Bioenergetics and mechanical actuation analysis with membrane transport experiments for use in biomimetic nastic structu
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Vishnu Baba Sundaresan Department of Mechanical Engineering, Center for Intelligent Materials and Smart Systems, Virginia Tech, Blacksburg, Virginia 24061
Victor Giurgiutiu Department of Mechanical Engineering, Laboratory for Active Materials and Smart Structures, University of South Carolina, Columbia, South Carolina 29208
Donald J. Leo Department of Mechanical Engineering, Center for Intelligent Materials and Smart Systems, Virginia Tech, Blacksburg, Virginia 24061 (Received 31 January 2006; accepted 18 April 2006)
Nastic structures are synthetic constructs capable of controllable deformation and shape change similar to plant motility, designed to imitate the biological process of nastic movement found in plants. This paper considers the mechanics and bioenergetics of a prototype nastic structure system consisting of an array of cylindrical microhydraulic actuators embedded in a polymeric plate. Non-uniform expansion/contraction of the actuators in the array may yield an overall shape change resulting in structural morphing. Actuator expansion/contraction is achieved through pressure changes produced by active transport across a bilayer membrane. The active transport process relies on ion-channel proteins that pump sucrose and water molecules across a plasma membrane against the pressure gradient. The energy required by this process is supplied by the hydrolysis of adenosine triphosphate. After reviewing the biochemistry and bioenergetics of the active transport process, the paper presents an analysis of the microhydraulic actuator mechanics predicting the resulting displacement and output energy. Experimental demonstration of fluid transport through a protein transporter follows this discussion. The bilayer membrane is formed from 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-[Phospho-L-Serine] (Sodium Salt), 1-Palmitoyl-2-Oleoyl-sn-Glycero- 3-Phosphoethanolamine lipids to support the AtSUT4 H+-sucrose cotransporter.
I. INTRODUCTION
In the plant kingdom, plants are capable of localized movement due to a biological process called nastic motion generated with the help of specialized motor cells. The motor cells cause a change in confirmation of the leaves or stem from external stimulus like sunlight or a prey as in the case of insectivorous plants.1,3 Nastic motion in plants results from osmotic pressure regulation in cellular compartments causing bulk expansion in the tissue. A nonuniform volume change throughout the
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0250 2058
J. Mater. Res., Vol. 21, No. 8, Aug 2006
tissue results in different configurations of the tissue.1 Motor cells respond to the stimulus by converting biochemical energy in sugars into mechanical. This response to an external stimulus in plants qualifies it as a biological actuator. To determine the feasibility of constructing synthetic nastic structures, the natural bioenergetic system needs to be studied to develop analytical models for determining the possible range of energy release and fluid tr
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