Microstructured devices for generating electroadhesion

Abstract

Disclosed is a microstructured device (200) that utilizes Coulomb field modification of surface energy and electroadhesion to localize the device surface or levitate it relative to a target surface. The surface energy modification can be permanent or reversible, depending on whether charge is delivered to the device externally or galvanically induced on the device. Aspects of the device's microstructure induce various hydrophilic / hydrophobic interactions with the target surface. Coulomb fields can be used to enhance or decrease hydrophilic / hydrophobic interactions. In combination, the disclosed electrical microstructured devices provide a means for localizing implants within a mammalian body and further controlling cellular interactions with the implant.

Description

[Technical field]

[0001] The present disclosure relates to microstructured devices having electrical management systems that can change the state of the physical properties of the microstructured device. The present disclosure also relates to microstructured surfaces that can interact with target surfaces through electroadhesion and electrowetting by changing the surface energy of the disclosed microstructured surfaces. Additionally, electroadhesive microstructured surfaces, both embeddable surfaces and general grip enhancing surfaces, are disclosed herein. [Background technology]

[0002] It is known in the prior art that a surface can change its wetting properties by an applied electric field, known as electrowetting. Electrowetting can be understood based on the forces resulting from an applied electric field. Generally, electrowetting is utilized on hydrophobic surfaces. Usually, water approaches a sphere when placed on a hydrophobic surface, because the attractive forces between water molecules counteract gravity, which tends to flatten the water on the surface. Conversely, non-polar liquids have little self-attraction, so they can spread on a hydrophobic surface under the action of gravity. In contrast, when water is placed on a hydrophilic surface, gravity dominates and the water droplets spread, as the water is attracted to the hydrophilic surface, counteracting the tendency of the water to form a sphere by self-attraction. When a non-polar liquid is placed on a hydrophilic surface, gravity dominates, but in some cases, surface tension dominates, and it can be considered that non-polar liquids often form a sphere-like configuration on a hydrophobic surface.

[0003] In recent years, exogenous electric fields have been found to be useful in regulating cell function, for example cell migration in wound healing. There has been a steady increase in therapeutic devices and wound dressings that exploit the effects of static or dynamic electric fields, especially in bone repair. These devices use large electrodes and macroscopically uniform electric fields.

[0004] However, the disclosure provided herein relates to electric field strengths on the order of magnitude of 100 kV / m. When such electric fields are placed on large electrodes spaced macroscopically, this field strength is typically sufficient for large-scale electroporation and electrofusion of tissue. In contrast, the fields generated as described in more detail below are on the micrometer scale and therefore do not cause tissue electroporation or electrofusion. Thus, high electric field gradients are not equivalent to high energy densities on the microscale.

[0005] Those who have experimented with electroadhesion know that the forces generated in practice are much smaller than those calculated from theory. This deviation from theory is due to the fact that real materials are not perfectly homogeneous dielectrics. This heterogeneity inhibits electroadhesion if the heterogeneity is random. On the other hand, hierarchically structured heterogeneity can enhance the gripping force beyond theoretical expectations. Microstructured dielectrics combined with microstructured charge localization can be used to geometrically control electroadhesion forces. For example, the same device can both localize the device in biological tissue and direct the mobility of cells relative to the device.

[0006] Another deviation from theory is the fact that the contact between the dielectric and the target object is never perfect. As explained below, the surface microstructure can play an important role. The purpose of this disclosure is to describe the use of hierarchically microstructured surfaces, which can induce dielectric breakdown through both localized electric forces (high electric field gradients) and the formation of composite hydrophilic / hydrophobic domains known as Wenzel-Cassie interfaces. The physical contact can be greatly improved.

[0007] It should be understood that the electrostatic adhesion effect is an effect in which the total energy of two surfaces when they are separated is greater than the total energy when they are in contact. Conversely, the electrorepulsion effect is an effect in which the total energy of two surfaces when they are separated is less than the total energy when they are in contact. Although the term electrostatic adhesion is used herein to describe adhesive surfaces with high shear and peel forces, the opposite is also possible, i.e. surfaces with low shear and peel forces.

[0008] These effects due to the hierarchical arrangement of microscopic surface textures, both random and ordered, create spatial resonance effects that reinforce and amplify relatively weaker effects. In particular, spatial resonance can result in interlocking regions of highly attractive and repulsive microscopic domains at the interface between the microstructured surface and a wide variety of target surfaces.

[0009] These interlocking regions of attractive and repulsive microscopic domains allow the engineered surface to strongly adhere to a surface without causing friction or abrasion damage to the target surface. This type of engineered surface is particularly valuable in the operating room where tissue manipulation can cause friction or abrasion tissue damage, resulting in post-operative adhesions. Generally, this frictional tissue damage is not observable to the naked eye and is often ignored. Thus, many of the beneficial aspects, and therefore applications, of the microstructured electroadhesive devices herein have yet to be recognized or anticipated. Summary of the Invention

[0010] The present disclosure provides, in one embodiment, an electrical microstructured device that may include a microstructured surface and at least one electrode. The microstructured device may include at least one of a Wenzel wetting state or a Cassie wetting state that may be altered by charging the electrode, and may generate an electroadhesion state by charging the electrode.

[0011] In one embodiment, the electrical microstructured device can include at least one electroadhesion state that can cause adhesion to a target surface.

[0012] In one embodiment, an electrical microstructured device can include at least one electroadhesion state that can cause a change in the Wenzel-Cassie wetting state.

[0013] In one embodiment, an electrical microstructured device can include electroadhesion states combined with Wenzel-Cassie states that can localize the device to a target surface.

[0014] In one embodiment, the electrical microstructure transformation The device may include an electrical charge on at least one electrode that may transition at least a portion of a surface of the device from one wetted state to another wetted state.

[0015] In one embodiment, an electrical microstructured device can include charging of at least one electrode that can alter the surface energy gradient on the device.

[0016] In one embodiment, an electrical microstructured device can include the electrification of at least one electrode in combination with a hierarchical microstructure that can generate a fluidic valve state.

[0017] In one embodiment, the electrical microstructured device can include an electrical charge on at least one electrode that can transition the electrical microstructured device from at least one of a hydrophobic surface and a hydrophilic surface to at least one of a hydrophilic surface and a hydrophobic surface.

[0018] In one embodiment, the electrical microstructured device is capable of producing a wet condition comprising structured water. This may include charging at least one electrode.

[0019] In one embodiment, the electrical microstructured device can be configured to function as a braking system.

[0020] In one embodiment, the electrical microstructured device can be configured to function as a fluid / particle separation system.

