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Supramolecular polymers treat spinal cord injury in mice

Motion of monomers plays key role in targeting receptors

by Celia Henry Arnaud
November 21, 2021 | A version of this story appeared in Volume 99, Issue 42

A line structure of a peptide amphiphile and a model of part of the fiber it forms.
Credit: Science
Peptide amphiphiles form supramolecular polymer fibers used to treat spinal cord injury. Various sections of the amphiphile confer different functions. Signaling peptides (green) on the surface of the fiber target receptors. A sequence of four amino acids (red) controls motion of the monomers within the fiber.

There are no currently available ways to reverse spinal cord damage, but researchers are working to develop methods to regenerate neurons after spinal cord injury. A team has moved closer to that goal with supramolecular polymer threads that successfully treat spinal cord injury in mice. According to the researchers, properly tuned mobility of the individual molecules within the threads proved to be a key characteristic leading to the successful healing of nerve damage in mice.

Samuel I. Stupp of Northwestern University and coworkers made the supramolecular fibers—tube-shaped assemblies of molecules with one end of each molecule pointing to the center of the tube and the other pointing out (Science 2021, DOI: 10.1126/science.abh3602). At the outward-facing end is a peptide that activates a targeted receptor associated with nerve growth. An alkyl tail at the other end drives assembly of the supramolecular structure into a squashed tubular shape. Another segment controls mobility of the individual molecules within the supramolecular structure.

The researchers tested structures with varying amounts of molecular mobility and incorporated different amounts of two signaling peptides. One signal promotes the regeneration of nerve fibers; the other promotes cell proliferation and blood vessel formation.

Fluorescence micrographs of spinal cord injuries treated with saline (top) and a supramolecular polymer (bottom).
Credit: Science
Spinal cord injuries in mice were treated with a saline solution (top) or a supramolecular polymer (bottom); treatment with the polymer led nerve fibers (red) to regrow.

To treat spinal cord injury in mice, the researchers injected an aqueous solution of the supramolecular polymer into a mouse’s spinal cord. Mice that received supramolecular polymers with the right combination of motion-control sequences for the two signaling peptides had much more nerve fiber regrowth, blood vessel formation, and functional recovery than ones that received polymers with other combinations.

“The observations made by the authors in this study could open the door for new avenues and materials to be explored by researchers for tissue engineering research,” Charlotte A. E. Hauser, an expert on biomedical supramolecular materials at King Abdullah University of Science and Technology, writes in an email.



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