before turning to the figures , which illustrate the exemplary embodiments in detail , it should be understood that the present application is not limited to the details or methodology set forth in the description or illustrated in the figures . it should also be understood that the terminology is for the purpose of description only and should not be regarded as limiting . a multi - drug delivery device stores individual drugs , pharmaceuticals , hormones , vaccines , or nutrients in separate containers for storage and administration . in a typical embodiment , the drugs are therapeutic or prophylactic vaccines . the vaccines may be , for example , the individual monovalent vaccines of the denvax vaccine . in another example , the drugs are a combination of monovalent and polyvalent vaccines for the seasonal influenza , pneumonia , chicken pox and shingles delivered from individual fluid containers . the device is employed to deliver the contents to discrete but nearby areas of the intradermal layers of skin . the delivery of vaccines to the intradermal layers may elicit a more robust immune response compared to a standard needle and syringe delivery to the muscle or subcutaneous layer . for example , simultaneous but independent delivery of the dengue monovalent vaccines , i . e ., multi - monovalent delivery , to the dermal layer provides all four monovalent vaccine viruses equal opportunity to replicate thus avoiding the interference observed when delivered in a single tetravalent formulation . several vaccines including polio and influenza , rabies , yellow fever have been demonstrated to have improved efficacy when delivered intradermally compared to intramuscularly . the multi - monovalent vaccines are injected into the dermal layer of the skin , mimicking the natural route of dengue infection that occurs , for example , from the bite of an infected mosquito . the vaccine may encompass but is not limited to a live or killed virus , a subunit or conjugate , a viral protein , a dna plasmid encoding for viral antigens , an anti - sense rna , a liposome containing viral peptides , a polysaccharide , or any combination of these provided as a liquid formulation . the vaccine may be intended for use in humans or in veterinary applications whether for domestic , dairy or livestock . for vaccination purposes , skin is a highly accessible organ and represents an effective immune barrier , mainly attributed to the presence of langerhans cells residing in the epidermis and dendritic cells in the dermis . skin immunization elicits a broad range of immune responses , including humoral , cellular , and mucosal responses . no single device exists that allows for the simultaneous delivery of multiple vaccines to the intradermal layers of the skin . multiple vaccine delivery intramuscularly is currently achieved by sequential delivery , resulting in multiple injections for individual recipients . such delivery of separate vaccines to neighboring but non - overlapping skin sites could be performed using sequential administrations by needle and syringe . this approach is extremely inefficient and requires additional time for the healthcare worker as well as the patient . referring to fig1 , a multiple drug delivery device 2 is shown . delivery device 2 provides concomitant delivery of multiple vaccines from discrete containers through separate needles and to distinct but proximal sites . delivery device 2 is shown as a housing 4 having a base 6 and four separate drug cartridges 12 . base 6 of delivery device 2 may be provided with an adhesive to secure delivery device 2 to the skin of a patient , thereby tensioning the skin of the patient during needle insertion and drug or vaccine injection . drug cartridges 12 are inserted and held within housing 4 of delivery device 2 . housing 4 further contains a main spring , trigger , and retraction actuator as discussed in further detail below . in one embodiment , base 6 of delivery device 2 has a footprint of 5 cm by 7 cm . in other embodiments , the delivery device may be configured with one , two , three , or five or more drug cartridges . in some embodiments , delivery device 2 may be configured to hold four cartridges , but an operator can insert fewer than the maximum number of cartridges and actuate the device . each drug cartridge 12 stores a drug or vaccine and delivers it , via a dedicated fluid path , to a discrete location in the skin or subcutaneous tissue . thus , delivery device 2 allows the simultaneous but independent delivery of different vaccines . in some embodiments , each vaccine is a monovalent vaccine so that simultaneous delivery multi - monovalent delivery . in other embodiments , one or more cartridges 12 may contain a combination vaccine while other cartridges 12 contain monovalent vaccines . in a typical embodiment , drug cartridges 12 are spaced at a distance of less than 1 cm from adjacent drug cartridges . in other embodiments , a larger spacing between drug cartridges 12 may be provided . referring to fig2 , a cross - sectional view of a drug cartridge 12 prior to actuation is shown . drug container 12 is a generally cylindrical cartridge having a cartridge housing 12 defining a central bore 14 . drug cartridges 12 are inserted into the base of the delivery housing prior to patient administration . drug cartridge 12 may be provided with retaining barbs 16 to lock the drug cartridge 12 into housing 4 and prevent removal after insertion . drug containers 12 usable with delivery device 2 are preferably cartridges that can be filled and stored outside