Kinesin motor proteins and the microtubule cytoskeleton function as an intracellular railroad system-a railroad with nanometer-scale engines running on nanometer-scale tracks. Our long-term objective is to take the molecular machinery of this sub-cellular railroad out of the cell and integrate it into micron-scale devices with moving parts driven by kinesin motors. The microtubule tracks are hollow tubes, 24 nm in diameter, formed by the self-assembly of tubulin protein subunits. The engines of this transport system, kinesins, are remarkable molecular machines. Force production is coupled to hydrolysis of ATP, a high-energy biomolecule. For each ATP it hydrolyzes, kinesin steps 8 nm (1) on the microtubule surface and can generate forces up to 6 pN (2,3). With a cross-sectional area on the order of 10 nm2 (4), kinesin can be surface immobilized with a packing density approaching 105 motors per µm2. With each motor generating forces as high as 6 pN, cumulative forces on the order of 10s of nN per µm2 are theoretically possible. The size, efficiency, and potential power density suggest that it will be possible to build sophisticated microdevices powered by these motors. As a first step toward this objective we have coupled kinesin to 10 x 10 x 5 µm silicon microchips that were patterned photolithographically and etched from silicon membranes. The microchips were observed by light microscopy to move on microtubules aligned and immobilized on the surface of a microscope flowchamber. In some instances, microchips translated through the flow chamber at about 0.8 µm/sec. In other cases, microchips were observed to rotate in place at approximately 18°/sec. A few examples of kinesin-powered microchips flipping over were also observed. From transporting, rotating, and flipping microchips, we can imagine the extension of our kinesin technology to moving more elaborate microparts, like gears, or rotors, or levers. This will allow kinesin forces to be coupled to a useful action in a MCMS. For example, a micro-rotor turned by kinesin could demonstrate the feasibility of creating a kinesin-powered micro-generator or micro-pump.
Svoboda, K., Schmidt, C., Schnapp, B. & Block, S. (1993). Nature 365:721-727.
Svoboda, K. & Block, S. (1994). Cell 77:773-784.
Hunt, A., Gittes, F. & Howard, J. (1994) Biophysical J. 67:766-780.
Kull, F., Sablin, E., Lau, R., Fletterick, R., & Vale, R. (1996). Nature 380:550-555.