Cell storage or culture device

Abstract

A biological cell holding or culturing device (20) comprises a chamber defining a fluid holding space (30) for holding a body of fluid (34) in use, and a deformable membrane (36) communicating with the fluid holding space and being manipulable by an electroactive polymer actuator device (38) to undergo a defined topological change to induce a pattern of fluid flow in the fluid by which fluid is exchanged between a sub-region (46) proximate to the deformable membrane and a sub-region (48) removed from the deformable membrane.

Description

Technical Field

[0001] The present invention relates to cell preservation or culture devices, including, for example, organ-on-a-chip cell culture devices or apparatus, or devices or apparatus for preserving or storing biological substances such as blood. Background Art

[0002] When biological cells or microorganisms grow on the surface, they consume nutrients (including dissolved gases) and excrete metabolites. In the absence of active exchange of liquid near the surface with the bulk phase liquid, only diffusion can supply nutrients from the bulk phase liquid, and only diffusion can transmit metabolites away from the surface to the bulk phase. For nutrient and metabolite exchange, diffusion is a slow and inefficient mechanism. Therefore, cell growth can be limited by this diffusion process, limiting the supply of nutrients and limiting the removal of excretion metabolites, which may be harmful (e.g., yeast cells producing ethanol on the surface) at higher concentrations. In addition, when several layers of cells are cultivated, the cells in the lower floor will encounter more and more difficulties in obtaining enough nutrients and in removing harmful metabolites.

[0003] Relevant difficulties arise when blood is donated, and / or blood is being stored, or blood is being used as a culture medium in a cell culture device. One type of cell present in the blood is a platelet (or thrombocyte). Platelets are responsible for blood coagulation, and in the body perform this function by gathering at the site of broken skin, adhering to the skin and then activating, after which they irreversibly change shape. When blood is removed from the body and stored, premature activation of platelets can be triggered unless the blood is continuously agitated. Therefore, in the absence of agitation, the activity of the blood is severely weakened, and in addition coagulation may even occur.

[0004] To prevent this from happening, the platelets must be supplied with sufficient oxygen, and sufficient carbon dioxide removed, among other things. Therefore, for example, in the case where the blood is stored in bags, each bag must be placed on a bulky shaker in a temperature-controlled storage cabinet.

[0005] It is known that platelets can be activated without agitation, particularly during transport. Shakers have been developed to continuously agitate the platelets when contained in a storage bag. However, these are bulky devices which are a burden, particularly during transport. It is also known that smooth surfaces promote activation of platelets. Therefore, the inner surface of blood bags is patterned.

[0006] Means for achieving more efficient or reliable culture or preservation of biological cells, wherein the cells are carried or otherwise surrounded by a fluid, are sought that can alleviate the problems outlined above. In particular, solutions that can provide more efficient fluid exchange of gases or other substances with cells without the need for large mechanical shakers are desirable. Summary of the invention

[0007] According to an example according to one aspect of the present invention, there is provided a biological cell preservation or culture device, comprising:

[0008] a chamber defining a fluid holding space adapted, in use, to hold a volume of fluid and adapted, in use, to hold biological cells for preservation or cultivation;

[0009] an impermeable deformable membrane disposed within the chamber or bounding a surface of the chamber;

[0010] an electroactive polymer actuator device arranged to deform the deformable membrane, wherein the membrane maintains its impermeability, the electroactive polymer actuator device being controllable to achieve a controlled change in the surface topology of the deformable membrane; and

[0011] The deformable membrane is arranged such that in use the surface topology changes to promote a pattern of fluid flow within the volume of fluid wherein fluid is exchanged between a first sub-region proximate the deformable membrane and a second sub-region distal to the deformable membrane.

[0012] Embodiments of the present invention are based on the provision of a deformable membrane driven by a device of an electroactive polymer (EAP) actuator, the device of the electroactive polymer (EAP) actuator being controllable to produce a fluid flow within a fluid, such that the fluid is exchanged between the surface and the bulk region of the fluid. In this way, nutrients or oxygen can be effectively supplied to cells or other substances disposed near or proximal to the deformable membrane, and waste can be effectively flushed away from such cells and into the bulk. This therefore helps promote cell growth (including, for example, tissue or organ growth), and therefore helps the cultivation of cells, tissues or organs. In addition, in the case of blood, this flow produces a stirring effect on the blood (particularly, blood near the deformable membrane). Thus, effective stirring is produced using a small form factor, unnoticeable and relatively low-cost solution. Activation of platelets as well as coagulation can be avoided by the device, and thus blood cells are preserved.

[0013] By biological cell preservation or culture device may be meant a device or apparatus for use in growing or culturing cells or tissues (including, for example, tissue extracted during a biopsy), including, for example, an organ-on-a-chip device or apparatus. The device may additionally or alternatively be a device or apparatus for preserving biological cells, tissues, or substances such as for preserving blood (cells), for example by preventing activation of platelets and / or coagulation of blood. The device may be used for the preservation of biological cells or tissues, such as biopsied tissue extracted during a biopsy.

[0014] The device may include a controller configured to control the electroactive polymer actuator device to achieve a controlled change in the surface topology of the deformable membrane. The controller may be provided as part of the device, or in another example, the controller may be external to the device, wherein the electroactive polymer actuator device is adapted to communicate with the external controller to allow control of the actuator device.

[0015] Throughout the following description, reference to a controller should be interpreted as a controller that may be part of the biological cell holding or culturing device or may be external to the device and in communication with the device.

[0016] Described device comprises the chamber that limits fluid holding space, and described fluid holding space is used to keep the main body of fluid in use.Therefore, chamber is suitable for keeping or sealing at least one volume of fluid in use or preventing the escape of at least one volume of fluid.Therefore, the localized main body of fluid can be consistently included by chamber, which is important for cell culture and preservation.Therefore chamber provides cell culture or preservation chamber.

[0017] The deformable membrane is arranged within the chamber, or is arranged so as to define a surface of the chamber in use, for example by forming part of a wall of the chamber, or part of a wall of at least a fluid holding space defined by the chamber. In this way, the membrane is arranged to be in direct contact with the fluid held within the chamber, so that the controlled topological changes of the membrane drive the fluid flow pattern within the fluid.

[0018] The deformable membrane may have a continuous layered form. By this may be meant that the deformable membrane is a continuous or uninterrupted membrane, such as a non-perforated or non-interrupted membrane. In this case, the membrane may form a continuous layer.

[0019] The chamber may be adapted so that the fluid flow pattern generated by the topological change is contained within the chamber. This facilitates efficient exchange of fluid between the region adjacent to the deformable membrane and the bulk phase. By retaining the fluid within the chamber, the generated fluid flow is contained within the chamber and is effectively directed to facilitate fluid exchange between the bulk phase and the membrane, rather than, for example, being directed out of the chamber, which does not facilitate efficient exchange with the bulk phase. Exchange with the bulk phase enables efficient replenishment of nutrients to biological cells located at or near the deformable membrane and efficient flushing of waste from cells at the deformable membrane.

[0020] The deformable membrane is an impermeable deformable membrane, by impermeable deformable membrane is meant a fluid impermeable membrane which is impermeable to the fluid held in the chamber in use. By impermeable is meant that the fluid cannot pass through the membrane from one side to the other. Furthermore, the membrane retains its fluid impermeability even after the membrane is deformed by the electroactive polymer device.

[0021] In particular, the fluid holding space may be defined by a single closed chamber, rather than, for example, a network of chambers.

[0022] The chamber may be a fluid-closed chamber for keeping the volume of fluid in use. By fluid closure may be meant a chamber that is fluidically sealed in use, or is a packaging chamber in use, and / or at least so closed that after deformation of the deformable membrane, the escape or departure of the fluid is prevented. Therefore, the chamber defines a closed fluid system in use.

[0023] The chamber may be closed in the sense of being fluidly isolated from any other fluid chamber or reservoir in use so as to form its own closed fluid system.The fluid closed chamber defining the fluid holding space may be an encapsulated chamber.

[0024] By providing fluid holding space as the inner area of ​​the fluid closed chamber, the fluid flow pattern can be effectively isolated or contained in the chamber itself. This provides a more effective exchange of fluid between the region adjacent to the film and the body phase of the fluid. Chambers according to these examples are preferably closed in a manner to prevent fluid from flowing out of the chamber after promoting the fluid flow pattern.

[0025] In an alternative example, the chamber may not be completely fluidically closed. In an example, the chamber may be fluidically connected to an overflow region for accommodating a portion of the total volume of the fluid that may be held in the holding space in use via an outflow gate. The outflow gate and the chamber may be shaped or arranged so that most of the fluid contained in the holding space is held therein during use. Therefore, most of the volume of the fluid may be held in the fluid holding space in use. In the case where the fluid holding space is completely filled with fluid, the overflow region may allow the deformable membrane to move into the holding space.

[0026] In an example, in use, the fluid holding space may be only partially filled with fluid to thereby leave room for accommodating displacement of the fluid within the space due to deformation of the deformable membrane.

[0027] In an example, at least a boundary wall of the chamber or fluid holding space may be flexible to allow accommodation of the displaced fluid within the space being displaced by the deformable membrane.

[0028] The ratio of the dimensions of the chamber may advantageously be selected to facilitate fluid flow that promotes efficient fluid exchange between the deformable membrane and the bulk phase. In particular, the ratio of the chamber dimension extending outwardly (i.e. in a substantially perpendicular direction) from the surface of the deformable membrane to the dimension extending transversely to the surface of the deformable membrane may be made sufficiently large to achieve fluid flow directed substantially outwardly from the membrane (into the bulk phase) as opposed to fluid flow diverted laterally. The chamber of the present invention is thus distinguished from, for example, a channel, wherein the diameter or height of the channel is typically small compared to the length.

[0029] For example, in a (non-limiting) advantageous example of the invention, the ratio of the dimension of the chamber extending outwards (i.e. substantially perpendicularly) from the deformable membrane surface to the dimension extending transversely to the deformable membrane surface may be between 1:1 and 1:20, or between 1:2 and 1:10. This may be compared, for example, with fairly typical such ratios for channel-like devices, which are typically anywhere between 1:50 and 1:500. In such cases, the fluid flow directed away from the deformable membrane is blocked by the channel boundary and thereby diverted laterally. This does not promote efficient exchange of fluid between the surface and the bulk phase.

