Drug Heating Cycle Limiter For Injection Device

Abstract

An injection assembly includes a dispensing chamber housing, a temperature control device, a thermal sensor, a switch, and a controller. The dispensing chamber housing has an inner surface and an outer surface. The inner surface partially defines a dispensing chamber for receiving a quantity of a substance. The temperature control device at least partially surrounds the dispensing chamber housing and alters a temperature of a substance in the dispensing chamber. The thermal sensor is located near the temperature control device and reads a temperature near the temperature control device. The switch is coupled to the temperature control device. The controller controls the temperature control device and the switch such that a first voltage is applied to the temperature control device until the temperature control device reaches a desired temperature, and a second voltage is applied to the temperature control device thereafter to maintain the temperature control device at the desired temperature.

Description

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 11/581,629 filed Oct. 16, 2006, U.S. patent application Ser. No. 11/581,630 filed Oct. 16, 2006, U.S. patent application Ser. No. 11/581,591 filed Oct. 16, 2006, and is related to U.S. patent application Ser. No. 11/435,906 filed May 17, 2006.

BACKGROUND OF THE INVENTION

The present invention relates to a single-use medical device and more particularly to a two-piece ophthalmic injection device with a disposable tip end containing a temperature control device and temperature sensor assembly.

Several diseases and conditions of the posterior segment of the eye threaten vision. Age related macular degeneration (ARMD), choroidal neovascularization (CNV), retinopathies (e.g., diabetic retinopathy, vitreoretinopathy), retinitis (e.g., cytomegalovirus (CMV) retinitis), uveitis, macular edema, glaucoma, and neuropathies are several examples.

These, and other diseases, can be treated by injecting a drug into the eye. Such injections are typically done manually using a conventional syringe and needle. FIG. 1 is a perspective view of a prior art syringe used to inject drugs into the eye. In FIG. 1, the syringe includes a needle 105, a luer hub 110, a chamber 115, a plunger 120, a plunger shaft 125, and a thumb rest 130. As is commonly known, the drug to be injected is located in chamber 115. Pushing on the thumb rest 130 causes the plunger 120 to expel the drug through needle 105.

In using such a syringe, the surgeon is required to pierce the eye tissue with the needle, hold the syringe steady, and actuate the syringe plunger (with or without the help of a nurse) to inject the fluid into the eye. The volume injected is typically not controlled in an accurate manner because reading the vernier is subject to parallax error. Fluid flow rates are uncontrolled and tissue damage may occur due to an “unsteady” injection. Reflux of the drug may also occur when the needle is removed from the eye.

An effort has been made to control the delivery of small amounts of liquids. A commercially available fluid dispenser is the ULTRA™ positive displacement dispenser available from EFD Inc. of Providence, R.I. The ULTRA dispenser is typically used in the dispensing of small volumes of industrial adhesives. It utilizes a conventional syringe and a custom dispensing tip. The syringe plunger is actuated using an electrical stepper motor and an actuating fluid. Parker Hannifin Corporation of Cleveland, Ohio distributes a small volume liquid dispenser for drug discovery applications made by Aurora Instruments LLC of San Diego, Calif. The Parker/Aurora dispenser utilizes a piezo-electric dispensing mechanism. Ypsomed, Inc. of Switzerland produces a line of injection pens and automated injectors primarily for the self-injection of insulin or hormones by a patient. This product line includes simple disposable pens and electronically-controlled motorized injectors.

U.S. Pat. No. 6,290,690 discloses an ophthalmic system for injecting a viscous fluid (e.g. silicone oil) into the eye while simultaneously aspirating a second viscous fluid (e.g. perflourocarbon liquid) from the eye in a fluid/fluid exchange during surgery to repair a retinal detachment or tear. The system includes a conventional syringe with a plunger. One end of the syringe is fluidly coupled to a source of pneumatic pressure that provides a constant pneumatic pressure to actuate the plunger. The other end of the syringe is fluidly coupled to an infusion cannula via tubing to deliver the viscous fluid to be injected.

