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Bio-Nanorobotics 205

of nature’s mechanism, while the DNA-based molecular machines use the basic properties of DNA
to design various synthetic mechanisms (which might not be present in the nature). Nature deploys
proteins to perform various cellular tasks — from moving cargo to catalyzing reactions, while it has
kept DNA as an information carrier. It is hence understandable that most of the natural machinery is
built from proteins. With the powerful crystallographic techniques available in the modern world,
the protein structures are clearer than ever. The ever increasing computing power makes it possible
to dynamically model protein folding processes and predict the conformations and structure of
lesser known proteins (Rohl et al., 2004). All this helps unravel the mysteries associated with the
molecular machinery and paves the way for the production and application of these miniature
machines in various fields including medicine, space exploration, electronics, and military.

7.2 BIOMOLECULAR MACHINES: BACKGROUND AND SIGNIFICANCE

7.2.1 Significance

The recent explosion of research in nanotechnology, combined with important discoveries in
molecular biology, has created a new interest in biomolecular machines and robots. The main
goal in the field of biomolecular machines is to use various biological elements — whose function
at the cellular level creates motion, force, or a signal, or stores information — as machine
components. These components perform their preprogrammed biological function in response to
the specific physiochemical stimuli but in an artificial setting. In this way proteins and DNA could
act as motors, mechanical joints, transmission elements, or sensors. If all these different compo-
nents were assembled together in the proper proportion and orientation, they would form
nanodevices with multiple degrees of freedom, able to apply forces, and manipulate objects in
the nano-scale world. The advantage of using nature’s machine components is that they are highly
efficient (Kinosita et al., 2000) and reliable. Just as conventional macro-machines are used to
generate forces and motions to accomplish specific tasks, bionanomachines can be used to ma-
nipulate nano-objects to assemble and fabricate other machines or products and to perform
maintenance, repair, and inspection operations.
Such bio-nanorobotic devices will hopefully be part of the arsenal of future medical devices and
instruments that will: (1) perform operations, inspections, and treatments of diseases inside the
body, and (2) achieve ultra-high accuracy and localization in drug delivery, thus minimizing side
effects. Figure 7.3 shows an idealized rendition of a biomolecular nanorobot repairing an infected
cell in a blood vessel. The bio-nanorobot will be able to attach to the infected cell alone and deliver
a therapeutic drug that can treat or destroy only the infected cell, sparing the surrounding healthy
cells.
Development of robotic components composed of simple biological molecules is the first step in
the development of future biomedical nanodevices. Since the planned complex systems and devices
will be driven by these components, we must first develop a detailed understanding of their
operation. From the simple elements such as structural links to more advanced concepts as motors,
each part must be carefully studied and manipulated to understand its functions and limits.
Figure 7.4 lists the most important components of a typical robotic system or machine assembly
and the equivalence between macro and potential bio-nano components. Beyond the initial com-
ponent characterization is the assembly of the components into robotic systems. Figure 7.5 shows
one such concept of a nano-organism, with its ‘‘feet’’ made of helical peptides and its body using
carbon nanotubes while the power unit is a biomolecular motor. For this phase to be successful, a
library of biological elements of every category must be available. At that point, conventional
robotics can be used as a guide for fabrication of bio-nanorobots that function in the same manner.
There will be systems that have mobile characteristics to transport themselves, as well as other
objects, to desired locations.