Patent Publication Number: US-2020297918-A1

Title: An injection device with a cleaning reservoir

Description:
THE TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to an injection device having a cleaning reservoir for cleaning the distal tip of the needle cannula between subsequent injections. The invention especially refers to such injection device wherein the cleaning reservoir is movable in an axial direction between a cleaning position and a position allowing injection. 
     DESCRIPTION OF RELATED ART 
     Injection devices wherein the needle cannula is covered by a telescopically movable needle shield during injection are widely known. In some of the more recent of these injection devices, the telescopically movable needle shield carries a cleaning reservoir which cleans the distal tip of the needle cannula between subsequent injections. WO 2015/062845, WO2015/173151, WO2017/032599 and WO2017/050694 provide examples of such injection devices. 
     In the injection device disclosed in WO 2015/062845, a volume of the preservative containing liquid drug contained in the cartridge of the injection device is filled into the cleaning reservoir to be used as a cleaning agent for cleaning the injection tip of the needle cannula between injections. In order to allow air trapped in the cleaning reservoir to escape as the preservative containing liquid drug is being filled in to the cleaning reservoir one of the two septum sealing the cleaning reservoir are provided with a venting area through which the trapped air can escape. 
     WO2015/173151 discloses a medical injection device wherein the cleaning reservoir is provided with an opening which connects to an overflow reservoir such that any volume expansion of the liquid cleaning solvent inside the cleaning reservoir can flow into the overflow reservoir. Due to the opening the liquid cleaning solvent flows back into the cleaning reservoir when the volume of the liquid cleaning solvent decreases. 
     In WO 2017/032599 it is suggested to provide the cleaning reservoir with a valve to let the air out as the preservative containing liquid drug flows into the cleaning reservoir. Different examples of such valves are provided in WO 2017/050694. 
     No matter if the cleaning reservoir is to be filled with the same preservative containing drug as present in the cartridge or is to filled with a different liquid cleaning agent it is always necessary to remove the air inside the cleaning reservoir as the cleaning reservoir is being filled and preferably to seal the cleaning reservoir once the reservoir has been filled 
     DESCRIPTION OF THE INVENTION 
     The valves described in the prior art are all mechanical on-off valves which requires the user to actively operate the valve in order to close the valve and thus seal the cleaning chamber. 
     As the user occasionally forgets to activate the mechanical valve it is an object of the present invention to provide a valve which does not depend on the memory of the user. 
     Accordingly, in one aspect, the present invention relates to a medical injection device for injection of a liquid drug. In a first example the injection device comprises:
         A housing structure supporting or securing a cartridge. The cartridge contains the liquid drug to be injected and comprises a plunger which is movable preferably in a distal direction to thereby pressurize the liquid drug contained in the cartridge.   A needle cannula having a distal part and a proximal part. The distal part has a distal tip and the proximal part connects to the cartridge at least during injection. The needle cannula is mounted relatively to the housing structure such that the distal tip extends in a distal direction and wherein a hollow longitudinal lumen stretches along a centre line.   An axially movable cleaning reservoir which is movable in relation to the housing structure. The cleaning reservoir contains a liquid cleaning agent and the distal tip of the needle cannula is positioned inside the cleaning reservoir at least between injections.       

     According to the present invention an overflow reservoir connects to the cleaning reservoir through a one-way pressure valve which comprises a flexible element changeable from a default closed state to an activated open state and vice versa. 
     Further, and according to the present invention, the flexible element is changeable from the default closed state and into the activated open state when the pressure inside the cleaning chamber surpasses a predetermined level. In the default closed state the flexible element seals off the cleaning reservoir and in the activated open state the flexible element allow the cleaning agent and/or air to flow from the cleaning reservoir and into the overflow reservoir. 
     Due to various tolerances it often happens that the amount of the liquid cleaning agent filled into the cleaning reservoir has a volume larger than the physical volume of the cleaning reservoir. In such case it is very beneficial if the extra volume is able to escape to thereby avoid that the cleaning reservoir is pressurized. Further, it is necessary that the air inside the cleaning reservoir can escape as the cleaning reservoir is being filled. 
