF MAGNETIC HYDROGEL MICROROBOTS FOR ADVANCED FUNCTIONALITIES

In the past decade, magnetic microrobots have gain lots of attention because of their potentials in biomedical applications, such as cell/tissue manipulation, biopsy, and drug delivery. Recent development on materials and microfabrication techniques also provide more opportunities for microrobots. Especially, the emergence of smart polymers that are responsive to environments like hydrogels has given microrobots an additional degree-of-freedom. In the meantime, the two-photon polymerization (TPP) microscale 3D printing technique has enable fabrication process that cannot be achieved easily by traditional microfabrication techniques. In general, the goal of the research presented in this dissertation is to use both hydrogels and TPP to realize novel microrobots with multiple advanced functionalities, including adaptive locomotion and micromanipulation, and modular microrobots capable of changing end-effectors for different modes of micromanipulation to facilitate the development of the field.

This dissertation can be divided into four main parts: (i) a proof-of-concept study on adaptive helical microrobots with finite element analysis (FEA) and dynamic calculation, (ii) material calibrations and property testing, (iii) a helical adaptive multi-material microrobot (HAMMR), and (iv) a modular microrobot achieved by a responsive mating component. A environment-responsive hydrogel is adopted here to realize the adaptive locomotion for helical microrobot and the responsive mating component for the modular microrobot. All microrobots fabricated in this dissertation are achieved by the combination of TPP and traditional photolithography techniques.

In part (i), FEA is applied with classic parameters for a proof-of-concept study of helical microrobot made of the classic hydrogel upon the stimulation of temperature. At different temperature, the hydrogel is going to deform and therefore the microrobot. Based on the geometrical parameters predicted by FEA before and after stimulations, dynamic calculations are then applied to predict the change of swimming performance accordingly. In part (ii), material calibrations have been done in order to realize a homogeneous material for testing (for oil-immersion mode). However, due to the limitation of the custom-built testing system, a different approach (dip-in mode) is adopted and the material properties are successfully obtained. In part (iii), two generations of HAMMRs are investigated. The first generation of HAMMR is prepared by the oil-immersion mode which shows a record-breaking swimmering velocity with the capability of adaptive locomotion. The second generation is obtained by the dip-in mode which provides the opportunities for combining FEA, dynamic calculation, and experiment to realize a comprehensive studied for such microrobot. Moveover, advances have been made to the microrobot with a functional end-effector for micromanipulation tasks. In part (iv), a modular microrobot is proposed and realized by the introduction of a responsive mating component. The responsive mating component provides a locking mechanism between different modules of the microrobot. The microrobot is able to change its end-effector to perform different types of tasks.

By using TPP to pattern microscale hydrogel structures, microrobots are able to be implemented with advanced functional structures. The helical microrobots capable of adaptive locomotion and micromanipulation, and the modular microrobot that can switch end-effectors for different applications are advances toward the next generation of microrobots. Moreover, a standardized method is proposed for adaptive helical microrobots towards future biomedical applications. Both the proposed helical microrobot and the modular microrobot show great potential for future application and we believe the development of these microrobots will facilitate the development of the field of microrobot.