From Biology to Technology

Bio-Inspired engineering will enable us to design novel sustainable bio-medical devices and harvest sustainable energy within the body to run these devices.

In 1954 while studying the human circulatory system Liebau observed the presence of a pumping mechanism which provided insight into the heart’s ability to circulate blood effectively despite the fact the energetics required for circulation cannot be explained by its function alone. In addition to reporting his observations Liebau was also able to demonstrate this mechanism by the construction of a simple experiment. Decades later the Gharib group, inspired by this original work and the elegant simplicity of the mechanism, began to seek an explanation to elucidate the fluid dynamics behind this relatively unappreciated form of pumping. Initially through experiments similar to those used by Liebau and later through computational models, the Gharib group has demonstrated that resonant wave based interactions gave rise to the observed pumping mechanism [1]. As a result of the dependence on the magnitude and direction of the flow on the driving frequency the pumping mechanism was renamed the impedance pump. Since then impedance pumps have been built on variety of size scales for a wide range of applications [2-3].

The impedance pump concept has demonstrated huge potential to function as a modular fluid driving system for lab-on-a-chip microfluidic systems and microscale implantable devices. The micro impedance pump is valveless, and therefore is well suited to pumping sensitive biological molecules or cells which may be damaged by the presence of valves. The pump also has a number of other useful characteristics such as very high mechanical to fluid work conversion efficiency, simplicity in terms of fabrication, reliability as well as being robust; the principles of the mechanism are applicable to a wide range of geometries and size scales (cm to μm) with relatively few material limitations. As a result, micro impedance pumps have found applicability in a wide number of applications ranging from cooling of electronic circuits to biological sampling/analysis and biomedical devices for treating diseases such as glaucoma and hydrocephalus.

Simultaneously, collaboration between the Gharib and Fraser groups at Caltech on zebrafish cardiogenesis yielded conclusive evidence that the embryonic heart is a dynamic impedance pump that functions throughout morphogenesis, deriving its function from a suction mechanism that mirrors mature ventricular diastolic function. Early on, the heart is nothing more than a simple tube consisting of concentric rings of endocardium and myocardium separated by an elastic cardiac jelly. At this stage, prior to the formation of valves, the embryonic heart functions purely as a microscale impedance pump. This mechanism is different from peristaltic pumping in that it only requires excitation in a single location and the presence of reflection sites created by a mismatch in mechanical compliance or change in geometry making it much easier to implement and coordinate at the early stages of embryonic development. Unlike peristaltic pumping, increasing the frequency of excitation (holding all other parameters constant) driving an impedance pump does not result in a situation where the fluid displaced varies linearly with the frequency (as in the case of a peristaltic pump) but instead can exhibit resonant peaks or flow reversals. These findings first appeared in Science Magazine [4].

As is often the case with Nature, the observations of Liebau and the research on Zebrafish morphogenesis by the Gharib group contributed to the development of a new bioinspired concept for pumping at the microscale. In 2004, Caltech was awarded a NIH grant to develop a micro impedance pump to enhance the performance of current stent designs by further lowering the intraocular pressure aiding in the therapy as well as the recovery process. More recently, due to its low power operation, high thermodynamic efficiency and reliability, the micro impedance pump has been shown effective solution for cooling of electronic circuits. These basic principles, borrowed from Nature, have returned full circle to generate a device which shows vast potential for enhancing current biomedical and semiconductor thermal management technologies as well as many others.

Team
Derek Rinderknecht, Idit Avrahami, Laurence Loumes, Jian Lu, Arian Forouar, and Anna Hickerson

Collaborators

• Scott E. Fraser, Mary E. Dickinson, Michael Liebling
  California Institute of Technology Biological Imaging Center
  
• Freddy (Y.C.) Boey, Ma Jan, Erwin Wouterson
  Nanyang Technological Institute, Singapore
• Glaukos Corporation (Laguna Hills, CA.)

References

[1] Hickerson, A.I. and M. Gharib. On the resonance of a pliant tube as a mechanism for valveless pumping. Journal of Fluid Mechanics. 555, pg. 141-148 (2006).

[2] Hickerson, A. I., et al. Experimental study of the behavior of a valveless impedance pump. Experiments in Fluids. 38, 534-540 (2005).

[3] Rinderknecht, D., et al. A valveless micro impedance pump driven by electromagnetic actuation. J. Micromech. Microeng. 15, 861– 866 (2005).

[4] Forouhar A.S., et al. The Embryonic Vertebrate Heart Tube is a Dynamic Suction Pump. Science. 312, 751 (2006).

 

From Hydrodynamic Features of Boxfish to Aerodynamic Performance of a Mercedes-Benz Concept Car

Boxfishes are rigid-bodied marine fishes that live predominantly in shallow-water, highly energetic, tropical reef environments. Despite their ungainly appearance (2/3 to 3/4 of their bodies is encased in a bony and often ornamented carapace), boxfishes are remarkably stable and maneuverable swimmers. They are able to maintain smooth swimming trajectories with minimal pitching, rolling, and yawing even in highly turbulent waters. Moreover, they are capable of swimming rapidly (>6 body lengths s^-1), can spin around with a minimal turning radius, and can hold precise control of their positions and orientations. The Doctoral research work of Dr. Ian Bartol at Caltech and UCLA (see references 1 & 2) revealed that keel contours and other physical characteristics of the rigid carapace produce spiral vortices that are central to the boxfishes' sophisticated self-correcting mechanism. For example, when a boxfish pitches upwards in a turbulent environment, spiral flows develop and grow above the keels, with maximum vortex circulation and peak vorticity occurring at the posterior edge of the carapace. The low pressures that result from the vortices pull the back-end of the fish upwards, returning it to a level trajectory. Our research also indicates that some species of boxfishes, such as the buffalo trunkfish, have drag coefficients (C_D) < 0.1.  The characteristics of boxfishes, i.e., rigid exteriors, boxy cross sections with low C_D, high stability, and high maneuverability, lend themselves well to biomimetic design. In fact, Mercedes-Benz (reference 3) unveiled a bionic concept car in June 2005 that is based on the contours of the boxfish carapace and takes advantage of its drag reduction benefits. The Office of Naval Research, which funded our research, is applying our findings to the development of underwater robots. Understanding how fins interact with the body-induced flows to improve maneuverability is the focus of current boxfish research by our group.

Collaborators
Ian K. Bartol, Daniel Weihs, Paul W. Webb, Malcolm S. Gordon, and Jay Hove

References

(1) Hydrodynamic stability of swimming in ostraciid fishes: role of the carapace in the smooth trunkfish Lactophrys triqueter (Teleostei: Ostraciidae), Ian K. Bartol, Morteza Gharib, Daniel Weihs, Paul W. Webb, Jay Hove, and Malcolm S. Gordon, The Journal of Experimental Biology: 206, 725-744 (2003)

(2) Body-induced vertical flows: a common mechanism for self-corrective trimming control in boxfishes, Ian K. Bartol, Morteza Gharib, Paul W. Webb, Daniel Weihs, and Malcolm S. Gordon, Journal of Experimental Biology: 208, 327-344 (2005)

(3) The Mercedes-Benz Bionic Car as a Concept Vehicle (link to web DaimlerChrysler page)