     For these purposes an overflow reservoir is provided and in order to prevent the escaped liquid cleaning agent and/or air from flowing back into the cleaning reservoir, the two chambers are separated by a one-way pressure valve. 
     The one-way pressure valve is shaped such that the pressure of the liquid cleaning agent and/or air automatically opens the one-way pressure valve when the pressure has reached a certain level. The one-way pressure valve also automatically closes once the pressure has fallen below this level. 
     This is preferably achieved by making at a part of the one-way valve from a flexible member which is changeable from a default closed state to an activated open state in response to the pressure inside the cleaning reservoir. 
     Once this pressure surpasses a predetermined value the flexible member opens automatically in response to the pressure build up and thus allow liquid cleaning agent and/or air to flow into the overflow reservoir. Once the pressure falls below this predetermined level again the flexible member resumes its initial closed state and seals off the cleaning reservoir. 
     The one-way valve is thus opened and closed in response to the pressure inside the cleaning reservoir and does henceforth not rely on a user manually opening and closing the valve. Further, the one-way pressure valve prevents backflow from the overflow reservoir and back into the cleaning reservoir as the one-way pressure valve only opens in response to an overpressure inside the cleaning reservoir 
     The medical injection device is in a further example provided with an axially movable needle shield which is movable between a first position and a second position. 
     In the first position, the needle shield covers the distal tip of the needle cannula. By covers is only meant that the movable needle shield radially conceals the needle cannula. In the axial direction the movable needle shield is slidable to move to a position wherein the distal tip of the needle cannula is in front of the movable needle shield. The latter position of the movable needle shield thus being the second position. 
     The movable needle shield preferably carries the cleaning reservoir, such that the distal tip of the needle cannula is positioned inside the cleaning reservoir when the needle shield is in the first position which is usually between injections. 
     In the second position, which is usually during injection, the distal tip of the needle cannula extends distally in relation to the cleaning reservoir. 
     The cleaning reservoir and the overflow reservoir preferably connect through a channel. This channel can be radial or axial or any combination thereof. 
     In one example the hollow opening inside the channel is sealed by a rubber element which blocks the passageway through the channel. This rubber element preferably has a resilient lip which is flexible in at least one direction and which thus seals against a part of the injection device. This resilient lip and the part against which the lip seals thus makes up the one-way pressure valve. In one example, the flexible lip seals against a part of the element carrying the cleaning reservoir. 
     The flexibility of the lip allows passage through the channel and into the overflow reservoir when the pressure inside the cleaning reservoir surpasses a predetermined level defined as the opening pressure. 
     The cleaning reservoir is distally sealed by a distal septum and proximally sealed by a proximal septum whereas the overflow reservoir distally is sealed by the distal septum and proximally is sealed by the rubber element. 
     In a further example, the medical injection device comprises a removable protective cap as it is generally known from injection devices. This protective cap preferably covers the part of the injection device carrying the liquid drug. A preferred shape of a medical injection device seems to be that of a fountain pen i.e. an oblong longitudinal pen-shaped device. In such devices is the cartridge containing the liquid drug usually provided at the distal end of the pen-shaped injection device which end is also the end covered by the removable protective cap. 
     In the above example, the removable protective cap carries the cleaning reservoir contrary to the first example wherein the cleaning reservoir was carried by the axially movable needle shield. 
     An injection device wherein the cleaning reservoir is carried by the protective cap is known from WO 2014/029018. Herein a cleaning reservoir is provided at a distal end of the protective cap such that the distal tip of the needle cannula is positioned inside the cleaning reservoir when the protective cap is mounted on the injection device, and the distal tip of the needle cannula is positioned outside the cleaning reservoir when the protective cap is removed from the injection device. 
     However, this known solution has no overflow reservoir connecting to the cleaning reservoir and thus no valve at all. 
