Spinobots given legs by rat muscle and spinal cord tissue

Previous biological robots - or bio-bots - could move forward by simple muscle contraction, but the integration of the spinal cord gives them a more natural walking rhythm, said study leader Martha Gillette, a professor of cell and developmental biology at the University of Illinois at Urbana-Champaign.

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"These are the beginnings of a direction toward interactive biological devices that could have applications for neurocomputing and for restorative medicine," Gillette said in a statement.

The researchers have published their findings in APL Bioengineering.

To make the so-called spinobots, the researchers first printed two posts for legs and a flexible backbone, measuring a few millimetres across. Then, they seeded it with muscle cells, which grew into muscle tissue. Finally, they integrated a segment of lumbar spinal cord from a rat.

"We specifically selected the lumbar spinal cord because previous work has demonstrated that it houses the circuits that control left-right alternation for lower limbs during walking," said graduate student Collin Kaufman, the first author of the paper. "From an engineering perspective, neurons are necessary to drive ever more complex, coordinated muscle movements. The most challenging obstacle for innervation was that nobody had ever cultured an intact rodent spinal cord before."