It would be desirable to have a portable hand piece for injecting a drug into the eye. Such a hand piece can include a limited reuse assembly attachable to and removable from a disposable tip segment. The disposable tip segment contains the drug, a needle for administering the drug, and a temperature control device, such as a heater, for altering the temperature of the drug. Typically, the drug is suspended in a compound that is heated. In order to maintain the integrity of the drug, it is desirable to limit the number of times it is heated. Therefore, it would be desirable to implement a drug delivery hand piece with such a heating limitation.

SUMMARY OF THE INVENTION

In one embodiment consistent with the principles of the present invention, the present invention is a dispensing assembly including a dispensing chamber housing, a temperature control device, a thermal sensor, and a controller. The dispensing chamber housing has an inner surface and an outer surface. The inner surface partially defines a dispensing chamber for receiving a quantity of a substance. The temperature control device at least partially surrounds the dispensing chamber housing and alters a temperature of a substance in the dispensing chamber. The thermal sensor is located near the temperature control device and reads a temperature near the temperature control device. The controller controls the temperature control device such that the substance in the dispensing chamber is not exposed to temperature stress.

In another embodiment consistent with the principles of the present invention, the present invention is an injection assembly including a dispensing chamber housing, a temperature control device, a thermal sensor, a switch, and a controller. The dispensing chamber housing has an inner surface and an outer surface. The inner surface partially defines a dispensing chamber for receiving a quantity of a substance. The temperature control device at least partially surrounds the dispensing chamber housing and alters a temperature of a substance in the dispensing chamber. The thermal sensor is located near the temperature control device and reads a temperature near the temperature control device. The switch is coupled to the temperature control device. The controller controls the temperature control device. The controller controls the switch such that a first voltage is applied to the temperature control device until the temperature control device reaches a desired temperature, and a second voltage is applied to the temperature control device thereafter to maintain the temperature control device at the desired temperature.

In another embodiment consistent with the principles of the present invention, the present invention is a method of operating a dispensing assembly including checking a count of a number of times a temperature control device has been activated; if the count does not exceed a preset number, incrementing a counter; applying a first voltage across a temperature control device to bring the temperature control device to a desired temperature; after the temperature control device reaches the desired temperature, applying a second voltage across the temperature control device to maintain the temperature control device at the desired temperature; then starting a timer to count the amount of time that the temperature control device is activated; and if the amount of time that the temperature control device is activated exceeds a preset amount of time, the temperature control device is turned off.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the invention as claimed. The following description, as well as the practice of the invention, set forth and suggest additional advantages and purposes of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.

FIG. 1 is a perspective view of a prior art syringe.

FIG. 2 is a view of an ophthalmic medical device including a disposable tip segment and a limited reuse assembly according to the principles of the present invention.

FIG. 3 is an embodiment of a limited reuse assembly according to the principles of the present invention.

FIG. 4 is a cross section view of a disposable tip segment and a limited reuse assembly according to the principles of the present invention.

FIG. 5 is a cross section view of a disposable tip segment according to the principles of the present invention.

FIG. 6 is a block diagram of an implementation of a drug heating cycle limiter according to the principles of the present invention.

FIG. 7 is a block diagram of an implementation of a drug heating cycle limiter according to the principles of the present invention.

FIG. 8 is a graph of one operation of a drug heating cycle limiter according to the principles of the present invention

FIG. 9 is a flow chart of a method of operating a drug heating cycle limiter according to the principles of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is now made in detail to the exemplary embodiments of the invention, examples of which are illustrated in the accompanying figures. Wherever possible, the same reference numbers are used throughout the figures to refer to the same or like parts.

FIG. 2 depicts one view of an ophthalmic medical device including a disposable tip segment and a limited reuse assembly according to an embodiment of the present invention. In FIG. 2, the medical device includes a tip segment 205 and a limited reuse assembly 250. The tip segment 205 includes a needle 210, a housing 215, and an optional light 275. The limited reuse assembly 250 includes a housing 255, a switch 270, a lock mechanism 265, and a threaded portion 260.

Tip segment 205 is capable of being connected to and removed from limited reuse assembly 250. In this embodiment, tip segment 205 has a threaded portion on an interior surface of housing 215 that screws onto the threaded portion 260 of limited reuse assembly 250. In addition, lock mechanism 265 secures tip segment 215 to limited reuse assembly 250. Lock mechanism 265 may be in the form of a button, a sliding switch, or a cantilevered mechanism. Other mechanisms for connecting tip segment 205 to limited reuse assembly 250, such as those involving structural features that mate with each other, are commonly known in the art and are within the scope of the present invention.