[0030] In general, the fluid holding space should be at least suitable for holding a volume of liquid, and references to fluid should be interpreted accordingly.

[0031] By 'culture device' may generally mean a device or apparatus for promoting or supporting the growth and culture of cells, or a device or apparatus for promoting cell growth. By 'preservation device' may generally mean a device or apparatus for maintaining or preserving cells in a viable state so that they can be subsequently utilized in that viable state.

[0032] The present invention proposes a different approach from the mechanism employed, for example, in most microfluidic type systems, in which a specialized laminar flow is produced in which the fluid is driven to flow parallel to a surface or wall. In such a flow, there is little mixing between the fluid driven along the wall and the fluid further away from the wall into the bulk phase; the only exchange between these two fluid regions is by diffusion. However, as mentioned above, diffusion as a means of fluid transport of substances is slow and inefficient. The present invention differs from this approach in that the actuator device is controlled to deform the deformable membrane in a manner that causes flow in a direction away from the membrane, thereby promoting mixing and exchange of fluid (and therefore nutrients and / or waste carried by the fluid) between the membrane surface and the bulk fluid.

[0033] More specifically, embodiments of the present invention provide an actuator device operable to manipulate a deformable membrane to deform in a controlled manner to achieve a specific defined change in the surface topology of the membrane. This topological movement of the surface imparts a defined force and pressure pattern to a fluid in close proximity to the surface, thereby facilitating a specific associated fluid flow pattern within the fluid related to the specific topological change achieved. Thus, by facilitating appropriate displacement of the surface topology in the deformable membrane, a specific pattern of flow paths within the fluid can be generated in a controllable manner.

[0034] For the avoidance of doubt, by 'topology' generally means the relief pattern of a surface or the contour of a surface.

[0035] Embodiments of the present invention rely on surface topological changes that achieve sufficiently strong forces on the fluid to agitate the fluid flow pattern between the membrane surface and the bulk phase. In particular, this is possible through the use of actuator devices that employ electroactive polymers (EAPs). Electroactive polymers (EAPs) are a class of materials within the field of electrically responsive materials. EAPs can be easily fabricated into a variety of shapes that allow for easy integration into a wide variety of systems. Specific advantages of EAPs include low power, small form factor, flexibility, noiseless operation, accuracy, the possibility of high resolution, fast response times, and periodic actuation.

[0036] The use of EAPs specifically for actuator devices provides the advantageous properties of relatively large deformation and force in a small volume or thin form factor compared to conventional actuators. EAPs also provide noiseless operation, accurate electronic control, fast response, and a large range of possible actuation frequencies, such as 0–1 MHz, most typically below 20 kHz.

[0037] Due to the high strokes and forces they are able to generate in such a small form factor, EAPs are ideal for providing the functionality of deforming a deformable membrane in a controlled manner that enables a defined topological change to be achieved. The actuator device may include multiple actuator elements, or may include, for example, a single layer of actuator material that is shaped or constrained in a manner that enables a shaped actuation pattern to be generated.

[0038] According to any embodiment of the present invention, the controller may be adapted to control the actuator means so as to achieve regular or simultaneous changes in the surface topology of the membrane on a continuous basis, thereby generating a fluid flow in which the fluid is continuously or simultaneously exchanged between the first and second sub-regions. The simultaneous changes may be intermittent, but the changes in the topology (i.e., discrete displacements of the topology of the surface) occur at regular intervals on a continuous basis. By providing a continuous or continuous surface displacement, a continuous fluid flow is generated between the surface and the bulk phase, thereby ensuring a reliable exchange of nutrients and waste between the region adjacent to the membrane surface and the bulk phase of the fluid.

[0039] In an example, the deformable membrane may at least partially define or enclose the fluid holding space. The deformable membrane may form at least a portion of a closed or boundary wall of the fluid holding space. This provides an effective device because the drive electronics and interconnections of the associated actuator device can be provided on the opposite side of the surface, bringing them outside the fluid holding space, avoiding the need to fluidically protect or isolate these elements. If provided on or as part of the wall of the space, the wall can provide useful structural support for the surface and / or the actuator device.

[0040] According to one or more groups of embodiments, a topological change achieved by an actuator device under the control of a controller may include a surface deformation of a membrane directed inwardly or outwardly from a fluid holding space, wherein the inward deformation is volumetrically balanced with the outward deformation such that there is a zero net change in the volume of the fluid holding space before and after the topological change.

[0041] By 'balanced in volume' it is meant that the change in volume subtended by the deformation directed inwardly towards the fluid holding space (i.e. bulge) is made equal to the change in volume subtended by the deformation directed outwardly away from the fluid holding space (i.e. depression). Equivalently, the change in volume of the bulge directed inwardly towards the fluid holding space (from the membrane) is balanced by the change in volume of the bulge directed outwardly or away from the fluid holding space (from the membrane).

[0042] In some examples, the deformable membrane can be deformed from a first flat configuration to a second undulating (or uneven) configuration. Alternatively, the membrane surface can be deformed, for example, to move from a first undulating (or uneven) surface profile to a second different undulating profile, but wherein the net total volume of the convex and concave reliefs does not change (wherein the concave volume is negatively increased and the convex volume is positively increased, or vice versa).

[0043] The effect of this configuration is to ensure that deformation of the membrane does not affect the overall change in volume of the fluid holding space. This means that the device is able to generate fluid flow within the fluid holding space even when the space is fluidically sealed and completely filled with liquid so as to leave no air gaps into which the liquid can expand. Due to the incompressibility of the liquid, it would normally be impossible to generate fluid flow under such conditions, since in order to generate flow, a certain displacement of the boundaries of the space is necessary to provide accommodation for the fluid displaced within the bulk phase.

[0044] The novel solution provided by this set of embodiments solves this problem by controlling the surface topological changes of the membrane so that displacement at the boundaries is achieved (because the membrane at least partially defines the fluid holding space), but in a way that is volumetrically balanced so that the incompressibility of the fluid does not prevent the movement of the fluid (i.e., the changes in the surface do not reduce the total volume of the fluid holding space, which would be impossible due to the resulting resistance exerted by the fluid on the surface). In addition, the volume-balanced topological changes ensure that the total volume of the space is not increased due to the membrane topological changes, which in a closed space would result in a vacuum effect within the space, thereby exerting strong forces within the space and possibly causing significant damage to the cells being cultured or preserved therein.

[0045] The actuator device may comprise an array of actuator elements, each actuator element comprising an electroactive polymer. The array is preferably an ordered array, for example comprising linear rows or columns. However, other arrangements and configurations are of course possible, such as curved rows of elements or less ordered arrangements. Ordered arrays provide the advantage of achieving maximum flexibility in the shape of topological variations that can be produced.

[0046] In a preferred example, each actuator element may be actuatable to undergo a bending motion. The bending motion may be an out-of-plane actuation. The bending motion may thus effect an out-of-plane deformation of the deformable membrane in the region of the actuator element in a direction generally outward from the surface and inward from the volume of the fluid. In this way, where an array of such actuators is provided and so configured, a surface topology change (i.e. a change in the surface relief pattern) can be achieved.

[0047] Each actuator element may be anchored at opposite sides, such as to be actuable to undergo the bending motion. When electrically stimulated, the EAP actuator elements may typically undergo an in-plane deformation. The anchoring constrains the actuator at its edges, thereby forcing the in-plane deformation outward to achieve the bending motion.

[0048] In a specific example, the electroactive polymer actuator device may include an actuation layer, the actuation layer including the array of actuator elements. The layer may be arranged near the deformable membrane, for example under the deformable membrane, for example in a bonding manner, to enable physical manipulation of the membrane by the actuator elements. This may provide efficient transmission of force from the elements to the membrane and provide a compact device. However, other arrangements are also possible.

[0049] The actuation layer may be a carrier layer carrying an array of actuator elements. The actuation layer may contain the actuator elements; i.e. the actuator elements may be integrally comprised by the actuation layer. In this case, the layer may be a passive layer surrounding the actuator elements or at least covering the actuator elements for protection or electrical insulation.

[0050] Optionally, the actuator device may comprise a layer of electroactive polymer material, and wherein each actuator element comprises a segment of the electroactive polymer layer. In this case, the layer forms the actuator element.

[0051] The layer may be segmented by forming localized interruptions in the layer such that each segment is controllable to undergo an individual bending motion.

[0052] The layer may additionally or alternatively be segmented by anchors or clamps or clips, provided local points or lines of anchoring the layer are provided such that segments of the layer between the anchors or clamps or clips undergo a bending action outwards from the surface. Providing a single segmented EAP layer may represent the simplest arrangement in terms of ease of manufacture; providing a segmented layer may be less time consuming and less burdensome than forming a plurality of individual actuator elements separately. This is particularly the case where a bending action is desired such that each may need to be configured with individual clamping means to constrain its edges.

[0053] According to one or more embodiments, each actuator element may be electrically drivable to move between a first stable actuation position and a second stable actuation position. By stable is meant that the actuator element requires only a drive signal to transition from one position to the next, and then remains stable at that position in the absence of any further drive signal. Bi-stability is achieved by an actuator member formed by an EAP layer coupled to an elastic carrier layer, the actuator member being held constrained in a curved configuration by a clamping device. Driving of the EAP layer by electrical stimulation causes the actuator member to deform, causing it to flip or transition from a first curved configuration to an alternative curved configuration within the clamping device.

[0054] Full details of the bistable actuator arrangement are provided in WO2016193412A1.

[0055] Such an arrangement provides a particularly simple construction for driving changes in topology. When changing each actuator element between actuation positions, only a current or voltage needs to be applied; once the position has been changed, the signal can be removed. Each element has only two stable positions, limiting the number of possible configurations, thus reducing the complexity of the associated drive electronics and their control.

[0056] When the driving surface topology changes in order to realize the continuous or continuous exchange of fluid, this configuration may be useful. Film can be for example simply in the first surface topology of various first positions of actuating element and each element is changed to the second surface topology of its alternative position and alternately. For the film surface deformation realizing volume balance, this configuration may also be useful, by for example making element in the surface arrangement of various first actuating positions to each element being changed to the surface arrangement of its second actuating position and alternately. Therefore, for each change of element in one direction, there is another element along the balance change of the opposite direction.

