February 28, 2014

Got Shrilk? Insect Inspired Bioplastic. ~ Ansel Oommen

silkworm cocoon

Since their inception after World War II, synthetic plastics have left an indelible mark on society.

From cars, computers, and appliances to textiles, packaging and home insulation, their usage has only been surpassed by their notorious effect on the environment.

According to the U.S. National Park Service, plastic bottles can take up to 450 years to decompose. While they do indeed break down, plastics are not truly biodegradable. Instead, they accumulate in landfills and oceans, leaching chemicals and killing wildlife.

Several plastics, including polyvinyl chloride, phthalates and Bisphenol A, have been linked to endocrine disorders, cancers and birth defects.

But researchers from Harvard University have devised a new alternative. Javier Fernandez and Donald Ingber of Harvard’s Wyss Institute for Biologically Inspired Engineering have found their muse in the most successful of organisms: insects. With 95 percent of all animal species being six legged critters, many bugs like crickets, beetles and ants, are armored with cuticles that are not only strong, but flexible and light due to evolutionary pressures. As a result, they are a rich basis for natural plastics.

In an exceptional case of biomimicry, Fernandez and Ingber have developed a process that layers two common polymers together. Fibroin, one of the components, is a silk protein obtained from the domestic silkworm Bombyx mori. The other, chitin, is derived from shrimp shells. The product, a composite of shrimp and silk, has been aptly coined shrilk.

The key ingredients of shrilk could not be any more abundant, making the invention highly resourceful and economically viable.

The boiled silkworm pupae, once a byproduct of silk extraction, have since become a key source of dietary protein in many Asian countries such as China, Thailand and South Korea. Chitin, a waste material of the shrimp industry, is given a valuable second life.

Both polymers are then laminated into a unique molecular arrangement, imparting mechanical strength and durability.

“The process of layering shrilk is not chemical” Fernandez explains, “Except in the interface of layers. The original components (chitin and fibroin) have the same chemical composition before and after the process.”

In nature, the hardness of insect cuticles is determined by three major steps: dehydration, sclerotization and molecular arrangement. Here, Fernandez and Ingber have emulated only the former and latter processes.

“There is no schlerotization (this is a chemical reaction). The properties of shrilk are derived from a molecular arrangement, not from a molecular reaction.”

The result: a material with the strength and toughness of aluminum alloy at half the weight. The new matrix is also hydrophilic, or water-loving, allowing for its mechanical properties to change depending on how much water is involved.

Unlike traditional plastics, shrilk is fully biodegradable. In fact, chitin is a great nitrogenous fertilizer and organic fungicide.

Because of its durable yet transient nature, shrilk may find future use in the biomedical field. Foreseeable applications include surgical sutures, gauzes and a short-term scaffold for tissue implants that provides initial support and soon dissolves upon a successful graft. Amazingly, it can be molded into various complex shapes. Many more possibilities, for both internal and external treatments, are being explored.

Of course, cost is also a concern. Fernandez notes a cheaper version is currently under development.

As a bioplastic, shrilk has all the advantages of its traditional counterparts with none of the associated environmental risks.

“The plan is to replace synthetic plastics in plastic ware” hopes Fernandez.

In a world where six pack rings and garbage bags overburden our landfills, that little housefly hovering above it all may hold the key to a more sustainable future.


Data was also taken from:

David Bradley. (2012). A cuticle new composite: Biomaterials. Materials Today, 15 (1-2): 8


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Editor: Renée Picard

Photo: Mot the Barber at Flickr

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