Sea Cucumbers on the Brain

Advancements in biomedical science come from the study of all different sorts of organisms, from humans to roundworms, fruit flies, and yes, even sea cucumbers. The authors of a recent study in Science suggest research involving the sea cucumber has potential for improving treatments for Parkinson’s disease, stroke, and spinal cord injuries. They speculate it may conceivably even be used in the development of flexible body armor or bullet-proof vests.

You might be wondering what it is about the sea cucumber that would make it an interesting organism to study, and how such an ostensibly mundane creature could possibly lead to intriguing breakthroughs in science. The answer lies in the skin of this echinoderm, which can transform from soft and pliable to rigid and inflexible in a matter of seconds.

The sea cucumber gets its name from its appearance, which consists of an elongated, stocky body that resembles the precursor of the pickle. It is a scavenger, sliding along the sea floor in tropical waters, living off of plankton and debris for food. Normally, it is pliable, using its flexibility to slither around rocks or position itself along lines of current to suck up potential food particles that may float by. If touched, however, its skin goes from supple to stiff. This defensive mechanism provides it with a temporary sort of body armor to protect it from predators. The transformation is enabled by a complex matrix of collagen fibrils and fibrillin microfibrils whose interaction can be changed by the release of macromolecules from effector cells. The effector cells are activated by touch.

A group of researchers at Case Western Reserve University in Cleveland investigated the mechanism underlying this transformation in the hopes of creating a nanocomposite material analogous to the sea cucumber dermis. Nanocomposites are products of nanotechnology that involve the insertion of nanoparticles into macroscopic materials. This can alter the function or diversity of the macroscopic material, for example by making it more conductive or, in this case, adjusting its rigidity.

The group used an elastic polymer and inserted into it a rigid cellulose nanofiber network, made up of cellulose whiskers taken from other sea creatures known as tunicates. The authors note that, once the mechanism is perfected, cellulose from renewable resources like wood and cotton could also be used. The interaction between the cellulose fibers is made through hydrogen bonds, which keep the material rigid when it is dry. When soaked in water, however, the cellulose fibers are separated as water preferentially forms hydrogen bonds with them. This causes the substance to become malleable.

Neat, right, but how does it apply to the brain? Well, currently there is a lot of interest in using intracortical microelectrode implants to measure and influence brain electrical activity. This brain pacemaker method has shown a great deal of promise in treating Parkinson's disease, pain, stroke, and spinal cord injuries, among other disorders. Unfortunately, however, with current procedures the electrode signals tend to diminish after a few months, causing the treatment to have questionable long-term usefulness. It is hypothesized that the reason the signal decays is due to the rigidity of the electrode, which damages surrounding cortical tissue, leading to the electrode’s corrosion when glial cells respond to the threat.

Thus, the authors of this study suggest the use of an electrode that resembles the nanocomposite material they designed, which could be made rigid for penetration of the outer layers of the brain, then more flexible when implanted in cortical tissue to avoid doing harm to its environment. The aqueous makeup of the cortex could be suitable to displace the hydrogen bonds made between cellulose fibers and cause the electrode to become pliable.

This is a valuable find for the promising area of deep-brain stimulation. The authors suggest its potential may extend beyond such biomedical applications if the mechanism can be designed to react to nonchemical stimuli, like electrical or optical triggers. This is where technology like body armor could be involved—flexible at one moment yet rigid and protective at the next. That type of application involves all sorts of other dimensions, however, and is a long way off. Regardless, this is quite a bit of potential to come out of an organism many people have only heard of due to its seemingly incongruous comparison to its vegetable counterpart.

Capadona, J.R., Shanmuganathan, K., Tyler, D.J., Rowan, S.J., Weder, C. (2008). Stimuli-Responsive Polymer Nanocomposites Inspired by the Sea Cucumber Dermis. Science, 319(5868), 1370-1374. DOI:10.1126/science.1153307

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