[0057] Biological cell preservation or culture devices are generally suitable for use in any application where reliable fluid exchange between a surface and a bulk region of a volume of fluid is beneficial to promote cell preservation or culture. Particularly contemplated applications include devices dedicated to culturing cells and devices for storing blood.

[0058] Thus, according to at least one set of embodiments the device is a cell culture device and wherein the pattern of fluid flow is for achieving nutrient replenishment of cells located at or near the deformable membrane.

[0059] By cell culture device is meant a device or apparatus for culturing biological cells (including, for example, culturing or growing tissue). The device may, for example, be for culturing a biopsy obtained by biopsy. The device may, for example, be for culturing or growing organ tissue or for culturing or growing an organ. The device may, for example, be for growing or culturing an organ on a chip.

[0060] The biological cell preservation or cultivation device may include a substrate for culturing biological cells, the substrate being arranged in a chamber. Optionally, the substrate may be adapted to hold the cells in a fixed position on the substrate. This avoids displacement or interference with membrane surface deformation of the cells.

[0061] In an example, the substrate may be comprised by a deformable membrane.

[0062] For example, the deformable membrane may be covered by an isolating (or insulating) coating. In an example, the coating constitutes the substrate. Alternatively, a dedicated (e.g., flexible) substrate may be arranged to be coupled across the surface of the deformable membrane. In a further example, the deformable membrane may be shaped to define a non-actuating region or space surrounded by the membrane for accommodating the substrate.

[0063] The substrate may form at least a portion of a chip for growing organ-on-chip cells. Organ-on-chip is a term generally referring to the field of chips, most of which typically have devices that allow fluids to move around the chip and more generally devices for simulating the activities, mechanics or physiological responses of organs and organ systems. It is an emerging field of technology that has made initial breakthroughs but still has much work to do, especially in improving microfluidic mechanisms for more efficient nutrient supply.

[0064] According to at least one further set of embodiments, the device may be a blood storage device or apparatus, and wherein the deformable membrane is used to agitate the blood stored in the fluid holding space to prevent activation of platelets in the blood and / or prevent clotting of the blood.

[0065] Optionally, the blood storage device may include a blood storage bag, the bag forming the chamber of the device. By 'bag' is generally meant a flexible container or enclosure defined by a flexible outer skin. A bag may mean a fluid-tight enclosure enclosed by a flexible wall, for example formed of a plastic material.

[0066] In an example, the deformable membrane may form at least a portion of a closed wall of a fluid holding space of the blood storage device. Optionally, the actuator device may include an actuation layer, the actuation layer including an electroactive polymer, the layer being arranged to deform the deformable membrane forming the wall of the fluid holding space for deforming the membrane.

[0067] This provides an economical means of implementing the invention for blood storage bags. The blood storage bags are disposed of after a single use to avoid contamination. If the actuator means were contained within the wall of the bag itself, this would prove expensive as the actuator and electronics would need to be thrown away with each bag. Alternatively, these embodiments provide means for the actuator means to be external to the bag, the means being implemented in the form of a layer that can be applied or pressed onto the deformable membrane for deforming it. This can simply be a fixed surface or layer on which the bag can be located or on which the bag can be hung or pressed. The bag can then be removed from the actuation layer when the bag is needed for use, and the layer reused for a different bag.

[0068] The actuation layer may be disposed against the deformable membrane in a conformal manner (ie such that the two surfaces conform to each other).

[0069] By 'enclosed wall' may be meant a fluid enclosing wall.

[0070] In an example, the blood storage device may comprise two deformable membranes, each deformable membrane forming at least a portion of a closed wall of the fluid holding space, and wherein each deformable membrane is arranged relative to a respective electroactive polymer actuator device for deformation by the actuator device.

[0071] In an alternative example, the electroactive polymer actuator means may be comprised by, contained in or fixedly coupled to a deformable membrane forming at least a portion of a wall of a chamber or fluid holding space. Thus, the blood bag may comprise or contain the EAP actuator means for deforming the deformable membrane.

[0072] In certain examples, a cell culture device or apparatus configured to hold blood as a culture medium may be provided. In these examples, the device advantageously provides the dual functions of facilitating efficient exchange of nutrients between the bulk phase and the walls of the chamber and facilitating agitation of the blood culture medium to prevent activation of platelets and coagulation of the blood.

[0073] In a preferred example of any embodiment according to the present invention, the electroactive polymer actuator device may include an electrostrictive electroactive polymer material.

[0074] The cell culture or preservation device may comprise a plurality of deformable membranes, each deformable membrane being arranged to be deformed by a respective electroactive polymer actuator device, the plurality of deformable membranes being supported in a spaced-apart manner from one another by a frame structure.

[0075] As mentioned above, the present invention allows controlled generation of fluid flow patterns within the volume of fluid held by the fluid holding space. This is controlled by specific topological changes that are implemented. These different fluid flows can be generated by any embodiment of the present invention.

[0076] By way of example, the controller may be adapted to control actuation of the actuator elements in a sequential manner according to one or more examples, the actuation describing a sequential actuation path across the actuator arrangement to thereby induce a wave-like fluid flow at least along a direction of the actuation path.

[0077] By way of yet another example, the controller may be adapted to control actuation of the actuator elements in a cascaded manner according to one or more examples, wherein the actuators are actuated in sequentially successive groups, each actuated group being larger than the previous actuated group.

[0078] Further examples described herein include a cell culture or preservation device, comprising: a biological cell culture device as described in the above examples or as defined in the claims of this specification, and also including a certain volume of cell culture fluid maintained in the fluid holding space; and / or a blood storage device as described in the above examples or as defined in any corresponding claims, and also including a volume of blood maintained in the fluid holding space.

[0079] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Examples of the present invention will now be described in detail with reference to the accompanying drawings, in which:

[0081] Figure 1 and Figure 2 Two possible modes of operation of an EAP device are shown;

[0082] Figure 3 An exemplary biological cell preservation or culture device according to one or more embodiments of the present invention is shown;

[0083] Figure 4 illustrates the structure and operation of an example EAP actuator device and a deformable membrane according to one or more embodiments;

[0084] Figure 5 illustrates operation of an example biological cell holding or culturing device in accordance with one or more embodiments to induce a fluid flow pattern;

[0085] FIG6 illustrates an example control mode of an actuator device according to one or more embodiments;

[0086] FIG. 7 illustrates yet another example control mode of an actuator device according to one or more embodiments;

[0087] FIG8 illustrates yet another example control mode of an actuator device according to one or more embodiments;

[0088] Fig. 9 The structure and operation of an example biological cell preservation or culture device including a fluid retention bag are illustrated;

[0089] FIG10 illustrates a mode of controlling a biological cell preservation or culture device including a fluid holding bag;

[0090] Fig.11 schematically illustrates an example biological cell preservation or culture device according to one or more embodiments;

[0091] Fig.12 An example control circuit for controlling an array of actuator elements according to one or more embodiments of the present invention is shown; and

[0092] Fig.13 Shows the use of Fig.12 An example control circuit generates a voltage that is applied across an actuator element as a function of time. DETAILED DESCRIPTION

[0093] The present invention provides a biological cell preservation or culture device comprising a chamber and a deformable membrane, wherein the chamber defines a fluid holding space for holding a body of fluid during use, the deformable membrane being mechanically connected to the fluid holding space and being manipulable by an electroactive polymer actuator device to undergo a defined topological change, thereby inducing a pattern of fluid flow in the fluid, by which the fluid is exchanged between a sub-region adjacent to the deformable membrane and a sub-region remote from the membrane.

[0094] Embodiments of the present invention utilize electroactive polymers (EAPs) to facilitate actuation.

[0095] Electroactive polymers (EAPs) are an emerging class of materials within the field of electrically responsive materials. EAPs can function as sensors or actuators and can be easily fabricated into a variety of shapes allowing for easy integration into a wide variety of systems.

[0096] Over the past decade, materials have been developed with significantly improved properties such as actuation stress and strain. Technical risk has been reduced to acceptable levels for product development, making EAPs increasingly attractive commercially and technically. Advantages of EAPs include low power, small form factor, flexibility, noiseless operation, accuracy, the possibility of high resolution, fast response time, and cyclic actuation.

[0097] The improved properties and specific advantages of EAP materials lead to suitability for new applications.

[0098] EAP devices can be used in any application where small amounts of movement of a component or feature based on electrical actuation are desired. Similarly, the technology can be used to sense small movements.

[0099] The use of EAPs enables previously impossible functionality or provides large advantages over conventional sensor / actuator solutions due to a combination of relatively large deformations and forces in a small volume or a thin form factor compared to conventional actuators. EAPs also offer noiseless operation, accurate electronic control, fast response, and a large range of possible actuation frequencies, such as 0–1 MHz, most typically below 20 kHz.

[0100] Devices using electroactive polymers can be subdivided into field-driven materials and ion-driven materials.

[0101] Examples of field-driven EAPs include piezoelectric polymers, electrostrictive polymers (such as PVDF-based relaxor polymers), and dielectric elastomers. Other examples include electrostrictive grafted polymers, electrostrictive papers, electrets, electrostrictive elastomers, and liquid crystal elastomers.

[0102] Examples of ion-driven EAPs are conjugated / conductive polymers, ionic polymer metal composites (IPMCs), and carbon nanotubes (CNTs). Other examples include ionic polymer gels.

[0103] Field-driven EAPs are actuated by electric fields through direct electromechanical coupling. They typically require high fields (volts per meter) but low currents. The polymer layer is typically thin to keep the driving voltage as low as possible.

[0104] Ionic EAPs are activated by electrically induced transport of ions and / or solvents. They generally require low voltages but high currents. They require liquid / gel electrolyte media (but some material systems can also operate using solid electrolytes).

[0105] These two categories of EAP have multiple family members, each with its own advantages and disadvantages.

[0106] The first significant subclass of field-driven EAPs is piezoelectric and electrostrictive polymers. Although the electromechanical properties of conventional piezoelectric polymers are limited, a breakthrough in improving this property has resulted in PVDF relaxor polymers that exhibit autonomous electric polarization (field-driven alignment). These materials can be pre-strained to obtain improved properties in the direction of the strain (pre-strain leads to better molecular alignment). Typically, metal electrodes are used because the strains are usually in the moderate regime (1-5%). Other types of electrodes (such as conductive polymers, carbon black-based oils, gels or elastomers, etc.) can also be used. The electrodes can be continuous or segmented.