[0021] In one embodiment, the electrical microstructured device can be configured such that the device can adhere to a wet non-conductive surface.

[0022] In one embodiment, the electrical microstructured device can be configured such that the device can adhere to a wettable conductive surface.

[0023] In one embodiment, the electrical microstructured device may be configured such that the device can be switched between hydrophilic and hydrophobic states, and water is removed from a portion of a wet surface as the device is passed over the wet surface.

[0024] In one embodiment, an electrical microstructured device can include a substrate having a hierarchical microstructure disposed thereon. The substrate can include a thickness in which at least one electrode can be at least partially embedded within the thickness of the substrate. The electrodes can be further connected to a charge source, the at least one electrode configured to provide a localized charge when powered by the charge source, and charging the electrodes creates an electroadhesion state.

[0025] In one embodiment, an electrical microstructured device can be configured such that a localized charge on at least one electrode generates an electric field on the micrometer scale.

[0026] In one embodiment, the electrical microstructured device may include a first electrode and a second electrode. The first and second electrodes may each be embedded within a thickness of the substrate. The first electrode may be configured to generate a positive charge and the second electrode may be configured to generate a negative charge, and the first and second electrodes may be adjacent to one another.

[0027] In one embodiment, an electrical microstructured device can include a substrate that is a dielectric.

[0028] In one embodiment, the electrical microstructured device can be configured such that a space between adjacent first and second electrodes can include an electrical insulator.

[0029] In one embodiment, the electrical microstructured device can include a plurality of electrodes that can be at least partially embedded within the thickness of the substrate and arranged in a spatially periodic pattern.

[0030] In one embodiment, an electrical microstructured device may include a hierarchical microstructure that may utilize composite pillars. The composite pillars may include at least a first microfeature and a second microfeature, and the second microfeature may be disposed about the first microfeature. In some embodiments, the composite pillars may further include a third microfeature disposed about the second microfeature, a fourth microfeature disposed about the third microfeature, and a fifth microfeature disposed about the fourth microfeature, etc.

[0031] In one embodiment, electrical microstructuring device may include a first microfeature having a height of 100 microns or less and a diameter of 20 microns or less.

[0032] In one embodiment, the electrical microstructured device can include a second microfeature having a height of 5 microns or less and a diameter of 2 microns or less.

[0033] In one embodiment, an electrical microstructured device can include a substrate having at least a portion that is hydrophobic. The electrical microstructured device can further include an electrode disposed with the hierarchical microstructure capable of changing the portion of the substrate that is hydrophobic to a portion that is hydrophilic when the electrode is charged.

[0034] In one embodiment, an electrical microstructured device can include a substrate having at least a portion that is hydrophilic. The electrical microstructured device can further include an electrode disposed with the hierarchical microstructure to change the portion of the substrate that is hydrophilic to a portion that is hydrophobic when the electrode is charged.

[0035] In one embodiment, the electrical microstructured device can include at least a portion of an electrode disposed within the first microfeature.

[0036] In one embodiment, the electrical microstructured device can include at least a portion of an electrode disposed within the second microfeature.

[0037] In one embodiment, the electrical microstructured device can include a surface having a thickness and including a hierarchical microstructure disposed thereon. The hierarchical microstructure can include a layer of metal particulates disposed thereon. Additionally, the device can include at least one electrode embedded at least partially within the thickness of the substrate and connected to a charge source, the at least one electrode configured to provide a localized charge when powered by the charge source, charging the electrode to generate an electroadhesion state.

[0038] In one embodiment, the electrical microstructured device can be configured such that the hierarchical microstructure can include a composite pillar. The composite pillar can include at least a first microfeature and a second microfeature, the second microfeature being disposed about the first microfeature.

[0039] In one embodiment, the electrical microstructured device can include metal particulates having diameters in the range of 0.1 to 1.0 microns.

[0040] In one embodiment, the electrical microstructured device can be configured such that the hierarchical microstructure includes two separate microstructure regions, a first region in which the metal particulate includes zinc and a second region in which the metal particulate includes silver.

[0041] In one embodiment, the electrical microstructured device can be configured such that the hierarchical microstructure comprises two separate microstructure regions, a first region in which the metal particulate comprises zinc and a second region in which the metal particulate comprises gold. [Brief description of the drawings]

[0042] [Figure 1] 1 is an embodiment of an electroadhesive device. [Diagram 2] 1 is an embodiment of an electrical microstructured device. [Diagram 3] 1 is an embodiment of an electrical microstructured device. [Figure 4] 1 is an embodiment of a tissue scaffold with electroselection of cell types. [Diagram 5] 1 is an embodiment of a non-contact brake utilizing a reversible Wenzel-Cassie domain. [Figure 6] 1 is an embodiment of a blood filtration device using structured water valves and charge repulsion. [Figure 7] 1 is an embodiment of a hierarchical electrical microstructured attachment device. [Figure 8] 1 is an embodiment of a four-level hierarchical arrangement of electrodes and surface microstructures on an electrical microstructure device. [Figure 9] 1 is an embodiment of a superhydrophobic / superhydrophilic conversion electrical microstructured device. [Figure 10] 1 is an embodiment of a spiral field effect electrical microstructured device. [Figure 11] 1 is an embodiment of an electroadhesive microstructured device for wet conductive surfaces. [Figure 12] 1 is an embodiment of an electroadhesive microstructured device for a non-conductive surface. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] Exemplary applications of the apparatus and method according to the present disclosure are described in this section. These examples are provided merely to add context and aid in understanding the present disclosure. Thus, it will be apparent to one skilled in the art that the present disclosure may be practiced without some or all of these specific details. In other examples, well-known process steps have not been described in detail to avoid unnecessarily obscuring the present disclosure. Other applications are possible, and the following examples should not be construed as limiting.

[0044] In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments of the present disclosure. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, but it is understood that these examples are not limiting, and that other embodiments may be used, and changes may be made without departing from the spirit and scope of the present disclosure.

[0045] As the term is used herein, "electroadhesion" refers to the attachment of two objects using electrostatic forces. Electroadhesion as described herein can enable temporary and removable adhesion between two objects using electrical control of these electrostatic forces. This electrostatic adhesion holds the two surfaces of the objects together by Coulombic attraction or by increasing the formation of Wenzel-Cassie domains between the device surface and the target surface. Wenzel-Cassie domain formation can be initiated or enhanced by increasing the surface energy of the microstructured surface.

