New Method Joins Human Cells with Plastic
ARLINGTON, Va., June 23, 2005 — Biomedical engineers at The University of Texas at Austin have identified a protein that helps human cells attach to plastic molecules, an advance that could have applications in tissue engineering, nerve regeneration, drug delivery, implants and medical sensors.
In research described in the May 15 issue of the journal Nature Materials, researchers identified from among 1 billion candidates a specific protein, T59, which could perform the unusual feat of attaching to a synthetic polymer. This unique ability of the T59 protein, or peptide, allowed researchers to attach human cells to the synthetic polymer polypyrrole in laboratory dishes.
Polypyrrole is an electroactive polymer, a nontoxic plastic with the unique ability to conduct electricity. This property makes polypyrrole useful for a variety of applications in both the laboratory and clinic. “We feel that this new modification approach can be used for a number of medical applications, including tissue engineering, drug delivery and biomedical sensors,” says Christine Schmidt, Ph.D., an associate professor of biomedical engineering at UT and principal author. “We are particularly interested in modifying our electroactive polymers with various growth factors to enhance nerve regeneration.”
Schmidt adds that the material would also be attractive for electrodes in sensors and neural probes; the T59 peptide could be used as a means to render the electrode or probe surface more biocompatible or selective to certain tissue types. “The T59 peptide that we have identified provides us with a unique and easy way to modify our conducting polymer surface,” she says, “which is not easily modified with other methods.”
To find the unique T59 peptide, Schmidt and her colleagues, including co-author Angela Belcher, Ph.D., professor of materials science and engineering and biological engineering at Massachusetts Institute of Technology, began with a solution of different viruses called bacteriophages. Each bacteriophage displayed a different peptide on its outer surface, which it uses to attach to certain molecules. Because the container was lined with the synthetic polymer polypyrrole, the researchers focused only on the bacteriophages that adhered to the lining, which led them eventually to the T59 peptide.
To further show that T59 was responsible for bonding to polypyrrole and not some other element of the bacteriophage, the researchers used isolated synthetic copies of T59 and demonstrated that, by itself, T59 can attach to immobilized polypyrrole. The researchers speculate that some of the dozen amino acids that compose the T59 structure influence the peptide’s 3-D shape and make it adhere more readily to plastic.
Schmidt’s laboratory intends to study T59 as a link to other molecules, including vascular endothelial growth factor, which stimulates the growth of new blood vessels. They will use the bacteriophage analysis approach, called high-throughput combinatorial screening, to look for peptide linkers for other plastics, such as polyglycolic acid now being studied for tissue repair or tissue engineering.
“In general, we feel that this approach of selecting for sequences that bind specifically and strongly to polymers could provide a useful approach for modifying a number of different polymers for various biomedical applications, without the need for chemical processing and without affecting the bulk polymer properties,” says Schmidt. “We have only shown this for polypyrrole, but we are excited about the possibility of seeing peptides selected for other polymers of biomedical importance.
“This is a powerful technique that can be used for biomaterials modification,” Schmidt says, “and it hasn’t really been explored very much in this application until now.”
Schmidt received a Whitaker Research Grant in 1998 to analyze neurite growth in response to electrical stimulation.
Source: The Whitaker Foundation