Engineers at The University of Texas at Austin have found a way to modify a plastic to anchor molecules that promote nerve regeneration, blood vessel growth or other biological processes.
In the study led by Dr. Christine Schmidt, the researchers identified a piece of protein from among a billion candidates that could perform the unusual feat of attaching to polypyrrole, a synthetic polymer (plastic) that conducts electricity and has shown promise in biomedical applications. When the protein piece, or peptide, was linked to a smaller protein piece that human cells like to attach to, polypyrrole gained the ability to attach to cells grown in flasks in the laboratory.
"It will be very useful from a biomedical standpoint to be able to link factors to polypyrrole in the future that stimulate nerve growth or serve other functions," said Schmidt, an associate professor of biomedical engineering at the university.
Schmidt is the principal author for the study conducted with colleague Dr. Angela Belcher at Massachusetts Institute of Technology. It was published online May 15 by the journal Nature Materials.
Polypyrrole is of interest for tissue engineering and other purposes because it is a non-toxic plastic that conducts electricity. As a result, it could be used to extend previous experiments in Schmidt’s laboratory. The experiments involve wrapping a tiny strip of plastic around damaged, cable-like extensions of nerve cells called neurites to help them regenerate.
"We can apply an electric field to this synthetic material and enhance neurite repair," said Schmidt. The newly gained ability to attach proteins to polypyrrole, she said, will mean that growth-enhancing factors could also be linked to this plastic wrapping, further stimulating neurite regeneration.
Working with Schmidt and Belcher, the paper’s lead authors, graduate students Archit Sanghvi and Kiley Miller identified the peptide that attaches to polypyrrole from among the billion alternatives initially analyzed. These unique peptides were displayed on the outer surface of a harmless type of virus called a bacteriophage that was purchased commercially.
To hunt for the plastic-preferring peptide, Sanghvi and Miller added a solution containing bacteriophages that displayed different peptides to a container with polypyrrole stuck on its inner surface. The bacteriophages that didn’t wash away when exposed to conditions that hinder attachment were retested on a new polypyrrole-coated container, a process that was repeated four more times.
The sticky peptide selected, known as T59, is a string of 12 amino acids. To make certain that something else on the outer surface of the bacteriophage virus wasn’t responsible for its perceived stickiness, the researchers demonstrated that T59 by itself could attach to immobilized polypyrrole, using synthetic copies of it made at the university’s Institute for Cellular and Molecular Biology. In addition, they determined that a certain amino acid, aspartic acid, had to be a part of T59 for it to attach well to the plastic.