[0046] As used herein, the term "hierarchical microstructure" when used to describe a three-dimensional plastic web, a matrix of protrusions, porosity, and any surface geometric modifications made to conform to the surface of a three-dimensional formed structure, both surfaces of which exhibit a three-dimensional pattern of the formed structure that is not readily visible to the normal human eye when the perpendicular distance between the viewer's eye and the plane of the microstructure is about 12 inches. It will be understood that a microstructure may be defined as any geometric shape and may include portions that are flat, circular, spherical, pyramidal, pillar-like, etc. The cross section of a single microfeature of a microstructure may be circular, square, triangular, circular grooved, rectangular, or other geometric shapes (including combinations thereof).

[0047] Generally, as used herein, the term "macroscopic" is used to refer to structural features or elements that are readily visible to the normal human eye when the perpendicular distance between the viewer's eye and the plane of the web is approximately 12 inches.

[0048] The present disclosure describes devices having microstructured surfaces where portions of the surface may include discrete regions of charge. In some embodiments, the charge may be applied using a charge source and discrete electrodes embedded in the surface. In some embodiments, the charge may be environmentally generated. The application or generation of charge in an embodiment may be generated by multiple and / or different sources. It will be understood that

[0049] One embodiment utilizing electroadhesion is shown in Figure 1. Electroadhesive device 100 can include a charge source 102 that can be connected to an electrode 104 embedded in a dielectric substrate 106. The charge source 102 can charge one half of the electrode 108 with a positive charge and the other half of the electrode 110 with a negative charge. When the power source is turned on, the powered electroadhesive device 100 can attract the substrate 112. When the charge source 102 is switched off, the substrate 112 and the dielectric substrate 106 can no longer be attracted to each other.

[0050] Zinc is known to generate an electrical potential when placed in a humid environment. Referring to FIG. 2, an electrical microstructured device 200 can include a flat polymer substrate 202 that can include composite pillars 204. The composite pillars 204 can be comprised of base pillars 206 and top pillars 208. The base pillars 206 can be spaced in a triangular array with a pitch 208 (center-to-center distance) of 50 microns. The base pillars 206 can have a vertical height 210 of 100 microns and a diameter 212 of 20 microns. The vertical surface of the base pillars 206 can include a triangular profile fin 214 with a width of 5 microns. The top pillars 208 can have a diameter 216 of 2 microns and a vertical height 218 of 5 microns. The top pillars 208 can be disposed on top of the base pillars 206 arranged in a triangular array with a pitch of 4 microns. In some embodiments, the base pillars 206 can be of two types, shown as Type A 220 and Type B 222. The base pillar of type A 220 may include an upper pillar 208 disposed on an upper surface thereof, and further, the upper surface 224 of the upper pillar 208 may include a zinc particulate deposit (0.1-1.0 micron diameter). The base pillar of type B 222 may include an upper pillar 208 disposed on an upper surface thereof, and further, the upper surface 224 of the upper pillar 208 may include a silver particulate deposit (0.1-1.0 micron diameter). The metal particulate may be applied using a solution that may include the polymer substrate 202, for example, a solution of ethanol and a non-crosslinked polyurethane polymer.

[0051] When the device 200 is implanted in the body, zinc can generate a voltage of -0.6 V and silver can generate a voltage of +0.2 V. The type A and B pillars 220, 222 may be spaced with a spacing between each pillar of about 30 microns, determined by the pitch measured center-to-center of each pillar minus the diameter of each pillar (50 micron pitch - 20 micron diameter), which can generate an electric field gradient of 26 kV / m. It can be seen that the adhesion force is proportional to the square of the electric field gradient.

[0052] The electroadhesive force generated may also be affected by the contact area between the electroadhesive surface and the target surface, and the polarization properties or dielectric constant of the target substrate. The contact area may be directly affected by the substrate surface texture of both surfaces, i.e., the electroadhesive surface and the target surface. Thus, the substrate surface texture may need to be taken into account when developing a microstructured surface. One way to eliminate variability due to surface texture may be to build electroadhesive aspects at multiple scales, referred to as hierarchical scaling.

[0053] The microstructured electroadhesive surfaces of the present disclosure can adhere to both conductive and insulating surfaces. The principles of generating electroadhesive forces on conductive versus insulating substrate materials are different and are further detailed herein.

[0054] Electrostatic adhesion on conductive surfaces can be based on electrostatic induction as disclosed herein, whereas electrostatic adhesion on insulating surfaces can be primarily due to electrical polarization. Modeling of electrostatic adhesion forces on conductive substrates can be approximated by theories based on parallel capacitance, i.e., coplanar capacitance. Modeling of electrostatic adhesion forces on insulating substrates can be modeled by complex dynamic polarization processes.

[0055] In the embodiment shown in FIG. 2, type A electrodes 220 and type B electrodes 222 can be exposed. The fluid interface can act as a dielectric layer between the electrodes of type A pillars 220 and type B pillars 222. If the fluid interface is substantially conductive, the electrodes can be coated with a polymer solution containing a suitable dielectric. For conductive substrates, Coulomb forces dominate when the volume resistivity of the dielectric material covering the electrodes is greater than about 10 Ω cm. In contrast, Johnsen-Rahbek forces can dominate when the volume resistivity is about 10 Ω cm to 10 Ω cm.

[0056] For conductive substrates, saturated electrostatic adhesion can be achieved quickly (typically within a second), but in some embodiments, a dynamic electrostatic attraction development process is desirable. For example, in embodiments where short-term reversibility of adhesion is desired, the porosity of the dielectric can be tailored to slow down the galvanic potential of the electrodes, thereby allowing reversibility when the development of the galvanic potential is delayed. In the embodiment shown in FIG. 2, where the electrodes are externally charged rather than galvanically, much dynamic functionality can be enabled.

[0057] The electroadhesive devices of the present disclosure can use electrostatic forces between a target surface and a microstructured electroadhesive surface at a microscopic level. In the case of Coulomb-type electrostatic surfaces, electrostatic forces can be generated by dielectric polarization due to potential differences. Based on the charge (or electrode) configuration, microstructured electroadhesive surfaces can be classified into two types: monopolar (plate-plate-capacitor) and bipolar (interdigitated electrodes). These basic electrode configurations can be arranged in various hierarchical levels. If the electrodes are externally charged, more complex mixtures of these basic electrode configurations can be possible.

[0058] 3, an externally charged electrical microstructured device 300 including a flat polymer substrate 302 may include composite pillars 304. The composite pillars may be comprised of base pillars 306 and top pillars 308. The base pillars 306 may be spaced in a triangular array with a pitch (center-to-center distance) of 50 microns. The base pillars 306 may have a vertical height of 100 microns and may have a diameter of 20 microns. Additionally, the base pillars 306 may include triangular profile fins 314 with a diameter of 5 microns. The top pillars 308 may include a diameter of 2 microns, a vertical height of 5 microns. The top pillars 308 may include a pitch of 4 microns center-to-center. In some embodiments, the top pillars 308 may be arranged in a triangular array.