Needle 210 is adapted to deliver a substance, such as a drug, into an eye. Needle 210 may be of any commonly known configuration. Preferably, needle 210 is designed such that its thermal characteristics are conducive to the particular drug delivery application. For example, when a heated drug is to be delivered, needle 210 may be relatively short (several millimeters) in length to facilitate proper delivery of the drug based on thermal characteristics.

Switch 270 is adapted to provide an input to the system. For example, switch 270 may be used to activate the system or to turn on a heater. Other switches, buttons, or user-directed control inputs are commonly known and may be employed with limited reuse assembly 250 and/or tip segment 205.

Optional light 275 is illuminated when tip segment 205 is ready to be used. Optional light 275 may protrude from housing 215, or it may be contained within housing 215, in which case, optional light 275 may be seen through a clear portion of housing 215. In other embodiments, optional light 275 may be replaced by an indicator, such as a liquid crystal display, segmented display, or other device that indicates a status or condition of disposable tip segment 205. For example, optional light 275 may also pulse on and off to indicate other states, such as, but not limited to a system error, fully charged battery, insufficiently charged battery or faulty connection between the tip segment 205 and limited use assembly 250. While shown on tip segment 205, optional light 275 or other indicator may be located on limited reuse assembly 250.

FIG. 3 is another embodiment of a limited reuse assembly according to the principles of the present invention. Limited reuse assembly 250 includes a button 310, a display 320, and a housing 330. Disposable tip segment 205 attaches to end 340 of limited reuse assembly 250. Button 310 is actuated to provide an input to the system. As with switch 270, button 310 may activate a heater or other temperature control device or initiate actuation of a plunger. Display 320 is a liquid crystal display, segmented display, or other device that indicates a status or condition of disposable tip segment 205 or limited reuse assembly 250.

FIG. 4 is a cross section view of a disposable tip segment and a limited reuse assembly according to an embodiment of the present invention. FIG. 4 shows how tip segment 205 interfaces with limited reuse assembly 250. In the embodiment of FIG. 4, tip segment 205 includes plunger interface 420, plunger 415, dispensing chamber housing 425, tip segment housing 215, temperature control device 450, thermal sensor 460, needle 210, dispensing chamber 405, interface 530, and tip interface connector 520. Limited reuse assembly 250 includes mechanical linkage 545, actuator shaft 510, actuator 515, power source 505, controller 305, limited reuse assembly housing 255, interface 535, and limited reuse assembly interface connector 525.

In tip segment 205, plunger interface 420 is located on one end of plunger 415. The other end of plunger 415 forms one end of dispensing chamber 405. Plunger 415 is adapted to slide within dispensing chamber 405. An outer surface of plunger 415 is fluidly sealed to the inner surface of dispensing chamber housing 425. Dispensing chamber housing 425 surrounds the dispensing chamber 405. Typically, dispensing chamber housing 425 has a cylindrical shape. As such, dispensing chamber 405 also has a cylindrical shape.

Needle 210 is fluidly coupled to dispensing chamber 405. In such a case, a substance contained in dispensing chamber 405 can pass through needle 210 and into an eye. Temperature control device 450 at least partially surrounds dispensing chamber housing 425. In this case, temperature control device 450 is adapted to heat and/or cool dispensing chamber housing 425 and any substance contained in dispensing chamber 405. Interface 530 connects temperature control device 450 and thermal sensor 460 with tip interface connector 520.

The components of tip segment 205, including dispensing chamber housing 425, temperature control device 450, and plunger 415 are at least partially enclosed by tip segment housing 215. In one embodiment consistent with the principles of the present invention, plunger 415 is sealed to the interior surface of dispensing chamber housing 425. This seal prevents contamination of any substance contained in dispensing chamber 405. For medical purposes, such a seal is desirable. This seal can be located at any point on plunger 415 or dispensing chamber housing 425.

