For a millennium, traders brought silk fabrics from the Far East along the Silk Road to Europe, where the beautiful yet tough material was fashioned into dazzling clothes. Today bioengineers are infusing the natural protein fibers spun by silkworms with enzymes and semiconductors. They are processing the modified strands under varying temperature, shear and acidic conditions to create novel materials with remarkable properties.
Physicians like silk sutures because they are strong and compatible with human tissue, meaning the body’s immune system doesn’t reject them. Our laboratory at Tufts University has recently extended those traits to make thin tubes that can be used as grafts to replace sections of clogged arteries, which could eliminate the need to extract a vein for that purpose from a patient’s leg for a coronary bypass, the usual procedure. James Goh and his colleagues at the National University of Singapore have regenerated an anterior cruciate ligament in a live pig’s knee using stem cells implanted in silk scaffolding.
Biocompatibility also gives engineers a way to devise interesting sensors. Engineers at Tufts and elsewhere have crafted electronic and photonic materials by patterning metals or thin films onto silk’s surface. Doctors might one day slip such films deep into the brain to treat epilepsy or spinal cord injuries. Silk implants in animals have already demonstrated the slow release of medication to control seizures.
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Scientists can foresee implanted sensors that electronically monitor nutrients, drug doses, or cells in blood or tissue and that optically record and transmit the information along silk fibers. They could design such devices to degrade at the end of their lifetimes, so they do not need to be surgically removed. We can program silk to dissolve over a specific amount of time by adjusting the size and arrangement of the protein’s crystalline structure (which gives silk cloth its shimmering sheen).
Genetic advances are at hand, too. In September, Kraig Biocraft Laboratories in Lansing, Mich., announced it had genetically altered silkworms to produce spider silk, which has greater tensile strength than worm silk and could improve artificial ligaments or even bulk products such as bulletproof vests.