[0059] In some embodiments, the base pillar 306 may include two types of pillars 320, 322. The base pillar 306 may include a type A pillar 320, which may include an upper pillar 308 arranged hierarchically thereon, and the upper surface 324 of the upper pillar 308 may include a gold layer deposited thereon. In addition, the upper pillar 308 may further include a conductor 326 that may be embedded in the substrate and traverse the hierarchical composite. The base pillar 306 may further include a type B pillar 322, which may include an upper pillar 308 arranged hierarchically thereon, and the upper surface 328 of the upper pillar 308 may include a gold layer deposited thereon. In addition, the upper pillar 308 may further include a conductor 332 that may be embedded in the substrate and traverse the hierarchical composite. In one embodiment, the flat polymer substrate 302 may include a circular layer 334 of deposited gold that may contact the conductor 336. In some embodiments, the gold layer may be coated, or may be left exposed, or may include one area that is coated and another area that is exposed.

[0060] In some embodiments, the electrode configuration can be obtained by charging the gold layer of the type A pillar and the gold layer of the type B pillar with a potential difference. In one embodiment, +0.5V on conductor 326 and -0.5V on conductor 332 generate a charge by the conductor potential difference. In another embodiment, the conductor 336 can be charged differently than the conductor that charges the gold layer(s). When the gold layers 324 and 328 generate an electric field gradient, the electrode configuration can be approximately monopolar. When the gold layers 324 and 328 are differently charged, the electrode configuration can be bipolar.

[0061] Electrode shapes and spacing as disclosed herein can work synergistically with microstructured surfaces. In some embodiments, the microstructured surfaces can be stacked hierarchically, providing the opportunity to stack electrodes in a monopolar configuration on different hierarchical levels. Within a hierarchical level, the electrodes can be further spaced apart in a bipolar configuration. With an externally applied charge, different regions of the electrical microstructured device can be monopolar and other regions bipolar.

[0062] A monopolar microstructured electroadhesive surface can generate an adhesive force. In this embodiment, one of the electrodes can contact the target surface, and the second electrode is insulated from the target surface by a dielectric layer. The target surface can be conductive such that a capacitor is formed between the electrode and the conductive target surface.

[0063] A bipolar microstructured electroadhesive surface may typically be constructed by combining electrodes of two charged regions. In this embodiment, the electrodes may be insulated from the target surface by a dielectric layer. The space between the electrodes may be filled with an electrical insulator. In the case of a microstructured device, a Wenzel-Cassie interface may be formed where an air bubble is trapped between the electrodes. The air bubble may act as an insulator. In some embodiments, the trapped material may be oil attracted by the hydrophobic substrate. When the oil is trapped, for example, between the base pillars, the oil may act as an insulator and a dielectric.

[0064] When alternating positive and negative charges are induced on adjacent electrodes and the device is placed in contact with a target surface, the electric field can generate an opposite charge on the target surface, thereby causing electrostatic adhesion between the electrodes and the induced charges on the target surface.

[0065] One important difference in the monopolar configuration is that each hierarchical level does not have to be continuous. This configuration is advantageous because the discontinuity creates a "hole" or gap between the plates. This configuration can be counterintuitive based on the prior art because the electric field can be highest in the dielectric between the two electrodes, rather than on the target surface where the device contacts.

[0066] The gap may allow the electric field to essentially "leak" through the target surface. This "leakage" may generate stronger electric fields than traditional bipolar designs because the hierarchical design allows the gap between the electrodes to be significantly reduced. The gap size may have a strong effect on the adhesion force per unit area. In this configuration, smaller gaps may be possible because the hierarchical design may allow for dielectrics with higher voltage breakdown constants compared to standard bipolar designs.

[0067] Further considerations regarding the gap size between the electrodes depend on any residual material in the gap, foreign particles, and trapped air. Due to the susceptibility of the gap to these issues, the addition of microstructures to the surface can play a key role. By designing the microstructures to have a particular juxtaposition of surface energies, it is possible to attract or repel interfacial components.

[0068] Generally, prior art techniques rely on macroscopic electrode structures, typically larger than a few millimeters. For such macroscopic designs, empirical formulas can be used to estimate electroadhesion stress and energy. However, these formulas do not hold at the microstructured level. Furthermore, There is a lack of theoretical models to clarify the relationship between adhesion and microstructural parameters disclosed herein.

[0069] Optimal design principles are not available for electroadhesive and electrorepulsion devices as used in the prior art. Some progress has been made on the problem of electrostatic levitation, but the models apply to macroscopic electrodes. When microscopic electrodes are involved, attention must be paid to optimizing the charge ratio, especially with respect to the geometric parameters of the electrodes, if the goal is to create a surface that is periodically electroadhesive and non-electroadhesive. An example would be the development of a wall-climbing robot foot surface.

[0070] The examples below may employ 4 and 5 layer hierarchical textures, although it will be appreciated that in practice any number of layers (as long as it is hierarchical) may suffice for most applications.

[0071] With respect to electrostatic adhesion on a conductive target surface, the phenomenon of electrostatic induction can occur, in which the formation of a negative charge on one side of the target conductor and a positive charge on the opposite side can be induced by an external electrostatic field generated by a charged electrode embedded in an insulator that contains a microstructured surface.

[0072] It will be understood that "conductive material" may generally refer to a material that consists of a large amount of mobile free charge carriers. In some embodiments, the moist tissue can make the concentration of free moving charge carriers as large as the number of molecules. These charges can be quickly and easily rearranged. After applying a high electric field gradient on the electrical microstructured surface / device, equal and opposite charges can be induced on the surface of the target conductive substrate. Electrostatic adhesion forces between the device and the target surface can then be formed.

[0073] In some embodiments, the electrical microstructured device can be monopolar, bipolar, and / or even tripolar. In the prior art, the dipolar design has generally been the most frequently used design in electroadhesion applications. For a Coulomb-type bipolar electrical microstructured device, the electroadhesion force between the device and the target substrate can be derived from a series of parallel connections of some ideal capacitors with a dielectric in series. Certain parameters can be given special attention to effectively generate electroadhesion forces, including the air gap between the device and the target substrate, the thickness of the dielectric, the capacitance of the dielectric material, and the capacitance of the interface between the dielectric and the target substrate surface. The total capacitance between the device and the target substrate and between the pad and the substrate can depend on the number of electrodes, the effective electroadhesion area, the dielectric constant of the interfacial volume, and the relative permittivity of the dielectric. The electroadhesion force varies as the square of the total capacitance.

