Abstract:
An ophthalmic injection device has a dispensing chamber housing, a plunger, an actuator for driving the plunger, a temperature control device, and a temperature release mechanism. The dispensing chamber housing has an inner surface and an outer surface. The inner surface partially defines a dispensing chamber for holding a quantity of a substance. The plunger is engaged with the inner surface of the dispensing chamber housing, is capable of sliding in the dispensing chamber housing, and is fluidly sealed to the inner surface of the dispensing chamber housing. The temperature control device at least partially surrounds the dispensing chamber housing and is capable of altering the temperature of the substance in the dispensing chamber. The temperature release mechanism is in a locked position when the substance is outside the proper temperature range and an unlocked position when the substance is in the proper temperature range.

Description:
RELATED APPLICATIONS 
     This Application claims priority to U.S. patent application Ser. No. 60/921,497 filed Oct. 16, 2006 and is a continuation-in-part of U.S. patent application Ser. No. 11/435,906 filed May 17, 2006 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a single-use medical device and more particularly to an ophthalmic drug delivery device with a temperature controlled delivery mechanism. 
     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 manually made 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 puncture 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 the vernier on the syringe is not precise relative to the small injection volume. Fluid flow rates are uncontrolled. Reading the vernier is also subject to parallax error. 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 reliably injecting a drug into the eye. In the case where the drug is to be heated or cooled, it is desirable to bring the drug to the proper temperature before it is injected into the eye. A switch, button, or other mechanism that can only be activated when the drug reaches the proper temperature can be used to ensure that the drug is at the proper temperature before being injected. Such a system provides numerous benefits over prior art injectors. 
     SUMMARY OF THE INVENTION 
     In one embodiment consistent with the principles of the present invention, the present invention is an ophthalmic injection device having a dispensing chamber housing, a plunger, an actuator for driving the plunger, a temperature control device, a power source for providing power to the temperature control device, a controller for controlling the temperature control device, and a temperature release mechanism. The dispensing chamber housing has an inner surface and an outer surface. The inner surface partially defines a dispensing chamber for holding a quantity of a substance. The plunger is engaged with the inner surface of the dispensing chamber housing, is capable of sliding in the dispensing chamber housing, and is fluidly sealed to the inner surface of the dispensing chamber housing. The temperature control device at least partially surrounds the dispensing chamber housing and is capable of altering the temperature of the substance in the dispensing chamber. The temperature release mechanism activates the actuator only when the substance is in a proper temperature range. 
     In another embodiment consistent with the principles of the present invention, the present invention is an ophthalmic injection device having a dispensing chamber housing, a needle, a plunger, an actuator for driving the plunger, a temperature control device, a power source for providing power to the temperature control device, a controller for controlling the temperature control device, and a temperature release mechanism. The dispensing chamber housing has an inner surface and an outer surface. The inner surface partially defines a dispensing chamber for holding a quantity of a substance. The plunger is engaged with the inner surface of the dispensing chamber housing, is capable of sliding in the dispensing chamber housing, and is fluidly sealed to the inner surface of the dispensing chamber housing. The needle is fluidly coupled to the dispensing chamber. The temperature control device at least partially surrounds the dispensing chamber housing and is capable of altering the temperature of the substance in the dispensing chamber. The temperature release mechanism is in a locked position when the substance is outside the proper temperature range, and an unlocked position when the substance is in the proper temperature range. 
     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 drawings, 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 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. 
         FIG. 3  is another 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 an embodiment of the present invention. 
         FIG. 5  is an exploded cross section view of a tip segment for an ophthalmic medical device according to an embodiment of the present invention. 
         FIGS. 6A and 6B  are exploded cross section views of temperature release mechanism according to the principles of the present invention. 
         FIGS. 7A-7H  are exploded cross section views of a portion of a temperature release mechanism 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 drawings. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like parts. 
       FIG. 2  is 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. 
     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  308 , a display  320 , and a housing  330 . Disposable tip segment  205  attaches to end  340  of limited reuse assembly  250 . Button  308  is actuated to provide an input to the system. As with switch  270 , button  308  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  453 . Limited reuse assembly  250  includes mechanical linkage interface  545 , actuator shaft  510 , actuator  515 , power source  505 , controller  305 , limited reuse assembly housing  255 , temperature release mechanism  400 , interface  535 , and limited reuse assembly interface connector  553 . 