In limited reuse assembly 250, power source 505 provides power to actuator 515. An interface (not shown) between power source 505 and actuator 515 serves as a conduit for providing power to actuator 515. Actuator 515 is connected to actuator shaft 510. When actuator 515 is a stepper motor, actuator shaft 510 is integral with actuator 515. Mechanical linkage interface 545 is connected to actuator shaft 510. In this configuration, as actuator 515 moves actuator shaft 510 upward toward needle 210 mechanical linkage interface 545 also moves upward toward needle 210.

Controller 305 is connected via interface 535 to limited reuse assembly interface connecter 525. Limited reuse assembly interface connecter 525 is located on a top surface of limited reuse assembly housing 255 adjacent to mechanical linkage interface 545. In this manner, both limited reuse assembly interface connector 525 and mechanical linkage interface 545 are adapted to be connected with tip interface connector 520 and plunger interface 420 respectively.

Controller 305 and actuator 515 are connected by an interface (not shown). This interface (not shown) allows controller 305 to control the operation of actuator 515. In addition, an interface (not shown) between power source 505 and controller 305 allows controller 305 to control operation of power source 505. In such a case, controller 305 may control the charging and the discharging of power source 505 when power source 505 is a rechargeable battery.

Controller 305 is typically an integrated circuit with power, input, and output pins capable of performing logic functions. In various embodiments, controller 305 is a targeted device controller. In such a case, controller 305 performs specific control functions targeted to a specific device or component, such as a temperature control device or a power supply. For example, a temperature control device controller has the basic functionality to control a temperature control device. In other embodiments, controller 305 is a microprocessor. In such a case, controller 305 is programmable so that it can function to control more than one component of the device. In other cases, controller 305 is not a programmable microprocessor, but instead is a special purpose controller configured to control different components that perform different functions. While depicted as one component, controller 305 may be made of many different components or integrated circuits.

Tip segment 205 is adapted to mate with or attach to limited reuse assembly 250 as previously described. In the embodiment of FIG. 5, plunger interface 420 located on a bottom surface of plunger 415 is adapted to mate with mechanical linkage interface 545 located near a top surface of limited reuse assembly housing 255. In addition, tip interface connector 520 is adapted to connect with limited reuse assembly interface connector 525. When tip segment 205 is connected to limited reuse assembly 250 in this manner, actuator 515 and actuator shaft 510 are adapted to drive plunger 415 upward toward needle 210. In addition, an interface is formed between controller 305 and temperature control device 450. A signal can pass from controller 305 to temperature control device 450 through interface 535, limited reuse assembly interface connector 525, tip interface connector 520, and interface 530.

In operation, when tip segment 205 is connected to limited reuse assembly 250, controller 305 controls the operation of actuator 515. Actuator 515 is actuated and actuator shaft 510 is moved upward toward needle 210. In turn, mechanical linkage interface 545, which is mated with plunger interface 420, moves plunger 415 upward toward needle 210. A substance located in dispensing chamber 405 is then expelled through needle 210.

In addition, controller 305 controls the operation of temperature control device 450. Temperature control device 450 is adapted to heat and/or cool dispensing chamber housing 425. Since dispensing chamber housing 425 is at least partially thermally conductive, heating or cooling dispensing chamber housing 425 heats or cools a substance located in dispensing chamber 405. Temperature information can be transferred from thermal sensor 460 to controller 305 via any of a number of different interface configurations. This temperature information can be used to control the operation of temperature control device 450. When temperature control device 450 is a heater, controller 305 controls the amount of current that is sent to temperature control device 450. The more current sent to temperature control device 450, the hotter it gets. In such a manner, controller 305 can use a feed back loop utilizing information from thermal sensor 460 to control the operation of temperature control device 450. Any suitable type of control algorithm, such as a proportional integral derivative (PID) algorithm, can be used to control the operation of temperature control device 450.

FIG. 5 is a cross section view of a disposable tip segment for an ophthalmic medical device according to an embodiment of the present invention. In FIG. 5, disposable tip segment 205 includes housing 215, needle 210, plunger 415, plunger interface 420, dispensing chamber 405, dispensing chamber housing 425, temperature control device 450, thermal sensor 460, interface 530, and tip interface connector 520. Disposable tip segment 205 operates as a disposable injection device.