[0107] Another interesting subclass of field-driven EAPs is dielectric elastomers. Films of this material can be sandwiched between compatible electrodes, forming a parallel plate capacitor. In the case of dielectric elastomers, the Maxwell stresses induced by the applied electric field lead to stresses on the film, which cause the film to compress in thickness and expand in area. The strain properties are usually amplified by pre-straining the elastomer (requiring a framework to maintain the pre-strain). The strain can be quite large (10-300%). This also constrains the type of electrodes that can be used: for low and medium strains, metal electrodes and conductive polymer electrodes can be considered, for high strain states, carbon black-based oils, gels or elastomers are usually used. The electrodes can be continuous or segmented.

[0108] In some cases, when the polymer itself lacks sufficient conductivity (dimension by dimension), a membrane electrode is added. The electrolyte can be a liquid, gel, or solid material (i.e., a complex of a high molecular weight polymer and a metal salt). The most common conjugated polymers are polypyrrole (PPy), polyaniline (PANi), and polythiophene (PTh).

[0109] Actuators can also be formed by carbon nanotubes (CNTs) suspended in an electrolyte. The electrolyte forms a double layer with the nanotubes, which allows the injection of charge. This double layer charge injection is considered to be the main mechanism in CNT actuators. The CNT acts as an electrode capacitor with the charge injected into the CNT, which is then balanced by the electric double layer formed by the electrolyte moving to the CNT surface. Changing the charge on the carbon atoms causes a change in the C-C bond length. Therefore, the expansion and contraction of a single CNT can be observed.

[0110] Figure 1 and Figure 2 Two possible modes of operation of an EAP device are shown.

[0111] The device comprises an electroactive polymer layer 14 sandwiched between electrodes 10 , 12 on opposite sides of the electroactive polymer layer 14 .

[0112] Figure 1 An unclamped device is shown. As shown, a voltage is applied to cause the electroactive polymer layer to expand in all directions.

[0113] Figure 2 A device is shown which is designed so that expansion occurs in one direction only. The device is supported by a carrier layer 16. A voltage is used to cause the electroactive polymer layer to bend or curve.

[0114] The electrodes, the electroactive polymer layer and the support together may be considered to constitute the entire electroactive polymer structure.

[0115] For example, the nature of the motion arises from the interaction between the active layer, which expands when actuated, and the passive carrier layer.To obtain asymmetric bending around an axis as shown, molecular orientation (membrane stretching) may be applied, forcing movement in one direction.

[0116] Expansion in one direction may be caused by asymmetry in the EAP polymer, or may be caused by asymmetry in the properties of the carrier layer, or a combination of both.

[0117] Electroactive polymer structures as described above can be used for actuation and sensing. The most prominent sensing mechanisms are based on force measurement and strain detection. For example, dielectric elastomers can be easily stretched by external forces. By applying a low voltage across the sensor, strain can be measured as a function of voltage (voltage is a function of area).

[0118] Another approach to sensing with a field driven system is to directly measure the change in capacitance or the change in electrode resistance as a function of strain.

[0119] Piezoelectric and electrostrictive polymer sensors can generate an electric charge in response to an applied mechanical stress (assuming the crystallinity is high enough to generate a detectable charge). Conjugated polymers can exploit the piezoelectric ionic effect (mechanical stress causes ions to be affected). CNTs experience a change in charge on the surface of the CNT when exposed to stress that can be measured. It has also been shown that the electrical resistance of CNTs changes when in contact with gaseous molecules (e.g., O2, NO2), allowing CNTs to be used as gas detectors.

[0120] Embodiments of the present invention utilize a deformable membrane that may be part of an in vitro culture device or apparatus (e.g., a so-called organ-on-a-chip) in an advantageous example, or may be part of a storage container for blood or platelets in another example. In some examples, multiple such membranes may be used, for example comprising two surfaces that are sealed at their peripheries to define a fluid holding space therebetween that may be used as a collapsible container (such as a blood bag).

[0121] Embodiments utilize electroactive polymer based actuation to deform a deformable membrane.

[0122] In some examples, the deformable membrane may consist of or include or necessarily carry electroactive polymer actuators, such as electroactive polymer actuators for deforming the surface. In other examples, the surface may be a thin flexible layer or foil arranged on an actuation surface, the actuation surface including electroactive polymer actuators, such as organized in a segmented manner for deforming the layer.

[0123] Thus, a controllably deformable surface having a thin form factor may be provided, for example compared to electromechanical or other electromechanical actuated devices.The resulting device has a much smaller form factor than, for example, mechanical agitation or shaking devices for blood bags known in the art.

[0124] Figure 3 A first exemplary biological cell preservation or cultivation device according to one or more embodiments of the present invention is illustrated.Device 22 includes a chamber 24 whose lumen defines a fluid holding space 30 for holding a volume of fluid 34 during use of the device.

[0125] In mechanical communication with the fluid holding space 30 is a deformable membrane 36. Figure 3 In the example of , the deformable membrane extends across the base of the chamber 24 to form a closed or sealed wall of the fluid holding space. The deformable membrane is fluid impermeable. Coupled to the lower surface of the deformable membrane is an electroactive polymer (EAP) actuator device 38, which includes an array of electroactive polymer actuator elements 42 that can be independently controlled by a controller 50, which is provided to be operatively coupled to the actuator device. The controller is adapted to control the actuator device to implement a controlled deformation of the deformable membrane to thereby induce one or more defined changes in the surface topology of the membrane.

[0126] Despite Figure 3 In a specific example, the controller is provided as part of the cell preservation or culture device itself, but in another example, the controller may be external to the device, and wherein the actuator device is adapted to be connected to and communicate with the external controller for controlling the actuator device. All subsequent features, examples and descriptions may be understood to be implemented by a device in which the controller is provided as part of the device, or in which the controller may be provided external to the device.

[0127] Figure 4 The deformable membrane 36 and the EAP actuator device 38 are shown in more detail. In this example, the actuator device comprises a continuous layer 38 of electroactive polymer (EAP) material coupled to a substrate layer 52. The substrate layer has greater flexural rigidity or elasticity than the deformable membrane. Provided across the substrate layer in an array are a plurality of slits or anchoring elements 54 formed in or coupled to the substrate layer. These slits or anchoring elements effectively segment the actuator device 38, 52 into a plurality of individual actuator elements 42.

[0128] like Figure 4 As shown in FIG. 1 , after the EAP material layer 38 is electrically stimulated by a current or voltage applied by an electrode arrangement (not shown), the EAP layer responds by deforming in a plane. The elastic substrate layer 52 resists in-plane deformation, thereby forcing out-of-plane deformation or bending. The array of local slits or anchor points 54 decomposes the induced full motion into localized bending regions, which are localized to the regions subtending between the anchor points. Thus, each actuator element 42 undergoes a localized bending motion.

[0129] By applying electrical stimulation to only certain areas of the actuator arrangement 38, 52 covering only certain actuator elements 42, these actuator elements can be driven individually to actuate. Thus, individualized control of each actuator element is possible. In an example, this can be facilitated by a segmented electrode arrangement or by providing each actuator element with an individually drivable electrode arrangement.

[0130] By selectively controlling the specific pattern of actuator elements 42 to deform, it can be seen that controlled changes in the surface topology of the deformable membrane 36 can be achieved. By appropriate actuation of the actuator elements of the EAP actuator device 38, any specific topological pattern or contour can be produced in the membrane.

[0131] like Figure 5 , after actuating the actuator element 42 to induce a change in the surface topology of the deformable membrane 36, the associated pattern of fluid flow 56 within the fluid 34 of the fluid holding space 30 due to contact with the membrane. Due to the out-of-plane directionality of the topological change, the fluid flow is in a direction generally away from the surface of the deformable membrane. Thus, a fluid flow pattern is generated in which fluid is exchanged between a first sub-region 46 immediately adjacent to or proximate the deformable membrane and a second sub-region 48 further away from the deformable membrane, i.e., in the bulk phase of the fluid 34.

[0132] Many different fluid flow patterns can be generated by appropriate control. In some examples, the change in surface topology is a change in deformation of the membrane 36 from the fluid holding space 30 inward and from the fluid holding space outward (e.g. Figure 5 This represents a simple mechanism for inducing fluid flow towards and away from the deformable membrane, thereby ensuring the supply of nutrients to the surface of the membrane and flushing of waste away from the surface.

[0133] for Figure 3-5 In an exemplary embodiment, the actuator device 38 is preferably controlled to cyclically deform the membrane 36 back and forth between the flat configuration and the contoured configuration, such as to provide efficient transport of fluid toward and away from the membrane.

[0134] In an example, the fluid holding space 30 can be fluidically sealed, and wherein the fluid is an incompressible liquid that completely fills the space without any air pockets (or other gases). In this case, only if there are some overflow devices that allow a portion of the fluid in the space to be temporarily discharged or adapted, a surface topological change in the membrane 36 that causes a net inward bending of the membrane (toward the fluid holding space) will be possible, so that the membrane displacement can be volumetrically adapted. The overflow device can be another flexible membrane that forms at least a portion of the sealing wall of the fluid holding space, and the membrane can bulge (point outward relative to the space) to accommodate excessive displaced fluid. This requires the incompressibility of the liquid. In an example, the boundary wall of the fluid holding space or chamber can simply be flexible to accommodate the displaced fluid.

[0135] Overflow means may alternatively be provided by an overflow outlet (not shown) of the fluid holding space 30, which allows the fluid displaced by the deformation of the deformable membrane 36 to temporarily escape, for example, to an overflow chamber. In an example, the outlet may be provided by a permeable membrane element comprising small fluid permeable holes to allow the escape of the fluid. The permeable membrane may preferably be provided with holes small enough to prevent contamination by microorganisms.

[0136] Alternatively, overflow in the deformable membrane can be avoided by controlling the surface topology changes that are volumetrically balanced between deformations directed inwardly and outwardly relative to the fluid holding space 30. Thus, there is zero net change in the total volume of the fluid holding space, since any local decrease in volume by the inwardly bending actuators is balanced by a local increase by the outwardly bending actuators.

