By Sally Pobojewski
News and Information Services
If spiders and silkworms could talk, U-M scientist David Martin has a few questions he’d like to ask.
For instance, how and why does a spider change the consistency and chemical structure of its web? How do substances like salt and water cross the membrane barrier into a spider’s silk-producing gland? And how does the way a silkworm excretes its silken thread change the structure and properties of the fiber itself?
Martin and his graduate students are studying a material that is genetically engineered to mimic the molecular structure of natural silk. It is called SLPF—a silk-like protein polymer created by Protein Polymer Technologies Inc. of San Diego, Calif., and marketed under the trade name ProNectin F.
Because SLPF incorporates a specific property of the human protein fibronectin, it has the intriguing ability to bond with different types of cells. SLPF can be processed into a variety of forms, including thin films and microstructured coatings. Martin’s job is to learn how to manipulate SLPF to adapt it for a wide variety of potential uses with living tissue.
If Martin is successful, it could be the beginning of a new field of bioengineered medical devices. Possible applications include miniature sensors to monitor or stimulate the function of living cells, bioactive coatings for heart valves and blood circulation devices, superstrong glues for prosthetic implants, and biodegradable sutures that only bind to specific types of tissue.
“SLPF starts out as a protein in solution similar to what’s found inside the silk-producing glands of spiders or silkworms,” explains Martin, assistant professor of materials science and engineering and of macromolecular science and engineering. “Our research to date has focused on how the protein changes when it transforms from a liquid to a solid as we deposit thin films of SLPF on various substrates.”
After two years of research, Martin says he still has more questions than answers about the silk-like protein polymer. But he has learned how to change SLPF’s structure and properties by varying different factors—including the time allowed for the liquid-to-solid transformation; the relative amounts of polymer, water and solvent; and the method used to deposit SLPF on silicon wafers.
“Once we completely understand and can manipulate the material’s microstructure, we can begin to control the manner in which the material binds to specific types of tissue,” Martin says.
Martin discussed the effects of several variables on SLPF’s crystal structure and function at the fall meeting of the Materials Research Society in Boston last week. Erwin Stedronsky, director of materials science at Protein Polymer Technologies Inc., presented information related to additional applications of SLPF (ProNectin F) during the same session.
Macromolecular science graduate student J. Philip Anderson assisted in the SLPF research project. The research is funded by Protein Polymer Technologies Inc., and the National Young Investigator program of the National Science Foundation.