In the embodiment of FIG. 5, plunger 415 is located in dispensing chamber housing 425. Dispensing chamber 405 is enclosed by dispensing chamber housing 425 and plunger 415. Plunger 415 forms a fluid seal with the interior surface of dispensing chamber housing 425. Needle 210 is fluidly coupled to dispensing chamber 405. In this manner, a substance located in dispensing chamber 405 can be contacted by plunger 415 and pushed out of needle 210. Temperature control device 450 is located adjacent to dispensing chamber housing 425 and at least partially surrounds dispensing chamber 405. Housing 215 forms an outer skin on disposable tip segment 205.

In various embodiments of the present invention, temperature control device 450 is a heating and/or a cooling device. Temperature control device 450 is in thermal contact with dispensing chamber housing 425. As such, temperature control device 450 is capable of changing the temperature of the substance in dispensing chamber 405. Interface 530 and tip interface connector 520 couple temperature control device 450 to a limited reuse assembly. In such a case, temperature control device 450 can be powered and controlled by the limited reuse assembly. In one embodiment of the present invention, temperature control device 450 receives voltage via interface 530 from a limited reuse assembly. Providing a positive voltage across the temperature control device 450 causes it to produce heat. Providing a negative voltage across the temperature control device 450 causes it to cool.

A substance to be delivered into an eye, typically a drug, is located in dispensing chamber 405. In this manner, the substance is contacted by the inner surface of dispensing chamber housing 425 and one face of plunger 415. Typically, dispensing chamber 405 is cylindrical in shape. Temperature control device 450 is in thermal contact with dispensing chamber housing 425. In this manner, temperature control device 450 is adapted to control the temperature of the contents of dispensing chamber 425. Thermal sensor 460 provides temperature information to assist in controlling the operation of temperature control device 450.

In one embodiment of the present invention, the substance located in dispensing chamber 405 is a drug that is preloaded into the dispensing chamber. In such a case, disposable tip segment 205 is appropriate as a single use consumable product. Such a disposable product can be assembled at a factory with a dosage of a drug installed.

When a drug is preloaded into dispensing chamber 405, a set quantity of the drug can be preloaded. For example, 100 microliters of a drug can be loaded into dispensing chamber 405, and any quantity up to 100 microliters can be dispensed. In such a case, the plunger 415 can be moved a precise distance to deliver a precise dosage of drug from the dispensing chamber 405, through the needle 210, and into an eye. This provides for flexibility of dosing and for ease of assembly.

FIG. 6 is a block diagram of an implementation of a drug heating cycle limiter according to the principles of the present invention. In FIG. 6, controller 305 interfaces with temperature control device 450 and thermal sensor 460. Controller 305 receives temperature information from thermal sensor 460 and uses that information to control temperature control device 450.

FIG. 7 is a block diagram of an implementation of a drug heating cycle limiter according to the principles of the present invention. In FIG. 7, controller 305 includes counter 720 and timer 730. Controller 305 interfaces with thermal sensor 460 and switch 710. Switch 710 interfaces with temperature control device 450. In the embodiment of FIG. 7, controller 305 controls the operation of switch 710 to supply a first voltage (V1) or a second voltage (V2) to temperature control device 450.

Switch 710 is any suitable type of mechanical or electronic switch. Since the voltage supplied to temperature control device 450 is typically a low DC voltage, any number of different electronically implemented switches may be used. In one embodiment, a comparator is used as switch 710. Controller 305 provides an input to control switch 710.

Controller 305 also includes a counter 720 and a timer 730. While shown as separate blocks within controller 305, counter 720 and timer 730 may be implemented with software or hardware contained in controller 305. Many electronic controllers, such as microcontrollers, contain such timing and counting functions. Counter 720 provides a counting function, and timer 730 provides a timing function.

In operation, controller 305 operates switch 710 to provide a first voltage (V1) to temperature control device 450. This first voltage (V1) is typically higher then the second voltage (V2). The first voltage (V1) brings the temperature control device to a set point temperature quickly. When temperature control device 450 is a heater, such as a resistive heater, applying a relatively high first voltage (V1) brings the temperature of the heater up quickly. Thermal sensor 460 measures the temperature of the heater (or a temperature near the heater) and provides this information to controller 305. When this temperature reaches the set point, controller 305 operates switch 710 to provide the second voltage (V2) to temperature control device 450. Again, when temperature control device 450 is a heater, this second, relatively lower voltage (V2), maintains temperature control device 450 at the set point. In sum, the first voltage (V1) is chosen to bring the temperature control device 450 to a desired temperature quickly, and the second voltage (V2) is chosen to maintain the temperature control device 450 at the desired temperature.