     In a further example, the needle shield is divided into two parts; a first shield part and a second shield part which are axially movable in relation to each other. One of the two parts can then be moved proximally by the protective cap whereas the other part maintains its position. Further, the part moving with the protective shield can be provided with a special tool inserted in the shield part. This special tool thus straightens the distal part of the needle cannula should it be bended during injection. 
     Regarding the liquid cleaning agent then any liquid substance that are able to clean the distal tip of the needle cannula can be used. The liquid cleaning agent can in one example be filled into the cleaning reservoir by the manufacture of the injection device and delivered to the user in a ready-to-use state. 
     Alternatively, the user is required to fill the cleaning agent into the cleaning reservoir when taking the injection device into use. 
     In one example, the liquid pharmaceutical drug contained in the cartridge contains a preservative. In such case, the preservative containing liquid drug can be used as the liquid cleaning agent. This would require the user to transfer a predetermined volume of the preservative containing liquid drug from the cartridge and into the cleaning reservoir. This is preferably done by either moving the plunger forward inside the cartridge or moving the glass part of the cartridge relatively to the plunger. In either way, a predetermined volume is pumped from the cartridge and into the cleaning reservoir. 
     Definitions 
     An “injection pen” is typically an injection apparatus having an oblong or elongated shape somewhat like a pen for writing. Although such pens usually have a tubular cross-section, they could easily have a different cross-section such as triangular, rectangular or square or any variation around these geometries. 
     The term “Needle Cannula” is used to describe the actual conduit performing the penetration of the skin during injection. A needle cannula is usually made from a metallic material such as e.g. stainless steel and connected to a hub to form a complete “injection needle” also often referred to as a “needle assembly”. A needle cannula could however also be made from a polymeric material or a glass material. The hub also carries the connecting means for connecting the needle assembly to an injection apparatus and is usually moulded from a suitable thermoplastic material. 
     As used herein, the term “liquid drug” is meant to encompass any drug-containing flowable medicine capable of being passed through a delivery means such as a hollow needle in a controlled manner, such as a liquid, solution, gel or fine suspension. Representative drugs includes pharmaceuticals such as peptides, proteins (e.g. insulin, insulin analogues and C-peptide), and hormones, biologically derived or active agents, hormonal and gene based agents, nutritional formulas and other substances in both solid (dispensed) or liquid form. The term “preservative containing liquid drug” is preferably used to describe a liquid drug containing a preservative. Such liquid drug could in one example be a blood sugar regulating liquid drug such as insulin, insulin analogue, GLP-1 or GLP-2, and the preservative contained in the liquid drug could in one example be phenol, meta-cresol or any combination thereof. 
     “Cartridge” is the term used to describe the container actually containing the drug. Cartridges are usually made from glass but could also be moulded from any suitable polymer. A cartridge or ampoule is preferably sealed at one end by a pierceable membrane referred to as the “septum” which can be pierced e.g. by the non-patient end of a needle cannula. Such septum is usually self-sealing which means that the opening created during penetration seals automatically by the inherent resiliency once the needle cannula is removed from the septum. The opposite end is typically closed by a plunger or piston made from rubber or a suitable polymer. The plunger or piston can be slidable moved inside the cartridge. The space between the pierceable membrane and the movable plunger holds the drug which is pressed out as the plunger decreased the volume of the space holding the drug. However, any kind of container—rigid or flexible—can be used to contain the drug. 
     Since a cartridge usually has a narrower distal neck portion into which the plunger cannot be moved not all of the liquid drug contained inside the cartridge can actually be expelled. The term “initial quantum” or “substantially used” therefore refers to the injectable content contained in the cartridge and thus not necessarily to the entire content. 
     By the term “Pre-filled injection device” or “Disposable injection device” is meant an injection device containing a predetermined quantum of a liquid drug and which injection device is disposed of once this predetermined quantum has been used. The cartridge containing the liquid drug is permanently positioned or embedded in the injection device such that the user cannot remove the cartridge without permanent destruction of the injection device. Once the predetermined amount of liquid drug in the cartridge and thus in the injection device is used either in one injection or in a series of multiple injections, the user discards the entire injection device including the embedded cartridge. 
