Motor proteins form microscopic biological machines essential for many types of movement, from swimming bacteria to contracting muscles. However, the efficient integration of motor proteins into macroscopic robotic systems is a challenge. In a recent study, Japanese scientists developed a biologically inspired strategy to produce artificial muscle that self-assembles from motor proteins. Their approach, compatible with modern 3D printing, paves the way for printable robots that look more like living creatures.
Inside our cells and those of the most famous life forms, there are a variety of complex compounds called “molecular motors”. These biological machines are essential for different types of movements in living systems, from the microscopic rearrangement or transport of proteins within a single cell to the macroscopic contraction of muscle tissue. At the crossroads between robotics and nanotechnology, a much-sought-after goal is to find ways to harness the action of these tiny molecular motors to perform larger tasks in a controllable way. However, achieving this goal will certainly be difficult.
“So far, even though researchers have found ways to scale up the collective action of molecular motor networks to show macroscopic contraction, it is still difficult to effectively integrate these networks into real machines and generate forces large enough to actuate components on a macroscopic scale, ”explains Associate Professor Yuichi Hiratsuka of the Japan Advanced Institute of Science and Technology, Japan.
Fortunately, Dr Hiratsuka, together with Associate Professor Takahiro Nitta of Gifu University and Professor Keisuke Morishima of Osaka University, both in Japan, have recently made remarkable strides in the quest to make the link between micro and macro. In their latest study published in Materials from nature, this research team reported the design of a new type of actuator driven by two genetically modified biomolecular motors. One of the most attractive aspects of their biologically inspired approach is that the actuator self-assembles from basic proteins by simple light irradiation. Within seconds of light reaching a given area, surrounding motor proteins fuse with rail-shaped proteins called microtubules and organize themselves into a hierarchical macroscopic structure that resembles muscle fibers.
When training around the target (illuminated) area, this “artificial muscle” immediately contracts and the collective strength of individual motor proteins is amplified from a molecular scale to a millimeter scale. As the scientists have shown experimentally, their approach could be ideal for small-scale robotic applications, such as actuating microscopic tweezers to manipulate biological samples. Other millimeter-scale applications have also been demonstrated, including assembling separate components, such as miniature cogwheels, and feeding minimalist robotic arms to create a crawling insect-like microrobot.
What is also very remarkable about this technique is that it is compatible with existing 3D printing techniques that use light, such as stereolithography. In other words, microrobots with built-in artificial muscles can be 3D printable, allowing their mass production and thus increasing their applicability to solve various problems! “In the future, our printable actuator may become the indispensable ‘actuator ink’ for seamless 3D printing of entire robots. We believe that such a biomolecule-based ink can push the frontier of robotics by allowing the printing of complex bones. and the muscle components needed to make robots look more like living creatures, ”says Dr. Hiratsuka.
A potential improvement in the current technique would be to find ways to effectively relax artificial muscles (reversibility). Alternatively, the present strategy could also be modified so as to produce spontaneous oscillatory behavior instead of contraction, as seen in the motile cilia of microbes or in the flight muscles of insects.
In any case, this study effectively shows how imitating the strategies devised by nature is often the recipe for success, as many scientists in the field of robotics have already understood!