     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 . The 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  with tip interface connector  453 . 
     Optional thermal sensor  460  provides temperature information to assist in controlling the operation of temperature control device  450 . Thermal sensor  460  may be located near dispensing chamber housing  425  and measure a temperature near dispensing chamber housing  425  or may be located in thermal contact with dispensing chamber housing  425 , in which case it measures a temperature of dispensing chamber housing  425 . Thermal sensor  460  may be any of a number of different devices that can provide temperature information. For example, thermal sensor  460  may be a thermocouple or a resistive device whose resistance varies with temperature. Thermal sensor  460  is also electrically coupled to interface  530  or other similar interface. 
     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  5   10 . 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 . In other embodiments of the present invention, mechanical linkage interface  545  and actuator shaft  510  are a single component. In other words, a shaft connected to actuator  515  includes both actuator shaft  510  and mechanical linkage interface  545  as a single assembly. 
     In limited reuse assembly  250 , power source  505  is typically a rechargeable battery, such as a lithium ion battery, although other types of batteries may be employed. In addition, any other type of power cell is appropriate for power source  505 . Power source  505  provides current to dispensing chamber housing  425  to heat/cool it and change its shape. Optionally, power source  505  can be removed from housing  255  through a door or other similar feature (not shown). 
     Controller  305  is connected via interface  535  to limited reuse assembly interface connecter  553 . Limited reuse assembly interface connecter  553  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  553  and mechanical linkage interface  545  are adapted to be connected with tip interface connector  453  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 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 in  FIG. 4 , controller  305  may be made of many different components or integrated circuits. 
     Limited reuse assembly  250  also includes temperature release mechanism  400 . Temperature release mechanism  400  allows actuator  515 to be activated to deliver the substance only when the substance is in the proper temperature range. Temperature release mechanism  400  and its operation are more fully described below. 
     Tip segment  205  is adapted to mate with or attach to limited reuse assembly  250 . In the embodiment of  FIG. 4 , 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  453  is adapted to connect with limited reuse assembly interface connector  553 . 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  553 , tip interface connector  453 , 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 activated by temperature release mechanism. When actuator  515  is actuated, 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  and its contents. 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  through interface  530 , tip interface connector  453 , limited reuse assembly interface connector  553 , and interface  535  back to controller  305 . 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 . 
     A substance to be delivered into an eye, typically a drug suspended in a phase transition compound, is located in dispensing chamber  405 . In this manner, the drug and phase transition compound are contacted by the inner surface of dispensing chamber housing  425 . The phase transition compound is in a solid or semi-solid state at lower temperatures and in a more liquid state at higher temperatures. Such a compound can be heated by the application of current to temperature control device  450  to a more liquid state and injected into the eye where it forms a bolus that erodes over time. 
     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, 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. 
     While shown as a two-piece device, the injection system of  FIG. 4  may be a single piece device. In such a case, the tip segment is integrated into the limited reuse assembly to form a single medical device. 
       FIG. 5  is an exploded cross section view of a tip segment for an ophthalmic medical device according to an embodiment of the present invention. In  FIG. 5 , tip segment  205  includes dispensing chamber housing  425 , tip segment housing  215 , thermal sensor  460 , needle  210 , dispensing chamber  405 , plunger  415 , plunger shaft  380 , plunger interface  420 , temperature control device  450 , interface  530 , tip interface connector  453 , and temperature release mechanism  400 . 
     In the embodiment of  FIG. 5 , temperature control device  450  is activated to bring a substance in dispensing chamber  405  to within a proper temperature range. Thermal sensor  460  provides temperature information to controller  305  (not shown) to control temperature control device  450 . After the substance has reached the proper temperature, temperature release mechanism  400  is actuated to drive plunger toward needle  210  to dispense a substance contained in dispensing chamber  405 . Temperature release mechanism  400  can only be activated when the substance is in the proper temperature range. In this manner, the substance in dispensing chamber  405  is delivered only when it is in the proper temperature range. 
