International. Researchers at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, develop a nontoxic, environmentally friendly paintable protein that inhibits fouling. The APL team published their results in the Journal of Coatings Technology and Research.
Antifouling coatings, which slow the growth of organisms, often rely on the toxicity of copper and small-molecule additives that act as pesticides in the water near a ship's hull.
Poisonous paints seep into seawater and destroy aquatic life. Researchers have identified active proteins, or enzymes, as potential nontoxic antifouling agents.
"Many marine animals don't want to be covered in biofouling and have evolved enzymes to protect themselves," said project leader Reid Messersmith, a molecular engineer in APL's Department of Exploratory Research and Development (REDD).
"Taking inspiration from animals, we developed an enzymatic coating that could be applied directly to surfaces," he said.
Biological scientist Ryan Baker-Branstetter, who led the enzyme and antifouling research, added that biofouling develops from bacteria that are deposited on a surface. So if the team could prevent the formation of small bacteria, larger organisms wouldn't follow.
"It's hard to get enzymes to attach to anything and stay active in the process. Bioconjugation is a technique for coupling natural biomolecules and synthetic compounds," Messersmith explained.
"There have been promising lab results proving that certain enzymes can bind to certain surfaces, but those results have not translated into real-world applications," he added.
"We wanted to create a paint bucket approach, where someone could walk around and apply the coating efficiently and effectively on a surface," Messersmith continued.
They identified an effective "linker," an agent capable of binding an enzyme to a synthetic compound.
APL researchers developed an enzyme-based polymer coating with an orthophthaldialdehyde-based linker (oPA), which is capable of binding enzymes to surfaces and doing so quickly, taking less than five minutes to form a layer of material.
The oPA-based linker maintained activity for extended periods of time in the experiments, compared to no linker and a commercially available linker.
"The first protein we painted, red fluorescent protein, established that the chemistry behind the coating system and our linker worked. This allowed us to review which proteins would effectively prevent biofouling in our latest research," Messersmith said.
To achieve efficacy and compatibility with the coating system, APL staff members opted for xylanase, a natural enzyme produced by fungi, bacteria, seaweed and many other organisms, often used in commercial baking and a mixture of complex enzymes from lysis, a molecule extracted from a fungus.
The team used a method called click chemistry, which allowed them to bond the coating without any catalyst or heat. After two months immersed in artificial seawater, the xylanase and lysis complex coatings proved to be very active, demonstrating the longevity of the material and its potential as an environmentally friendly antifouling. Surprisingly, the approach was successful on the first try.
"I've worked on a lot of projects and usually the tenth thing you try works. But it's very rare that the first approach works," Baker-Branstetter said.
"Having early success with enzymes allowed us to delve into other interesting questions, such as longevity and paint activity under a variety of environmental conditions," he said.
In addition, the team found that their coatings not only prevented bacteria from adhering to a surface, but could also eliminate bacteria that had already settled.
Beyond their antifouling potential, paintable proteins could have a variety of applications. The oPA linker can work with a wide variety of proteins because it acts on the outside of proteins without interfering with their functioning. As an example, Messersmith said this approach could be used to create a paint sensor to detect toxic gases in the air.
"Traditional sensors must analyze each toxic gas independently, but the biochemistry of the proteins that can be painted could act as an integral sensor," Messersmith said.
"The approach that can be painted can be used for a variety of different proteins, each protein performs a different function and, with this system, you could theoretically coat any protein you want," Messersmith added.
