Abstract:
A drug delivery device ( 50 ) is provided comprising a drug reservoir ( 10 ) and a piston ( 11 ). The drug reservoir ( 10 ) is provided for comprising a drug and comprises a flexible wall ( 22 ) and a dispensing hole ( 15 ) for dispensing the drug into an environment of the drug de delivery device ( 50 ). The piston ( 11 ) is provide for pressing against the flexible wall ( 22 ) to compress the drug reservoir ( 10 ) for pushing an amount of the drug through the dispensing hole ( 15 ). An adhesion interface ( 51 ) between a surface of the piston ( 11 ) and the flexible wall ( 22 ) prevents sliding between the surface of the piston ( 11 ) and the flexible wall ( 22 ).

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a drug delivery device, comprising a piston and a drug reservoir for comprising a drug and a piston. The drug reservoir comprises a flexible wall, and a dispensing hole for dispensing the drug into an environment of the drug delivery device. The piston is arranged for pressing against the flexible wall to compress the drug reservoir for pushing an amount of the drug through the dispensing hole. 
       BACKGROUND OF THE INVENTION 
       [0002]    Such a drug delivery device may comprise a small sized electrical motor, e.g. stepper motor, of which the action is controlled by an on-board microprocessor. The stepper motor moves the piston forward against the wall, e.g. pushed by a screw rod mechanism. The piston is moved in a controlled way as far as speed and stroke are considered. The piston pushes the flexible wall into the drug reservoir. As a result, the volume of the drug reservoir decreases and the pressure inside the drug reservoir increases. The increasing pressure causes an amount of the drug to be pushed out of the dispensing hole. While the piston pushes the flexible wall into the drug reservoir, it takes a shape that corresponds to minimum surface energy. Such shapes usually are irregular, resulting in a smaller usable drug reservoir volume and a higher resistance for the piston to move forward. When the drug reservoir becomes emptier, the flexible wall starts to fold until the piston can no longer overcome resistance from the folds and the drug viscosity and stops dispensing. When the piston stops dispensing, drugs stay behind in the folds. Consequently, it is not possible to fully empty the drug reservoir. Additionally, there is a problem of the piston sliding along the folded flexible wall surface without causing any drug to be pushed out of the dispensing hole because the piston mechanism cannot be effective. 
       OBJECT OF THE INVENTION 
       [0003]    It is an object of the invention to provide a drug delivery device as described above, wherein the drug reservoir can be emptied more reliably. 
       SUMMARY OF THE INVENTION 
       [0004]    According to a first aspect of the invention, this object is achieved by providing a drug delivery device, comprising a drug reservoir, a piston and an adhesion interface. The drug reservoir comprises a flexible wall and a dispensing hole for dispensing the drug into an environment of the drug delivery device. The piston is arranged for pressing against the flexible wall to compress the drug reservoir for pushing an amount of the drug through the dispensing hole. The adhesion interface is situated between a surface of the piston and the flexible wall for preventing sliding between the surface of the piston and the flexible wall. 
         [0005]    The adhesion interface keeps the flexible wall surface conformed to the piston surface and prevents both surfaces from slipping between each other. With every step of the piston into the flexible wall and in the direction of the delivery hole, a greater part of its surface gets covered by and adheres to the flexible wall surface. The flexible wall surface does not fold, but is slid around the piston surface. 
         [0006]    The adhesion interface may, e.g., be a sticky coating on the piston surface and/or on the flexible wall. Alternatively, a magnetic coating is used on at least one of the two surfaces for providing the required adhesion. 
         [0007]    In a preferred embodiment, the flexible wall comprises at least one non-flexible part located at the adhesion interface. An advantage of a non-flexible part is that it cannot be folded or wrinkled. When the piston pushes against a non-flexible part, its shape does not change. The flexible parts of the flexible wall meanwhile ensure that the flexible wall as a whole is still deformable and can be used for compressing the drug reservoir. 
         [0008]    In a flexible wall with only one or a few non-flexible parts, the surface of the non-flexible parts preferably follows the contours of the piston surface at the contact area of both surfaces. This ensures an optimal distribution of the pressure exerted by the piston upon the flexible wall and further facilitates the emptying of the reservoir. In addition, the preformed flexible wall makes it easier to fill the reservoir to the right dose without the piston already placed against the flexible wall. 
         [0009]    These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    In the drawings: 
           [0011]      FIG. 1  shows a drug delivery device according to the invention, 
           [0012]      FIG. 2  shows a piston and an uncompressed drug reservoir, 
           [0013]      FIGS. 3 and 4  show partially compressed drug reservoirs in a drug delivery device according to the prior art, 
           [0014]      FIG. 5  shows a partly compressed drug reservoir in a drug delivery device according to the invention, 
           [0015]      FIG. 6  shows a partly compressed drug reservoir with a non-flexible part in the flexible wall, and 
           [0016]      FIG. 7  shows a partly compressed drug reservoir with multiple rigid parts in the flexible wall. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]      FIG. 1  shows a drug delivery device  50  according to the invention. The drug delivery device  50  is a swallowable capsule comprising a drug to be released somewhere along the gastro-intestinal tract of a patient and an actuation mechanism  11 ,  12  for controlling the amount of drugs to be released and the moment of said release. It is to be noted that the current invention may also be used with implantable drug delivery devices. The drug to be released is stored in a compressible medicine reservoir  10 . The drug may, e.g., be stored as dry powder, dissolved in water or as a gel or liquid. 
