Six years ago, we first heard about tiny two-legged "bio-bots" that used spinal muscle tissue to walk. Well, they've now received a big upgrade, in the form of spinal cord tissue that essentially makes them self-powered.
Developed by scientists at the University of Illinois, the 2014 version of the bio-bots (short for "biological robots") were each less than a centimeter in length, and constructed of a 3D-printed hydrogel. They incorporated mouse spinal muscle tissue, which caused the legs to alternately step forward as it contracted. In order to get that tissue to contract, however, the bots had to be exposed to an external electrical field.
In 2016 a new version of bio-bot was created, in which a light-sensitive gene had been added to the muscle tissue. This caused the tissue to contract in response to flashes of blue light – so electrical fields were no longer needed, but a light source was.
Now, though, a U Illinois team led by Prof. Martha Gillette has added a segment of lumbar spinal cord tissue to the mix. Harvested from a rat, that tissue was placed in a bio-bot body and then cultured along with the spinal muscle tissue for seven days, causing connections to form between the two. The choice of using tissue from the lumbar region was an important one, as it contains the circuit that controls left-right alternation of the legs while walking.
When a neurotransmitter called glutamate was introduced, it prompted the cord tissue to send signals to the muscle tissue, causing the latter to repeatedly and continuously contract. This in turn caused the bot to move forward, in what is described as "a natural walking rhythm." Once a glutamate inhibitor was added, though, the walking ceased.
The scientists are now developing the new "spinobot" bio-bots further, in order to give them an even more lifelike gait. It should be noted that the original 2012 version of the bots – which incorporated beating heart tissue – also walked on their own, but in a much less stable fashion.
Ultimately, the latest incarnation of the technology may find use in the field of medical research.
"The development of an in vitro peripheral nervous system – spinal cord, outgrowths and innervated muscle – could allow researchers to study neurodegenerative diseases such as ALS in real time with greater ease of access to all the impacted components," says graduate student Collin Kaufman, first author of a paper on the study. "There are also a variety of ways that this technology could be used as a surgical training tool, from acting as a practice dummy made of real biological tissue to actually helping perform the surgery itself. These applications are, for now, in the fairly distant future, but the inclusion of an intact spinal cord circuit is an important step forward."
The paper was published this week in the journal APL Bioengineering.
Sources: University of Illinois at Urbana-Champaign, American Institute of Physics via EurekAlert