The future is near: robots made from biological tissues
The diversity and perfect arrangement of living organisms have always inspired artists and engineers. Now roboticists copy the structure, ways of movement, and even the behavior of living creatures, so perfectly designed by nature in the course of evolution. To simulate the complex motor functions involved in jumping, swimming, and running, robots are assembled from plastic materials. Robots made of hydrogels, soft plastics, and metals like aluminum move smoothly, can grab objects, overcome obstacles, and move underwater.
However, artificial materials are not yet able to surpass living tissues in functionality. Therefore, researchers are trying to combine the properties of artificial and biological tissues in hybrid mechanical systems. Heart and skeletal muscle cells have already been tested outside the body.
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The heart tissues provide rhythmic contractions and do not require external devices to trigger movement. But the frequency of contractions does not change much. The muscles of the motor apparatus of living creatures, on the contrary, provide a wide range of movements. Hybrids of engineered muscle tissue with living cells are able to continuously contract for 250 days but need an external control mechanism. Invertebrates, the control of muscle contraction is provided by the nervous system: the brain stem and spinal cord.
Stimulation of engineered muscle tissue with electric fields, chemicals, and light cannot replace the smooth functioning of the nervous system. A new work by researchers from the University of Illinois at Urbana-Champaign demonstrates a hybrid biorobot, whose artificial muscles are controlled by the real spinal cord of a rat. The work, published in the journal APL Bioengineering, showed that there are patterns of contractions in the spinal cord, and the involvement of the trunk in the regulation of movements is not required.
In experiments, scientists extracted the spinal cord from the lumbar spine of newborn rats. The muscles of the hind limbs are attached to the neurons in this area. Muscle tissue was artificially grown on columnar "tendons" made of polyethylene glycol (PEG) printed on a 3D printer. A gel consisting of myoblast proteins, precursors of the body's muscle cells, and blood proteins was sown around the pillars. At the stage of artificial muscle development, which corresponded to the" age " of the spinal cord during natural embryonic growth, the muscles were connected to the neurons of the extracted rat spinal cord.
7 days after inserting the spinal cord into the grown muscle tissue, motor neurons sprouted into the artificial muscles and began to show electrical activity, causing contractions in the muscles. The spinal cord reproduced the activity of the peripheral nervous system to control the motor functions of a living organism, while outside the body! The muscle contractions were spontaneous. To trigger contractions in certain muscles, the associated neurons were stimulated with glutamate. A drug with anti-glutamate properties blocked artificial muscle contractions. The combination of drugs made it possible to create a complex pattern of movement of the biorobot with the desired amplitude and in the required sequence.
The ability to observe the activity of the spinal cord outside the body is useful in medical research. For example, in the study of Lou Gehrig's disease, also known as amyotrophic lateral sclerosis. The disease leads to the death of neurons and the possible loss of motor function. Replacing the muscles and tissues of the spinal cord with a hybrid system developed by scientists will help track the interaction of diseased neurons with healthy tissues. Biorobot is also useful in training operations of future surgeons and in the development of medical products.