Shrilk is similar in strength and toughness to an aluminum alloy, but it is only half the weight. Shown here is a replica of an insect wing, which was made with the new material. Image: Wyss Institute
A biodegradable, biocompatible material that replicates the strength, toughness, and versatility of an insect cuticle could one day replace plastics in consumer products, and be used safely in medical applications.
Natural insect cuticle, such as that found in the rigid exoskeleton of a housefly or grasshopper, provides protection without adding weight or bulk. It can deflect external chemical and physical strains without damaging the insect’s internal components, while providing structure for the insect’s muscles and wings. It is so light that it doesn’t inhibit flight and so thin that it allows flexibility. Also remarkable is its ability to vary its properties, from rigid along the insect’s body segments and wings to elastic along its limb joints.
Insect cuticle is a composite of layers of chitin—a polysaccharide polymer—and protein organized in a laminar, plywood-like structure. Mechanical and chemical interactions between these materials provide the cuticle with its unique mechanical and chemical properties. By studying these complex interactions and recreating this chemistry and laminar design in the laboratory, researchers at the Wyss Institute for Biologically Inspired Engineering at Harvard University engineered a thin, clear film that has the same composition and structure as insect cuticle. The material was called Shrilk because it is composed of fibroin protein from silk and from chitin, which is commonly extracted from discarded shrimp shells.
Shrilk is similar in strength and toughness to an aluminum alloy, but it is only half the weight. It is biodegradable and can be produced at a very low cost, since chitin is readily available as a shrimp waste product. It is easily molded into complex shapes, such as tubes. By controlling the water content in the fabrication process, the researchers were able to reproduce the wide variations in stiffness, from elasticity to rigidity.
These attributes could have multiple applications as a cheap, environmentally safe alternative to plastic for trash bags, packaging, and diapers that biodegrade quickly; as biocompatible material to suture wounds; or as a scaffold for tissue regeneration.
The research was conducted by Wyss Institute postdoctoral fellow, Javier G. Fernandez, PhD, with Wyss Institute Founding Director Donald Ingber, MD, PhD. Ingber is the Judah Folkman Professor of Vascular Biology at Harvard Medical School and Children’s Hospital Boston and is a professor of bioengineering at the Harvard School of Engineering and Applied Sciences.
Harvard University, www.wyss.harvard.edu/