Patent Description:
This invention was made with government support under Grant Number 2R44DA041173-<NUM> awarded by the National Institute on Drug Abuse at the National Institutes of Health.

The invention relates to valves for fluidic devices, particularly to valves that rest in a metastable state where multiple valves on a fluid path are open before switching to a stable state that allows only one inlet or outlet valve on a fluid path to be open at a time.

Fluidic microvalves can be constructed of cantilevered spring arms squeezing a compressible tube. <CIT> teaches a pinch valve consisting of a lever arm actuated preferably by a solenoid, but alternatively by a cam, that pinches a soft tube. <CIT> teaches a microfluidic pinch valve consisting of cantilevered arms squeezing a compressible tube where compression force is provided by an actuator. Actuator mechanisms such as magnetic, piezoelectric, pneumatic, and mechanical are mentioned. This patent makes no mention, however, of valves synchronized such that closing one fluid path allows for the opening of another flow path. International Patent App. No. <CIT> teaches a dual latching microvalve wherein both valves close momentarily before one valve opens. This application makes no mention of initially positioning the dual latching valves in a metastable state permitting both inlet and outlet fluid paths to be open to allow for fill and priming of the fluidic network. <CIT> teaches of a dual latching cam microvalve comprised of a cam that when rotated causes a valve arm to either pinch or un-pinch a compressible tube. No specification of cam shape is made, nor is there any mention of a metastable state permitting flow through both fluid paths. <CIT> discloses a multi-type medicinal fluid flow rate control apparatus and a medicinal fluid injector.

The present invention is directed to dual latching microvalves capable of a metastable state where multiple valves on a fluid path are open before switching to a stable state that allows only one inlet or outlet valve on a fluid path to be open at a time. Because embodiments of the present invention involve a new feature of dual latching valves, normal operation of these valves will be described first, followed by differentiation of the present invention. Normal operation of the dual latching valves is the stable state. One important application of dual latching microvalves is metered control of fluid flow from a large reservoir into a smaller reservoir and then to the outlet. One valve (the inlet valve) of the set of dual latching valves is between the large reservoir and the small metering reservoir and the second valve (the outlet valve) of the set is between the metering reservoir and the outlet. A set of dual latching microvalves work in concert such that one valve is always latched closed when the other valve is open, which prevents an open pathway from the reservoir to the outlet. A valve mechanism controls operation of the two valves and physically prevents them from being open at the same time. The benefits of such an arrangement become apparent when used in on-body drug delivery pods. An example is insulin delivery where contents of the reservoir could be fatal if accidentally delivered all at once. This danger can be mitigated using a set of dual latching microvalves and a much smaller, intermediate metering chamber.

The cam embodiments of dual latching microvalves are constructed using a cam as the valve mechanism so that rotation of a single cam controls the timing of opening and closing of the inlet and outlet valves such that both valves are closed temporarily before one of the valves is opened. In certain implementations, the valve mechanism is actuated by passing a current through a shape memory alloy (SMA) wire, causing the wire to heat and contract. The wire rotates the cam which pinches a resilient compressible tube stopping flow, or releases the tube permitting flow. This can be achieved with the cam directly or using a cam follower, such as a valve end, that compresses and releases the resilient tubing.

One non-limiting application of the cam embodiment of a dual latching microvalve is in drug delivery (for example insulin) using an electrochemiosmotic reciprocating pump with a built-in metering chamber. The cam-controlled dual-latching microvalves provide an important safety feature as the coordinated operation of the pump inlet and outlet valves prevent an open line between reservoir and patient.

The present invention provides for a metastable state for the dual latching microvalves that is in direct contradiction to the stable operating state where only one valve is open at a time. The metastable state uses an interference mechanism to intentionally allow both valves to open at the same time, providing a direct fluid path from the reservoir to the outlet (i.e. both valves are open at once) so that the entire fluid path can be easily primed with solution prior to stable operation. The metastable state permits easy filling of the fluidic system.

Alterations to a standard dual-latching cam microvalve that allow for a metastable state out of the plane of the valve seat can include a valve arm comprising a valve arm end that returns to a stable state after being held in the metastable state, shaping of the cam to create a space for the valve arm end to move into position for normal operation under its own resilience, a slope to the cam and or valve arm end that allows for the valve arm end to slide easily into position for normal operation and a raised edge on the surface of the cam or the valve arm end to help hold the valve arm end in the metastable state during storage. Other interference mechanisms besides a cam can also possess these features for the creation of a metastable state.

