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Conducting polymer actuators and sensors utilize electrochemical reactions and associated ion transport at the polymer-electrolyte interface for their engineering function. Similarly, a bioderived active material utilizes ion transport through a protein and across a bilayer lipid membrane for sensing and actuation functions. Inspired by the similarity in ion transport process in a bilayer lipid membrane (BLM) and conducting polymers, we propose to build an integrated ionic device in which the ion transport through the protein in the bilayer lipid membrane regulates the electrolytic and mechanical properties of the conducting polymer. This article demonstrates the fabrication and characterization of a DPhPC planar BLM reconstituted with alamethicin and supported on a polypyrrole bridge measuring 100 μm × 500 μm and formed across micro-fabricated gold pads. The assembly is supported on silicon dioxide coated wafers and packaged into an electronic-ionic package for electrochemical characterization. The various ionic components in the integrated ionic device are characterized using electrical impedance spectroscopy (EIS), cyclic voltammetry (CV), and chronoamperometry (CA) measurements. The results from our experimental studies demonstrate the procedure to fabricate a rugged electro active polymer supported BLM that will serve as a platform for chemical, bioelectrical sensing and VOC detection.Copyright © 2011 by ASME

Current water desalination technologies such as reverse osmosis (RO) and nanofiltration (NF) use tortuous structures and cylindrical nanopores to reject salts by size exclusion. The selective rejection of salts dissolved in water using nanopores requires large pressure gradients across the membranes to produce reasonable flow rates. The electrical power required for generating large pressure gradients increases the operational cost for desalination and limits its application as portable units in small communities and in third-world countries. Further, recently proposed desalination methods using carbon nanotubes and nanofluidic diodes have limited lifetime due to clogging and fouling from contaminants in feed water. Thus, existing or evolving technologies are expensive, bulky and not practical where it is needed the most. In order to develop a desalination system that is not limited by the disadvantages of existing systems, this article investigates the feasibility of a novel active nanopore membrane with superior ion rejection and water transport properties. An active nanopore is a shape-changing hyperboloidal pore that is formed in a rugged electroactive composite membrane and utilizes coupled electrostatic, hydrodynamic and mechanical interactions due to reversible mechanical oscillations between the charged pore walls and dissolved ions in water for desalination. This novel approach takes advantage of the shape of the pore to create a pumping action in the hyperboloidal channel to selectively transport water molecules. In order to demonstrate the applicability of this novel concept for water desalination, the paper will use a theoretical model to model the ion rejection properties and flow rate of salt-free water through an active nanoporous membrane.Copyright © 2011 by ASME

Conducting polymers possess similarity in ion transport function to cell membranes and perform electro-chemo-mechanical energy conversion. In an in vitro setup, protein-reconstituted bilayer lipid membranes (bioderived membranes)perform similar energy conversion and behave like cell membranes. Inspired by the similarity in ionic function between a conducting polymer membrane and cell membrane, this article presents a thin-film laminated membrane in which alamethicin-reconstituted lipid bilayer membrane is supported on a polypyrrole membrane. Owing to the synthetic and bioderived nature of the components of the membrane, we refer to the laminated membrane as a hybrid bioderived membrane. In this article, we describe the fabrication steps and electrochemical characterization of the hybrid membrane. The fabrication steps include electropolymerization of pyrrole and vesicle fusion to result in a hybrid membrane; and the characterization involves electrical impedance spectroscopy, chronoamperometry and cyclic voltammetry. The resistance and capacitance of BLM have the magnitude of 4.6×109 Ω-cm2 and 1.6×10−8 F/cm2 .The conductance of alamethicin has the magnitude of 6.4×10−8 S/cm2 . The change in ionic conductance of the bioderived membrane is due to the electrical field applied across alamethicin, a voltage-gated protein and produces a measurable change in the ionic concentration of the conducting polymer substrate.Copyright © 2011 by ASME

This article continues our work to develop magnetoelectric materials as self-sensing actuators. Our research is directed at developing a two-segment cantilever device with closed-loop control. The actuator under study is fabricated as a laminated composite of the magnetostrictive material Iron-Gallium (Galfenol) and a Lead-Zirconate-Titanate piezoelectric material (PZT-5H). The mechanical and electrical characteristics of a single-segment cantilever are modeled using the equation of motion developed from variational principles in earlier work and are compared with experimental data from other groups. Additionally, parametric analysis is performed to determine the effect of varying the thickness fraction of the piezoelectric layer on the frequency response characteristics of the actuator. When applied to the dynamic behavior of the actuator, the model predicts behavior that closely resembles experimental results published by other groups. Parametric analysis of the piezoelectric layer thickness fraction indicates that the design of a magnetoelectric cantilever self-sensing actuator can be optimized by varying the thickness fraction.Copyright © 2010 by ASME

The magneto-electro-mechanical behavior of cantilevers is modeled with two novel applications in mind: micro-surgical ablation tools and larger actuators such as cutting tools for machining applications. By uniquely combining a energy based non-linear magnetostrictive model with Euler-Bernoulli structural model and a linear piezoelectric constitutive model, a modeling tool is developed to predict the deflections and electric responses of such cantilevers under different loading conditions and magnetic field. A reduced version of this model is validated with experimental data of a magnetostrictive cantilever in bending mode. Further a simple scaling law is developed to calculate the actuating forces that can be produced when the dimensions of the cantilever is changed.Copyright © 2009 by ASME