     This is in opposition to a “Durable” injection device in which the user can himself change the cartridge containing the liquid drug whenever it is empty. Pre-filled injection devices are usually sold in packages containing more than one injection device whereas durable injection devices are usually sold one at a time. When using pre-filled injection devices an average user might require as many as 50 to 100 injection devices per year whereas when using durable injection devices one single injection device could last for several years, however, the average user would require 50 to 100 new cartridges per year. 
     “Scale drum” is meant to be a cylinder shaped element carrying indicia indicating the size of the selected dose to the user of the injection pen. The cylinder shaped element making up the scale drum can be either solid or hollow. “Indicia” is meant to incorporate any kind of printing or otherwise provided symbols e.g. engraved or adhered symbols. These symbols are preferably, but not exclusively, Arabian numbers from “0” to “9”. In a traditional injection pen configuration the indicia is viewable through a window provided in the housing. 
     Using the term “Automatic” in conjunction with injection device means that, the injection device is able to perform the injection without the user of the injection device delivering the force needed to expel the drug during dosing. The force is typically delivered—automatically—by an electric motor or by a spring drive. The spring for the spring drive is usually strained by the user during dose setting, however, such springs are usually prestrained in order to avoid problems of delivering very small doses. Alternatively, the spring can be fully preloaded by the manufacturer with a preload sufficient to empty the entire drug cartridge though a number of doses. Typically, the user activates a latch mechanism e.g. in the form of a button on, e.g. on the proximal end, of the injection device to release—fully or partially—the force accumulated in the spring when carrying out the injection. 
     The term “Permanently connected” or “permanently embedded” as used in this description is intended to mean that the parts, permanently connected or permanently embedded, requires the use of tools in order to be separated and should the parts be separated it would permanently damage at least one of the parts thereby rendering the construction useless for its purpose. 
     All references, including publications, patent applications, and patents, cited herein are incorporated by reference in their entirety and to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     All headings and sub-headings are used herein for convenience only and should not be constructed as limiting the invention in any way. 
     The use of any and all examples, or exemplary language (e.g. such as) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. The citation and incorporation of patent documents herein is done for convenience only and does not reflect any view of the validity, patentability, and/or enforceability of such patent documents. 
     This invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained more fully below in connection with a preferred embodiment and with reference to the drawings in which: 
         FIG. 1  show an exploded perspective view of a first example of the invention (viewed from a distal position). 
         FIG. 2  show an exploded perspective view of the first example of the invention (viewed from a proximal position). 
         FIG. 3  show a side view of the first example of the invention. 
         FIG. 4  show a perspective view of the movable assembly as seen from a proximal position. 
         FIG. 5  show a perspective view of the movable assembly as seen from a different position. 
         FIG. 6  show a cross-sectional view of the first example of the invention with the distal tip of the needle cannula positioned inside the cleaning reservoir. 
         FIG. 7  show a cross-sectional view of the first example of the invention when rotated 90 degree around the centre axis X relative to  FIG. 6 . 
         FIG. 8  show a further cross sectional view of the first example of the invention with the distal tip of the needle cannula positioned outside the cleaning reservoir. 
         FIG. 9  show a perspective view into the chamber part of the first example of the invention when viewed from a proximal position. 
         FIG. 10  show a perspective view into the chamber part of the first example of the invention when viewed from a distal position. 
         FIG. 11  show a cross-sectional view of a second example of the invention. 
         FIG. 12  show an enlarged view of the distal part of the injection device circled in  FIG. 11 . 
     
    
    
     The figures are schematic and simplified for clarity, and they just show details, which are essential to the understanding of the invention, while other details are left out. Throughout, the same reference numerals are used for identical or corresponding parts. 
     Detailed Description of Embodiment 
     When in the following terms as “upper” and “lower”, “right” and “left”, “horizontal” and “vertical”, “clockwise” and “anti (or counter) clockwise” or similar relative expressions are used, these only refer to the appended figures and not to an actual situation of use. The shown figures are schematic representations for which reason the configuration of the different structures as well as their relative dimensions are intended to serve illustrative purposes only. 
