In this work we present the loading of cells into SU8 cages using dielectrophoresis (DEP). Simply attracting cells into the cages using positive DEP is impossible because of parasitic traps that are a result of electric field distortions produced by the cage. By implementing multiple frequencies on multiple electrodes simultaneously, one can cancel the parasitic traps. Using this technique, areas on the substrate in which dielectrophoresis takes place may now include features that would otherwise interfere with the manipulations. Numerical and experimental results are presented.

The ions present in the electrolyte in which a conjugated polymer actuator is cycled are known to affect performance. Understanding how force, response time, and strain are affected by ion size and other ion characteristics is critical to applications, but is not yet well understood. In this paper, we present the effect of alkali cation size on transport velocity and volume change in polypyrrole doped with dodecylbenzenesulfonate, PPy(DBS), which is a cation-transporting material. Volume change measured by mechanical profilometry is greatest for Li+ and decreases in order of atomic mass: Li+ > Na+ > K+ > Rb+ > Cs+. Ion transport, measured by phase front propagation experiments, is also fastest for Li+, contradicting the expectation that larger species would move more slowly.

Previously, we presented a model for ion transport in conjugated polymers during electrochemical reduction. In this paper, we will present a more advanced model that includes hole transport, which was neglected in the first-cut model. This addition takes into account the interactions between holes and cations during transport. The result is that the front between oxidized and reduced material now propagates with constant velocity, instead of slowing down over time. Also, an electrolyte layer has been added to the model, and as a result the ion concentration behind the phase front is more accurately predicted.

It is important to increase the switching speed of conjugated polymers between oxidized and reduced states for a wide range of devices, including capacitors, electrochromic displays, and actuators. In this paper, we compare the in-plane and the out-of-plane ion transport speed during electrochemical reduction of a conjugated polymer, polypyrrole doped with dodecylbenzenesulfonate. Results show that the in-plane ion transport is approximately 50 times faster than out-of-plane transport. The anisotropy is likely induced by the dodecylbenzenesulfonate, which has been shown previously to form layers parallel to the surface. An engineering method is presented to enhance the in-plane ion transport by etching pores into the polymer.

We present the concept of a MEMS kit with associated lesson plans that can be used to give students hands-on fabrication experience that is analogous to what is done in a clean room, but on a larger scale so that no expensive equipment is needed.

We describe a potentiostat designed for in situ control of MEMS actuators. This module will be integrated into cell clinics, a hybrid CMOS-MEMS biolab system-on-a-chip to confine and measure signals from individual cells. We briefly review the current status of cell clinics as it pertains to this effort. We specify the requirements of a potentiostat for this application and describe a design satisfying these requirements. The design has been fabricated in a commercially available 0.5 mm CMOS process. The fabricated chip has been successfully employed for the control of electroactive polymer films and actuators used in cell clinics.

A compliant electrode material is presented that was inspired by the electroding process used to manufacture ionic polymer-metal composites (IPMCs). However, instead of an ion-exchange membrane, a UV-curable acrylated urethane elastomer is employed. The electrode material consists of the UV-curable elastomer (Loctite 3108) loaded with tetraammineplatinum(II) chloride salt particles through physical mixing and homogenization. The composite material is made conductive by immersion in a reducing agent, sodium borohydride, which reduces the salt to platinum metal on the surface of the elastomer film. Because the noble metal is mixed into the elastomer precursor as a salt, the amount of UV light absorbed by the precursor is not significantly reduced, and the composite loses little photopatternability. As a result meso-scale electrodes of varying geometries can be formed by exposing the precursor/salt mixture through a mask. The materials are mechanically and electrically characterized. The percolation threshold of the composite is estimated to be 9 vol. % platinum salt, above which the compliant electrode material exhibits a maximum conductivity of 1 S/cm. The composite maintains its electrical conductivity under axial tensile strains of up to 40%.

Bilayer microactuators of gold and polypyrrole doped with dodecylbenzene sulfonate, PPy(DBS), are characterized with respect to their response times and the influence of operation temperature. These parameters are needed for biomedical applications such as microvalves. To fully open and close the valves, the bilayer hinges must be able to rotate within a few seconds at body temperature. Bilayers were subjected to potential steps to switch the PPy between the oxidized and reduced states. Actuation was viewed through an optical microscope and recorded by a digital camera. The velocity profiles during reduction and oxidation follow the same trends. Two different phases of actuation can be identified. In the first phase there is rapid movement, and in the second phase the velocities slowly decrease until the position reaches steady-state. In order to investigate the effects of elevated temperature on the actuators, the operation temperature was varied stepwise from 25 °C to 55 °C. The curvature increased irreversibly by up to 45% at elevated temperatures, and the output force dropped.

We report on a custom designed system for the deposition and characterization of polypyrrole bilayer actuators. Unlike conventional commercial electrochemical cells and potentiostats, the system described in this paper has specications commensurate to its application and thus can be readily implemented using off the shelf electronic components at relatively low cost. Deposition rates and actuation are computer controlled through a standard data acquisition interface card with a program written in Matlab. We also discuss the design of the masks that are employed to fabricate the polypyrrole structures. This is accomplished through silicon compilation using the CAD software LEDIT [1] from Tanner Research. We have implemented a selection of parameterized routines in the LEDIT script language LComp that greatly reduces design turnaround time.

