The hard but flexible protective exoskeleton of the American lobster (Homarus americanus) has allowed the species to survive for millions of years. While scientists have studied the hard plates, or cuticles, that make up lobster armor, little attention had been given to the soft, elastic membranes that connect the plates on the underside of the tail and abdomen—until recently. In a new study, researchers investigated the structure and mechanical properties of the membranes and unraveled some of the secrets behind the lobster’s tough exterior.
A team of engineers from Sichuan University, in Chengdu, China, Harvard University, and the Massachusetts Institute of Technology obtained lobsters from Boston fish markets to serve as test subjects. After carefully removing other tissue, they soaked the lobsters’ membranous material in saline and cut small (5×20mm, or less) samples from the joints and abdomen. The samples were evaluated for chemical composition, stretched to determine tensile strength, and examined with a scanning electron microscope to determine structure.
The research revealed that the lobster membrane is a natural hydrogel, made up of 75 to 90 percent water and a small amount of chitin-protein fibers. The membranes had high strength and toughness and were completely defect-tolerant when compared with materials like natural rubber and carbon-rubber composites. “If you cut a piece of rubber half open, it can’t take any further loading,” explains corresponding author Ming Guo. “But with the lobster membrane, . . . you can cut them and still stretch them a couple of times longer.” This is due to a “multi-layer twisted [plywood-like] structure with rotating fibers” that makes lobster membranes more resilient than other hydrogels.
While the research helps explain the resilience of lobsters to attacks from predators, the authors suggest the structure of the hydrogel could act as a blueprint for the development of new synthetic materials requiring both softness and strength—such as soft body armor that would not sacrifice limb mobility for protection, or vice versa. Guo has also used the hydrogel as design inspiration for the creation of a scaffold that better protects growing cells in tissue engineering. By mimicking the microstructure of the membranes, improvements could be made to materials used in multiple industries, from robotics to the energy sector. (Acta Biomaterialia)