BioMicrorobotics
Robots are currently exploring many environments that are difficult if not impossible for humans to reach, such as the edge of the solar system, the planet Mars, volcanoes on Earth, and the undersea world. The goal of these robotic explorers is to obtain knowledge about our universe and to answer fundamental questions about life and human origins. Microrobotics has entered this field by exploring life at a much smaller scale and more fundamental level. Microrobotic systems for physically exploring the structures of biological cells are being developed, and robotic motion planning strategies are being used to investigate protein folding. Microrobotic mechanisms have been used to investigate organism behaviors, such as the flight dynamics of fruit flies as well as the neurophysiology that govern many other biologically interesting behaviors. These recent research efforts and others like them illustrate how several areas of robotics research are rapidly converging to create this new discipline I refer to as BioMicroRobotics. These new directions in robotics represent only a beginning and indicate that robotics research, and biomicrorobotics in particular, has the capability of making significant contributions in the understanding of life.
Over the past decade the science of microrobotics has emerged as a subset of the general field of robotics. Microrobotics can be divided into two main categories: the manipulation of micron sized objects with larger robots and the fabrication of small intelligent robotic systems from micron sized parts. The main research challenges in microrobotics consist of understanding the predominate physical forces that govern part interactions at these scales, and the development of appropriate sensing and actuation strategies that can effectively and robustly operate in this domain. Furthermore, microrobotics means integrating these sensing and actuation strategies with a cognitive aspect that enables intelligent, complex interactions with the microworld.
Biomicrorobotics is an emerging field in which microrobotics is defined within a purely biological domain. A number of fascinating robotics research efforts fall within the category of biomicrorobotics, which the following research projects illustrate.
BioMicroRobotics Research @ IRIS
The current biomicrorobotics research focus of IRIS is on building sub-mm sized, untethered robots for in vivo medical applications, in particular for use in the vitreous humour (a clear, gel like substance that fills the bulk of the human eye) for retinal surgery. To put it simply, building a complete robotic system that “swims” inside the human body is quite a challenge and requires an innovative combination of Micro- and Nano-Technology with macro-scale medical robotics. Therefore, our efforts can be broadly divided into two main areas: 1) Building the microrobots using MEMS, NEMS and robotic microassembly technologies and 2) applying and controlling the microrobots for in vivo applications using medical imaging, and novel magnetic steering methods.
Untethered Magnetic BioMicroRobots with Hybrid MEMS Design
Although electronic and mechanical systems have been miniaturized by VLSI and MEMS technologies, no counterpart to these exists for electro-chemical energy storage. At IRIS, we are focused on the use of magnetic fields that are generated ex vivo for actuation and steering of these microrobots. We have built prototype microrobots with hybrid MEMS design to investigate magnetic steering, wireless actuation and hybrid design concepts. The first prototype model is a three dimensional, assembled structure. The significant advantage of the hybrid design is that the individual parts of the assembly can be produced with standard MEMS manufacturing processes which create planar geometries. This way, different sub-systems of the robot can be manufactured using the most suitable process for the purpose.
Currently four different types of robots are being assembled from a combination of planar parts that are manufactured using a nickel electroplating process and bonded with UV activated glue. The "winged-ellipsoid" shape has an axis of symmetry along the long axis of the ellipsoid. An external magnetic field acts to align and pull the robot along this axis (i.e. magnetic torque and force) due to the shape anisotropy effect, much like a needle always becoming magnetized along its long axis. On the other hand, the winged shape acts to reduce the side-ways drift of the microrobot by increasing the fluid drag along the axes perpendicular to the long axis.
Images
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Electroplating Steps -
Microrobot Parts -
Microrobot Types
Magnetic Steering of BioMicroRobots
When a ferromagnetic body is subject to an external magnetic field, it becomes magnetized. The magnetization vector is dependent on both the geometry and the material properties of the body. As a result, the body feels a magnetic torque that is directed to align it with the external field and a magnetic force that pulls it towards the direction of increasing field. In other words, a magnetic torque and force can be applied on the microrobot by controlling the external field and field gradient vectors.
There are two alternatives for generating external fields, electro-magnetic coils or permanent magnets. Coils enable more precise servo control of field strengths where as permanent magnets can provide strong fields while occupying a small volume and do not require cooling. At IRIS we are investigating both alternatives. We have demonstrated a coil-based system for magnetic steering of the prototype microrobots in a two-dimensional maze. The steering system uses two coaxial pairs of magnetic field generating coils in Helmholtz and Maxwell configurations respectively. While the Helmholtz configuration creates a uniform magnetic field at the center of the coils, the Maxwell pair creates a constant gradient field. The current through the coils can be individually servoed to control the strength of torque and force on the microrobot independently. A motor controls the orientation of the coils. With this system the microrobots can be easily steered inside 1000 micron wide, water-filled channels of the maze (video).
Magnetic Steering of BioMicroRobots
