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Figure 2.5: Design of nanoscale transport systems based on biological motor proteins (adapted from [9]).

these needs are communicated by chemical and mechanical signals [1]. In artificial sys-

tems, this process needs to be controlled, and ideally, in the future, automated. How can

we control fiber synthesis, composition, and stability?

Different groups have found different solutions to this problem. Actin monomers

self-assemble into linear fibers, and depending on the exact protein composition and

salt composition in the solution the fibers might be of different length or might even

aggregate into fiber bundles [15]. These fibers or bundles can be aligned by shear forces.

For further stability, these fibers can be chemically cross-linked.

Tubulin can be prepared in the same way to create microtubules [15]. In this case,

however, the fibers are continually polymerized on one end and depolymerized on the

other while transport happens, so the system has to be able to handle (or welcome) this.

A very accurate but difficult way to create the “streets” is using “tweezers” made

from a MEMS (micro-electrical-mechanical-systems) chip: due to polarity differences in

the microtubule as well as the chip the “tweezers” pick up a microtubule and drop it at

a precise location [16].

The transport system can also be inverted: the motor proteins can be attached to

a surface and then act as the track on which actin fibers or microtubules move. Motor

protein attachment often occurs via micropatterned (or nanopatterned) surfaces with

hydrophilic and hydrophobic regions [17]. Usually, the proteins are attached to the bot-