Silk on the Brain

On biotechnology, poetry, and worms

by Paige Parsons

Illustration by Ivan Rios-Fetchko

published September 22, 2017

The domesticated silkworm, bombyx mori, has become more human than its wild counterparts: its silken cocoon inflated to be more lucrative for the textile industry, its fibers engineered for strength, and its feeding reliant on people continually delivering chopped mulberry leaves. This coevolution with humans has unfolded over five millennia. Yet perhaps the most intimate moment in all human-silkworm relations is the present. 

In the past decade, the biotechnology industry has sought its own gains from the silkworm. With the developments of silk skin grafts, corneal implants, replacement bones, and nanosensors, biomedical interventions are integrating silk into the human body. The interface between human and silkworm has always been tangible: small interactions of human hands feeding silkworms mulberry leaves, the point of contact between silk threads and human skin. Silk filaments form protective casing for the silkworm pupae in the stillness of its final molting, but for humans, silk becomes garments; utility differs, but for both organisms the material comes to envelope the body—allowing possibilities of transformation.

Touch alone withholds the narrative or temporal aspects of the material. However, beneath the smoothness of the silken textile is the rougher subtext of its production. It takes approximately 2,000 silkworms to produce an average, industrially produced silk dress. For the wearer, the material appears exclusively as surface. The stitches of seams make human labor visible where it is forgotten, but the winding, reeling, and weaving of filament is imperceptible. 

Now, as bioengineers create transparent films from liquefied silk, that surface further obscures the fibers woven by silkworms. At the Tufts University Silk Lab, bioengineer Fiorenzo Omenetto is leading a team of researchers creating optical biosensors that can be implanted on the surface of the brain to monitor various health conditions. Silk allows doctors to monitor bacterial infections, cancer, and other conditions. The material is remarkably biocompatible and accepted by the body in sensitive places. It is even capable of biodegrading within the body without causing harm. 

Just as silk textile manufacturers have always done, the first step is to boil the cocoon, undoing the binding glycoprotein, sericin (though in the lab, the worm is cut out of the cocoon instead of boiled alive). Rather than reeling the fibers into thread, the bioengineers purify the silk further with a lithium bromide solution. The clear liquid is then sucked into a syringe and, depending on what biological properties the sensor needs to pick up, is deployed into a variety of protein combinations. This process is relatively fast, simple, and inexpensive compared to the production of other materials used for medical implants. 

The sensors communicate information optically through a soft-lithography process called nano-imprinting. The silk protein can be combined with another protein or enzyme in order to target a specific molecule—oxygen, for example—which can then be measured using an electron beam. The oxygen will interact with the nanoimprint in such a way that the sensor transmits information through the photodetection process. The nanoimprint can take on any shape. At first, the lab used the Tufts logo. Then a poet named Jen Bervin intervened in the process. Typically working at the intersection of text and textile, Bervin saw the use of the university symbol as a grave “content gap.” She claimed the logo left out the importance of the relationship between patient and the device entering their head. In her poetry, Bervin endeavors to close the gap, synthesizing the words to the silk’s 5,000 year history: “The poem addresses the patient from the point of view of the silkworm, and, suddenly, the animal from which this material derives becomes important again.”

With the imprint of the poem, the sensor itself enfolds deep historical time, beginning with the first silkworm cultivation in the Zheijiang Province of China as early as 5000 B.C. The beginnings of the relationship can be traced in myth to a chance encounter between an empress and a cocoon. Bervin’s silkworm narrates: “UNDER A MULBERRY TREE IN A TEACUP RESTING LIGHTLY IN THE HAND OF THE EMPRESS XILINGSHI A BRINE UNFURLS.” Silk expanded from a regional good to a global commodity, weaving together networks of places and people with diplomacy, goods, and ideas. Literary scholar Tamara Chin argues that the concept of the Silk Road, with its place in our historical narrative of globalization, makes human agency in planetary processes visible. She argues that mapping this network has always been an exercise in “humanity’s collective self-awareness of ‘forming one body with the planet itself’” rather than maximized commodity flow.

This gargantuan scaling-up elucidates the full view of the silkworm-human relationship. As Bervin tells it, a matrix-like formation surfaces across scales: the Silk Road trade routes wove East and West, the weft threads wind left to right as they interlace with the vertical warp threads, and the silkworm spins its cocoon by travelling back and forth in a figure-eight. This pattern continues to the molecular level, as one of the silk DNA structures, the beta sheet, forms a lattice-structure. Silk as connective tissue takes material and poetic form.

Bervin plays with this further by composing poetic lattices known as boustrophedons, an ancient Greek form that consists of a series of reversals, where each line is read in the opposite direction. On the sensor itself, the poem will be imprinted in the pattern a silkworm winds its filament, which stands anachronistically in the face of the liquefied silk of the sensor’s base. The actual imprint will be too small for human eyes to read, yet its presence on the sensor allows poetry into an internal place. 

Despite the expansive role bombyx mori inhabits in the human world as a species, the vitality of the animal is treated as disposable. The pupae undergoes five stages of molting, after which the cocoon is taken before the metamorphosed adult moth can emerge. Emergence permitted, the silkworm moth goes on to live another three weeks, in which it may lay hundreds of eggs; as Bervin writes, “THEY SAY I HAVE A SHORT LIFE BUT I HAVE AN EVEN SHORTER DEATH I HAVE SO MANY IT PAINS ME IMAGINE THIS FOR 5000 YEARS DEATH COMES OR IT COMES THREE WEEKS LATER ITS THE COMING BACK THATS HARD.” Attempts to produce silk without death open up new problems. The production of ahimsa, or “peace silk,” confronts the unruliness of reproduction, as moths can lay hundreds of eggs. When the number of hatchlings vastly exceeds the feeding capacities of the cultivators, hundreds of larvae are starved. Ironically, while the lifecycle of bombyx mori is incompatible with silk cultivation, its product is completely biocompatible with the human body.

The relationship between humans and silkworms is messy and interwoven; to untangle it in order to excavate the dynamics that leave one species with fatality and the other with profit would be too vast an undertaking. Given our position, we can only grasp at the human scales and try to imagine the silkworm’s. The suffering of mass death is apparent, yet the broader experience of the organism remains opaque. Through imagination, we may try to enter their perceptual world, as Bervin does, and try to trace the relationship between species. While we can point to an incipient moment in mythological time or the archaeological record, the human desire to construct a narrative out of a chaotic world is difficult to satiate within the expansive space between species. From Bervin’s silkworm: “THAT IS HOW PEOPLE LIKE TO TELL IT. YOU KNOW THE NIGERIAN PROVERB UNTIL THE LIONS HAVE THEIR OWN HISTORIANS HISTORY WILL ALWAYS BE TOLD BY THE HUNTERS IF YOU DON’T KNOW IT, WHY NOT.” And so the human and silkworm tangle has to continue on, not fully told.

PAIGE PARSONS B’18 prefers to wear her silk live.