[0137] In an example, this may include moving from a flat membrane surface profile to an undulating profile, with the amplitudes extending to either side of the undulations or planes of equal linear displacement defined by the previous flat configuration.

[0138] In an example, the actuator element 42 according to this control example may be a bistable electroactive polymer actuator that is drivable to move between a first stable actuation position and a second stable actuation position by application of an electric current or a field.

[0139] By stable is meant that the actuator element requires only a signal to transition from one position to the next, and then remains stable in that position in the absence of any further drive signal. Bi-stability is achieved by an actuator member formed of an EAP layer coupled to an elastic carrier layer, the actuator member being held constrained in a bent configuration by a clamping device. Actuation of the EAP layer using electrical stimulation stimulates the actuator member to deform, causing it to flip from a first bent configuration to an alternative bent configuration within the clamping device.

[0140] Full details of a bistable actuator arrangement are provided, for example, in WO2016193412A1.

[0141] By way of example, the actuator device 38 can be moved from a first surface topology state in which substantially half of the actuator elements 42 are in a common first state (e.g., a flat state) and substantially half are in a common second state (e.g., bent outwardly). The surface topology change can be effected by simply reversing the actuation state of each actuator element 42. Half will move to the bent outward state; the other half moves to the flat state, thus volumetrically balancing, allowing fluid flow paths to be created, but without compressing the fluid.

[0142] In any example, the actuator elements 42 may be activated simultaneously as a whole or in subgroups, or may be activated individually or separately, such as in an intermittent manner, to enhance mixing.

[0143] Advantageously, in embodiments of the present invention, the ratio of the dimensions of the chambers may be selected to facilitate efficient mixing of the fluid between a region 46 adjacent the deformable membrane 36 and a region 48 in the bulk phase of the fluid.

[0144] For example, in a (non-limiting) advantageous example of the invention, the ratio of the dimension of the chamber extending outwards from the deformable membrane surface (i.e. substantially perpendicular to the deformable membrane surface) to the dimension extending transversely to the deformable membrane surface may be between 1:1 and 1:20 or between 1:2 and 1:10. This may for example be contrasted with quite typical such ratios for (non-chambered) channel-like devices, which are typically anywhere between 1:50 and 1:500. In such cases, fluid flow directed away from the deformable membrane is immediately blocked by the boundaries of the same channel, diverting the fluid transversely to the deformable membrane. This does not promote efficient exchange of fluid between the membrane surface and the bulk phase.

[0145] By way of further explanation, and by way of purely non-limiting illustration only, an actuator element suitable for use in the present invention may have a maximum actuator displacement of approximately 70 microns (for an actuator element having a lateral width of 5 mm).

[0146] According to one set of embodiments, the chamber of the device may be a chamber formed by a blood bag. By way of non-limiting example, an exemplary blood bag according to an embodiment of the invention may have a "height", i.e. the dimension between the main surfaces of the bag carrying the actuator element, of about 30 mm. In a non-limiting example, a typical ratio of the dimension of the chamber perpendicular to the deformable surface to the maximum actuation displacement of the actuator element may be about 1:0.002, or for example in the range 1:0.00015 and 1:0.002.

[0147] This may be contrasted, for example, with a (non-chambered) blood transport tube device, where such a tube may have a typical height of about 4 mm. The ratio of channel height (perpendicular to the deformable surface) to maximum actuator displacement may be about 1:0.02, i.e. in the order of magnitude of less than a factor of 10. A typical range of ratios may be, for example, from 1:0.00125 to 1:0.035.

[0148] Devices according to one or more embodiments may provide a cell culture device, such as an organ-on-a-chip device. This may be a so-called 'tumor-on-a-chip' device. In a non-limiting example of such a device, the ratio of the chamber height (substantially perpendicular to the deformable surface) to the maximum actuator displacement may be about 2700 microns to 70 microns, i.e., a ratio of about 1:0.26 in a non-limiting example, or, for example, within the range of 1:0.0018 and 1:0.26.

[0149] This again can be contrasted with channel-like devices, where the ratio between channel height and actuator displacement can be as small as 1 : 1. A typical range for the ratio can be between 0.1 and 1, for example.

[0150] It can thus be seen that for chamber devices of embodiments of the present invention, the height:width ratio and height:actuator displacement ratio are generally greater than those of typical channel-like devices.

[0151] In the context of this art, the main difference between channels and chambers is that channels are used for continuous processes, whereas chambers are used for batch (localized) processes.

[0152] To illustrate, the following processes can be performed in a channel: transporting (one or more) substances from one location to another; mixing by using passive structural transport, like serpentine channels or special topological features in the channel; injecting two components into the channel and allowing a chemical reaction to occur between the two components during transport.

[0153] In contrast, and for non-limiting illustration only, the following may be performed in a chamber: mixing by active means; chemical reactions that are sampled by mixing reactants.

[0154] In cases where a process requires a certain localized volume, a chamber is needed rather than a channel. This is the case, for example, for cell culture (including tissue culture, including species culture) or storing blood.

[0155] It is impractical to store blood in a channel because this would dramatically increase the surface to volume ratio, significantly increasing the likelihood of adverse surface effects, i.e. activation or coagulation of platelets on the surface. Additionally, such a tube would be more expensive than a blood bag because the much larger surface area would require a greater number of actuating elements to adequately cover the surface to prevent platelet activation.

[0156] Furthermore, in the case of cell culture devices or apparatuses for the growth and angiogenesis of tumors, it is necessary to accommodate the minimum channel height required for the tumor to grow outward. Narrow chambers are generally not able to accommodate the growth of tumors or, for example, organs. In particular, the volume of a tumor is widely spread so as to cover, for example, a single cell layer (so that it can fit within the channel) without inducing angiogenesis.

[0157] In particular, a tumor can grow to a size of approximately 1-2 mm before its metabolic requirements are constrained due to diffusion limitations of oxygen and nutrients. In order to grow beyond this size, the tumor switches to an angiogenic phenotype and attracts blood vessels from the surrounding stroma. This process is regulated by various pro-angiogenic and anti-angiogenic factors and is a prerequisite for further tumor growth.

[0158] As mentioned above, the actuator elements 42 can be individually addressed. Thus, a wide variety of different surface topology patterns and associated fluid flows can be generated. A range of fluid flow patterns that can be generated will be described in the following embodiments, and include 1) localized wave-like fluid flow across the deformable membrane 36, 2) overall wave movement across the entire deformable membrane, thereby inducing large-scale exchange of fluid between the bulk and the membrane, and 3) localized circular movement between areas adjacent to the membrane surface and liquid in the fluid bulk away from the surface.

[0159] 6 illustrates an example control scheme for controlling changes in the surface topology of the deformable membrane so as to induce a wave-like fluid flow pattern in the fluid 34. According to the scheme, the controller 50 (not shown) is adapted to control the actuator elements 42 to actuate in a sequential manner, defining sequential actuation paths across the deformable membrane 36, to thereby induce a wave-like fluid flow at least along the direction of the actuation paths.

[0160] Fig. 6 (a)-(c) shows the actuation at successive time points, at each time point, other single actuator elements 42 have been sequentially activated. In the example, the elements are activated from left to right. This generates a wave-like fluid flow from right to left on the membrane 36 surface.

[0161] In this example, in the non-activated state, the deformable membrane 36 is flat. In the activated state, each actuator element 42 bends and pushes the liquid 34 in the fluid holding space 30 radially inward away from the membrane surface toward the bulk region 48 (see Figure 5 ). After the final (leftmost) actuator has been activated, the actuators are sequentially deactivated from right to left, generating a second wave on the surface. The start of the second wave may alternatively be started after the final (leftmost) actuator has been activated.

[0162] Since there is a net flow to the left on the surface, this also induces a parallel leftward movement in the bulk liquid region 48 spatially away from the membrane surface.

[0163] When the actuator element is sequentially activated from the bent configuration back to the flat configuration, liquid flow back toward the deformable membrane 36 is achieved. Figure 4In the example of , localized slits or fixing points 54 are provided in the substrate 52 of the actuator device 38 to segment the EAP layer 36 into localized actuator elements 42 .

[0164] Although right to left activation is illustrated in FIG6 , this is for illustration only. Any other directionality may also be implemented. The schematic illustration of FIG6 shows only a cross-sectional view of the membrane layer. In practice, a two-dimensional activation pattern is generated across the surface. Thus, the actuator elements may be activated in a linear manner that moves sequentially along the membrane surface, or may be activated sequentially and individually across the surface.

[0165] As discussed above, a specific volume-balanced control scheme can be implemented for changing the surface topology of the deformable membrane 36 to provide fluid flow in the incompressible volume of the fluid 36. In such a scheme, the resulting surface topology change includes membrane surface deformations directed both inwardly and outwardly from the fluid holding space 30, wherein the inward deformation is volumetrically balanced with the outward deformation. The result is a net change in the volume of the fluid holding space before and after the topology change.

[0166] FIG7 schematically illustrates such a control scheme.

[0167] In the example of Figure 7, an electroactive polymer actuator device 38 is provided comprising an array of EAP actuator elements 42. In a preferred example, bistable actuator elements may be present. In the Figures, the actuator elements are shown as rectangular for simplicity of illustration.

[0168] The control scheme illustrated in Figure 7 is a wave-like fluid flow from right to left on the surface of the actuator device 38. The order of activation is shown by images (a)-(e) moving sequentially downward in time. Each image shows the sequential activation of the actuator elements 42, as indicated by small arrows. It can be seen that for each actuator element that collapses from the outward actuated state to the flat state, another element is deformed in the opposite direction. Therefore, the total number of actuators that deform outward is the same at each point in time, and the same is true for actuators that are not deformed outward. The net volume change of the volume of the fluid holding space 30 is therefore zero.

[0169] The deformation mode causes sequential activation of the elements 42 moving from right to left. This creates a wave-like fluid flow while compensating for any volume changes by simultaneously collapsing the surrounding actuator elements.

[0170] FIG. 8 illustrates yet another example control scheme for inducing volume balancing of fluid flow in an incompressible fluid.