Counter 720 counts the number of times the temperature control device 450 is operated to alter the temperature of a substance contained in the dispensing chamber. Since the substance in the dispensing chamber is typically a drug, it is desirable not to stress the drug with excess heat or elevated temperatures. For example, when a drug is suspended in a phase transition compound, the phase transition compound is heated to bring it to a more liquid state suitable for injection into the eye. Too much heat may have a negative effect on the drug or may degrade it. Therefore, it can be important to monitor the amount of heat that is applied to the drug. Counter 720 achieves this by counting the number of heating cycles the drug undergoes. For example, if a doctor turns on the temperature control device to heat the phase transition compound, and then leaves the device on without performing an injection, the device turns itself off after a preset period of time (the time the device is left on is calculated by timer 730). The doctor may then turn the device on a second time, in which case the counter increments by one. After a preset number of counts are reached, the device is disabled indicating that the drug has been exposed to a level of heating that is not desirable. In such a case, the tip segment may be disabled to prevent it from being used.

Timer 730 tracks the amount of time that temperature control device 450 is on (and altering the temperature of the drug/phase transition compound). Timer 730 begins timing when the temperature control device 450 is turned on or when it reaches a steady state temperature. In this manner, timer 730 keeps track of how long the drug is exposed to heat (when temperature control device 450 is a heater). In conjunction with counter 720, timer 730 can be used to determine how much heat is applied to the drug.

FIG. 8 is a graph of one operation of a drug heating cycle limiter according to the principles of the present invention. In FIG. 8, time is depicted on the x-axis and temperature on the y-axis. At time, t, the voltage applied across temperature control device 450 is switched from V1 to V2. The temperature of temperature control device 450 (when it is a heater) is depicted. The temperature, T, is the set point or steady state temperature. In this manner, voltage V1 is applied to bring temperature control device to its set point in a relatively quick manner, and voltage V2 is applied to maintain temperature control device at the set point.

FIG. 9 is a flow chart of a method of operating a drug heating cycle limiter according to the principles of the present invention. In 1110, it is determined whether the limit number has been reached. The limit number is the preset number of times that the temperature control device is allowed to cycle in the tip segment. Each cycle corresponds to a heating of the drug in the dispensing chamber. For example, this limit number may be five. In such a case, the temperature control device in a tip segment is allowed to cycle five times before being disabled. If in 1110, the limit number has been reached, then the system is disabled in 1130. In one embodiment, a fuse located in the tip segment is blown to prevent its reuse. If the limit number has not been reached, then in 1120, the counter is incremented. Incrementing the counter indicates that the temperature control device is to be cycled.

In 1140, a first voltage V1 is applied to the temperature control device. In 1150, it is determined whether the temperature control device has reached the steady state temperature (or set point). If it has not reached its steady state temperature, then the first voltage V1 continues to be applied across the temperature control device. If it has reached its steady state temperature, then in 1160, the second voltage V2 is applied to the temperature control device. As previously mentioned, this second voltage V2 keeps the temperature control device at the steady state temperature. In 1170, the timer is started. This timer counts the amount of time that the temperature control device is at the steady state temperature (and heating the drug—when the temperature control device is a heater).

In 1180, it is determined whether the time limit has been reached. The time limit is the amount of time that the temperature control device is allowed to be left on without an injection being performed. In one embodiment, the time limit is five minutes. In such a case, the temperature control device is allowed to be on for five minutes. If the doctor does not perform the injection procedure within five minutes, then the time limit has been reached. In such a case, the system is turned off (1190).

From the above, it may be appreciated that the present invention provides an improved system for delivering precise volumes of a substance into an eye. The present invention provides a single use, disposable delivery device tip segment that is capable of delivering a dosage of a drug. The tip segment interfaces with a limited reuse assembly. The disposable tip segment has a temperature control device and a thermal sensor. The system monitors the amount of time that the temperature control device is turned on and the number of cycles that the temperature control device undergoes. Preset limits on these variables are used to prevent further use of the device when the limits are exceeded. In this manner, the drug contained in the tip segment is not subjected to excessive temperature stresses.

