Vishnu Baba Sundaresan

Investigation on High Energy Density Materials Utilizing Biological Transport Mechanisms

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

Experimental Investigation for Chemo-Mechanical Actuation Using Biological Transport Mechanisms

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

Chemoelectrical Energy Conversion of Adenosine Triphosphate using ATPases

Biological ion transport processes in proteins have inspired the development of bio-sensors, actuators, photoelectric, and chemoelectric energy conversion devices. These bio-inspired devices use ion transport through a protein energized by biochemical reactions in the protein’s sub-units to perform their engineering function. In an effort to advance the use of biological processes in synthetic systems, a chemoelectrical energy conversion device is demonstrated in this article that uses hydrolysis of adenosine triphosphate (ATP) in ATPase enzyme to generate electrical power. The ATPase enzyme in the device is reconstituted in a bilayer lipid membrane (BLM) and supported on a porous substrate. ATP is dissolved in pH7 buffer and added to one of the chambers in this bicameral device. The transmembrane gradient established by proton transport, resulting from hydrolysis of ATP in the enzyme, is converted into electron flow in an external circuit via silver-silver chloride electrodes placed in the buffer solution on both the sides of the membrane. The chemoelectrical energy conversion of ATP is demonstrated in this article using electrical impedance spectroscopy and load characterization experiments on BLMs supported in the pore(s) of a 25% porous polycarbonate membrane and single-pore silicon nitride chip. In electrical impedance spectroscopy, the change in conductance states of the membrane quantified by specific resistance is used to demonstrate protein activity. The mean electrical impedance of the BLM with ATPase supported on a single pore silicon nitride chip drops from 7 kΩ cm2 to 250 Ω cm2 on adding ATP to one side of the membrane. This change in ionic conductance of the BLM with ATPase in the presence of ATP demonstrates protein activity in the membrane. Impedance analysis of the membranes (BLM, BLM with ATPase) supported in multi-pore polycarbonate substrate demonstrates similar trend confirming ion transport and energy conversion in the membrane. In load characterization experiments, a resistive load of known magnitude is connected to the device and voltage across the membrane and current through the circuit are measured. The current−voltage characteristics of the device resembles a constant current power source and the slope of the response represents the internal resistance of the device. The current through the membrane supported on the single pore substrate is below the range of our data acquisition equipment and hence the device with the porous polycarbonate membrane is used in load characterization experiments. This polycarbonate membrane-based device has an open-circuit voltage of 87.5(±7.5) mV with a specific power output of 1.85 μW/cm2 and an internal resistance of 30.5k(±8.5k)Ω. The theoretical maximum specific power available from the membrane supported on the multi-pore polycarbonate membrane and the single pore silicon-nitride substrate are estimated from the current−voltage response to be 7.65 and 18 μW/cm2.

Controlled fluid transport using ATP-powered protein pumps

Plants have the ability to move fluids using the chemical energy available with bio-fuels. The energy released by the cleavage of a terminal phosphate ion during the hydrolysis of a bio-fuel assists the transport of ions and fluids in cellular homeostasis. The device discussed in this paper uses protein pumps cultured from plant cells to move fluid across a membrane barrier for controllable fluid transport. This paper demonstrates the ability to reconstitute a protein pump extracted from a plant cell on a supported bilayer lipid membrane (BLM) and use the pump to transport fluid expending adenosine triphoshate (ATP). The AtSUT4 protein used in this demonstration is cultured from Arabidopsis thaliana. This protein transporter moves a proton and a sucrose molecule in the presence of an applied proton gradient or by using the energy released from adenosine triphosphates hydrolysis reaction. The BLM supporting the AtSUT4 is formed from 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-[Phospho-L-Serine] (sodium salt) (POPS), 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-Phosphoethanolamine (POPE) lipids supported on a porous lead silicate glass plate. The BLM is formed with the transporter and the ATP-phosphohydrolase (red beet ATPase) enzyme, and the ATP required for the reaction is added as a magnesium salt on one side of the membrane. The ATP hydrolysis reaction provides the required energy for transporting a proton–sucrose molecule through the protein pump. It is observed that there is no fluid transport in the absence of the enzyme and the amount of fluid transported through the membrane is dependent on the amount of enzyme reconstituted in the BLM for a fixed sucrose concentration. This demonstrates the dependence of the fluid flux on the ATP hydrolysis reaction catalyzed by the ATP-ase enzyme. The dependence of fluid flux on the amount of ATP-ase provides convincing evidence that the biochemical reaction is producing the fluid transport. The fluid flux resulting from the ATP-powered transport is observed to be higher than the rates observed with a proton concentration gradient driven transport reported in our earlier work.

