by DAVID NIESEL and NORBERT HERZOG
The list of people waiting for organ transplants is far longer than that of available organs. Many of these people would die without new organs, so science is stepping in to come up with new ways of producing working organs. One of the leading efforts at this time is growing replacement organs using a person’s own stem cells. This would eliminate the search for a suitable donor as well as the need for immunosuppressive drugs that are currently used to prevent a person’s body from rejecting transplanted organs.
One of the many challenges in growing replacement organs is finding a foundation or scaffolding for the cells to grow upon in the lab. However, a possible solution has come from a source that people often find creepy: spiders. Genetically engineered fibers of spidroin, the substance from which spiders make spiderwebs, may be an effective basis for growing replacement hearts.
The scaffolding of a lab-grown heart must meet three major standards. First, it must be biocompatible, non-toxic and safely degradable in the body. Second, it must have mechanical and elastic properties similar to a natural heart. Third, it must be compatible with the electrical currents that are necessary for a heart to function.
Spider web proteins such as those used to create the draglines of a web seem to be good choices. Spider silk is a combination of spidroin proteins, although their exact composition varies according to the species of spider and its diet. These proteins are similar to some proteins humans produce, such as the collagen found in ligaments and the keratin found in hair and nails. Spider silk is incredibly strong, tough and elastic. On a weight-by-weight basis, dragline silk is several times stronger than steel but only one-tenth the diameter of a strand of human hair. Its strength and elasticity, as well as cells’ ability to adhere to it, make it an excellent candidate as a scaffold for organs. Spidroin also has high biocompatibility, accelerates tissue regeneration and encourages the formation of blood vessels and nerves in a wound. Spidroin has already been successfully used to create wound dressings, engineer other tissues and grow bone, tendon and cartilage implants to controllably deliver drugs. The scaffolds made from spidroin do not biodegrade quickly or trigger a strong response from the immune system.
Scientists used spinning with different blends of spidroin on glass disks. They then isolated heart cells from rats and applied them to the disks in a growth medium. After growing for three days, the heart cells formed a single uniform layer across the scaffold and began to show coordinated contracting activity. The signals were transmitted correctly but at about half the velocity, although this may be different in a complete heart grown using a spider silk scaffold. Further testing of functions critical to the heart is underway, but so far it’s encouraging.
This is good news for the 120,000 people in the U.S. who need a lifesaving organ transplant, especially since an average of 21 people die each day waiting for a transplant. So the next time you see a spider, you might think about giving it a bit more credit.