While the present invention is described in the context of a single-use ophthalmic drug delivery device, the present invention encompasses any medical device or injection device. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims

1. A dispensing assembly comprising:

a dispensing chamber housing having an inner surface and an outer surface, the inner surface partially defining a dispensing chamber for receiving a quantity of a substance;

a temperature control device at least partially surrounding the dispensing chamber housing, the temperature control device for altering a temperature of a substance in the dispensing chamber;

a thermal sensor located near the temperature control device, the thermal sensor for reading a temperature near the temperature control device; and

a controller for controlling the temperature control device such that the substance in the dispensing chamber is not exposed to elevated temperature nor overexposed to heat.

2. The assembly of claim 1 wherein the controller counts a number of times the temperature control device is activated.

3. The assembly of claim 2 wherein the controller disables a tip segment if the number of times the temperature control device is activated exceeds a set number.

4. The assembly of claim 1 wherein the controller times a period when the temperature control device is activated.

5. The assembly of claim 4 wherein the controller shuts off the temperature control device when the period when the temperature control device is activated exceeds a set period.

6. The assembly of claim 1 further comprising:

a switch coupled to the temperature control device.

7. The assembly of claim 6 wherein the controller controls the switch such that a first voltage is applied to the temperature control device until the temperature control device reaches a desired temperature, and a second voltage is applied to the temperature control device thereafter to maintain the temperature control device at the desired temperature.

8. The assembly of claim 1 wherein the temperature control device is a heater comprising a resistive element.

9. An injection assembly comprising:

a dispensing chamber housing having an inner surface and an outer surface, the inner surface partially defining a dispensing chamber for receiving a quantity of a substance;

a temperature control device at least partially surrounding the dispensing chamber housing, the temperature control device for altering a temperature of a substance in the dispensing chamber;

a thermal sensor located near the temperature control device, the thermal sensor for reading a temperature near the temperature control device;

a switch coupled to the temperature control device; and

a controller for controlling the temperature control device;

wherein the controller controls the switch such that a first voltage is applied to the temperature control device until the temperature control device reaches a desired temperature, and a second voltage is applied to the temperature control device thereafter to maintain the temperature control device at the desired temperature.

10. The assembly of claim 9 wherein the controller counts a number of times the temperature control device is activated.

11. The assembly of claim 10 wherein the controller disables a tip segment if the number of times the temperature control device is activated exceeds a set number.

12. The assembly of claim 9 wherein the controller times a period when the temperature control device is activated.

13. The assembly of claim 12 wherein the controller shuts off the temperature control device when the period when the temperature control device is activated exceeds a set period.

14. The assembly of claim 9 wherein the temperature control device is a heater comprising a resistive element.

15. A method of operating a dispensing assembly comprising:

checking a count of a number of times a temperature control device has been activated;

if the count does not exceed a preset number, incrementing a counter;

applying a first voltage across a temperature control device to bring the temperature control device to a desired temperature;

after the temperature control device reaches the desired temperature, applying a second voltage across the temperature control device to maintain the temperature control device at the desired temperature;

starting a timer to count the amount of time that the temperature control device is activated; and

if the amount of time that the temperature control device is activated exceeds a preset amount of time, turning off the temperature control device.

16. The method of claim 15 further comprising:

if the count exceeds a preset number, then disabling a tip segment so that an injection cannot be performed.

17. The method of claim 15 wherein applying a first voltage across a temperature control device to bring the temperature control device to a desired temperature further comprises controlling a switch to apply the first voltage.

18. The method of claim 17 wherein applying a second voltage across a temperature control device to bring the temperature control device to a desired temperature further comprises controlling a switch to apply the second voltage.

19. The method of claim 18 wherein starting a timer to count the amount of time that the temperature control device is activated further comprises starting the timer when the switch is controlled to apply the second voltage.

20. The method of claim 15 wherein starting a timer to count the amount of time that the temperature control device is activated further comprises starting the timer after the temperature control device has reached the desired temperature.