Other embodiments could include a pin or other removeable structure that would hold the valve arm end in the metastable state. Alternatively, the metastable state can be obtained with the valve arm in the plane of the valve seat by temporarily creating a gap on either side of the compressible tube that prevents the valve arm end from compressing the tube against the valve seat. In this case, the temporary gap is closed after prime and flush of the fluid line. These and other features, and advantages of the present invention will become better understood from a consideration of the following detailed description and drawings as follows:.

Before the present invention is described in further detail, it should be understood that the invention is not limited to the particular embodiments described, and that the terms used in describing the particular embodiments are for the purpose of describing those particular embodiments only, and are not intended to be limiting, since the scope of the present invention will be limited only by the claims.

As in the Brief Summary of the Invention, stable operation of dual latching valves will be described first (<FIG>) followed by a description of the present invention: the metastable state of dual latching valves (<FIG>). Although the focus of this description is on the metastable state of dual latching cam microvalves, embodiments can be envisioned for other types of dual latching valves.

The dual latching valve can be designed in different ways. <FIG> depicts the valve mechanism as a cam that is a rotating semi-circular disk <NUM> that acts to alternatively pinch two flexible tubes <NUM>, <NUM>. The cam valve wheel is rotated by actuation of the Shape Memory Alloy (SMA) wires <NUM>, <NUM> which have one end attached to the cam and the other attached to the base. <FIG> illustrates the cam in a stable operational state, wherein the left side tube <NUM> is open and the right-side tube <NUM> is pinched shut. The valve can stay in this state indefinitely and requires no power. When electric current passes through the right SMA wire <NUM> the wire contracts and the cam rotates clockwise. During clockwise rotation, the cam's profile continues pinching the right tube <NUM> and begins pinching the left tube <NUM>. As the cam continues to rotate clockwise, both fluid paths <NUM>, <NUM> are closed as shown in <FIG>. Upon completion of the clockwise rotation, the right fluid path <NUM> is open and the left fluid path <NUM> is closed. The valve is stable in this state indefinitely and requires no power. Rotation of the cam in the counterclockwise direction is prevented by the friction of the assembly. To switch the valve back to state <NUM>, the left SMA wire <NUM> is heated by the flow of electricity. As the left SMA wire <NUM> contracts, it both rotates the cam <NUM> counterclockwise and stretches the right SMA wire <NUM>. After counterclockwise rotation, the left fluid path <NUM> is open and the right fluid path <NUM> is closed, and the valve is returned to the original state in <FIG>. The cam is stable in this position until the right SMA wire <NUM> is energized. In summary, only one tube is open at a time preventing an open path between reservoir and patient. This significant safety feature prevents accidental overdose even in the case of device failure when used as a medicament delivery device for a patient.

In the previously described dual latching cam valve, the tube contact profile was on the circumference of the semicircular disk <NUM>. Another type of dual latching cam valve, shown in <FIG>, uses a cam with a varying radius <NUM> which displaces cam following valve arms <NUM>, <NUM>. The cam <NUM> may be actuated by the SMA wires <NUM>,<NUM> and use a cam follower attached, or integral, to a flexible beam to compress the tubing. When electric current passes through the right SMA wire <NUM>, the wire contracts, and the cam <NUM> rotates clockwise. Clockwise rotation pushes the right valve arm <NUM> to the right, pinching the right tube <NUM> to prevent fluid flow. Meanwhile, the left valve arm <NUM> is free to move to the right to its relaxed position allowing the left tube <NUM> to open, permitting fluid flow. In <FIG> both valve arms <NUM>, <NUM> are made from spring wire, though plastic or other materials could be used. The beams are capped with a plastic valve head to create a flat smooth surface for compressing the flexible tubes. The tube orientation relative to the valve arm can be in different orientations so long as the head of the valve arm can compress the tube to stop flow.

When the left SMA wire <NUM> is energized, it contracts, rotating the cam <NUM> counterclockwise. After passing through the interim position, where both tubes <NUM> and <NUM> are pinched shut similar to the condition in <FIG>, the cam will rest in a state in which the left tube <NUM> is compressed closed, and the right tube <NUM> is open. As depicted in <FIG> the cam rotation can be accomplished by SMA wires but it is not limited to this type of actuation and it can be achieved by any actuator that will cause the cam to rotate such as a motor, gear, magnet, or other method.