The transport of charged species, including both polarons/bipolarons and charge-compensating ions, occurs when conjugated polymers switch between oxidized and reduced states. However, physics-based models of the charge transport processes have not yet been developed. Previously, we presented an electrochromic device that made the path for ion transport much longer than that for electrons, ensuring that ion transport was the rate-limiting step so that the constitutive equation for ion transport could be formulated. Ion concentration profiles and velocities could be tracked by color changes. In this paper, we present the correlation between ion transport and volume change, measured in this device using a mechanical profilometer to scan height profiles during electrochemical reduction. In addition, the effects of electrolyte concentration, electrolyte temperature, film thickness, and ion barrier stiffness on ion transport velocities are explored.

We present the use of electroactive polymer actuators as components of a biolab-on-a-chip, which has potential applications in cell-based sensing.

We describe a CMOS capacitance sensor for measuring the capacitive coupling between living cells and the underlying substrate, a quantity that can be used to characterize cell adhesion strength and cell health. The capacitance sensor operates on the charge sharing principle, mapping sensed capacitance values to voltages. The sensor has been fabricated in a commercially available 0.5 mm, 2-poly 3-metal CMOS technology. Experimental results are presented for bench tests using a micropositioned electrode and in vitro tests with cells cultured directly on the chip surface. The sensor achieves an empirical distance resolution of 3 nm and capacitance resolution of 135 aF. The sensors have been successfully used for long term monitoring of cell viability in vitro.

Improving the lifetime of conjugated polymer-based devices that undergo repeated cyclic electrical stimulation, such as actuators, is important for commercialization.

Certain electroactive polymer actuators produce mechanical strains in excess of 1% under the application of a voltage. These actuator materials include conducting polymers, ionomeric polymers or IPMCs, carbon nanotube and polymernanotube composites, ferroelectric polymers and dielectric elastomer materials. The ability to generate mechanical strain in excess of 1% under voltage application differentiates electroactive polymers from other types of active materials, such as piezoelectric polymers and ceramics, which are generally limited to strains less than 1%. To date there has been no development of standardized testing methods for this class of electroactive materials. The development of standardized testing methods would create consistent metrics on which to compare actuator materials. In this work we present a set of standard testing methods for two classes of electroactive polymer actuators. Extensional actuators are defined as materials whose dominant response is expansion or contraction upon application of an electric field. Bender actuators are defined as those whose dominant response is a bending deflection upon the application of a voltage. The standardized testing method for each of these actuators contains detailed schematics of test fixtures for testing of mechanical, electrical, and electromechanical properties. The test method for each actuator type specifies the environmental conditions that must be controlled and reported for each test condition. Furthermore, methods of obtaining data and processing the results are discussed to create a consistent database of material properties and actuator performance metrics. The key properties tested in this method are the stress and strain induced by the applied voltage, material properties, and properties associated with the polymer composition. In addition, we propose the development of a standardized nomenclature and parameter definition that will facilitate analysis of published data and allow direct comparison of data between various research groups and materials developers.

There is a growing interest in developing low cost, low power, highly integrated biosensor systems to characterize individual cells for applications such as cell analysis, drug development, environmental monitoring, and medicine. In such micro-systems, it’s desirable to track individual cells in real time in order to steer cells using on-chip micro-actuators or monitor the movement of motile cells. To address this requirement, we are developing an embedded optical image sensor, called a contact imager, for imaging of a biological specimen directly coupled to the chip surface. The designed CMOS image sensor comprises an array of active pixel sensors (APS), logic and control signal generation, and readout circuits. The pixel layout has a pitch of 8.4 mm. The design was fabricated in a commercially available 0.5 ìm CMOS technology. The imager was first characterized on the bench as a normal CMOS image sensor, and then as a contact imager with microbeads (16 mm) placed directly on the chip surface. After further packaging with bio-compatible material, the chip was tested with cells cultured directly on the chip surface. Test results confirm successful detection of both beads and cells.

Polypyrrole/gold bilayer microactuators are being developed in our laboratory for biomedical applications such as microvalves. To fully open and close the valves, the bilayer hinges must be able to rotate between 0° and 180° within a few seconds against external forces. The layer thicknesses and hinge lengths must therefore be properly designed for the application. However, existing models fail to predict the correct behavior of microfabricated PPy/Au bilayer microactuators. Therefore, additional experimental data are needed to correctly forecast their performance. Bilayer actuators were fabricated with ranges of PPy thicknesses and hinge lengths. Bending angles were recorded through a stereomicroscope in the fully oxidized and reduced states. Isometric forces exerted by the hinges were measured with a force transducer, the output of which was read by a potentiostat and correlated with the applied potentials.

