Mimicking Sea Cucumbers to Find Medical Solutions

Cutting Edge Bio-Inspired Materials Research by Christoph Weder and Stuart Rowan

By Marianne Eppig on assignment for E4S

When you look at a sea cucumber—an ocean floor-dwelling animal that looks like a giant slug—medical solutions might not be the first item that pops into your mind.

(Sea Cucumber. Photo courtesy of WikiMedia)

A sea cucumber’s skin is soft and flexible to help it navigate obstacles as it travels along the ocean floor.  When a threat arises, our unlikely hero’s skin quickly transforms into a hard, rigid protective shield.  As soon as the threat dissipates, the sea cucumber again relaxes and goes along on its way.

Christoph Weder and Stuart Rowan, researchers and professors at Case Western Reserve University, have created a new material that mimics the sea cucumber’s ability to transition between states of rigidity.  Their bio-inspired material has resulted in a surprising new medical application.
    
Currently, paralyzed patients can get an electronic device—called a neural electrode—implanted into their brain to help send and receive brain messages.  The electrodes are typically made of metal, ceramic or silicon, but such brittle materials can cause brain tissue damage over prolonged periods of time.  On top of this sobering fact, the cells in the brain—in response to the foreign object—will attack the electrode, significantly decreasing the electrode`s recording ability and eventually causing it to fail.

Weder and Rowan’s material is being applied to neural electrodes that are rigid enough to insert in the brain, but once they come into contact with the brain’s water, they will become soft and flexible enough to avoid the brain tissue damage that current electrodes cause.

A Closer Look:
Making the Material
The material that these scientists created to mimic the sea cucumber’s ability is, according to Weder, “Cool because it can rapidly shift between a dynamic range of flexibility and rigidity.” 
 
Within the skin of the sea cucumber, the rigid nano-rods are made from collagen, a protein.  The rods do not interact with each other when the sea cucumber is relaxed, but when the organism feels threatened it releases a protein that binds to the collagen, and cross links all the rigid rods, essentially creating a scaffold that stiffens the skin.  The basic mechanism that Rowan and Weder are mimicking is control over the interaction of the rods.  Their material also mimics the matrix architecture of the sea cucumber’s skin. 

Weder noted, “Once you understand the architecture, the basic process, we can say, well, we can do this with a different material, with different chemistry, and different ingredients… certainly not as sophisticated as nature does it, but we can make materials that can change their properties.” 

Instead of using collagen, which is in sea cucumber skin, Rowan and Weder used cellulose—an easy-to-use and accessible protein—from tunicates (an underwater filter feeding organism).  They used the cellulose from tunicates because their fibers are especially long and thus the researchers could use a relatively small amount for testing.  The scientists noted that once the material is manufactured, however, cellulose could be taken from wood, cotton, or wheat, all of which are renewable, easily accessible resources that could even be taken from recycled waste products. 

(Tunicates. Photo courtesy of Wikipedia)

Rowan and Weder embedded the cellulose fibers into a pliable plastic, which yielded a rigid material.  The hydroxyl groups (molecules consisting of oxygen and hydrogen) on the surface of the cellulose fibers stick together, forming a fibrous web. 

To break the fiber bonds and loosen the web, Weder and Rowan’s team injected a water-based solvent, which was an artificial cerebral spinal fluid used to mimic the fluid in the brain.  The hydrogen groups of the solvent bond with those on the cellulose fibers, and as a result the fibers decouple from one another. 

Conversely, as the water evaporates, the cellulose fibers reconnect and the material becomes stiff again.  The researchers used water as the “switch” because of their desire to insert neural electrodes made of the material into the human brain, but they also would like to come up with other ways to switch the material, such as electrically, chemically, with light or other stimuli.


Discovering Success
In terms of the success of their project, Weder said, “As scientists we are delighted that we could take nature’s architecture and we could mimic the function in a very crude way.  That in and of itself is a success.” 

They recently published an article in Science magazine about their research on the bio-inspired material.  Despite this scientific victory, “There’s a lot more to it before we can make a product,” stated Rowan.  He continued, “All we’ve done is prove concept, and now we are working on the product.  We are trying to understand the process in a lot more detail, and how to control it.” 

The Advanced Platform Technology Veteran`s Affairs Medical Center and the National Institute of Health (NIH) approached Weder and Rowan to apply their new material to the neural electrode.  Testing is currently underway to ensure the efficacy of the electrodes.

There is a plethora of potential applications for this material.  The National Science Foundation (NSF) recently began funding Weder and Rowan to apply the material to electrically switchable medical braces, also called orthotic devices or “smart” casts.  The braces would be stiff to support broken body parts, but when the patient needed surgery or to rotate within the brace, it could become flexible with the push of a button. 


Looking to Nature
Since their research on the sea cucumber, the scientists have begun to look to nature for further inspiration.  Weder stated, “I’m sure that I could learn a lot from nature by going out and asking, ‘What other cool animals are out there?  What other cool tricks are out there that have not been researched to death?” 

Rowan added that, “There are a lot of animals that do incredibly cool things that at the moment we cannot do.  A lot of this is cutting edge stuff, just figuring out how organisms do what they do.” Rowan and Weder have ideas about future research involving biomimicry (imitating nature’s designs and processes to solve human problems) and have “other inspirations” from nature, but they claim that it is too early to talk about them. 

Despite all the unknowns of the future, Rowan stated, “I think this whole process has changed how I look at science, to the point that I look more at what nature does.  I look at nature a different way as well because of this process.”