[0074] Johnsen-Rahbek forces arise when an imperfect dielectric with finite volume resistivity, such as a semiconductor material, interacts with a high charge mobility target substrate. Current leakage or charge transfer can occur through the contact points between the device and the target substrate. In some embodiments, strong electrostatic attractive forces can be generated at the interface due to charge accumulation in non-contact areas. The small gap characteristics of the hierarchical microstructured surface can be responsible for these strong Johnsen-Rahbek adhesion forces.

[0075] The adhesion force of a Johnsen-Rahbek type electrical microstructure device may depend on a potential difference applied to the interface, rather than an electric field gradient applied through a dielectric layer. The Johnsen-Rahbek electrostatic attraction force is not dependent on the dielectric material between the device and the target substrate. Specific parameters that may be specified to generate these forces in a microstructured device may include the capacitance of the non-contact region, the potential difference across the interface, and the potential difference across the non-contact region. In some embodiments, a stacked hierarchical structure may be optimal for both gap and electrode configurations.

[0076] Generally speaking, the adhesion force due to the Coulomb potential is larger than the thickness of the dielectric material, especially when the interfacial gap is larger than the thickness of the dielectric material. In some embodiments, the force may be much smaller than the Johnsen-Rahbek force.

[0077] In embodiments of the annular attachment device, detachment times can be very fast when Coulombic forces are utilized. Additionally, power consumption can be reduced due to the low current leakage in the Coulombic configuration.

[0078] In some embodiments, an electrical microstructured device can include a total polarization, which includes the sum of electronic polarization, ionic polarization, orientation polarization, space charge polarization, hopping polarization, interface polarization, spontaneous polarization, and other types of polarization such as wandering polarization.

[0079] In embodiments with contacting electrical microstructured devices, orientational polarization and interfacial polarization can be responsible for the generation of electrostatic adhesion forces. The electrostatic adhesion phenomenon can be non-contact on both conductive and insulating substrates. In embodiments with non-contacting electrical microstructured devices, atomic polarization and electrical polarization can be responsible for the generation of electrostatic adhesion forces.

[0080] It should be understood that in devices of the present disclosure, electroadhesion may strengthen over time. The steady state value of adhesion may generally be much greater than the initial value. The time period to reach the steady state value may depend on various design parameters.

[0081] In embodiments involving certain unipolar electrode geometries, the electrodes may generally be arranged in a spatially periodic pattern. In general, the length of an electrode may be much greater than its width and / or thickness, and the electrode area may be much greater than the area between individual electrodes. For this reason, in some embodiments, a symmetrical pattern may be preferred.

[0082] Those skilled in the art will appreciate that various embodiments of the present disclosure include hierarchical structures. When analyzing the performance of a hierarchically structured electroadhesive device, each hierarchical scale can be considered as an additional layer, and calculations can be performed as if the device were a composite device with an effective dielectric constant. The effective dielectric constant can be evaluated by the parallel mixing rule. Calculations reveal that as the height of each hierarchical layer increases, electroadhesion can be reduced. Thus, in some embodiments, the height of the hierarchical layers may decrease as the dimension decreases, so that more layers can increase the electroadhesive properties of the device.

[0083] Some embodiments can combine electroadhesive forces with van der Waals forces of a microstructured surface to generate strong adhesive forces. Microstructures with dimensions down to the microscale or nanoscale can generate strong adhesive forces. Thus, very small structures can not only reduce the gap between the device and the target surface, but can also increase the absolute force of attraction. In one embodiment, an electroadhesive device may be capable of generating both electroadhesive and van der Waals forces.

[0084] Another parameter that may be useful is the inclusion of a semiconducting material for the insulating layer or microstructure substrate, which may improve the electrostatic clamping force at lower electric field levels. This increase in clamping force may be due to the Johnsen-Rahbek effect, which may occur at the interface between the metal electrode and the surrounding semiconducting material. Thus, the same clamping force may be achieved using lower voltages and currents when using a semiconducting insulator rather than a fully dielectric insulator.

[0085] Polyurethane is known to work well as a semiconductor material, although a variety of other materials can be used. These other semiconductor materials can typically have bulk resistivities in the range of about 107-1013 Ωm, with a more preferred range being about 109-1012 Ωm. For example, various polyurethanes, nitrile halogenated or latex rubbers, and certain silicones are suitable insulating materials for some embodiments of the disclosed electroadhesive devices. It may also be used as a edging material. One example of a material that works well is Deerfield Polyurethane PT7811.

[0086] In some embodiments, additive particles, dopants, and / or solutions may be included to enhance the electrical conductivity of an otherwise insulating polymer. These additive particles include, but are not limited to, carbon, quaternary salts, and plasticizers such as dioctyl phthalate or diisooctyl phthalate.

[0087] In one embodiment using such materials, it may be possible to achieve clamping forces of up to about 70 psi. In one embodiment utilizing a coating on the electrode rather than a complete insulating layer, the coating may be about 10-30 micrometers thick. In other embodiments, the use of semiconducting insulators may allow the use of insulating layers that may be up to 100 microns thick. In various embodiments, the insulating material may include a compliant material having an elastic modulus of less than about 1 GPa, which may facilitate better clamping.

[0088] In addition to the use of high resistance materials in some embodiments of the disclosed attachment devices, semiconducting materials with different properties may also provide advantages when applied as the electrodes themselves. In an embodiment, various polyurethanes or other materials may be used on the surface of at least one or more of the electrodes. In an embodiment having a high resistance electrode, the static dissipative conductive strip material has a surface resistivity in the range of about 0.1-1000 MΩ / □, a thickness of about 1-50 micrometers, is relatively inexpensive, readily available, and is mechanically and electrically robust. More preferably, the surface resistivity may be in the range of 1-100 MΩ / □. It is contemplated that an embodiment may include carbon particles mixed with a relatively soft polyurethane. Such polyurethane may be sprayed, dip coated, or otherwise applied to a suitable electrode surface in any suitable manner. Another alternative for the electrode material may utilize nanotubes, which may be conductive at very low loading levels. Yet another option is a graphite electrode with a thin coating as a sealing layer that may be applied by spraying or the like. An embodiment having this sealing layer may include very low carbon black loading, or none at all in some embodiments. Other options may include adding plasticizers or soft polyurethane blended in tetrahydrofuran. Diisooctyl phthalate can also be used as a polyurethane plasticizer. Various specific examples of materials that have been found to work well include Dupont 100XC10E7, Scicron ABF-300, and TMF-300 materials.