Despite great strides in materials science and control, an automated surgical tool is still in the fiction pages due to the lack of a surgical tool employing a self-sensing actuator. In an attempt to fill this void, we present magnetoelectric materials as a solution for designing surgical tools. This paper discusses our ongoing work to model the dynamics of the magnetoelectric material for use in a control loop. The surgical tool is a two-segment magnetoelectric cantilever in which one of the two magnetoelectric segments is attached to a fixed support called the base. A floating segment called the cutting tip is attached to the base using a flexible hinge. The two-segment tool is placed in a remote magnetic field to generate the cutting force in the magnetoelectric tip. Displacement in the tip generates a proportional electrical response from the piezoelectric layer and serves as the self-sensing signal. The self-sensing signal from the two segments is used for operating the tool in closed loop operation. The dynamic characterization of the magnetoelectric cantilever in bending is derived from constitutive equations for the magnetoelectric material. The strain terms in the constitutive equation is expressed using generalized coordinates in the shape function for the cantilever in bending mode. The equivalent stiffness of the magnetoelectric cantilever is derived using variational principles for calculating the tip displacement in the cantilever.Copyright © 2009 by ASME

A new mechanical actuation concept is demonstrated based on the controlled transport of fluid across semipermeable membranes. This concept is based on the pressurization of cells similar to the process that plants use to maintain homeostasis and regulate cell function. In all plant systems, the transport of ions and fluid produce localized pressure changes (called turgor pressure) that perform many cell functions, such as maintaining cell integrity and controlling plant growth. In this paper we demonstrate that the concept of fluid transport caused by protein transporters can be used to control the actuation properties of a mesoscale device. The device considered in this work consists of two chambers separated by a semipermeable membrane substrate that contains protein transporters suspended in a lipid bilayer. The protein transporters convert biochemical energy in the form of ATP into a protein gradient across the semipermeable membrane. The proton gradient, in turn, induces a flow of fluid across the porous substrate and pressurizes a closed volume. The experimental demonstration uses a directly applied gradient The pressurization of the closed volume produces a deformation in the coverplate of the chamber, thus transforming the chemical energy of the ATP into a measurable motion in the actuator. Experiments on the device demonstrate that micron-scale displacements can be induced in a millimeter-scale actuator. The time constant of the response is on the order of tens of seconds, and results clearly demonstrate that the amount of ATP and ATPase control the actuation properties of the device. To our knowledge this is the first demonstration of using natural protein transporters as the active component of a mechanical actuator.Copyright © 2006 by ASME

Plants have the ability to develop large mechanical force from chemical energy available with bio-fuels. The energy released by the cleavage of a terminal phosphate ion during the hydrolysis of bio-fuel assists the transport of ions and fluids in cellular homeostasis. Materials that develop pressure and hence strain similar to the response of plants to an external stimuli are classified as nastic materials. Calculations for controlled actuation of an active material inspired by biological transport mechanism demonstrated the feasibility of developing such a material with actuation energy densities on the order of 100kJ/m3 by Sundaresan et. al [2004]. The mathematical model for a simplified proof of concept actuator referred to as micro hydraulic actuator uses ion transporters extracted from plants reconstituted on a synthetic bilayer lipid membrane (BLM). Thermodynamic model of the concept actuator discussed in Sundaresan et. al [2005] predicted the ability to develop 5% normalized deformation in thickness of the micro-hydraulic actuator. Our experimental demonstration of controlled fluid transport through AtSUT4 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 lead silicate glass plate having an array of 50 μm holes driven by proton gradient is discussed here.Copyright © 2005 by ASME

Nastic structures are potentially high-energy density smart materials that will be capable of achieving controllable deformation and shape change due to internal microactuation that functions on principles found in the biological process of nastic motion. In plants, nastic motion is accomplished through osmotic pressure changes causing a respective increase or decrease in cell volume, thereby causing net movement. In nastic structures, osmotic pressure is increased by moving fluid from low concentration to high concentration areas by means of active transport, powered by adenosine triphosphate (ATP) hydrolysis. Power analysis involves calculating possible ranges of actuation as a result of interior pressure exchanges and hydraulic flux rates which will determine the speed of actuation. Because pressure inside the actuating cylinder is uniform, the cylinder undergoes deformation in all the three dimensions. Predicting the work-energy balance involves considering the factors that determine the total volumetric change, including cylinder wall expansion, surface bulging and stretching, and outside forces that oppose the actuation. The hydraulic flux rates determine both the force magnitude and the actuation speed. Energy analysis considers the pressure variation range needed to accomplish the desired actuation deflection, and the energy required for active transport mechanisms to move the volume of fluid into the nastic actuator. Nonlinear effects are present, as the pressure inside the actuation cylinder increases, it takes more energy for active transport to continue moving fluid into it. The chemical reaction of ATP hydrolysis supplies the energy for active transport, which is related to the ratio of the reactants, to the products, as well as to the pH level. As the pH lowers, more energy is released through ATP hydrolysis. Therefore, as pH decreases, ATP Hydrolysis releases more energy, enabling active transport to move more fluid into the actuation cylinder, thereby increasing the internal osmotic pressure and causing material deformation work and actuation.Copyright © 2005 by ASME

Biological systems such as plants produce large deformations due to the conversion of chemical energy to mechanical energy. These chemomechanical energy conversions are controlled by the transport of charge and fluid across permeable membranes within the cellular structure of the biological system. In this paper we analyze the potential for using biological transport mechanisms to produce materials with controllable actuation properties. An energetics analysis is performed to quantify the relationship between the introduction of chemical energy in the form of ATP to the resulting osmotic pressure variation within an enclosed membrane. Our analysis demonstrates that pressure variations of between 5 and 15 MPa are achievable. The pressure variations are then coupled to a finite element analysis to determine the ability of organized arrays to produce extensional and bending actuation in thin membranes. Our analysis demonstrates that internal pressure variations on the order of 10 MPa can produce actuation materials with extensional energy density on the order of 100 kJ/m3 and bending energy density on the order of 10 kJ/m3 .Copyright © 2004 by ASME