     In that context it may be convenient to define that the term “distal end” in the appended figures is meant to refer to the end of the injection device which usually abut or points towards the skin of the user during injection and which end carries the injection needle whereas the term “proximal end” is meant to refer to the opposite end pointing away from the skin during injection and which is often provided with a rotational button to set the size of the dose to be injected. Distal and proximal is meant to be along an axial orientation of the injection device along a virtual centre line marked “X” in  FIG. 3 . 
       FIGS. 1 and 2  each disclose a perspective exploded view of the front end of the injection device according to a first embodiment whereas  FIG. 3  is an exploded side view. 
     The depicted front end comprises a stationary part  10  and a movable assembly  20 . The stationary part  10  is a part of the housing structure of the injection device and is secured to the remaining housing structure by having a radial protrusion  11  which is click fitted to the remaining housing structure. The movable assembly  20  is indicated with a broken line in  FIG. 3 . 
     The remaining housing structure includes a cartridge holder  15  as best seen in  FIG. 8 . The cartridge holder  15  secures the cartridge  55  which contains the liquid drug to be injected as it is commonly known from injection devices. The injection itself is performed by moving a plunger  56  forward inside the cartridge  55  thus creating an overpressure inside the cartridge  55 . 
     The stationary part  10  is further provided with a longitudinal track  12  for guiding the movable assembly  20  via a guiding protrusion  33  provided on the movable assembly  20 . In the depicted embodiment, the guiding protrusion  33  is provided on a chamber part  30 . 
     The longitudinal track  12  connects to a radial track  14  as e.g. seen in  FIGS. 2 and 3 . When the guiding protrusion  33  is positioned inside this radial track  14 , the movable assembly  20  is prevented from moving in the axial direction. A relative rotation between the movable assembly  20  and the stationary part  10  thus unlocks the injection device and makes it possible to move the movable assembly  20  axially relatively to the stationary part  10 . 
     In the disclosed example, the axial track  12  connects to the radial track  14  via a helical track  13 . When using such a helical track  13 , the movable assembly  20  can be moved a predetermined distance in the axial direction upon rotation. However, the axial track  12  could easily connect directly to the radial track  14 . 
     The stationary part  10  also carries a needle cannula  5  which has a distal part  6  which extend in the distal direction and a proximal part  8  which extend in the proximal direction. The proximal part  8  is usually connected to a reservoir such as a cartridge  55  containing the liquid drug to be injected whereas the distal part  6  is provided with a sharp tip  7  for penetrating the skin of the user during injection. Stretching in the longitudinal direction along the axis X, the needle cannula  5  is provided with a hollow lumen  9  through which the liquid drug flows during injection. 
     Since the stationary part  10  carries the needle cannula  5  it could also be denoted as the hub when comparing to well-known needle assemblies. 
     The movable assembly  20  comprises a chamber part  30  sandwiched between a bottom part  40  and a top part  50  as best seen in  FIG. 3 . 
     Proximally, the chamber part  30  is provided with a number of radially extending chamber part openings  31  into which radially extending bottom part protrusions  41  on the bottom part  40  clicks during assembly of the movable assembly  20 . In the same fashion, outwardly extending chamber part protrusions  32  provided on the chamber part  30  clicks into top part openings  51  provided in the top part  50  such that the chamber part  30 , the bottom part  40  and the top part  50  can be click fitted together to form one cleaning assembly as disclosed in  FIGS. 4 and 5 . 
     As seen in  FIG. 8 , the movable assembly  20  can be connected to a telescopically movable needle shield  45  to move with the needle shield  45 . The top part  50  is henceforth provided with outwardly pointing shield protrusions  52  for this purpose, and the needle shield  45  is provided with radial openings  46  for receiving these outwardly pointing shield protrusions  52 . The movable assembly  20  thus moves telescopically together with the needle shield  45 . 