[0089] The following are embodiments that may be directed to the design of electrical microstructured surfaces. These embodiments are not meant to be exhaustive, but rather are examples of the principles disclosed to guide one in the practice of this patent.

[0090] Example 1. Tissue scaffolds with electrical selection of cell types

[0091] Biomaterials are widely used in the medical field to maintain, improve, and / or repair diseased tissues or organs. The successful integration of a biomaterial with a host tissue may depend on the underlying surface properties, as well as the quality of the host tissue and the surrounding environment. The embodiments, more fully defined below, may take advantage of these various factors to allow for better incorporation of the host tissue and the biomaterial.

[0092] 4, tissue scaffold 400 can include microstructured pillars 402 disposed on a polymer substrate 404. The microstructured pillars 402 can be arranged in rows. In some embodiments, the rows of microstructured pillars 402 can further include smaller pillars 406 disposed between two opposing rows of microstructured pillars. The opposing columns may include a spacing 408a between the two columns of about 10 microns. Additionally, the microstructured pillars 402 in the same row may be spaced 408b apart by about 10 microns. The microstructured pillars 402 may include an inner portion 410 that may include an electrode 412 along a centerline of the microstructured pillar. Some of the electrodes 412 may be electrically connected by conductors 414, 416. The conductor 414 may have a positive potential and the conductor 416 may have a negative potential, thereby creating an electric field gradient in a region 418 located between the two opposing columns of the microstructured pillars 402. The opposing columns of the microstructured pillars 402 may be positioned to create a symmetrical relationship, as shown by squares 420, 422, and 424. Within each square is a Y-shaped configuration 426 having a base 428 and a left branch 430 and a right branch 432. The left and right prongs may connect to adjacent bases as shown at 434, thereby creating a repeating pattern on the polymer substrate 404.

[0093] In some embodiments, the microstructured pillars 404 may have a circular cross-section and be about 10 microns high and about 3 microns in diameter. The smaller pillars 406 may have a circular cross-section and be about 3 microns high and about 1 micron in diameter. In one embodiment, the open area 436 of the substrate surface 404 may have a ridge 438 disposed therein, which may have a rectangular cross-section and be about 10 microns high and about 3 microns thick.

[0094] In some embodiments, cells disposed around the periphery 440 of the tissue scaffold 400 can migrate along paths 411 between opposing rows of microstructured pillars 402. In some embodiments, the Y-shaped configuration 426 can promote the formation of blood vessels by endothelial cells.

[0095] Example 2. Non-contact braking utilizing reversible Wenzel-Cassie domain formation.

[0096] 5, the braking system 500 may include a braking element 502 and a rolling element 512. The braking element 502 may include a surface including a first hierarchical level 504, a second hierarchical level 506, and a third hierarchical level 508. In some embodiments, the first hierarchical level 504 may have a square cross-section. In some embodiments, the second hierarchical level 506 may have a circular cross-section. And, in some embodiments, the third hierarchical level 508 may have a circular cross-section. In some embodiments, the braking element 502 may include two or more bearing channels 510.

[0097] In some embodiments, the rolling element 512 may include a surface that may be smooth. In other embodiments, the rolling element 512 may include a surface having microstructures disposed thereon. In some embodiments, the rolling element 512 may include a surface having both smooth and microstructured portions. In some embodiments, the rolling element may include at least two bearing channels 514. The bearing channel 510 of the braking element 502 and the bearing channel 514 of the rolling element may be aligned to create a cavity. The cavity in some embodiments may include at least one ball bearing 516. In addition, the cavity may also contain an anti-friction composition 518 that coats and / or surrounds the at least one ball bearing 516. In some embodiments, the bearing channels 510 and 514 may be located along the peripheral sides of the braking element 502 and the rolling element 512, thereby creating an interior chamber 520. In some embodiments, the interior chamber 520 may be sealed and contains a hydrophilic liquid 522 and an insoluble hydrophobic liquid 524 therein. The volumes of hydrophilic liquid 522 and insoluble hydrophobic liquid 524 may vary depending on the application. In some embodiments, there may be more volume of hydrophilic liquid 522 than insoluble hydrophobic liquid 522. In other embodiments, there may be more volume of insoluble hydrophobic liquid 524 than hydrophilic liquid 522. Also, in some embodiments, the volume of each liquid 522, 524 may be greater than the volume of insoluble hydrophobic liquid 524. The volumes may be approximately the same. Although the term "liquid" is used herein, it will be understood that the term encompasses semi-liquids, gels, viscous compositions, etc. In some embodiments, the insoluble hydrophobic liquid 524 is of a smaller volume than the hydrophilic liquid 522 and can form globules 532 while the hydrophobic liquid is disposed in the hydrophilic liquid when the braking element 500 is in motion.

[0098] Some embodiments of the rotating element 512 may include a surface including a first hierarchical level 526, a second hierarchical level 528, and a third hierarchical level 530. The first hierarchical level 526 may have a square cross-section. The second hierarchical level 528 may have a circular cross-section. The third hierarchical level may also have a circular cross-section. In some embodiments, the combined hierarchical microstructures 526, 528, and 530 may create a hydrophobic effect. Similarly, in some embodiments, the combined hierarchical microstructures 504, 506, 508 of the damping element 502 may also create a hydrophobic effect.

[0099] From a practical standpoint, one embodiment of the braking system 500 can be used such that the braking element 502 is not powered and the rotating element 512 is moving in rotation. When this occurs, the globules 532 of the hydrophobic liquid 524 can come into contact with the microstructures 528, 530 of the rotating element 512 and the microstructures 506, 508 of the braking element 502. In this embodiment, the globules 532 themselves can function as microscopic ball bearings. The hydrophilic liquid 522 can flow or move within the gaps formed between the microstructures 526 and the braking element surface, and between the microstructures 504 and the rotating element surface.

[0100] In some embodiments, the first hierarchical level 504 may include alternating electrodes 534, 536 between adjacent microstructures. The electrodes 534 may be positively charged and the electrodes 536 may be negatively charged. By applying power to the electrodes 534 and 536, the second and third hierarchical microstructures 506, 508 may be transitioned from a Cassie state to a Wenzel state. When this transition occurs, the hydrophobic liquid 524 may migrate from the second and third hierarchical microstructures 506, 508 disposed on the damping element 502 to the second and third hierarchical microstructures 528, 530 on the rotating element 512. This transition of the hydrophobic liquid may cause the rotating element 512 to enter an anchored Wenzel-Cassie state reducing its rotation. Attitude It can be produced.