Topical tissue nano-transfection mediates non-viral stroma reprogramming and rescue

Although cellular therapies represent a promising strategy for a number of conditions, current approaches face major translational hurdles, including limited cell sources and the need for cumbersome pre-processing steps (for example, isolation, induced pluripotency). In vivo cell reprogramming has the potential to enable more-effective cell-based therapies by using readily available cell sources (for example, fibroblasts) and circumventing the need for ex vivo pre-processing. Existing reprogramming methodologies, however, are fraught with caveats, including a heavy reliance on viral transfection. Moreover, capsid size constraints and/or the stochastic nature of status quo approaches (viral and non-viral) pose additional limitations, thus highlighting the need for safer and more deterministic in vivo reprogramming methods. Here, we report a novel yet simple-to-implement non-viral approach to topically reprogram tissues through a nanochannelled device validated with well-established and newly developed reprogramming models of induced neurons and endothelium, respectively. We demonstrate the simplicity and utility of this approach by rescuing necrotizing tissues and whole limbs using two murine models of injury-induced ischaemia.

Self-Healing of Ionomeric Polymers with Carbon Fibers from Medium-Velocity Impact and Resistive Heating

Self-healing materials science has seen significant advances in the last decade. Recent efforts have demonstrated healing in polymeric materials through chemical reaction, thermal treatment, and ultraviolet irradiation. The existing technology for healing polymeric materials through the aforementioned mechanisms produces an irreversible change in the material and makes it unsuitable for subsequent healing cycles. To overcome these disadvantages, we demonstrate a new composite self-healing material made from an ionomer (Surlyn) and carbon fiber that can sustain damage from medium-velocity impact and heal from the energy of the impact. Furthermore, the carbon fiber embedded in the polymer matrix results in resistive heating of the polymer matrix locally, melts the ionomer matrix around the damage, and heals the material at the damaged location. This paper presents methods to melt-process Surlyn with carbon fiber and demonstrates healing in the material through medium-velocity impact tests, resistive heating, and imaging through electron and optical microscopy. A new metric for quantifying self-healing in the sample, called width-heal ratio, is developed, and we report that the Surlyn-carbon fiber-based material under an optimal rate of heating and at the correct temperature has a width-heal ratio of >0.9, thereby demonstrating complete recovery from the damage.

CONCEPTS FOR POWER AND ENERGY ANALYSIS IN NASTIC STRUCTURES

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

Protein-based microhydraulic transport for controllable actuation

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 a 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 100 kJ/m3. 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 predicted the ability to develop 5 percent normalized deformation in thickness of the micro- hydraulic actuator. Controlled fluid transport through AtSUT4 (Proton-sucrose co-transporter 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 a porous lead silicate glass plate (50μm with 61μm pitch) was driven by proton gradient. Bulk fluid flux of 1.2 μl/min was observed for each microliter of AtSUT4 transporter suspension (16.6 mg/ml in pH7.0 medium) reconstituted on the BLM. The flux rate is observed to be dependent on the concentration of sucrose present in pH4 buffer. Flux rate of 10 μl/min is observed for 5 mM sucrose in the first 10 minutes. The observed flux scales linearly with BLM area and the amount of proteins reconstituted on the lipid membrane. This article details the next step in the development of the micro hydraulic actuator - fluid transport driven by exergonic Adenosine triphosphate (ATP) hydrolysis reaction in the presence of ATP-phosphohydrolase (red beet ATP-ase) enzyme in the reconstituted bilayer.

Dynamic characterization of elastico-mechanoluminescence towards structural health monitoring

Light emission from zinc sulfide phosphors during elastic loading (elastico-mechanoluminescence, or EML) is characterized for application in structural health monitoring. Micron-sized EML particles are dispersed in an elastomeric matrix for characterization experiments. Numerical models and experimental investigations are combined to arrive at a correlation between EML emission intensity and average stress acting on phosphor particles. A maximum luminance of 25 cd/m2 is observed from composites with a 6.25:3 phosphor–matrix weight ratio. This intensely bright EML emission is visible under indoor lighting and is attributed to efficient interfacial stress transfer between the matrix and particles facilitated by a moisture-resistant coating. EML emission is captured over 2.5 million actuation cycles and a correlation between the structural health of the elastomer and the measured EML intensity is made. A significant drop in EML emission is observed right before the onset of structural failure which enables real-time prediction and prevention.

Polypyrrole-based amperometric cation sensor with tunable sensitivity

This article presents a novel technique to quantify the kinetics of faradaic response in polypyrrole (doped with dodecylbenzenesulfonate) (PPy(DBS)) and its application in developing a cation sensor. This technique is based on the analysis of the impedance/admittance transfer function of PPy(DBS) and the representation of its reduction chronoameprometric response using system poles and residues. The results presented in this paper demonstrate that the pole of the transfer function is an intrinsic quantity and the residue corresponding to the system pole is an extrinsic quantity. The residue of the system pole for a redox-step potential is dependent on the concentration of cations and is observed to have linear dependence on electrolyte concentration (R 2 > 0.9). Thus, the residues can be used to accurately estimate the concentration of cations in an electrolyte solution and enables the use of PPy(DBS) as a high-precision cation sensor. The experimental investigation supporting this analysis demonstrates that the sensitivity of residue to concentration can be varied by equilibrating PPy(DBS) a priori in the cation containing solution of known concentration and by varying the morphology of PPy(DBS).