We describe a bioMEMS system for confining and electrically interfacing to single cells for long-term studies. The system comprises microvials that can be covered and uncovered by lids actuated by polypyrrole/gold hinges. Within each vial are integrated bio-amplifiers and/or other sensing circuits to form a biolab-on-a-chip. We have developed a process sequence for fabricating lidded microvials with actuated lids on CMOS die. Initial testing of these “cell clinics” with bovine aortic smooth muscle cells yields successful sensing of the extracellular action potentials from bovine aortic smooth muscle cells using a custom VLSI bioamplifier.

In this paper, we present a biolab-on-a-chip that integrates microstructures for capturing and culturing living cells together with electronics for in-situ measurement and characterization. The microsystem is composed of an array of cell-holding vials (150 x150x10 mm3, LxWxH) on a custom IC chip (1.5x1.5 mm2) fabricated in a commercially available 1.5 mm CMOS technology. In order to encage the cells, each vial is opened and closed by a lid (Figure 2) that is rotated by a polypyrrole/gold bilayer hinge. The hinges require only 1 V for actuation, which is compatible with the CMOS circuitry and with the cells. Inside each vial, an electrode connected to a VLSI bio-amplifier circuit will acquire electrical measurements on the cells, which are electrically isolated from the aqueous medium and other cells when the lids are closed.

We have developed a method to fabricate substrates that can fold themselves. The microstructures are actuated by an electroactive polymer, polypyrrole (PPy). A series of bilayers is defined on one surface of the substrate, and hinges are formed by etching the substrate from the back side to undercut the bilayers. A shape-morphing object is demonstrated that comprises multiple hinges. This object was able to bend both forward and backward. We are applying this technology to fabricate medical devices that operate in bio-fluids.

In this work, we investigated the electrochem. actuation of gilded polyaniline bilayers in acidic aqueous electrolytes. Gilding was found to be a useful method to ensure a uniform potential distribution across polyaniline films so that well-defined electrochemistry and electrochemical actuation could be obtained. Electrochemical actuation of gilded polyaniline bilayers was studied by means of bending and linear actuation. Actuation could be obtained by a number of electrochemical stimulation modes, including cyclic voltammetry (CV), square wave potential (SWP), and square wave current (SWC). Within the potential range of -0.2 to 0.6 V (vs Ag/AgCl), the polyaniline films expanded upon oxidn. and contracted upon reduction, which corresponds to the first redox process of polyaniline between the leucomeraldine and emaraldine oxidn. states. Actuation obtained in this potential range is related to the insertion/deinsertion of the electrolyte anion upon oxidation/reduction of polyaniline. It was found that, due to the thin thickness of the gold layer, not only fast bending actuation but also linear actuation could be achieved for the resulting gilded polyaniline bilayers. Extending the applied potential to more positive potentials, polyaniline degradation and oxidation of gold layer were observed.

The volume change that the conducting polymer polypyrrole (PPy) undergoes upon electrochem. oxidn. and redn. can be used to make microactuators. The authors have made microactuators based on a PPy/Au bilayer. These actuators have been combined with other micromachined structures to make biomedical microdevices. By using an area of bilayers, one can potentially arrest (nerve) fibers. They can also be used to close a micrometer-sized cavity with a lid. In addition, the authors demonstrate a microrobotic arm that may be developed for the manipulation of small particles.

We present the results of a study of the effect of photolithographed gratings on glass and silicon wafers on the alignment of smectic liq. crystal mols. The gratings have periods in the range of 200 nm -200 mm, and depths of up to 2 mm. We found that smectic liq. crystals align sharply along the gratings, depending on the temp. cycling method used in loading the roughness obsd. in glass gratings. The quality of the alignment is uniform in the range 664 nm-24 mm, and breaks down outside this region, setting lower and upper boundaries for gating prepn.

The results of structural measurements on smectic liquid crystal films deposited on photolithographed gratings on both glass and Si substrates are presented. These gratings have periods in the range of 664 nm-200 mm, and depths of up to 2 mm. Both Si and glass gratings are able to align the liquid crystal in the period range 664 nm -24 mm, as determined using both x-ray diffraction and optical microscopy. This result sets upper and lower boundaries for grating preparation. The results of the measurements were fit to a multilayer orientational model to determine the thickness of the observed aligned layer. The possible impact of the results on large area display packaging and preparation are discussed.

The strain field was examined in the film as a function of annealing time. The technique chosen was grazing incidence x-ray scattering. The BaTiO3 {110} and {101} reflections were monitored. A substantial relaxation of the d-spacing of planes parallel to the surface was measured after a 64 h annealing. The d-spacing of planes perpendicular to the surface remained essentially unchanged.

An optical sensor sensitive to changes in light absorption and other optical interactions, and consisting of 2 fibers twisted around each other, is described. The sensor can be used as a refractometer, is sensitive to the presence of H2O in oil, can be used to determine the amount of a solvent in oil, and might be useful in monitoring degradation of internal combustion engine oil. In addition, by surrounding the fibers with a film of solution, and observing the changes in output over time, additional information can be obtained. Used in this manner, the sensor can be used to identify specific solutions.