of delivery device 2 and inserted into the device as needed . in other embodiments , drug cartridges 12 may be secured in delivery device 2 by an adhesive , ultrasonic welding , a retaining ring , etc ., and may be installed as part of an integrated manufacturing process and prior to use . each cartridge is made up of a primary drug container 20 , which includes components that contain and protect the dosage form . primary drug container 20 moves inside central bore 14 of cartridge housing 12 during needle insertion and retraction . primary drug container 20 is formed generally as cylinder having top cap 22 , cylinder wall 24 , plunger interference latches 26 , and bottom wall 28 . components of primary drug container 20 , for example , top cap 22 , bottom wall 28 , and microneedle array 38 , may be ultrasonically welded to cylinder wall 24 . needle arrays are nested inside the cartridge housing for safety and are protected by a label that is to be removed just prior to actuation . cartridge housing 12 is provided with one or more recesses 30 sized to receive plunger interference latches 26 . a plunger 32 is fitted within cylinder wall 24 , defining a fluid chamber 34 . a plunger spring 36 is interposed between top cap 22 and plunger 32 . prior to actuation , plunger spring 36 is in a compressed state between top cap 22 and plunger 32 , and plunger 32 is held in place by plunger interference latches 26 molded or formed into cylinder wall 24 . primary drug container 20 is further provided with a microneedle array 38 . microneedle array 38 is an array of one or more hollow microneedles as described in u . s . patent application ser . no . 13 / 288 , 266 , which is hereby incorporated by reference in its entirety . microneedle array 38 may be , for example , an array of polymeric microneedles less than 2 mm in length , and having a hollow lumen and multiple ports located near each tip for fluid delivery . the polymeric material may be a liquid crystal polymer . the microneedles thereby direct vaccine to the immune - rich intradermal layers of the skin leading to improved efficacy . in other embodiments , microneedles may be shorter , e . g . 1 mm in length . in still other embodiments , the microneedles may be longer , e . g . 3 mm , 4 mm , or more , thereby allowing for subcutaneous delivery of the contents of fluid chamber 34 to a patient . microneedle array 38 is in fluid communication with fluid chamber 34 through opening 40 in bottom wall 28 . prior to actuation , microneedle array 38 is nested inside cartridge housing 12 . a protective label 8 seals the microneedle array 38 of primary drug container 20 from contact with external objects . in another embodiment , cartridge 38 may be provided with one or more metal needles in place of polymeric microneedle array 38 . in such an embodiment , the metal needles may be at least 3 - 4 mm in length , thereby allowing for subcutaneous delivery of the contents of fluid chamber 34 to a patient . in a preferred embodiment using metal needles , each container 12 is provided with a single metal needle . in other embodiments , one or more metal needles may be shorter , e . g . 2 mm , 1 mm , or less , thereby allowing for intradermal delivery of the contents of fluid chamber 34 to a patient . geometry of the primary drug container 20 , position of plunger latches 26 and dimensions of the plunger 32 may be varied to develop cartridges of different volumes ( e . g . 100 μl , 250 μl , and 500 μl ). in a preferred embodiment , drug cartridges 12 are designed to be filled through the center of top cap 22 with a septum over - molded into plunger 32 to prevent tampering . the geometry and size of drug cartridges 12 may be selected for compatibility with existing aseptic liquid fill technology . for example , according to iso 13926 - 1 the standard dimensions for cartridges and pen systems include outside diameters of 8 . 65 mm , 10 . 85 mm , and 10 . 95 mm . primary drug container 20 and the components thereof are formed from suitably inert materials , for example polypropylene , medical grade liquid crystal polymer , stainless steel , glass , etc . the primary drug container , plunger and microneedle array materials a preferably selected based on usp recommendations for primary drug containers in a parenteral device and on materials currently cleared for long - term storage of injectable fluids . in some embodiments , primary drug container 20 may be provided with a glass liner . vapor barriers may be included if the selected materials exhibit higher than acceptable vapor transmission rates at intended storage conditions . in one embodiment , delivery device 2 may be provided with an aluminum vapor barrier . still referring to fig2 , one or more main springs 42 are provided . a single main spring 42 may be provided for multiple drug cartridges 12 , or independent springs may be provided for one or more drug cartridges 12 . as shown in fig2 main spring 42 is a flat cantilever spring element . in a preferred embodiment , main spring 42 is formed from stamped steel . in other embodiments , main spring 42 may be a coil spring , a torsion spring , or another mechanical spring . in still other embodiments , main spring 42 may be a gas spring , or pressure may be applied to top cap 22 by gas discharge or by another pressure source . in a preferred embodiment , main spring 42 is optimized to ensure positive needle penetration into skin . the force required to fully penetrate the skin generally depends on the number and geometry of needles in microneedle arrays 38 , and the distance