[0101] Example 3. Hemofiltration device using structured water valves and charge repulsion.

[0102] Sialylated glycoproteins on the surface of red blood cells may be responsible for generating a negative electric zeta potential. Referring to FIG. 6, a blood filtration device 600 may include a surface having composite pillars disposed thereon. The composite pillars may be arranged in a hierarchical manner and may include a first pillar 602 and a second pillar 604. The second pillar 604 may be arranged in a hierarchical manner on top of the first pillar 602. In some embodiments, the composite pillars may be arranged in rows 606. In some embodiments, the rows of composite pillars may be further arranged such that a plurality of rows 608 are located adjacent to each other in parallel to form a column.

[0103] In some embodiments, each of the first pillars 602 may include an electrode 610 associated therewith. In embodiments having at least three parallel rows 608, the rows may be electrically configured such that two adjacent columns 612 may be of the same charge and a third column 614 may be of the opposite charge. For example, two adjacent columns 612 may be positively charged and a third column 614 may be negatively charged. Due to such a configuration, the space between adjacent columns 612 and 614 of opposite charge creates a structured water state 615 where the polarity of the water aligns the water molecules and may exclude particulates such as red blood cells 616. An embodiment having this or a similar configuration may result in a valve-like mechanism that may exclude particulates but allow water flow within the channel 618. Two positively charged rows of pillars 612, 620 can be subjected to sinusoidal variations in electrical potential that can attract and then pass red blood cells 616 in a direction 622 along lines of spatially varying surface energy.

[0104] In some embodiments, the inlet 624 may be configured to allow the entry of whole blood under slight pressure. The entry of whole blood through the inlet 624 may then travel along the rows and columns of the microstructured pillars. Although FIG. 6 shows an oriented surface perpendicular to gravity, it is envisioned that other embodiments may include different configurations that may be advantageous. In one embodiment, a chimney effect may be created by arranging parallel rows and columns perpendicularly. Furthermore, it may be effective to arrange the red blood cell conducting channels in the direction opposite to gravity and the filtrate conducting channels in the direction of gravity. In this opposing configuration, a chimney-drain configuration is envisioned, in which the chimney effect may be achieved by a spatially varying gradient and the drain effect may be achieved by gravity. In filtering other components of blood, such as platelets, this chimney-drain configuration may be reversed.

[0105] Example 4. Hierarchically electrical microstructured deposition devices.

[0106] 7, an electrical microstructured attachment device 700 is disclosed and may include composite pillars 702. In some embodiments, the composite pillars 702 may be flexible, and in some embodiments, the composite pillars may be rigid. In some embodiments, the composite pillars 702 may be arranged in a regular pattern or a random pattern. In certain embodiments, a random pattern of composite pillars 702 may be preferred to promote attachment of the device 700 to various microstructured surfaces. The composite pillars 702 may be of any cross-sectional shape. In some embodiments, the cross-section may be circular or elliptical. In embodiments having an elliptical cross-section, the major axes of the ellipses may be arranged randomly or in a concentric pattern.

[0107] In some embodiments, the composite pillars 702 may be comprised of a first pillar 704, on which a second pillar 706 is stacked, and on which a third pillar 708 is stacked, thereby incorporating a hierarchical structure. The first pillars 704 may be spaced apart on center over a length equal to the total height of the entire hierarchical structure. In some embodiments, the first pillars 704 may be 100-1000 microns in height. The second pillars 706 may be 35-100 microns in height. The third pillars 708 may be 1-35 microns in height. In some embodiments, the third pillars 708 may be spaced apart on center over a length equal to 0.1-1.5 times the length of the pillars 708 height.

[0108] In some embodiments, the composite pillars 702 may be disposed on a substrate 710 of the device 700. The substrate 710 may have a thickness embedded with positively charged electrodes 712 and negatively charged electrodes 714. In some embodiments, adjacent to every positively charged electrode 712 is a negatively charged electrode 714.

[0109] In some embodiments, electrostatic adhesion of device 700 to a target surface can be generated by charging electrodes 712, 714 via conductive lines 716, 718.

[0110] Example 5. Four-level hierarchical arrangement of electrodes and surface microstructures on an electrical microstructure device.

[0111] 8, a single four-level microstructure 800 is shown. In some embodiments, the microstructure 800 may be used to replace the composite pillar 702 as disclosed in Example 4. In some embodiments, the overall electrode structure of Example 4 may remain the same as the four-level microstructure 800. In one embodiment, the first microstructure 802 may be hemispherical and is disposed around the surface 810 of the device. The second microstructure 804 may be a hemispherical microstructure 802 that is disposed around the surface 810 of the device. The first microstructure 802 may be cylindrical and disposed about the first microstructure 802. The third microstructure 806 may be cylindrical and disposed about the second microstructure 804. The fourth microstructure 808 may be a circular fibrous structure and disposed about the third microstructure 806. The electrode 812 may be hemispherical and contoured to a similar geometry as the first microstructure 702. The electrode 812 may be associated with a lead 816 and may be electrically charged thereby.

[0112] Example 6. Superhydrophobic / superhydrophilic conversion electrical microstructured device.

[0113] Referring now to FIG. 9, a superhydrophobic / superhydrophilic conversion electrical microstructure device 900 is shown. FIG. 9 is divided into two sections, with the right side 902 showing the superhydrophobic state and the left side 904 showing the superhydrophilic state. The electrical microstructure device 900 may include a substrate layer 906. A first pillar 908 and a second pillar 910 may be disposed about the substrate layer 906. The first and second pillars 908, 910 may be arranged in a hierarchical manner. In some embodiments, the first pillar 908 may have a hexagonal cross section. In some embodiments, the second pillar 910 may have a circular cross section. In some embodiments, the substrate layer 906 may include a thickness at which an electrode 914 is disposed. In some embodiments, a second electrode 912 may be disposed about the second pillar 910. Additionally, in some embodiments, a final hydrophobic coating layer 916 may also be included.

[0114] In one embodiment, the second electrode 912 may be disposed near the top of the second pillar 910. The second electrode 912 may be disposed to cover the entire top surface of the second pillar 910 or may be disposed to partially cover the top surface. In one embodiment, the electrode may be of opposite charge to the first electrode 914. The first electrode 914 may be disposed within the thickness of the substrate layer 906 and may be generally located in the area between the first pillars 908. When the electrodes 912, 914 are of opposite charge, the structure has superhydrophilic properties and can achieve a Wenzel wetting state 918. When the electrodes 912, 914 are of the same charge, the structure exhibits superhydrophobic properties and can achieve a Cassie non-wetting state 920.

