For much of the history of robotics, research has focused on systems that have some relation in operational capability or length scale to humans. From the perspective of the layman, the very definition of robot is most often closely tied to the subclass of robotics relating to humanoids. Perhaps this isn't particularly surprising, since the methods of machining and the tools that we first developed are correlated with our ability to easily observe and manipulate objects at macroscopic length scales. That is, with the naked eye we can easily see objects down to the millimeter, and our hands are not adept at working with smaller objects. It is also not surprising that we have developed strong capabilities at developing much larger structures such as bridges and skyscrapers. In a sense, the bottom of the scale limits engineers more than the top, and we can consider the largest structures to be considered ‘bottom-up,’ a concept that is prevalent in nanotechnology. In the last decade, significant advances have been made in the field of microrobotics due to relatively recent advancements in both micromachining and microscopy. With the proliferation of several advanced tools for imaging and analysis, such as atomic force, electron, and confocal microscopies, coupled with the increasing availability of microfabrication technology, we can expect to see tighter integration between fundamental discovery and engineering applications.

Experimentalists in microscale robotics are inevitably led to consider two fundamental questions. Firstly, what can we learn from cells in terms of mimicking or integrating natural phenomena with robots? Secondly, how can we apply new microrobotic technologies to the fields of cell biology and medicine?

Cells are, in a sense, highly optimized and specialized microrobots. If we look at the function of a cell from the perspective of a beginning robotics course, we find striking analogs between cells and robots. Motor proteins perform as actuators, neurons and ion channels act as wiring, DNA and RNA act as memory and software, etc. The cellular systems are composed of elements that are self-assembled in the truest, atomistic sense from the bottom up. Proteins are the functional subunit of the cellular machinery, assembled into myriad actuators and sensors. In the current state of micro- and nanorobotics, we either mimic behaviors that are otherwise performed by these proteins, or we use whole, intact cells. For example, the behavior of the flagellum is currently replicated not by proteins, but by external magnetic fields [1–4], and the sensing of chemical compounds may be interfaced with mechanical measurements and solid-state microelectronics [5]. In the long view, however, it is only reasonable to expect that cellular subsystems will be successfully integrated with microfabricated, inorganic elements. Indeed, there is a significant progress being made in the effort to harness the power of motor proteins as microactuators.

The branches of bioengineering related to genetic engineering and synthetic biology will also inevitably be interfaced with microbiorobotics, from both the standpoint of sensors and actuators, or even combinations. In the field of optogenetics, we see a step toward this combination, the coupling of light exposure with muscle actuation [6]. If we're willing to expand our definition of robotics, another viable option is to reprogram whole cells to suit our needs. Bacterial and yeast cells have been reprogrammed to perform basic operations such as counting and timing [7,8].

One of the great challenges in microrobotics is expanding the current control capabilities from single or few-robot systems to many-robot systems. Since many of the current techniques are field based, it is no small task to accomplish. That is, individual control is limited by the divergence or resolution of the applied fields. In many current systems, sensing and control are performed at a much larger scale using the microscope as an interface. Despite the current limitations on the ability to create systems of independent microrobots, it is easy to imagine how such capabilities would greatly enable otherwise difficult tasks, such as the collective propulsion of large objects relative to the robot size, or collecting data in from disparate locations.

From the biomimetic point of view, multirobot systems seem like an obvious step along the continuum of technological advancement. Although there are certainly countless examples of microorganisms that go about their life cycle in a largely independent manner, there are also many examples of single-cell organisms that demonstrate collective behaviors, such as swarming bacteria [9].

Passive, circulating multirobotic systems can also easily be envisioned. Although much of the focus to date has been on actuation methods, sensing networks of passively flowing, perhaps even communicating robots. For instance, leukocytes detect and defend against infection in the human body. Although many of these cells circulate freely in the blood, they are able to sense and respond to foreign bodies. One can imagine another layer of robotic protection tasked with monitoring or even responding to disease.

As described, there are clearly myriad options for fundamental study on several levels with direct applicability to microbiorobotics. While the fundamental research by itself serves to motivate the subject as a whole, the application of microbiorobots to cellular research, drug delivery, or as working tools for other microscale tasks should prove to be fascinating.