Giant clams could inspire better biofuel processes

Giant clams in the Indian and Pacific Oceans could provide insights into improving biofuel production processes, researchers from the University of Pennsylvania (Penn) are claiming.

Alison Sweeney, an assistant professor of physics in the Penn School of Arts and Sciences, and her collaborator Shu Yang, a professor of materials science and engineering at Penn’s School of Engineering and Applied Science, are working to develop a method to use photosynthesis to enhance the efficiency of biofuel production. In doing so, they’re taking inspiration from massive tropical molluscs.

Giant clams, which can grow up to three feet long and weigh hundreds of pounds, anchor themselves to ocean coral reefs. The surfaces of these clams are iridescent, sparkling before the naked eye. The lustrous cells on the surface of the clam scatter bright sunlight, which, according to Sweeney, typically runs the risk of causing fatal damage to the cell, but the clams efficiently convert the sunlight into fuel.

Sweeney and Yang refer to the clams as “solar transformers” because they are able to absorb bright sunlight at a high rate and scatter it over a broad surface area. When the light is distributed evenly among the thick layer of algae living inside the clam, the light is quickly converted into energy.

“What those sparkly cells are doing,” Sweeney explained in the Penn statement, “is causing light to propagate very deeply into the clam tissue and spread out.”

 

Pearls of wisdom

Sweeney and Yang are working to mimic the clams by creating a material that works in a similar way.

Yang and PhD student Hye-Na Kim devised a method of synthesising nanoparticles and adding them to an emulsion – a water, oil and soapy molecule mixture called surfactants – to form microbeads. These microbeads can mimic iridocytes, the cells in the giant clams responsible for solar transforming.

If the nanoparticles are added to the oil-water emulsion and shook at the right speed, the droplet size can be controlled. After doing an optical characterisation of the beads, the researchers found that they function very similarly to the clam cells.

​​​​​​​​​​​​​​“It’s very efficient, and it’s very difficult to achieve,” Yang says. “People are trying to do this by designing nanoparticles, but you need to do a lot of synthesis and find ways to precisely control their size, shape and optical properties, which becomes complicated and expensive. Our method is both simple and inexpensive and at the same time achieves better results than all these other systems.”

 

Next steps

According to a statement from Penn, the next step is to replicate the organisation of the algae within the clams by getting the clams to grow in gel pillars. Once this has been achieved, the researchers hope to marry their artificial iridocytes and the algae before measuring the system to determine if it can produce fuel to the same high efficiencies as the giant clam.

As well as being used to enhance the efficiency of biofuel production, the innovative method could be used in solar panels for generating, storing or preventing heat to allow for better temperature control in buildings.

“It’s exciting to see the clever, non-intuitive ways that life has come up with to solve problems,” Sweeney says. “Typically, evolution is a lot more clever than human engineers, and the trick is to ask smart questions about what design problem is being solved in each evolutionary case. It’s figuring out these really clever design strategies that you wouldn’t get to from a top-down human approach.”

Supported by a grant from the National Science Foundation, the research has been published in the journal Advanced Materials.