     The combined unit  10 ,  20  disclosed in  FIGS. 6 and 7  can be sterilized as one unit and for that purpose the combined unit  10 ,  20  is sealed by a pierceable foil  16  provided distally on the stationary part  10 . This foil  16  is removed or broken when the distal part  8  of the needle cannula  5  is penetrated into the cartridge  55  as disclosed in  FIG. 8 . 
     As best seen in the  FIGS. 6 to 8  (and in  FIG. 1-2 ), a distal septum  21  is provided between the chamber part  30  and the top part  50 , and a proximal septum  22  is provided between the chamber part  30  and the bottom part  40 . 
     The distal septum  21  is moulded as an integral part of the top part  50  and the proximal septum  22  is moulded to form an integral part of the bottom part  40  as disclosed in  FIGS. 1  and  2 . The septae  21 ,  22  are preferably moulded from a suitable rubber material (TPE) whereas the bottom part  40  and the top part  50  are moulded from a suitable polymer. The moulding technique used could be a so-called multi-component moulding using different materials supplied through different injection points in a sequential injection moulding process, such multi-component moulding are often referred to as 2K moulding. However, the two septae  21 ,  22  could alternatively be provided as individual septae sandwich in their respective positions. 
     Further, the septae  21 ,  22  are pierceable in a self-sealing manner as generally known from septae used in medical containers, and both the top part  50  and the bottom part  40  are provided with openings for passage of the needle cannula  5 . 
     The chamber part  30  has a through-going opening which when closed by the distal septum  21  and the proximal septum  22  makes up a cleaning reservoir  35 . Between subsequent injections, the distal tip  7  of the needle cannula  5  is maintained inside this cleaning reservoir  35  as disclosed in  FIGS. 6 and 7 . 
     The proximal end surface of the chamber part  30  is provided with an axially extending circular protrusion  34  which seals against the proximal septum  22  as best seen in  FIGS. 6 and 7 . 
     Further, in the centre of the chamber part  30  and surrounding the cleaning reservoir  35 , a tower  39  is erected which distally seals against the distal septum  21 . The cleaning reservoir  35  is thus tightly sealed at both ends. 
       FIG. 9  discloses a view of the chamber part  30  as seen from the proximal end of the injection device and shows that the cleaning reservoir  35  is provided with a large radial opening  36  which connects to a continued small radial opening  37  (as also seen in  FIG. 7 ). This small radial opening  37  terminates into a distal space  38  of the chamber part  30  as best seen in  FIG. 1  and in  FIG. 10 . However, in  FIG. 10 , the sealing part  60  is located inside the distal space  38 . 
     The design of a large radial opening  36  continuing into a small radial opening  37  is mainly due to the moulding technique used. During moulding one core can thus be used to make the large distal space  38  and a second core can be used to form the radial opening  36 . The small radial opening  37  will thus arise where the two cores abut. 
     As best seen in  FIGS. 1 to 3 , the distal space  38  of the chamber part  30  is occupied by a sealing part  60 . This sealing part  60  is a two component part and comprises a flexible rubber (TPE) part  61  and a more rigid plastic part  62 . The flexible rubber part  61  and the plastic part  62  are preferably made by 2K moulding, but could alternatively be two separate parts joined together e.g. by gluing. 
     The flexible rubber part  61  is on the outer surface provided with an outer seal  63  which seals against the inner surface of the chamber part  30 . This outer seal  63  is in the disclosed embodiment formed as two circular ridges or crests as e.g. disclosed in  FIG. 2 . On the inner surface, the flexible rubber part  61  seals against the tower  39  of the chamber part  30  preferably through a circular lip  65 . 
     This circular lip  65  is inclined towards the tower  39  with an inherent resiliency such that the circular lip  65  and the tower  39  together form a valve only allowing passage of the liquid drug when the pressure is able to open the valve i.e to force the circular lip  65  radially away from the outer surface of the tower  39 . 
     The part of the space  38  defined by the interior of the chamber part  30 , the circular lip  65  and the distal septum  21  makes up the overflow reservoir  70 . 
