How do you improve on one of nature鈥檚 most remarkable creations?
Medical technicians already spin spider silk, the strongest known natural fibre, to make mats and sponges as scaffolds on which to grow human cells. These structures would be even more useful if their stiffness could be adjusted. Cells grown on a scaffold as stiff as bone, for example, would more readily fuse with bone cells when reimplanted into the body.
Now a team of biomedical engineers from Tufts University in Boston, Nottingham Trent University in the UK and the Air Force Research Lab at Wright-Patterson Air Force Base, Ohio, have figured out how to stiffen spider silk. Their secret is to reinforce it with microscopic glass beads diatoms, a single-celled marine alga, use to reinforce their protein shells.
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To fuse the two materials, the engineers combined a silk gene from the golden orb-weaver spider (Nephila clavipes) with a gene for R5, a peptide that diatoms use to form silica beads inside their shells. They inserted the altered gene into bacterial cells, which then produced a 鈥渃himeric鈥� 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. The R5 coaxed silica beads of up to 2 micrometres across to form, which coated the strands of silk (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0601096103). The silk-silica strands will be used to build stronger scaffolds.
