Microhydraulic Actuation Using Biological Ion Transporters Reconstituted on Artificial BLM
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Microhydraulic Actuation Using Biological Ion Transporters Reconstituted on Artificial BLM Vishnu Baba Sundaresan, and Donald J Leo MECHANICAL ENGINEERING DEPARTMENT, VIRGINIA TECH, BLACKSBURG, VIRGINIA, 24061 ABSTRACT Plants and animals have the natural ability to exhibit force through controlled pressurization of cellular compartments. The mechanism through which force is generated is powered by biological fuels. The process involves moving ions against an established concentration gradient expending free energy from bio-fuels like Adenosine-tri-phosphate (ATP), kinesin etc., Materials exhibiting deformation using biological processes are called Nastic materials. The functional component in mass transfer across the cell boundary is the ion transporter embedded in cell membranes. The ion transporters which are complex protein molecules, move ions and water molecules for an applied chemical or electrical stimulus. The bio-inspired microhydraulic actuator uses the same functional component in plant cells reconstituted on a planar bilayer lipid membrane (BLM) formed from purified lipids. The protein transporters pump ions and fluid into an enclosed cavity to cause deformation. The controlled fluid transport through AtSUT4 (H+ -sucrose co-transporter extracted from Arabidopsis thaliana) reconstituted on a 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-[Phospho-L-Serine] (Sodium Salt) (POPS), 1-Palmitoyl-2-Oleoyl-sn-Glycero- 3-Phosphoethanolamine (POPE) BLM on porous lead silicate glass plate driven by a proton gradient demonstrated the ability to move fluid across the membrane. This article discusses a prototype microhydraulic actuator that increases in thickness for an applied pH and sucrose concentration gradient. INTRODUCTION Actuators translate an applied stimulus into controllable force and motion. Smart actuators are actuator materials that convert the applied stimulus in a direct energy conversion step and hence are also referred to as active materials. Broad classification of active materials group them based on the energy conversion step: electro-mechanical, thermo-mechanical and chemo-mechanical devices. Electro-mechanical (piezo electric materials, electro active polymers) and thermo-mechanical devices (shape memory alloys) undergo reversible change in their lattice configuration (or) internal molecular arrangement to exhibit force and strain [6, 4]. Chemo-mechanical devices like polymer gels use the chemical energy available as concentration gradient to transport fluid across a boundary to result in volumetric expansion. Most of the naturally occurring actuators are chemo-mechanical energy conversion devices. In plants and animals, sugars are converted into the primary energy currency Adenosine tri-phosphate (ATP) and hydrolyzed at the sites where the free energy of a chemical reaction is used to move species across the cell boundary [2]. Technological advances in molecular biology has helped us to observe the biological processes at length scales smaller than ever before and replicate the same using cellu
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