     In addition, the embodiment of  FIG. 5  includes a plunger shaft  380  that is connected to plunger  415 . In this embodiment, plunger  415  may be over-molded onto plunger shaft  380 . Plunger shaft  380  is generally cylindrical in shape with a middle diameter that is less than a diameter on its distal and proximal ends. Plunger interface  420  is a surface on the proximal end of plunger shaft  380 . Plunger shaft  380  is typically made of a rigid material such as stainless steel. Plunger  415  is made of a rubber or polymer material. In another embodiment of the present invention, the distal end of plunger shaft  380  has a lip over which plunger  415  can be applied. Plunger  415  can be press-fitted onto plunger shaft  380  and is retained in place by a lip on the distal end of plunger shaft  380 . This allows for easier assembly. Instead of over molding plunger  415  onto a shaft, plunger  415  can be manufactured as a separate part and pushed onto the distal end of plunger shaft  380 . Plunger interface  420  can be of any suitable shape. 
     As seen in  FIG. 5 , temperature release mechanism may be incorporated into tip segment  205 , in which case it is not present in limited reuse assembly  250 . In this manner, temperature release mechanism may be located in tip segment  205  or in limited reuse assembly  250 . When a single integrated unit (integrating tip segment  205  and limited reuse assembly  250  into a single device), temperature release mechanism may be located in the integrated unit. 
     Temperature release mechanism  400  may be located such that it operates to allow dispensing of the substance only when the substance is in the proper temperature range. Since different materials can be used to make temperature release mechanism  400  (as described below), the location of temperature release mechanism is dependent on its structure and the materials used to make it. For example, when temperature release mechanism  400  includes a Nitinol member (as described below), temperature release mechanism  400  should be positioned such that it can be activated only when the substance is in the proper temperature range. In this case, temperature release mechanism  400  may be placed near temperature control device  450  and dispensing chamber housing  425 , so that heat produced by temperature control device  450  and conducted by dispensing chamber housing  425  alters the shape of the Nitinol member in such a way as to permit dispensing of the substance when it is in the proper temperature range. 
       FIGS. 6A and 6B  are exploded cross section views of a temperature release mechanism according to the principles of the present invention. Temperature release mechanism  400  includes button  605 , spring  610 , shaft  615 , locking mechanism  620 , and triggering device  625 . In  FIG. 6B , shape memory alloy member  630  and disk  635  are also depicted. 
     Button  605  is located on top of shaft  615 . Shaft  615  is located in a notch in locking mechanism  620 . Spring  610  biases shaft  615  upward and away from locking mechanism  620 . Spring  610  also provides some resistance to button  605  when it is pushed. Triggering device  625  is located below locking mechanism  620 . As shown in  FIG. 6B , shape memory alloy member  630  and disk  635  are located in locking mechanism  620 . Shape memory alloy member  630  is connected to disk  635 . In one embodiment consistent with the principles of the present invention, shape memory alloy member  630  and disk  635  are made out of the same shape memory alloy material. 
     Triggering device  625  is a switch, contact, or other similar device that can initiate the actuation of substance delivery. For example, triggering device  625  may be a switch that activates actuator  515  to drive actuator shaft  510  and mechanical linkage mechanism  545  toward needle  210  to deliver the substance from dispensing chamber  405 . 
     In  FIG. 6B , shape memory alloy member  630  is made of a shape memory alloy (“SMA”). Shape memory alloys, such as various Nitinol (a nickel-titanium alloy) alloys, hold a deformed shape at room temperature. When heated to a higher temperature, the SMA reverts to its non-deformed shape. In other words, a shape memory alloy (also known as a smart alloy or memory metal) is a metal that “remembers” its geometry. After an SMA has been deformed from its original atomic configuration, it regains its original geometry by itself during heating. These properties are due to a temperature-dependent martensitic phase transformation from a low-symmetry to a highly symmetric crystallographic structure. Those crystal structures are known as martensite and austenite. The three main types of SMA are copper-zinc-aluminum, copper-aluminum-nickel, and nickel-titanium (Ni—Ti) alloys. The temperatures at which the SMA changes its crystallographic structure are characteristic of the alloy, and can be tuned by varying the elemental ratios. 
