Researchers from the Kiel University have successfully engineered artificial cilia—a type of organelle responsible for movement in some of nature’s earliest evolved organisms. These artificial cilia not only produce net movement on the nanoscale, but they also autonomously aggregate and self-assemble. Such technology might one day contribute to the development of ultra-precise drug delivery systems or the creation of nano-scale factories capable of producing other self-assembling molecular machines.
Long before the evolution of legs, wings, or fins, some of the earliest forms of life relied upon tiny structures called “cilia” for their movement. Cilia are tiny, finger-like protrusions that are found in great abundance on the surface of individual cells. Typically over 100 cilia are found on a single cell, and their collective waving action can either move that cell through a solution or, if the cell is fixed to a particular spot, can sweep matter over and away from the cell’s surface. This latter function is particularly relevant to complex multicellular organisms such as humans. Humans have cilia in their respiratory tracts which help sweep pathogen-laden mucous up from the lungs and to the back of the throat where it can be swallowed and be subsequently exposed to the destructive acids of the stomach. Cilia are also essential for helping eggs to travel through the fallopian tubes after ovulation. To this end cilia are so important that defective cilia are now recognized as a potential cause of infertility.
As a movement-based organelle, scientists and engineers are particularly interested in producing nanostructures that can reproduce the controllable net movements of cilia. According to a paper recently published in the European Journal of Organic Chemistry, engineers from Kiel University are very close to actualizing this dream.
Researchers have long known about different molecules that wiggle in the presence of light. This wiggling movement can be quite similar to the wagging and beating motions of cilia. However without some further guidance, this chaotic movement cancels itself out—much like a person that expends energy thrashing in water but who does not manage to swim anywhere.
To create smoother collective movements out of the their would-be cilia, chemists at Kiel University’s Collaborative Research Centre 677 “Function by Switching” affixed a chiral, unidirectional molecular switch to each beating molecule. In addition, the researchers also affixed a type of molecular “suction cup” so that the cilia could adhere to surfaces covered in gold. Once affixed, these cilia might be induced to either move a larger nanostructure or to pass fluid over the surface of the nanostructure. Even more exciting, the unit of cilia, switch, and suction-cup will autonomously self-assemble. The complexes attract each other and will naturally congregate on surfaces, forming lawns of artificial cilia that are similar to the epithelium layers found in nature. To see if this artificial epithelium displays the same properties of natural epithelium, the Kiel research team plans to next examine their creation in action using atomic force microscopy (AFM).
If successful, the creation of artificially ciliated epithelium could play a critical role in the development of nano-scale fabrication processes. Visionaries predict that someday molecular machines will be able to assemble other molecular machines in fabrication plants no bigger than a computer chip. Others predict that artificial cilia could be used to carry drugs through the blood stream for delivery at a specific site within the human body.
By Sarah Takushi