[0171] According to the control scheme, the controller is adapted to control the actuator elements to be actuated in a cascaded manner, wherein the actuators are actuated in sequentially successive groups, each actuated group being larger than the previously actuated group.

[0172] As in the example of FIG. 7 , a flexible surface 38 of a bistable actuator is provided, schematically represented as a rectangle in the illustration. A wave-like liquid flow pattern is generated in the fluid holding space, moving from right to left across the surface of the actuator device 38. Each of FIG. 7 (a)-(e) shows a sequential stage in the actuation mode. It can be seen that for each element that is actuated outward, the other is collapsed to flat, compensating the deformation volumetrically.

[0173] As can be noticed, viewing the pictures from (a) to (a), in each step, another group of actuators is activated, larger than the previously activated group. This causes a wave-like avalanche flow from right to left.

[0174] As in the previous examples, the illustration is only schematic and only a portion of the surface of the actuator device 38 is shown.

[0175] According to yet another set of example control modes, surface topology changes may be induced in a deformable membrane in such a mode to induce periodic or rotational movement of fluid within the fluid holding space 30 , circulating between a region 46 adjacent the membrane surface and a bulk region 48 of the fluid 34 .

[0176] exist Fig. 9 An example of such a control scheme is illustrated in FIG.

[0177] Fig. 9 A cell preservation device comprising a bag 64 (e.g., a blood bag) is shown by way of example, and the bag 64 (e.g., a blood bag) forms a chamber of the device. The bag is formed by two flexible deformable membranes or foils 66a, 66b that are joined together at its periphery to seal the internal fluid holding space 30. The two membranes thus define the corresponding surfaces or walls of the chamber. The bag is held between two parallel surfaces. The first (bottom) is an electroactive polymer actuator device 38 coupled to the elastic substrate layer 52 as described in the previous example. The actuator device is arranged against the flexible membrane 66b of the lower bag in a manner for deforming the membrane. The other (upper) of the parallel surfaces is a passive or stationary layer 62. The EAP actuator device 38 can be provided to be mechanically clamped to the flexible foil 66b or releasably coupled, but need not be combined, sealed, or fused to it. The actuator device 38 is held against the flexible foil 66b in an engaging manner so that the surface of the latter follows the topological changes of the former.

[0178] exist Fig. 9In the example of , the actuator elements 42 of the EAP actuator device 38 are shown as being actuated sequentially from right to left, with each actuated element 42a pushing the flexible foil 66b of the bag to induce its corresponding surface deformation. This surface deformation induces a consequent fluid displacement within the fluid holding space 30 of the bag 64. The combined action over time of a series of actuated actuator elements 42a produces a specific fluid flow pattern within the bag 64. Due to the shape of the bag 64 and the sequential actuation pattern, a periodic fluid flow pattern is induced in the fluid holding space 30, as indicated by the arrows. This periodic flow circulates between a region 46 adjacent to the lower flexible foil 66b and a region 48 in the bulk of the fluid away from the foil.

[0179] In this example, the fluid 34 in the fluid holding space 30 comprises pockets 65 that can accommodate the fluid 34 displaced by the full mode of the deformable foil 66b. This enables fluid flow to be achieved without volumetrically balancing surface deformations as in the examples of FIGS.

[0180] The bag 64 may be collapsible. The bag may be clamped between the two surfaces 62 and 36, 38. The upper surface 62 may be rigid, or may be flexible.

[0181] The benefit of providing the active layers 38, 36 outside the fluid holding space 30, such as to communicate only indirectly with the fluid 34 via the deformable foil 66, is that the bag 64 can be provided separately without disrupting the actuation mechanism of the actuator device 38. This is useful in the case where the bag provides the function of a blood bag. The blood bag can be used only once to avoid contamination. Fig. 9 The device allows the fluid in the bag to be actively agitated without integrating the actuation mechanism into the structure of the container itself.

[0182] Although in the illustrated example, the number of actuator elements 42 extending across the bag surface is relatively small, this is for schematic illustration only. Typically a large number of actuator elements will be included in the surface extending across the side of the bag.

[0183] Despite Fig. 9 Examples include air pockets 65 to accommodate displacement of fluid 34 due to deformation of flexible foil wall 66a, but in other examples, volume balanced control schemes (similar to those described in previous examples) can be implemented and wherein similar periodic fluid flow patterns can be induced.

[0184] FIG. 10 shows an example according to this approach.

[0185] 10(a)-(d) illustrate sequential actuation steps in a control scheme for cyclic fluid flow in fluid 34 of fluid holding space 30, wherein cavitation is not provided to accommodate fluid expansion.

[0186] The configuration shown includes Fig. 9 The example of the invention is a bag 64 consisting of two flexible foils 66a, 66b that are sealed together peripherally to define an internal fluid holding space 30. The bag is arranged between a pair of parallel surfaces, each surface including a corresponding electroactive polymer actuator device 38. Each electroactive polymer actuator device is provided to be applied to a corresponding flexible foil in the upper 66a and lower 66b flexible foils in a jointed manner so as to induce a surface topological change in the foil. The surface topological change induces an associated fluid flow pattern within the fluid 34 of the fluid holding space 30.

[0187] For the purposes of this example, it is assumed that a bistable EAP actuator element 42 is employed.

[0188] Figure 10(a) shows an initial configuration of the actuator element 42, where half the element is actuated 42a (also mirrored along the bottom surface), and half is not actuated.

[0189] FIG. 10( b ) shows a subsequent actuation state, in which the total number of active and inactivated actuator elements 42 has not been changed, but their positions have been moved. In particular, those elements surrounded by dashed lines are those whose actuation state has been changed. Those indicated by (A) are transformed first, wherein those indicated by (B) are subsequently transformed after a short delay. By activating these groups individually, the desired periodic flow is better induced (in this case a clockwise flow is produced).

[0190] Figure 10(c) shows the next actuation state. Again, the actuator elements 42 enclosed by the dashed lines are those that have changed state, with those indicated by (A) being changed first, followed by (B), to again achieve the desired periodic flow.

[0191] FIG. 10( d ) shows the final actuation state, in which those actuators enclosed by the dashed line have again changed actuation state, with those indicated by (A) being changed first, followed by (B).

[0192] The skilled person will readily appreciate that continuation of this activation pattern will maintain the periodic pattern of liquid flow.

[0193] In an example, a circuit may be provided that is configured to control the pattern of actuator activations required to maintain a periodic flow pattern while also maintaining a zero net change in the volume of the fluid holding space 30. This may be accomplished, for example, by means of a lookup table programmed with a sequence of actuator states for each sequential phase; however, other means may also be used.

[0194] Figure 10 shows only a cross-sectional view of the bag 64. It will be appreciated that cyclical motion in a direction transverse to that shown (i.e. into or out of the page) can also be produced by similar sequential control of the actuator elements 42 but arranged in a manner that changes orientation.

[0195] The use of a dual actuator device 38 and associated deformable membrane 66 as shown in Figure 10 is not limited to applications within or for bags. Such a configuration may also be provided for a cell culture device, wherein two or more deformable membranes each having an associated deformable EAP actuator device may be assembled, for example supported in a spaced-apart manner from one another by means of a frame structure. In an example, such an actuator device may be used as part of an organ-on-chip device. The deformable membrane may form an integral part of the organ-on-chip device, or may be arranged to be engaged against a flexible foil as part of the device.

[0196] Purely by way of illustration, an example blood bag according to one or more embodiments of the present invention may typically have a 500 cm 3 The average 'height' of the blood bag (the distance between the major surfaces of the bag) may be about 3.3 cm, such as 3-5 cm.

[0197] Thus, a typical aspect ratio (average length divided by height) may be about ((15+10) / 2) / 3.3, i.e. ~4. A typical example range may be, for example, between 1.8 and 8. In the case of a collapsible bag, the height may be about 5 cm near the central region of the bag, which decreases to zero at the edges of the bag.

[0198] This may for example be contrasted with a (non-lumen) channel which may typically give an internal diameter of -4 mm, with a length of for example about 50 cm, thereby giving an aspect ratio of about 50 / 0.4, ie -125. A typical example range may for example be between 62 and 500.

[0199] Thus, it can be seen that the aspect ratio (length / height) is typically much smaller for chambers (according to the present invention) than for channels. This smaller aspect ratio aids in the efficient exchange of fluid between the deformable membrane and the bulk phase, as the height of the chamber allows for the accommodation of free fluid flow in a direction outward from the deformable surface. In channels, the restricted height means that fluid flow is generally redirected laterally along the channel.

[0200] As mentioned above, in embodiments of the present invention, a cell culture device may be provided for culturing tumor growth. By way of illustration, a tumor may grow to approximately 5 mm with a height of, for example, ˜1.34 mm (diameter). 3In a preferred embodiment, the chamber of the cell culture device may have a width (i.e., transverse to the deformable surface) twice as large as the height (i.e., perpendicular to the surface of the deformable membrane 36) of the chamber. Thus, in an exemplary embodiment, the aspect ratio (length divided by height) would be 2. An exemplary range of suitable aspect ratios may be between 2 and 20.

[0201] In contrast, a typical (non-chamber) microchannel in an organ-on-a-chip device or apparatus may typically have a length of about 5 mm and a diameter of about 50 microns, giving an aspect ratio (length / height) of about 5000 / 50=100. A typical example range may be, for example, between 50 and 200.

[0202] It can thus be seen again that the aspect ratio (length / height) is typically much smaller for chambers (according to the invention) than for channels. This smaller aspect ratio aids in the efficient exchange of fluid between the deformable membrane and the bulk phase.

[0203] It is emphasized that the above exemplary dimensional ratios are purely illustrative and do not limit the concept of the present invention.

[0204] Although in the various examples described above, an actuator device 38 comprising an EAP layer coupled to an elastic substrate is provided, in further alternative examples, such a substrate may be omitted. In this case, a quasi-random bending configuration may be achieved after electrical stimulation of the EAP layer. For example, a wrinkling pattern may be induced. Here, a similar single, non-configurable fluid effect is achieved in the fluid holding space 30, where fluid is exchanged between a region 46 adjacent to the deformable membrane 36 and a region 48 within the fluid body away from the deformable membrane.