<FIG> depicts one embodiment of the current invention showing one valve arm in a metastable state with both valves open. In <FIG> the cam <NUM> is rotated to its counterclockwise position and the left resilient valve arm <NUM> is placed on the cam <NUM> where it remains under its own resilient force, leaving both sides open to flow. Having both sides open to flow is preferred during fluid loading and priming of the system. No power is required to remain in the metastable state. When the right SMA wire <NUM> is activated in this embodiment, the cam <NUM> will rotate clockwise first compressing the right tube <NUM> to close the valve. Further clockwise rotation will move the cam from under the left resilient valve arm <NUM> allowing it to transition to a stable operation position under its own resilience. In this non-limiting embodiment, <NUM>° of clockwise rotation of the cam <NUM> will pinch the right tube <NUM> shut and at <NUM>° of clockwise rotation the resilient valve arm <NUM> will be freed to enter the stable operating position.

The valve is then in the normal operational state with only one valve open to flow. Operation would then proceed as normal with the cam valve mechanism closing both valves before permitting a single open valve. After activation, when the resilient valve arm <NUM> enters the stable position, the valve cannot be placed back into the metastable state without an external force perpendicular to the direction of movement in the valve. The resilient force of the left valve arm presses the valve end down on the valve base <NUM>. Please note that the cam is shaped so that it provides space for the left resilient valve arm <NUM> to return to the stable operating position upon clockwise rotation. In this embodiment, the width of the head of the resilient valve arm is <NUM> and the notch in the cam can accommodate a valve head of <NUM>, ensuring that the resilient valve arm has sufficient room to begin stable operation when the metastable state is terminated. Either arm can be used for the metastable state, indeed the metastable state could be chosen at different cam positions based on cam and valve arm profile chosen.

In a non-limiting example, a drug delivery device with this dual latching valve could be placed in the metastable state during assembly. The valve would be stored in this state, permitting the user to easily fill the pod since there would not be an obstruction preventing air or fluid from escaping during filling. After filling, valve activation would transition the pod to a safe condition precluding an open path between reservoir and patient.

Improvements can be made to the drawing in <FIG> such that the metastable state would be more secure, such as a lip or a grove on the cam or valve arm end which would prevent the metastable state from terminating, for example, during shipping. Additionally, a taper could be added to the cam or valve arm end to ensure proper placement when the metastable state is terminated.

In other embodiments, a valve arm may be moved perpendicularly to the plane of a valve and placed on an interference mechanism that is not a cam, but that would still move out of the way upon activation of the valve. In this case, the resilience of the valve arm would move it back into the plane of the valve once the interfering mechanism had been moved through initial activation of the valve, terminating the metastable state.

In another embodiment, the interference mechanism may be a removeable pin or other obstruction that could be used to create a metastable state, as show in <FIG>. In this figure the cam <NUM> is designed so that the cam lobes push the valve arms into an open position, as opposed to the valves shown in <FIG> and <FIG>. In <FIG>, the cam is positioned so that the left valve arm <NUM> is in the open position and the right valve arm <NUM> would be in the closed position under stable operation. The restoring spring <NUM> would normally push the right valve arm <NUM> to compress the right tube <NUM>, however, that action is prevented by the presence of a removeable pin <NUM> that maintains the metastable state. Once the pin is physically removed, the right restoring spring <NUM> would push the right valve arm <NUM> to compress the tube <NUM>. From that point on, coordinated activation of the right SMA wire <NUM> and left SMA wire <NUM> would rotate the cam for stable operation of the dual latching valve. If it is desirable to return the right valve arm <NUM> back to the metastable state, the pin <NUM> could be placed back into position.

Another implementation can be set forth where the valve seat is located on a bi-stable membrane, spring wire, flexible beam, or is otherwise moveable. This embodiment would act in a similar fashion. For example, in a metastable state, a first valve seat is set away from the first tube, so that the first tube will no longer be pinched when the first valve arm is in a normally closed position. Once the first valve seat enters its stable position, the dual latching valve would initiate its normal operation.

An embodiment of a valve seat in a metastable state is shown in <FIG>. In this embodiment, the dual latching valve set is initially in the metastable state with a gap <NUM> that prevents pinching of the right tube <NUM> by the right valve arm <NUM> even though the cam is rotated clockwise in the closed position. This allows both fluid paths to be open for priming of the fluid network. After priming, the metastable state is deactivated by closing the gap along the latching slides <NUM>, which will result in pinching of the right tube <NUM> and stable operation of the dual latching cam valve.