     In case the liquid drug contained in the cartridge  55  also comprises a preservative, this preservative containing liquid drug can be used as a cleaning agent. This would require the user to eject a volume of the preservative containing liquid drug from the cartridge  55  and into the cleaning reservoir  35 . When the preservative containing liquid drug is ejected from the cartridge  55  and into the cleaning reservoir  35 , the air inside the cleaning reservoir  35  will be forced out through the valve and into the overflow reservoir  70 . At the end of filling liquid drug into the cleaning reservoir  35 , a small volume of the liquid drug also will pass through the radial openings  36 ,  37  and pass the circular lip  65  and is thus pressed into the overflow reservoir  70 . This is indicated by the line “F” in  FIG. 7 . 
     In  FIG. 7 , the cleaning reservoir  35  is shown as being filled with the same preservative containing liquid drug as present in the cartridge  55 . Further, a volume of the preservative containing liquid drug has flown through the valve and occupies a part of the overflow reservoir represented by the line “F”. Proximally to the line “F”, the air is now compressed. 
     Since the air contained in the proximal part of the overflow reservoir  70  is compressed, this air applies a pressure on the preservative containing liquid drug which helps urging the inclined circular lip  65  towards the tower  39 . The valve thus operates as a one-way valve only allowing passage from the cleaning reservoir  35  and into the overflow reservoir  70 . 
     Ejecting preservative containing liquid drug into the cleaning reservoir  35  is done by moving the plunger  56  and the cartridge  55  relatively to each other, preferably by either moving the plunger  56  distally or moving the cartridge  55  itself proximally or both. This builds up a pressure in the preservative containing liquid drug inside the cartridge  55  and the drug flows through the lumen  9  of the needle cannula  5  and into the cleaning reservoir  35  and further out through the one-way valve and into the overflow reservoir  70  until the pressure in the compressed air equalizes the pressure inside the cartridge. Once this balance has been reached, the preservative containing liquid drug stop to flow from the cartridge  55  and into the cleaning reservoir  35 . 
       FIG. 10  discloses a view inside the chamber part viewed from a distal position. As seen segments of the rigid plastic part  62  of the sealing member  60  has been cut away to allow the interior space  38  of the chamber part  30  to have a larger volume. 
       FIG. 8  discloses the injection device during injection. The movable assembly  20  together with the needle shield  45  has been moved to a proximal position preferably by pressing the top part  50  against the skin of the user as indicated by the line “S” in  FIG. 8 . During injection, the plunger  56  is moved forward inside the cartridge  55  preferably by an automatic drive mechanism as generally known. Following the injection, when the user removes the injection device from the skin, a not-shown spring element moves the movable assembly  20  in the distal direction to the position disclosed in  FIGS. 6 and 7  wherein the distal tip  7  of the needle cannula  5  is positioned inside the cleaning reservoir  35 . 
     Second Embodiment—Reservoir in Cap 
       FIGS. 11 and 12  discloses a different embodiment wherein the same or similar elements are numbered with the same numbers as in the first embodiment, however, with a “1” in front. The needle cannula which in the first embodiment is numbered  5  is the second embodiment numbered  105 . 
     The needle cannula  105  has a distal tip  107  which penetrates the skin of the user during injection and a proximal part  108  which is inserted into a cartridge  155  such that liquid drug can flow from the cartridge  155 , through the lumen of the needle cannula  105  and through the skin of a user. 
     In this second embodiment, the cleaning reservoir  135  is carried by a removable protective cap  120 . This protective cap  120  is releasable mounted on the housing structure as is commonly known form injection devices. 
     As depicted in  FIG. 11 , the stationary part  110  carrying the needle cannula  105  is click-fitted to the cartridge holder  115  and is as such a part of the housing structure. 
     As also disclosed in the first embodiment, the needle cannula  105  is anchored in the stationary part  110  which thus operates a hub in a needle assembly. 
     The removable protective cap  120  is distally provided with an insert  125 . This insert has a circular inner wall  126  and a circular outer wall  127 . Both these circular walls  126 ,  127  stretch in the proximal direction. 
