Shilk

Figure 3. Fabrication of more complex shrilk materials. a) Micropatterned surface topography of the fibroin covering layer of shrilk containing tightly packed rectangular lacunae created using a micromolding method (scale bar, 50 ìm). b) Higher magnification view of (a). Horizontal bands on the walls correspond to marks on the original mold used for imprinting that resulted from deep reactive-ion etching (scale bar, 5 ìm). c) Shrilk formed into a cylindrical shape that contains a structured region containing the micromolded topography shown in a and a smooth unstructured region. The white arrow indicates a defect in the fibroin protein film that reveals the underlying chitosan layer. (scale bar, 1 mm). d) Schematic of a multi-laminate design composed of three tightly bonded shrilk bilayers. e) A scanning electron microscopy image of a cross section of a microfabricated multi-laminate material with the design shown in (d) (F, fibroin layer; C, chitosan layer; scale bar, 50 ìm). 

Taking design cues from insects and shrimp, materials scientists at Harvard have created a material that’s as strong as aluminum alloy but only half the weight. The substance, dubbed “Shrilk” by its creators, is a material analog for insect cuticle--the material found in the exoskeletons of insects--and is the synthetic equivalent to one of nature’s strongest, lightest, and most interesting materials.


Insect cuticle is nature’s way of providing serious strength and protection without adding weight that would inhibit movement or flight. Moreover, it exhibits a variety of properties, often being rigid through the bulk of the insects body but flexible in the appendages and wings and elastic through joints. It is composed of specific proteins and layers of chitin, a polysaccharide polymer found in biological materials like shrimp shells.
 
That’s exactly where the researchers started. Using chitin derived from discarded shrimp shells, the team was able to mimic the mechanical and chemical interactions that make insect cuticle so remarkable between their chitin and a fibroin protein from silk, which they organized in laminar structure. The result is a thin, clear film that exhibits the same properties as real, natural insect cuticle. It’s cheap, biodegradable, and offers the strength and toughness of a metal alloy at roughly half the weight.


Potential applications include a biodegradable replacement for many plastics, making everything from trash bags to diapers to packaging more eco-friendly without sacrificing strength or integrity. The researchers from Harvard’s Wyss Institute for Biologically Inspired Engineering also envision Shrilk becoming a strong biocompatible material used in medical practice for everything from load bearing wound sutures to scaffolds for regenerative tissue therapies. Meaning that someday soon, human beings may repair their bodies with the stuff of insect exoskeletons.


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