Medical researchers have come up with a novel way to stiffen the spider silk – using glass. The discovery could make it easier to grow replacement parts for human bodies by improving the silk scaffolds on which human cells are grown.
Medical technicians already spin spider silk, the strongest natural fibre known, to make mats and sponges as scaffolds on which to grow human cells. But these structures would be even more useful if their stiffness could be adjusted to more closely suit the tissue being grown on them. For example, surgeons often need to replace bone lost during surgery or in an accident. Cells grown on a scaffold as stiff as bone should more readily fuse with bone cells when implanted into the body.
Now a team of biomedical engineers from Tufts University in Boston, Massachusetts, US, Nottingham Trent University in the UK and the US Air Force Research Lab at Wright-Patterson Air Force Base, Ohio, have figured out how to stiffen spider silk. The secret is to reinforce it with the same microscopic glass beads that single-celled marine algae (called diatoms) use to reinforce their protein shells.
To fuse silk and glass, the engineers combined a silk gene from the golden orb-weaver spider (Nephila clavipes) with a gene for a peptide called R5 that encourages the formation of silica beads in the shells of diatoms.
The engineers inserted the resulting combination gene into bacterial cells, which then produced a “chimeric” protein that had the properties of silk married with the unique chemistry of R5.
The team then spun the chimeric protein into strands of silk and dunked them in a solution of water and silicon-rich molecules. They found that the R5 coaxed silica beads of up to 2 micrometres across to form, which coated the strands of silk and made them stiffer. The resulting silk-silica strands will be used to build stronger scaffolds.
Now the team is trying to fuse silk genes with genes for proteins that capture other minerals, such as hydroxyaptite, which is found in human bone. They hope that scaffolds containing minerals found in the body will encourage appropriate cell growth on those surfaces, making for increasingly tailored human implants.
Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0601096103)