Skin-inspired hull hydrogel may sense and repel barnacles
Barnacles may seem fairly low down the list of troublemaking sea creatures, but their habit of building up on ship hulls can be the bane of a boat-owner's existence. Known as biofouling, this problem is a serious drain of time and money for the Navy, and existing control methods can harm aquatic ecosystems. Now a project out of the Office of Naval Research (ONR) and MIT has developed a coating to make anti-fouling hydrogels more effective and, in future, it could actively detect and respond to their presence.
Ship hulls are designed to slice through the water smoothly, but bumps of barnacles increase drag and, as a result, a vessel's fuel consumption by as much as 40 percent. Copper oxide paints are the main line of defense used by the US Navy, and while they've proven effective in barnacle control, they tend to leach their toxins into the water. The pursuit of cleaner solutions has led to some inventive ideas over the years, including hull-scrubbing robots, paints containing antiparasitic agents, seed-inspired silicon surfaces, and materials that zap away stowaways.
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"Biofouling is a major concern for the Navy, leading to hundreds of millions of dollars a year in fuel and maintenance costs," says Dr. Steve McElvany, an ONR program manager who oversaw the study. "It's especially bad when the ship is docked in port. Barnacles like those environments and tend to accumulate rapidly, in large quantities."
With their slippery, water-absorbing and easily-spreadable nature, hydrogels may be useful to keep barnacles at bay, and in this new research the team found a way to improve their effectiveness, strength and flexibility by combining hydrogels with elastic polymers (elastomers) using the chemical bonding agent, benzophenone.
"Our approach was inspired by human skin," says Xuanhe Zhao, lead researcher on the project. "The skin has an outer epidermis that protects nerves, capillaries, muscles and organs – and keeps them from drying out, maintaining their compliance. However, we can actually stretch the hydrogel-elastomer hybrid to seven times its original length and the bond still holds. It's that strong and flexible."
Zhao previously worked on a material that removes the bacteria that attract barnacles in the first place by twitching in response to electrical stimuli, and this new project may eventually utilize a similar mechanism. The hydrogel-elastomer hybrid could potentially transport ions, allowing it to detect the presence of barnacles on the hull and fight them off with repellent enzymes pumped to the desired location through grooves in the material.
"Our main focus is helping the Navy deal with the issue of biofouling," says Zhao. "But it's also exciting to think of the other possibilities for this material. This is still very basic research, but we envision numerous potential applications and uses for hydrogels and elastomers."
Other applications the team suggests include a smart bandage made up of electronics and drugs embedded into the hybrid material. In theory, the device could watch over wounds and respond to the presence of bacteria by administering antibiotics.
Source: Office of Naval Research