Rat spinal cord and 3D-printed hydrogel skeletons allow biobots to ‘walk’

Researchers at the University of Illinois at Urbana-Champaign (IL, USA) have managed to make tiny biobots ‘walk’ by applying rat muscle and spinal cord tissue to 3D-printed hydrogel skeletons.

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Researchers from the University of Illinois at Urbana-Champaign (IL, USA) have reported success in applying spinal cord and muscle tissue from rats to biobots to make them ‘walk’. 

Described in APL Bioengineering, the ‘spinobots’ are powered by the rat spinal cord and muscle tissue applied to a 3D-printed hydrogel skeleton. The team reports that while previous biobot models have been capable of walking by muscle contraction alone, the addition of a spinal cord allows for a more fluid or natural walking rhythm. 

These are the beginnings of a direction toward interactive biological devices that could have applications for neurocomputing and for restorative medicine," explained study leader and Professor of cell and developmental biology, Martha Gillette (University of Illinois at Urbana-Champaign). 

The spinobots were first developed by 3D printing a tiny skeleton comprised of two leg posts and a flexible backbone. The backbone, only a few millimeters across, was then seeded with muscle cells that later developed into muscular tissue. The final step was to then integrate a segment of a rat’s lumbar spinal cord. 

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," added first author, Collin Kaufman (University of Illinois at Urbana-Champaign). 
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," Kaufman continued. 

In order to successfully apply both the muscular and the spinal cord tissue to the biobot, the team had to design a methodology that would allow for the extraction, culture and integration of the intact spinal cord as well as the culture of both the spinal cord and muscle tissue, together. Another challenge was to ensure that the neurons formed junctions with the muscle.


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The team observed spontaneous muscle contractions in the spinobots which indicated the formation of neuromuscular junctions and that the different cell types were successfully communicating. 

In order to verify that the spinal cord was functioning to promote walking, the team added the neurotransmitter, glutamate, which caused the muscle to contract and the legs to move in a walking rhythm. When removed, the spinobots stopped walking.

The next steps beyond refining the spinobots movement could include the future development of in vitro models of the peripheral nervous system, which has previously been difficult to study in live models. 

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," Kaufman added. 
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," Kaufman concluded. 

>> To find out more from the American Institute of Physics (WA, USA), read further coverage of this story via our sister site, Neuro Central 

Sources: Kaufman CD, Liu SC, Cvetkovic C et al. Emergence of functional neuromuscular junctions in an engineered, multicellular spinal cord-muscle bioactuator. APL Bioeng. doi:10.1063/1.5121440 (2020) (Epub ahead of print); https://news.illinois.edu/view/6367/808277


Lead image: Bio-bot. Bio-bots are propelled by a ring of muscle on a hydrogel skeleton. Illinois researchers have been the first to innervate them with rat spinal cord segments, giving the 'spinobots' a natural walking rhythm. Credit: Image courtesy of Collin Kaufman, University of Illinois at Urbana-Champaign

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