[0205] In some embodiments, the controlled topological change of the deformable membrane 36 can serve a dual purpose. For embodiments providing a cell culture device, the topological change can be a useful mechanical stimulation of cells cultured on a surface (eg, a chip surface) carried by the deformable membrane.

[0206] For certain kinds of cells, this is useful, for example, to stimulate natural growth conditions. For example, cells in the alveoli in the lungs are stretched under normal conditions. Due to the contraction of the heart, the cells of the heart are continuously deformed or stretched. Therefore, mechanical stimulation of cells by a deformable membrane can usefully simulate in vivo conditions for cell growth. It is well known that such mechanical stimulation can have a significant effect on cell culture. For example, culturing cardiomyocytes requires such mechanical stimulation in order to induce the growth of a cell layer that exhibits muscle behavior.

[0207] According to one or more examples, a dedicated support structure for supporting cultured cells may be provided, the support structure having a carrier surface that is controllably deformable to allow controlled mechanical deformation of the cultured cells. In an example, the structure may be deformable independently of a deformable membrane, or may be mechanically or operatively coupled to the deformable membrane such that the deformable membrane stimulates deformation of the support structure.

[0208] In an example, the actuator device 38 may include a mixture of electroactive polymers and other types of responsive materials, or an additional actuator device composed of other responsive materials instead of EAPs may be provided. Responsive materials are a broader class of materials that have the property of reversibly deforming or changing in structural properties in response to one or more electromagnetic stimuli. By way of example, a wide variety of responsive materials include thermally responsive shape memory materials (such as shape memory alloys and shape memory polymers), magnetostrictive materials, magnetic shape memory alloys, piezoelectric materials, and light responsive materials (optomechanical materials). Optionally, in certain cases, particularly where certain cells may be sensitive to the electrical signals used to stimulate the EAP material, the responsive material has specific benefits.

[0209] The examples described above include EAP actuator devices formed from or segmented into an array of individual deformable EAP actuator elements 42. The size of each actuator element may be selected depending on the specific flow pattern that needs to be produced.

[0210] A typical human cell is about 10-20 microns wide, and a platelet is about 1-2 microns wide. By way of example, an actuator 5 mm wide is able to achieve a linear (out-of-plane) displacement amplitude of 70 microns, which is insufficient to generate surface flow and disturb the depletion layer near the biological cells. Since the generated flow originates from the deformed surface itself, even the fluid region around the cells directly adjacent to the surface is disturbed, both agitating the cells and providing an exchange of nutrients and waste to and away from the cells. Thus, platelet activation can be prevented, and these and other cells can be effectively preserved and cultured with nutrients.

[0211] It should be noted that the size of the fluid holding space 30 (particularly, the distance from the deformable membrane 36 to any relative boundary wall) will affect the flow pattern achieved by the specific surface topology change. A very narrow distance can result in a flow pattern that is diverted in the direction of substantially crossing the deformable membrane via the blocking of the relative wall. A much larger separation distance can result in a flow pattern that is directed more vertically relative to the membrane. A distance such as a flow that causes the latter to be directed more vertically can be preferred, because in this way, fluid exchange with the bulk phase can be better promoted.

[0212] According to one or more examples, the EAP actuator device 38 may include or accommodate an inactive surface area where no actuator elements 42 are provided or such actuator elements are not activated, such area preferably being positioned to be surrounded by the active area. The inactive area may be adapted for biological cells for culture and may include a membrane or substrate or chip that carries cells for culture or to which cells for culture may be attached. A covering and nutrient permeable membrane may be provided. By providing the cells in the inactive area, potential damage due to changes in the topology of the deformable membrane 36 can be avoided in the case of mechanosensitive cells, while at the same time facilitating fluid exchange between the area 46 adjacent to the cells and the fluid body 48.

[0213] Furthermore, although according to the examples described above an actuator device 38 and a deformable membrane 36 are provided which extend across the entire fluid retaining space 30, in other examples the membrane or actuator device may extend only partially across the space, or may be localised to a central region of the base of the space surrounded by the fluid.

[0214] A solution for accommodating the displacement of the fluid in the chamber by volumetrically balancing the deformation of the actuator means has been described above. Fig. 9 In the example of , displacement is accommodated by partially filling the fluid holding space 30 of the chamber with fluid, thereby leaving an air gap 65 into which the displaced fluid can move.

[0215] According to a further example, overflow means may alternatively be provided for temporarily accommodating fluid displaced by movement of the deformable membrane into the fluid holding space 30 of the chamber.

[0216] In an example, the overflow means may include an overflow outlet or conduit extending from the chamber to the overflow space to allow temporary drainage of fluid from the main chamber.

[0217] Fig.11 An example of such a device is schematically illustrated. The device shown represents a cell culture device according to one or more embodiments of the present invention. In an example, the device may be an organ-on-a-chip device.

[0218] The device comprises a main (propagation) chamber 24 for holding cells for culture, which is fluidically connected via an overflow outlet 26 to a secondary overflow chamber 25 for accommodating fluid that can be displaced from the main chamber 24 following deformation of a deformable membrane 36 of the main chamber. The deformable membrane 36 may define a portion of a wall of the main chamber, or may be arranged within the main chamber and in either case is adapted to be deformable to undergo a defined topological change.

[0219] The device also comprises an electroactive polymer actuator device 38 as described in the examples above arranged in engaging relationship with the deformable membrane 36 so as to deform the membrane and effect a controlled topological change of the membrane.

[0220] A portion of the wall of the overflow chamber 25 may comprise a flexible foil or membrane which is flexible to allow compensation of any volume changes induced by the electroactive polymer actuator device 38 of the main chamber 24. The flexible foil or membrane may be comprised by an upper portion of the outer wall or border of the overflow chamber.

[0221] In use, the inlet valve 23a and the outlet valve 23b of the device are closed to prevent the escape of the fluid contained in the fluid holding space of the device. The displacement of the fluid in the main chamber 24 due to the deformation of the deformable membrane 36 can flow through the overflow outlet 26 and be accommodated by the overflow chamber 25. Alternatively, both chambers can be filled with fluid, and wherein the deformable foil of the overflow chamber 25 is flexible to allow the volume of the fluid displaced in the main chamber by the deformable membrane 36 to be accommodated.

[0222] The entire device may be housed in a housing which is closed by a lid.The housing may be a rigid structure.

[0223] According to any of the embodiments or examples described above, it may generally be advantageous that different actuator elements 42 of the actuator device may be actuated independently of each other, for example to be actuated at different times (e.g. sequentially). An efficient drive circuit to achieve this is desirable to avoid the need to provide individual wire connections for each actuator element and to have an individual drive controller for each actuator element. This would be expensive and complex. For disposable devices, any such added cost is particularly an issue.

[0224] According to a first set of examples, the actuator elements may alternatively be connected in a multiplexed or serial bus manner. In this case, a plurality of actuator elements are arranged as a linear group, meaning they are electrically connected in a line manner. The data for controlling the drive of the individual actuator elements is provided on a data line, and a data line connection is made between each adjacent pair of actuator elements. The actuator elements are controlled in dependence on the data received from the data line.

[0225] Each actuator element comprises at least two power line terminals and at least one digital data line terminal. The device comprises at least two power lines and a data line, wherein each actuator element is connected in parallel between at least two power lines connected to the at least two power line terminals.

[0226] This approach represents a certain simplification, but still involves significant complexity and cost.

[0227] According to yet another preferred approach, individualized actuator control can be achieved by providing a drive electrode arrangement with independently controllable portions. For example, the electrodes arranged on at least one side of the actuator arrangement can be provided as interdigitated electrodes or variations thereof. Such an arrangement makes it possible to independently control the stimulation applied to two different actuator elements without adding any further complexity in the form of, for example, crossovers or vias.

[0228] In particular, interdigitated (eg comb) electrode structures use electrode pairs in the form of interdigitated combs (ie interlocking fingers). This allows for in-plane electrode arrangements by establishing an electric field or current for driving an actuator element in the plane between the fingers of the electrodes.

[0229] In an example, the electrode arrangements on both sides of the actuator arrangement may be provided as such interdigitated comb-type electrodes or variations thereof. It now becomes possible to independently activate four actuator elements - two (in-plane) from one side of the actuator arrangement and two (in-plane) from the other side. During actuation by the electrodes on one side, those on the other side may provide reference electrodes to establish an electric field or complete a current across the EAP actuator elements. In this way, it is possible to individually actuate a 2x2 square arrangement of actuator elements 42 (wherein the comb electrodes on both sides of the actuator arrangement are rotated 90 degrees relative to each other). Alternatively, a row of four adjacent electrodes may be individually actuated (if the comb electrodes on both sides are arranged in parallel with each other). The latter arrangement may be advantageous for generating a wave-like flow pattern in the fluid holding space 30.

[0230] A preferred arrangement for driving electronic equipment for an embodiment of the present invention will now be described.

[0231] Modes for controlling activation of the actuator elements 42 in a sequential or otherwise non-simultaneous manner are described above. Complex electronics and complex drive schemes for implementing these and other control schemes may be avoided by the novel drive scheme described above.

[0232] As the skilled person will appreciate, it is possible to drive each actuator element 42 by providing a separate control line or by implementing a 2D matrix type approach to allow the actuator elements to be activated in the required sequence. However, this would require a very large number of wires and connections between the actuator device 38 and the controller 50.

[0233] According to the proposed drive scheme, a simple and inexpensive analog electronic method is provided to activate in series a series of actuator elements 42. In particular, each actuator element is triggered to actuate by its predecessor after a variable time delay.

[0234] exist Fig.12 An example circuit is shown in FIG. This circuit is particularly suitable for embodiments in which the actuator elements 42 are activated sequentially in series. For illustration purposes, Fig.12 The circuit assumes that there are three actuator elements to be activated. However, it will be appreciated that the circuit can be extended to serve the activation of any number of actuator elements in series. Furthermore, for purposes of illustration, the actuator elements are assumed to be electroactive polymer-based elements that can be actuated by applying an electric field across the EAP layer.

