Inspired by the tough teeth of a marine snail and the remarkable process by which they form, assistant professor David Kisailus at the University of California, Riverside is working toward building cheaper, more efficient nanomaterials. By achieving greater control over the low-temperature growth of nanocrystals, his research could improve the performance of solar cells and lithium-ion batteries, lead to higher-performance materials for car and airplane frames, and help develop abrasion-resistant materials that could be used for anything from specialized clothing to dental drills.
By diversifying and specializing over hundreds of millions of years, life on Earth has evolved an extraordinary range of materials and mechanisms (from super-adhesives that leave no residue and sophisticated GPS systems down to, arguably, the internet) that scientists and engineers don't shy away from imitating.
After investigating the structure of the mantis shrimp's club (which can take quite the beating while still maintaining its integrity), assistant professor David Kisailus set out to study another very remarkable marine animal.
The gumboot chiton is marine mollusc and the largest type of chiton. It can be up to a foot (30 cm) long and is found along the shores of the Pacific Ocean from central California to Alaska. It has a leathery upper skin, which is reddish-brown in color, leading some to give it the nickname “wandering meatloaf.”
As with most molluscs, the chiton has a specialized rasping organ called a radula, a conveyer belt-like structure that contains 70 to 80 parallel rows of teeth. Unique to this marine snail, however, are teeth containing the hardest biomineral known on Earth, magnetite, which makes the tooth literally as hard as a steel. And so, in an effort to research new, low-cost ways to produce high-performance materials, Kisailus set out to determine how the hard tooth forms.
The process, as it turns out, occurs in three separate stages. First, crystals of hydrated iron oxide (ferrihydrite) nucleate on a fiber-like substrate rich in chitin. Then, these nanocrystalline particles convert to magnetite through a solid-state transformation. Finally, the magnetite particles begin to grow along these organic fibers, yielding rods parallel to the mature teeth that make them so hard and tough.
Remarkably, the entire process occurs at room temperature, and understanding its details means researchers can now start working on using a similar method to manufacture nanomaterials. A production method mimicking the way the chiton's teeth form would bring two main advantages: firstly, by requiring much lower temperatures, it would cut costs significantly; and secondly, it would allow researchers to grow crystals with a much finer control over their size, shape and orientation, tailoring them to their specific applications.
In solar panels, the quality of the crystals being used matters a great deal. Many low-grade solar cells rely on polycrystalline silicon, which results in efficiencies of around ten percent; using high-grade monocrystalline silicon, solar cells can approach efficiencies of 17 percent – but its manufacturing process is long, laborious and expensive, requiring sustained temperatures of over 1500° C (2700° F).
Kisailus's work could lead to an even finer control over the crystals, which would bring about solar panels that cost less to produce and absorb more of the Sun's energy. Similarly, the crystals could be grown so that lithium-ion batteries would need significantly less time to recharge.
Though solar cells and battery applications are currently on the radar, the same technique could also used to develop everything from materials for car and airplane frames to abrasion resistant clothing.
A paper detailing the study was published in the journal Advanced Functional Materials.
In the video below, Kisailus describes the salient features of chiton's radula.