     The space encompassed by the circular inner wall  126  is the cleaning reservoir  135  and the space located between the circular inner wall  126  and the circular outer wall  127  is the overflow reservoir  170 . 
     Proximally the circular inner wall  126  terminates in an inner wall end  128  whereas the circular outer wall  127  terminates in an outer wall end  129 . Both these ends  128 ,  129  abut a proximal cap septum  122 . 
     The proximal cap septum  122  is press fitted into the insert  125  such that the connection between the outer wall end  129  and the proximal cap septum  122  is fluid tight whereas the connection between the inner wall end  128  and the proximal cap septum  122  is able to open when the pressure inside the cleaning reservoir  135  surpasses a certain level. 
     The connection between the inner wall end  128  and the cap septum  122  in combination form a pressure valve which opens at a certain and predetermined pressure. 
     When preservative containing liquid drug is transferred from the cartridge  155  and into the cleaning reservoir  135 , the air contained in the cleaning reservoir  135  is pressed through the pressure valve  122 ,  128  and into the overflow reservoir  170 . If the cleaning reservoir  135  is overfilled, a surplus of preservative containing liquid drug also flows into the overflow reservoir  170 . The air previously contained inside the overflow reservoir  170  is henceforth compressed and pressurized during the filling of the cleaning reservoir  135 . 
     The needle shield is in this second example divided into two parts. A first shield part  145  and a second shield part  147 . The first shield part  145  is movable in the proximal direction against the bias of a compression spring  100  as disclosed in  FIGS. 11 and 12 . 
     When the user wants to perform an injection, the user removes the protective cap  120  whereby the spring element  100  moves the first shield part  145  distally and into alignment with the second shield part  147 . When the protective cap  120  has been removed, the distal end of the first shield part  145  thus abuts an inwardly pointing ring-shaped ridge  148  provided on the second shield part  147 . 
     During injection, the user pushes the second shield part  147  against the skin and the first shield part  145  follows in the proximal direction as the distal tip  107  of the needle cannula  105  penetrates the skin of the user. 
     The injection itself is preferably done automatically by a spring driven injection mechanism as it is commonly known. 
     Following an injection, when the user removes the distal end of the injection device from the skin, the spring element  100  urges the first shield part  145  and therewith also the second shield part  147  in the distal direction. 
     Following the injection, when the user remounts the protective cap  120  on the injection apparatus, the protective cap  120  pushes the first shield part  145  in the proximal position into the position depicted in  FIG. 11 . In this position, the distal tip  107  of the needle cannula  105  is once again positioned inside the cleaning reservoir  135 . 
     The first shield part  145  is in a further embodiment distally provided with an insert tool  149 . This insert tool  149  is made from a different material (e.g. TPE) and is in one example 2K moulded together with the first shield part  145 . The purpose of this insert tool  149  is to realign the needle cannula  105  should it somehow be bended during use. 
     During use it sometimes happens that the distal part  106  of the needle cannula  105  gets bended a little such that the distal part  106  of the needle cannula  105  deviates from the centre line X. This could potentially create problems when the distal tip  107  of the needle cannula  105  has to re-enter the cleaning reservoir  135 . In worst case, the distal part  106  of the needle cannula  105  could be bended to a degree wherein the distal tip  107  do not re-enter the cleaning reservoir  135 . In order to overcome this, the first shield part  145  is preferably provided with an insert tool  149  which will straighten out the distal part  106  of the needle cannula  105  during movement of the first shield part  145  and thus the insert tool  149  in the distal direction as it occurs when the second shield part  147  is removed from the skin of the user following an injection. 
     Once the distal part  106  is straight and aligned with the centre axis X, the distal tip  107  of the needle cannula  105  slides directly into the cleaning reservoir  135  when the protective cap  120  is re-mounted on the injection device. 
     Some preferred embodiments have been disclosed in the foregoing, but it should be stressed that the invention is not limited to these, but may be embodied in other ways within the subject matter defined in the following claims.