[0235] As is known in the art, an EAP actuator may be electronically modeled by a capacitor and a resistor connected in parallel, both connected in series to a further resistor. Fig.12 The circuit of includes three such EAP actuator elements, as implemented by dashed boxes 82a, 82b and 82c. Each actuator circuit 82 is driven by a DC signal, for example, having a voltage at or about 200V (which is assumed to be the maximum drive amplitude of the EAP). The EAP actuator circuits 82 are connected to a common ground. Other than a single series connection 88 running between the actuator elements (which serves as a trigger line), no additional wires need to be connected to each EAP actuator circuit.

[0236] In the example shown, the first EAP actuator element 82a is activated upon supply of the operating voltage V1 .

[0237] To activate the second 82b and third 82c actuator elements, two simple circuit blocks are connected to each of the following: an electronic switching circuit (circuits 84a and 84b) and a timing circuit (circuits 86a and 86b). The switching circuit 84 supplies energy to the EAP actuator element 82 depending on the state of the timing circuit 86. The timing circuit consists of a simple RC-timer followed by a transistor switch. If EAP actuator (n-1) is activated, the timer circuit n will activate switch n after a specific time delay, which is defined by the RC time constant τ=Rd·Cd, where Rd and Cd are the resistance and capacitance of the resistor and capacitor of the RC circuit, respectively. For illustration purposes, the values ​​shown in the example circuit have been chosen to achieve a delay of 200ms. Once actuator element n is activated, the same sequence occurs for actuator element (n+1), where the element is activated after the time delay implemented by the timer circuit n+1.

[0238] Figure 1 shows that 3 is applied according to time (x-axis, trace) through Fig.128. The voltage (y-axis, V) across each EAP actuator element 82 of an exemplary circuit of FIG. 8. Line 92 shows the voltage across actuator element 82a, line 94 shows the voltage across actuator element 82b, and line 96 shows the voltage across actuator element 82c. It can be seen that there is a 200 ms delay in the current provided through each of the actuator elements.

[0239] right Fig.12 Adaptations or extensions of the example circuit are possible and will be apparent to those skilled in the art, such as extending the circuit to accommodate an EAP element, or adding additional timing and switching circuitry to deactivate one or more actuator elements after a certain time delay. By adjusting the timing (by tuning the Rd and Cd of the timing circuit), other actuation profiles and behaviors may also be produced.

[0240] As mentioned above, embodiments of the present invention may be advantageously suited for so-called organ-on-a-chip applications, and in a further example for the storage of liquids (eg blood) requiring some kind of continuous agitation.

[0241] Although in the various examples above, an actuator device 38 comprising a single EAP material layer having a segmented substrate 52 to induce localized bending has been used, other configurations are possible. In another example, the actuator device may include an array of actuator elements formed of individuals distributed on a carrier layer and individually actuable by electrical stimulation. Each may be provided with a pair of electrodes surrounding the element for applying electrical stimulation. Each may include at least one EAP material layer, and preferably includes an elastic substrate layer that induces bending.

[0242] In the case of a single EAP layer with a segmented substrate to separate the layer into individual actuator elements, individualized control of the actuator elements can be achieved by providing each respective actuator element with individually controllable electrodes. Each set of electrodes induces localized stimulation only at the location of the actuator element in question, thereby providing individualized actuation of the specific actuator element.

[0243] Materials suitable for electroactive polymers of electroactive polymer actuator devices are known. Suitable electroactive polymers include, for example, but are not limited to, the following subclasses: piezoelectric polymers, electromechanical polymers, relaxor ferroelectric polymers, electrostrictive polymers, dielectric elastomers, liquid crystal elastomers, conjugated polymers, ionic polymer metal composites, ionic gels, and polymer gels.

[0244] Subclasses of electrostrictive polymers include, but are not limited to:

[0245] Polyvinylidene fluoride (PVDF), polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE), polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene (PVDF-TrFE-CFE), polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene (PVDF-TrFE-CTFE), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyurethane or a blend thereof.

[0246] Subclasses of dielectric elastomers include, but are not limited to: acrylates, polyurethanes, silicones.

[0247] Subclasses of conjugated polymers include, but are not limited to: polypyrrole, poly-3,4-ethylenedioxythiophene, poly-p-phenylene sulfide, polyaniline.

[0248] In all of these examples, additional inactive layers may be provided for influencing the electrical and / or mechanical behavior of the EAP particles in response to an applied electric field.

[0249] Each EAP particle can be sandwiched between electrodes. The electrodes can be stretchable so that they follow the deformation of the EAP material. Suitable materials for the electrodes should be ultrasound transparent and include, for example, metal films (such as gold, copper or aluminum) or organic conductors (such as carbon black, carbon nanotubes, graphene, polyaniline (PANI), poly (3,4-ethylenedioxythiophene) (PEDOT) (e.g., poly (3,4-ethylenedioxythiophene) poly (styrene sulfonate) (PEDOT: PSS))).

[0250] If the electrodes are arranged in an asymmetric structure, the applied voltage can induce various deformations, such as twisting, rolling, torsion, rotation, and asymmetric bending deformation.

[0251] As discussed above, some embodiments of the actuator device aspects of the present invention utilize a controller. The controller can be implemented in a variety of ways using software and / or hardware to perform the various functions required. A processor is an example of a controller that employs one or more microprocessors that can be programmed using software (e.g., microcode) to perform the desired functions. However, the controller can be implemented with or without a processor, and can also be implemented as a combination of dedicated hardware that performs some functions and a processor (e.g., one or more programmed microprocessors and associated circuits) that performs other functions.

[0252] Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field programmable gate arrays (FPGAs).

[0253] In various embodiments, a processor or controller may be associated with one or more storage media, such as volatile and non-volatile computer memory, such as RAM, PROM, EPROM, and EEPROM. The storage media may be encoded with one or more programs that perform the desired functions when run on one or more processors and / or controllers. The various storage media may be fixed within a processor or controller, or may be transportable so that one or more programs stored thereon may be loaded into a processor or controller.

[0254] Those skilled in the art will be able to understand and implement other variations of the disclosed embodiments in practicing the claimed invention by studying the drawings, the disclosure and the claims. In the claims, the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. Although specific measures are recited in mutually different dependent claims, this does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be interpreted as limiting the scope.

Claims

1. A biological cell preservation device, comprising: a chamber defining a fluid holding space (30) adapted, in use, to hold a volume of fluid (34) and adapted, in use, to hold biological cells for retention in said volume of fluid (34); an impermeable deformable membrane (36) disposed within the chamber or defining a surface of the chamber; an electroactive polymer actuator device (38) arranged to deform the deformable membrane, wherein the membrane maintains its impermeability, the electroactive polymer actuator device being controllable to achieve a controlled change in the surface topology of the deformable membrane, and comprising an array of actuator elements (42); and The deformable membrane is arranged such that, in use, the surface topology is changed in a sequence of topological changes by sequentially actuating the actuator elements (42) in a direction to produce a flow of the fluid in said direction, wherein said direction corresponds to the direction of said sequence of topological changes and is parallel to the plane of the deformable membrane, wherein the change in surface topology comprises surface deformation of the deformable membrane (36) directed inwardly and outwardly from the fluid holding space (30), the inward deformation being volumetrically balanced with the outward deformation such that there is a zero net change in the volume of the fluid holding space before and after the change in surface topology.

2. The biological cell holding device according to claim 1, further comprising a controller (50) configured to control the electroactive polymer actuator device (38) to achieve the controlled change of the surface topology of the deformable membrane (36).

3. The biological cell storage device according to claim 1 or 2, wherein: The chamber is a fluid closed chamber for retaining the volume of fluid in use.

4. The biological cell storage device according to claim 2, wherein: The controller (50) is adapted to effectuate regular or periodic changes in the surface topology of the membrane on a continuous basis, thereby creating a fluid flow in which fluid is continuously or simultaneously exchanged between the first sub-region (46) and the second sub-region (48).

5. The biological cell storage device according to any one of claims 1, 2 and 4, wherein: The deformable membrane (36) at least partially delimits the fluid holding space (30).

6. The biological cell storage device according to any one of claims 1, 2 and 4, wherein: Each actuator element comprises an electroactive polymer, and wherein each actuator element is actuatable to undergo a bending motion.

7. The biological cell storage device according to claim 1, wherein: The electroactive polymer actuator device (38) comprises an actuation layer, the actuation layer comprising the array of actuator elements (42), and, Wherein the electroactive polymer actuator device comprises an electroactive polymer layer, and wherein each actuator element comprises a segment of the electroactive polymer layer.

8. The biological cell storage device according to claim 1, wherein: Each actuator element is electrically drivable to move between a first stable actuation position and a second stable actuation position.

9. The biological cell storage device according to any one of claims 1, 2, 4, 7 and 8, wherein: The device is a cell culture device and wherein the flow of the fluid is used to achieve nutrient replenishment of cells positioned at or adjacent to the deformable membrane (36).

10. The biological cell storage device according to claim 9, wherein: The device comprises a substrate for culturing biological cells, the substrate being arranged within the chamber, and wherein the substrate is adapted to retain the cells on the substrate, and wherein the substrate forms at least part of a sheet for organ-on-a-chip cell growth.

11. The biological cell storage device according to any one of claims 1, 2, 4, 7 and 8, wherein: The device is a blood storage device, and wherein the deformable membrane (36) is used to agitate blood stored in the fluid holding space to prevent activation of platelets in the blood and / or to prevent coagulation of the blood, and wherein the blood storage device comprises a blood storage bag (64) forming the chamber.

12. The biological cell storage device according to claim 11, wherein: The deformable membrane (36) forms at least part of a closed wall (66a, 66b) of the fluid holding space (30), and wherein the electroactive polymer actuator device (38) comprises an actuation layer comprising an electroactive polymer, the layer being arranged to abut against the deformable membrane in an engaging manner to form a wall of the fluid holding space for deforming the membrane.

13. The biological cell storage device according to any one of claims 1, 2, 4, 7, 8, 10 and 12, wherein: The electroactive polymer actuator device (38) comprises an electrostrictive electroactive polymer material.

14. A biological cell preservation device according to any one of claims 1, 2, 4, 7, 8, 10 and 12, comprising a controller (50) configured to control the electroactive polymer actuator device to achieve the controlled change in the surface topology of the deformable membrane (36), wherein The controller (50) is adapted to control the actuator elements (42) to be actuated in a cascaded manner, wherein the actuators are actuated in sequentially successive groups, each actuated group being larger than a previously actuated group.

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