For any of the described cam valves, in addition to friction holding the cam in a stable position, it is envisioned that a mechanism with a notch, spring fingers, detent, or other methods can be utilized to hold the cam in specific positions unless the cam is actuated intentionally.

Results for control of fluid flow using a prototype cam valve are presented in the graph of <FIG>. The graph shows that both fluid paths are open at the beginning of the test. The test setup consists of a flask with water and two tubes, each having one end submerged in the water, with each tube passing through one of the flow paths of the valve. A Sensirion flow sensor is attached to each flow path and configured to measure the flow of water through the valve. A measured flow rate of approximately <NUM>,<NUM> nL/min indicates unobstructed flow. Both flow paths are filled with liquid and the flask is raised, establishing a siphon from the flask, through both paths of the valve, and through the flow sensors. Flow rate data for both fluid paths is shown in <FIG> represented as dotted and solid lines. The dual latching valve was left in the metastable state for approximately <NUM> minute and shows flow through both paths. Activation of one SMA wire switched the dual latching cam valve to normal operation and closed the first fluid path (dotted line). After approximately <NUM> seconds the other SMA wire was activated causing the second path to close (solid line) followed by opening of the first path (dotted line). Also shown is that opening of one fluid path is accompanied by closing of the other path after the initial metastable state is terminated.

In a simple embodiment of a fluid delivery device using a dual latching microvalve, a single set of dual latching microvalves is used to control the flow of fluid from a reservoir into a metering chamber of a reciprocating displacement pump and then from the pump into the target application (insulin to a patient for example). This is illustrated in <FIG>. Initially with the valve in a metastable storage state <FIG>, a syringe <NUM> is used to prime the reservoir and the fluid path with insulin <NUM>. This can be accomplished by loading drug into a syringe <NUM> and then injecting the insulin <NUM> through a resealable septum into the reservoir <NUM>, through the open the inlet valve <NUM>, pump metering chamber <NUM>, and open outlet valve <NUM>. A user would know that the system had been primed when a drop of insulin <NUM> exits the system. The valve would then be activated, terminating the metastable state and the system could be attached to the patient. <FIG> then show normal operation of the dual latching valves where only one fluid path is open at a time. <FIG> shows fluid flowing through the open valve <NUM> into the metering chamber <NUM>, further flow is then stopped by the closed valve <NUM>. The dual latching valves are then switched to the position shown in <FIG> and the dose is safely delivered from the metering chamber <NUM> out through the open valve <NUM> and delivered to the patient.

In another pumping scheme, two dual latching microvalves could be employed, either to allow continuous flow from a two-sided electrochemiosmotic pump such as the ePump from SFC Fluidics, Inc. , or to independently control fluid from both sides of an ePump to deliver two drugs (e.g., Insulin and Glucagon). In this embodiment with two sets of dual latching microvalves, both valve sets would be assembled in a metastable state permitting easy fluidic priming (drug loading) by the patient. Alternatively, a single cam (or other valve mechanism) could control fluid flow through two inlet and two outlet ports to allow continuous flow using a dual sided ePump. In this case, a single rotation of the cam would terminate the metastable state of two valve sets. Further variations on this theme can be expanded to encompass multiple inlet and outlet valves as well.

Many parts of the description herein refer to Shape Memory Alloy (SMA) wire as the actuation mechanism to terminate the metastable state and operate the valve normally. Cam actuation may also be accomplished by other methods such as motors, gears or linear actuators.

Claim 1:
A dual-latching valve operable in a metastable state, comprising:
a) first and second compressible tubes (<NUM>,<NUM>);
b) first and second valve arms (<NUM>) positioned adjacent to the first and second tubes (<NUM>,<NUM>), respectively, and thereby forming first and second valves;
c) a valve mechanism (<NUM>) operable to selectively open and close the first and second valves by selectively engaging with the first and second valve arms (<NUM>) wherein only one of the first and second valves is open at a time; and
d) an interference mechanism positioned to engage at least one of the first and second valve arms (<NUM>) whereby the dual latching valve enters a metastable state allowing fluid flow simultaneously through the first and second valves;
characterized in that the dual-latching valve is on a single flow path.