Nature highlights Hu's work on fluid-based gating mechanism

5/14/2015 Julia Cation

  A paper based on Assistant Professor Yuhang Hu’s postdoctoral work at Harvard University has recently been published in

Written by Julia Cation

A paper based on Assistant Professor Yuhang Hu’s postdoctoral work at Harvard University has recently been published in Nature
The paper, entitled, “Liquid-based gating mechanism with tunable multiphase selectivity and antifouling behavior,” is rooted in the fact that many natural organisms use tiny pores to regulate the flow of liquids, gases, and solids based on their environment. These so-called “flow-gating” mechanisms are also used in manmade applications such as blood filtration; the separation of oil, gas, and wastewater; and in microfluidic devices. But these synthetic mechanisms are often rigid in their ability to adjust to the material flowing through them, can become clogged during use, and are not very energy efficient.
In response, the team Hu worked with has developed a new, dynamic mechanism that can control the flow of materials through micropores, using fluid to regulate their opening and closing. This unique use of fluid mechanics could have important implications, for example, in crude oil transport, in gas/liquid separation, and in a wide variety of medical applications. 
The abstract states:
Living organisms make extensive use of micro- and nanometer-sized pores as gatekeepers for controlling the movement of fluids, vapors and solids between complex environments. The ability of such pores to coordinate multiphase transport, in a highly selective and subtly triggered fashion and without clogging, has inspired interest in synthetic gated pores for applications ranging from fluid processing to 3D printing and lab-on-chip systems. But although specific gating and transport behaviors have been realized by precisely tailoring pore surface chemistries and pore geometries, a single system capable of controlling complex, selective multiphase transport has remained a distant prospect, and fouling is nearly inevitable. Here we introduce a gating mechanism that uses a capillary-stabilized liquid as a reversible, reconfigurable gate that fills and seals pores in the closed state, and creates a non-fouling, liquid-lined pore in the open state. Theoretical modelling and experiments demonstrate that for each transport substance, the gating threshold—the pressure needed to open the pores—can be rationally tuned over a wide pressure range. This enables us to realize in one system differential response profiles for a variety of liquids and gases, even letting liquids flow through the pore while preventing gas from escaping. These capabilities allow us to dynamically modulate gas–liquid sorting in a microfluidic flow and to separate a three-phase air–water–oil mixture, with the liquid lining ensuring sustained antifouling behavior. Because the liquid gating strategy enables efficient long-term operation and can be applied to a variety of pore structures and membrane materials, and to micro- as well as macro-scale fluid systems, we expect it to prove useful in a wide range of applications.
Hu’s research focuses on new materials and phenomena emerging at the interface of mechanics and materials chemistry. Her study integrates experiment and theory, and the main areas of research include: (1) mechanics of soft materials, (2) mechanics of bio-inspired materials and structures (3) and mechanics of biomaterials. Fundamental concepts include poroelasticity, viscoelasticity, fracture, diffusion, contact mechanics, adhesion, and mechanical instability. Applications include the development of mechanical testing techniques, actuators, anti-fouling, energy efficiency, and cellular and tissue engineering.
Hu earned her bachelor’s degree in engineering mechanics from Shanghai Jiao Tong University in China in 2005; a master’s degree in civil and environmental engineering from Nanyang Technological University in Singapore in 2007; an MS in applied physics from Harvard in 2009; and a PhD in solid mechanics from Harvard in 2011. She completed her postdoctoral work in Harvard’s biomimetic lab.

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This story was published May 14, 2015.