of needle travel from pre - actuated to actuated / penetrated state . in one embodiment , a force of about 26 pounds of force may be used to insert needles of microneedle array 38 into the skin of a patient . in preferred embodiments , main spring 42 is actuated by use of a trigger mechanism , thereby actuating each drug cartridge 12 simultaneously . in other embodiments , a trigger may actuate multiple drug cartridges 12 sequentially rather than simultaneously . in an especially preferred embodiment , a trigger actuation force of less than 4 pound - foot is required to trigger delivery device 2 . in preferred embodiments , microneedle arrays 38 retract fully within device housing 4 after use , thereby preventing injury and contamination from sharps . in the embodiment shown , a retraction spring 44 is provided between cartridge housing 12 and primary drug container 20 . as shown , retraction spring 44 is a helical spring oriented coaxially with center bore 14 . prior to actuation , retraction spring 44 is in a generally uncompressed state . where a retraction spring is provided , main spring 42 additionally must overcome the force of the retraction spring 44 . the opening in the base of each cartridge 12 , dimension of microneedle arrays 38 , and distance between needles and base 6 of housing 4 when delivery device 2 is placed in a retracted state may be designed to minimize or eliminate any human exposure to the needles of microneedle array 38 . referring to fig3 , upon actuation main spring 42 applies a downward force to top cap 22 of primary drug container 20 , thereby driving primary drug container 20 downwards relative to cartridge housing 12 to a mechanical stop 46 . the downward motion of primary drug container 20 thereby injects the microneedles of microneedle array 38 into the intradermal layer of a patient . additionally , downward motion of primary drug container 20 compresses refraction spring 44 . as primary drug container 20 moves downward , plunger interference latches 26 move into alignment with recesses 30 of cartridge housing 12 . when the primary drug container 20 is moved inside cartridge housing 12 to the mechanical stop 46 , interference latches 26 are forced out of the way into recesses 30 of cartridge housing 12 by the spring force , thereby allowing plunger 32 to travel to the bottom of its stroke within cylinder wall 24 . in another embodiment , plunger interference latches 26 may be formed or provided with a spring bias such that the latches 26 rotate into recesses 30 , thereby releasing plunger 32 within cylinder wall 24 . upon release of plunger 32 by plunger interference latches 26 , plunger spring 36 moves plunger 32 downwards toward bottom wall 28 . as shown , plunger spring 36 is a helical spring oriented coaxially with center bore 14 and retraction spring 44 . as plunger 32 moves towards bottom wall 28 , plunger 32 forces the contents of fluid chamber 34 through opening 40 and the microneedles of microneedles array 38 , and thereby injects the contents of fluid chamber 34 into the skin of a patient . during injection , main spring 42 maintains a downward force on top cap 22 of primary drug container 20 . plunger interference latches 26 move back to their original state on the top side of the plunger once the plunger has completed its stroke . referring to fig4 , upon completion of injection , main spring 42 is removed from contact with top cap 22 . in one embodiment , main spring 42 is rotated off of top cap 22 of each drug cartridge 12 , thereby releasing primary drug container 20 within center bore 14 of cartridge housing 12 . upon release of the primary drug container 20 , retraction spring 44 forces primary drug container 20 upwards , thereby withdrawing the microneedle array 38 from the skin of the patient and retracting the microneedles into cartridge housing 12 . the force of retraction spring is generally selected to overcome any plunger interference latches 26 that may remain or protrude into recesses 30 in cartridge housing 12 . further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description . accordingly , this description is to be construed as illustrative only . the construction and arrangements , shown in the various exemplary embodiments , are illustrative only . although only a few embodiments have been described in detail in this disclosure , many modifications are possible ( e . g ., variations in sizes , dimensions , structures , shapes and proportions of the various elements , values of parameters , mounting arrangements , use of materials , colors , orientations , etc .) without materially departing from the novel teachings and advantages of the subject matter described herein . some elements shown as integrally formed may be constructed of multiple parts or elements , the position of elements may be reversed or otherwise varied , and the nature or number of discrete elements or positions may be altered or varied . the order or sequence of any process , logical algorithm , or method steps may be varied or re - sequenced according to alternative embodiments . other substitutions , modifications , changes and omissions may also be made in the design , operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present invention .
a drug delivery device is provided . the device is a wearable active transdermal drug delivery device which facilitates drug delivery using one or more vaccine cartridges having microneedles as the point of drug delivery . the device may be used to perform multiple vaccine deliveries to the intradermal layer of a patient .