www.3ders.org

Mar 30, 2016 | By Alec

Filters can be found all around us, from our cars to our coffee makers. But they have one universal quality: they get clogged eventually. But a 3D printed solution could be just around the corner, as the Professor of Biology and ichthyologist Laurie Sanderson from the College of William and Mary has a patent pending for a bio-inspired alternative. Learning from the mouth structure of filter-feeding fish (using 3D printed models), she has developed a new mechanism that prevents filter clogging by trapping particles in vortices in the fluids.

This intriguing solution is has just been covered in detail in a paper published in the journal Nature Communications, entitled Fish mouths as engineering structures for vortical cross-step filtration. Combining biomechanics, medicine and ecology into a single filtration system, Sanderson and her team studied exactly how fish retain and transport prey in their mouth – a technique that could be used to change filtration systems as we know them.

For some fish have filtering skills mankind has not yet mastered. “Since fish have been filtering particles for more than 150 million years longer than human beings, we suspected fish may have evolved filter designs that use unknown processes to remain unclogged. So we decided to investigate,” Sanderson said. While our existing filters screen particles out of a stream of fluid, these types of fish (including goldfish, menhaden and basking sharks) filter tiny cells or shrimp-like prey from the gallons of water they swallow without clogging their oral filters.

As she explains, Sanderson has essentially been working on a system that separates particles from fluids more effectively. “Just by way of example: What if you could design an oil filter that instead of clogging and needing to be changed, it would send the stream of concentrated particles in one direction and the clean oil in another?” Sanderson said of the design. “There are many cases in industry in which we need to do something quite similar to what these filter-feeding fish are doing. For example, in filtration of dairy products or fruit juices, we separate the hard parts — the fruit pulp, some of the congealed milk products — from the liquid. There is a filter, and that filter always clogs.”

And that’s where the fish come in. Sanderson has been studying fish mouths for about 30 years now, especially the “black box” of filter-feeding fish. “When you look at a live fish, the water and the particles come into this black box, and then only water exits from the sides of the head,” she said. “So — water and particles go in the mouth. Then, something mysterious happens.”

While many specialists believed that these fish essentially had a type of spaghetti strainer in their mouths, this is not what Sanderson saw when looking down with an endoscope. “We saw fluid and particles moving parallel to the filter. By the early 2000s, we had combined the endoscopy with computational fluid dynamics and realized that a diversity of fish species were using crossflow filtration. However, this just created another puzzle, because the fish crossflow filter never clogs, even though industrial crossflow filters always clog,” she says.

Joined by a team of students (Erin Roberts, Jill Lineburg and Hannah Brooks), Sanders began studying how to reverse-engineer these mouths – in part using preserved paddlefish and in part with cone-shaped 3D printed models of fish oral cavities (made from nylon). “We made our own filters by using computer-aided design (CAD) software and 3D printing to create cone-shaped plastic models of fish mouths. We covered the branchial arch “ribs” with a fine nylon mesh,” Sanderson explains. We based our physical models on paddlefish and basking sharks because their branchial arches form a series of tall ribs that are separated by deep grooves. In our models, each rib served as a backward-facing step that interacted with the crossflow of water traveling over the step.”

Using brine shrimp eggs as particles and dye to trace fluid movement, these 3D printed models helped them to discover that the unique structure of the arches in the mouths form “backward-facing steps” that created recirculation regions, behind each step. “The fish use these backward-facing steps and the resulting recirculation regions to manipulate and concentrate the particles,” she explained. This keeps the particles moving through the system without clogging.

As this system could have a revolutionary impact in industrial settings, Sanderson turned this into a fish-free filter design. The resultant crossflow filtration design (called cross-step filtration ) essentially concentrates particles, and directs and recirculates fluid flow through a structure that kind of looks like fish’s gullet. According to the designer, it can be used to separate particles in a controlled environment, and send them into any desired direction. “In theory, you could even separate different sizes out of the particle stream,” she said, “so it could send big particles in one direction and small particles in another direction."

Jason McDevitt, William & Mary’s director of technology transfer, is now working to bring this intriguing innovation to the marketplace and is very optimistic about its chances. “This is a great example of a biomimetic technology that could have significant advantages over the current state-of-the-art,” he said. “We are particularly hopeful that this technology will be commercially developed and widely used for crossflow filtration.” Importantly, they can be used on any scale, from filters for cell-sized particles to industrial pipelines. Sanderson and her lab, meanwhile, are still working with fish to gain more insight into the particle processing mechanisms inside fish mouths. It seems we can still find a lot of inspiration in nature.

 

 

Posted in 3D Printing Application

 

 

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