     For a shape memory alloy member  630  made out of Nitinol, the Nitinol is in a deformed shape at room temperature. In this deformed shape, the Nitinol has a martenistic crystal structure. In this deformed shape, when shape memory alloy member  630  is a wire-type structure, it has first length. As the temperature of shape memory alloy member  630  rises, its shape changes. When the temperature of shape memory alloy member  630  reaches 60 or 70 degrees Celsius, the Nitinol will revert to its non-deformed shape. In this process, the Nitinol changes from a martenistic crystal structure to an austenic crystal structure. In this non-deformed shape, when shape memory alloy member  630  is a wire-type structure, it has a second length. As the temperature of shape memory alloy member  630  increases, the transition from the first length to the second length can be gradual. 
     In  FIG. 6B , shape memory alloy member  630  is at the desired temperature range. In this temperature range, shaft  615  is able to traverse locking mechanism  620  through an opening in disk  635 . In this embodiment, shape memory alloy member  630  is a wire-type structure. However, shape memory alloy member  630  may be any convenient structure, such as a coil. In other embodiments, shape memory alloy member  630  is toroidal in shape, in which case the opening in the toroid can be varied by varying its temperature. 
     In operation, when shape memory alloy member  630  in locking mechanism  620  is at room temperature, shaft  615  is not able to contact triggering device  625  (as shown in  FIG. 6A ). As shape memory alloy member  630  is heated, its shape changes. As its shape changes, disk  635  slides in locking mechanism  620 . When shape memory alloy member  630  reaches the proper temperature range, disk  635  is located such that shaft  615  is able to pass through it and contact triggering device  625 . 
       FIGS. 7A-7H  are exploded cross section views of a portion of a temperature release mechanism according to the principles of the present invention.  FIGS. 7A-7D  are top cross section views, and  FIGS. 7E-7H  are side cross section views. 
       FIGS. 7A and 7E  are top and side cross section views of locking mechanism  620 . An opening  705  is shown. Locking mechanism  620  is hollow and, in this case, tubular. Shaft  615  is located above opening  705 , such that it can pass through opening  705  to activate triggering device  625  (as shown in  FIG. 6B ). 
     In  FIGS. 7B and 7F , shape memory alloy member  630  is at room temperature or in a low temperature range. Shape memory alloy member  630  is shown as a coil. In this position, disk  635  blocks opening  705 , thus preventing shaft  615  from contacting triggering device  625 . The opening in disk  635  is not aligned with opening  705 . 
     In  FIGS. 7C and 7G , shape memory alloy member  630  is in a proper temperature range. In this position, the opening in disk  635  is aligned with opening  705 , thus allowing shaft  615  to pass through locking mechanism  620  and contact triggering device  625 . In this manner, when the substance in the dispensing chamber is in the proper temperature range (and the opening in disk  635  is aligned with opening  705 ), actuator  515  can be activated to deliver the substance into an eye. 
     In  FIGS. 7D and 7H , shape memory alloy member  630  is in a high temperature range. In this position, disk  635  blocks opening  705 , thus preventing shaft  615  from contacting triggering device  625 . The opening in disk  635  is not aligned with opening  705 . 
     When temperature release mechanism  400  is located near dispensing chamber housing  425  (or temperature control device  450 ), shape memory alloy member  630  can be altered by the heat produced by temperature control device  450  (when it is a heater). As temperature control device  450  heats up, a substance located in dispensing chamber  405  also heats up. This in turn causes shape memory alloy member  630  to change shape and move disk  635 . When the substance is in the proper temperature range, shape memory alloy member  630  has changed shape so that the opening in disk  635  is aligned with opening  705  in locking mechanism  620 . When these two openings are aligned, shaft  615  can pass through locking mechanism  620  and disk  635  to contact triggering device  625 . In this case, when button  605  is pushed, the substance (which is in the correct temperature range) is delivered into an eye. If the substance is too hot, then the button cannot be depressed as the opening in disk  635  is not aligned with the opening  705  in locking mechanism  620 . In this manner, the actuation of drug delivery device only occurs when the drug is in the proper temperature range. 
     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 temperature release mechanism that ensures that a substance is delivered into an eye only when it is in a proper temperature range. In one embodiment, a disposable tip segment that interfaces with a limited reuse assembly is employed. In another embodiment, a single unit is employed. The present invention is illustrated herein by example, and various modifications may be made by a person of ordinary skill in the art. 
     While the present invention is described in the context of a single-use drug delivery device, the present invention encompasses any single-use medical 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.