[0115] Example 7. Spiral field effect electrical microstructured device.

[0116] Referring now to FIG. 10, a spiral field effect electrical microstructure device 1000 is shown. In some embodiments, such a spiral structure may be useful in rapidly reversing the hydrophilic / hydrophobic state of the device. The device 1000 may be composed of a conical pillar 1002 with a ridge 1004 on the outer wall of the pillar. In one embodiment, two conical pillars 1006, 1008 may be adjacent to each other, creating a rising surface energy between them in a downward direction 1010. This rising surface energy may create a capillary force in the downward direction 1010. In some embodiments, the conical pillar 1002 may have an interior in which an electrode 1012 is disposed. In one embodiment, the electrode 1012 may be arranged in a spiral configuration. The spiral configuration may be uniform, or the spiral configuration may taper outward as the diameter of the conical pillar 1002 increases. When no power is applied to the electrode 1012, the surface may be Wenzel wetted. When power is applied to the electrode 1012, in embodiments where the electrode tapers outward, the electric field strength increases as the electrode winds tighter toward the apex of the conical pillar 1002. If two adjacent conical pillars 1006, 1008 with tapered electrodes 1016, 1018 have opposite charges, the surface energy gradient may be reversed compared to the uncharged state, resulting in a Cassie wetting state.

[0117] Example 8. Electroadhesive microstructured devices for wet conductive surfaces.

[0118] Referring now to FIG. 11, an electrical microstructure device 1100 for adhesion to a wet conductive surface is shown. The device 1100 may include a substrate layer 1102, a first pillar 1104 having a ridge 1106, a second pillar 1108, an electrode 1110, and a conductor 1112. In some embodiments, the substrate material may be hydrophilic and naturally wettable. The device 1100 may be configured such that when the device contacts a wet conductive surface, water may be rapidly wicked up as indicated by arrow 1114. The rapid wicking of water may bring the electrode 1110 in close proximity to the conductive surface 1116, greatly enhancing electrostatic adhesion of the device 1100.

[0119] Example 9. Electroadhesive microstructured devices for non-conductive surfaces.

[0120] 12, an electrical microstructured device 1200 for attachment to a wet non-conductive surface is shown. The device 1200 may include a substrate layer 1202, a first pillar 1204 having a ridge 1206, a second pillar 1208, electrodes 1210, 1212, and conductors 1214, 1216. In some embodiments, the substrate material may be hydrophilic and naturally wet. The device 1200 may be configured such that water may be rapidly wicked up when the device contacts a wet non-conductive surface. Once the water is rapidly wicked up, the electrodes 1210 may be proximate in a monopolar configuration.

[0121] Thus, while particular embodiments of the present disclosure of novel and useful microstructured field effect devices have been described, such references are not intended to be construed as limitations on the scope of the disclosure, except as set forth in the claims that follow.

Claims

1. a substrate having a hierarchical microstructure disposed thereon, the substrate having a thickness; at least one electrode at least partially embedded within the thickness of the substrate and connected to a charge source, the at least one electrode configured to provide a localized charge when powered by the charge source, wherein charging the electrode creates an electrostatic adhesion state; and Including, the hierarchical microstructure comprises a composite pillar, the composite pillar comprising at least a first microfeature and a second microfeature, the second microfeature being disposed around the first microfeature; An electrical microstructured device, wherein at least a portion of the electrode is disposed within the first microfeature.

2. The electrical microstructured device of claim 1 , wherein the localized charge on the at least one electrode generates an electric field on a micrometer scale.

3. 2. The electrical microstructured device of claim 1 , wherein the at least one electrode comprises a first electrode and a second electrode, the first and second electrodes each embedded within the thickness of the substrate, the first electrode configured to generate a positive charge and the second electrode configured to generate a negative charge, and the first and second electrodes are adjacent to one another.

4. The electrical microstructured device of claim 1 wherein the substrate is a dielectric.

5. The electrical microstructured device of claim 3 wherein a space between adjacent first and second electrodes comprises an electrical insulator.

6. 10. The electrical microstructured device of claim 1, wherein said at least one electrode further comprises a plurality of electrodes at least partially embedded within said thickness of said substrate and arranged in a spatially periodic pattern.

7. 10. The electrical microstructured device of claim 1 wherein said first microfeature has a height of 100 microns or less and a diameter of 20 microns or less.

8. 10. The electrical microstructured device of claim 1 wherein said second microfeature has a height of 5 microns or less and a diameter of 2 microns or less.

9. 10. The electrical microstructured device of claim 1 , wherein the substrate further comprises at least a portion that is hydrophobic, and the electrode is disposed with the hierarchical microstructure to transform the portion of the substrate that is hydrophobic into a portion that is hydrophilic when the electrode is charged.

10. 10. The electrical microstructured device of claim 1 , wherein the substrate further comprises at least a portion that is hydrophilic, and the electrode is disposed with the hierarchical microstructure to transform the portion of the substrate that is hydrophilic into a portion that is hydrophobic when the electrode is charged.

11. The electrical microstructured device of claim 1 , wherein at least a portion of the electrode is disposed within the second microfeature.

12. a substrate having a surface material, the substrate having a thickness and including a hierarchical microstructure disposed on the substrate, the hierarchical microstructure including a layer of metal particulates disposed on the hierarchical microstructure; at least one electrode at least partially embedded within the thickness of the substrate and connected to a charge source, the at least one electrode configured to provide a localized charge when powered by the charge source, wherein charging the electrode creates an electrostatic adhesion state; and Including, the hierarchical microstructure comprises a composite pillar, the composite pillar comprising at least a first microfeature and a second microfeature, the second microfeature being disposed around the first microfeature; An electrical microstructured device, wherein at least a portion of the electrode is disposed within the first microfeature.

13. 13. The electrical microstructured device of claim 12 wherein said first microfeature has a height of 100 microns or less and a diameter of 20 microns or less.

14. 13. The electrical microstructured device of claim 12 wherein said second microfeature has a height of 5 microns or less and a diameter of 2 microns or less.

15. The electrical microstructured device of claim 12, wherein said metal particulates have diameters in the range of 0.1 to 1.0 microns.

16. 13. The electrical microstructured device of claim 12, wherein the hierarchical microstructure further comprises two distinct microstructure regions, a first region in which the metal particulate comprises zinc and a second region in which the metal particulate comprises silver.

17. 13. The electrical microstructured device of claim 12, wherein the hierarchical microstructure further comprises two distinct microstructure regions, a first region in which the metal particulate comprises zinc and a second region in which the metal particulate comprises gold.

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