The sundew plant is aptly named. Each leaf is covered with tiny hairlike-tentacles, on the tip of which is a drop of what looks like morning dew. In the sun, these droplets glisten and gleam, but they also conceal a carefully laid trap.
What appears to be dew is actually a sticky adhesive, and any insect that alights on a sundew leaf will promptly find itself stuck. As it struggles to escape, the plant's tentacles and leaves curl around the insect, before the carnivorous plant slowly digests its prey.
But now, the sundew may have a role to play in rebuilding bodies as well as dismantling them. Research, carried out by Mingjun Zhang, a biomedical engineer at the University of Tennessee, Knoxville, has shown the plant’s sticky adhesive may be suitable for a variety of cutting-edge medical procedures, including tissue engineering and chronic wound healing.
The emerging field of tissue engineering represents a new approach for replacing or repairing damaged body parts. The idea is to deliver a teeming mass of healthy, say, nerve, bone, or muscle cells to the site of a nerve, bone, or muscle injury, and hope the new cells integrate themselves into the body as healthy, functional tissue.
But doctors can't just inject a solution of cells into the body and expect new tissue to grow. Cells do best when they have a surface to adhere to - a "scaffold" to which they can anchor themselves as they proliferate and differentiate. So in tissue engineering procedures, cells are applied to one of these scaffolds—which come in a variety of materials and forms, including sponges, meshes, films, and gels. Then the whole construct is implanted or injected into the body. As the cells begin to multiply, the scaffold provides a literal support structure, facilitating cell growth and communication. Eventually, the biodegradable scaffold disintegrates into the body, leaving behind a sheet of brand new tissue.
Scaffolds need to meet many criteria, and engineers have spent a lot of time looking for just the right material. “This has been a major challenge,” says Zhang, whose lab specializes in bio-inspired engineering. As he scoured the natural world for a substance that might make a good cell scaffold, he began to think that the gluey, gelatinous substance secreted by sundews might fit the bill.
The material is natural and biodegradable, composed of a combination of sugars and acids. It is, of course, sticky, which means it should be able to tightly grip cells. And it’s highly elastic, which is crucial for tissue engineering; a scaffold has to be flexible enough to bend and stretch and shift as cells proliferate and tissues grow.
The more closely Zhang examined the sundew adhesive, the more suitable it seemed. For a study he published in 2010, he coated a silicon wafer with the sundew adhesive and let the material dry for 24 hours. Then he stuck the wafer under a microscope. What he saw thrilled him - the dried adhesive was composed of a complex network of nanofibers, linked and crosslinked to form a porous scaffold. What’s more, he discovered that the holes in the scaffold were a Goldilocks-like “just right” - neither too large nor too small, but the perfect size for cell attachment. From a tissue engineering perspective, Zhang says, the structure left behind by the dried adhesive had “a beautiful morphology”.
Then it was time for an even bigger test. Zhang smeared the sundew material onto glass slides and seeded the adhesive with living cells derived from the brains of rats. Twenty-four hours later, he returned to the slides. The cells had attached; an average of 1250 cells had colonized each square millimeter of the adhesive. Around 98% of the cells were viable, and they were stuck on securely - they stayed put even when Zhang tried to rinse them off. In a 2011 paper, Zhang showed that neurons attached to the sundew adhesive were capable of dividing and differentiating and that bone and skin cells also successfully adhere to the material.
The findings have convinced Zhang that the sundew adhesive is a good starting point for a variety of tissue engineering applications. He thinks engineers could modify and process the material into an implantable or injectable scaffold. Alternately, Zhang imagines brushing a mixture of liquid sundew adhesive and skin or stem cells onto the surface of a chronic, open wound. The sundew material would serve as a scaffold as the cells grew into a new, healthy layer of skin.
The sundew adhesive may also have a role to play in routine medical implant procedures, Zhang says. For instance, it could be brushed onto the surface of an artificial knee or hip, fostering a secure attachment between the implant and the living tissues surrounding it. Down the line, we may find that the best way to put human bodies back together is to borrow from a predatory plant. “Nature does beautiful things,” Zhang says. “We should definitely learn from that.”
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