         [0018]    The actuation mechanism  11 ,  12  comprises a piston  11  and a small sized electrical motor, e.g. a stepper motor  12 , for pushing the piston by means of a screw rod mechanism towards the drug reservoir  10 . Instead of a stepper motor  12 , different driving means may be used for driving the piston  12 . The driving of the piston  11  may, e.g., be realized using (electro-)magnetic forces or a swelling agent. When the piston  11  is pressed against the medicine reservoir  10 , the medicine reservoir is compressed and the pressure inside the medicine reservoir  10  increases. As a result of the increasing pressure, the drug is pushed out of the drug delivery device  50  through a dispensing hole  15 . The drug release may, e.g., be triggered by an internal clock, sensor values from a pH-sensor or trigger signals from an electrical or chemical detector element. If the drug delivery device  50  comprises means for wireless communication, the drug delivery may be externally triggered. The operations of all electronic functions of the device  50  are controlled by a microprocessor  17  and powered by a battery  16 . 
         [0019]      FIG. 2  shows a piston  11  and an uncompressed drug reservoir  10 . The drug reservoir  10  comprises a rigid dome shaped cap  21  and a flexible wall  22 . The drug reservoir  10  shown in  FIG. 2  is an example of a drug reservoir for which the current invention would be advantageous. The invention will however also improve the emptying of other drug reservoirs  10  with a flexible wall. For example, the complete drug reservoir  10  may be flexible or the dome shaped cap  21  and/or the flexible wall  22  may have different shapes than shown in the Figure. When the piston  11  is driven into the flexible wall  22  of the drug reservoir  10 , the reservoir volume is compressed and an amount of the drug is released through the delivery hole  15 . 
         [0020]      FIGS. 3 and 4  show partially compressed drug reservoirs  10  in a drug delivery device according to the prior art. In both Figures the flexible parts  22  of the drug reservoirs are compressed, while the dome shaped cap  21  keeps its shape. In  FIG. 3 , the flexible wall  22  has been compressed to a lesser extent than in  FIG. 4 . In  FIG. 3  it is already visible that, due to uneven surface tension, the flexible wall shape does not conform to the piston  11  profile. This will result in an increased resistance for the piston  11  and drugs staying behind in folds of the flexible wall  22 . As can be seen in  FIG. 4 , uneven surface tension and drug viscosity may cause the flexible wall  22  of a half full drug reservoir  10  to form multiple folds. Such folds increase the resistance to the piston  11  and may completely stop the dispensing of the drugs. In addition, the folds reduce the contact area between the flexible wall  22  and the piston  11 , leading to slip between both and the piston not moving along its central axis  41  because the screw rod mechanism does not function properly. 
         [0021]      FIG. 5  shows a partly compressed drug reservoir  10  in a drug delivery device  50  according to the invention. In this embodiment, the problems of the prior art are solved by the introduction of an adhesion interface  51  in between the piston  11  and the flexible wall  22 . The adhesion interface  51  keeps the flexible wall  22  conformed to the piston  11  surface and thus prevents slipping between both surfaces and folding of the flexible wall  22 . The adhesion  51  may cover the complete piston  11  surface and/or the complete surface of the flexible wall  22 . In a preferred embodiment the adhesion surface  51  only covers the parts of those surfaces which are designed to make contact with each other. Alternatively, the adhesion surface  51  may cover only part of the expected contact area. 
         [0022]    The adhesion surface  51  may be a sticky surface applied to the piston  11  and/or flexible wall  22  surface. Alternatively, a magnetic coating may cover one of the surfaces, while the other surface is either magnetic or magnetizable. Another option is to use electrostatic interaction using an electrostatically charged polymer. A skilled person will be able to come up with many other possible ways of providing a suitable adhesion surface  51 . The adhesion surface  51  used is preferably such that the drug reservoir  10  can still be removed from the adhered piston  11  surface for enabling refilling of the drug reservoir  10  without damaging the piston  11  or the drug reservoir. It is preferable that also the adhesion layer  51  keeps intact when the drug reservoir  10  and the piston  11  are separated. Alternatively, the drug reservoir  10  and/or the adhesion layer  51  are replaced when preparing the drug delivery device  50  for a second use. 
         [0023]    Such an adhesion layer  51 , which makes it possible to separate the surfaces without damaging the piston  11  or the reservoir  10 , also enables a further option. When the reservoir  10  is completely or partly compressed and the piston  11  movement is reversed, the pressure inside the reservoir  10  will drop and body fluid will be sucked into the reservoir  10 . 
         [0024]      FIG. 6  shows a partly compressed drug reservoir  10  with a non-flexible part  61  in the flexible wall  22 . The shape of the non-flexible part  61  follows the contours of the opposing piston  11  surface. In this embodiment this means that the non-flexible part  61  is dome shaped. An advantage of this non-flexible part  61  is that it cannot be folded or wrinkled. When the piston pushes against the non-flexible part  61 , its shape does not change. The flexible parts of the flexible wall  22  meanwhile ensure that the flexible wall  22  as a whole is still deformable and that drug reservoir  10  is still compressible. 
         [0025]    The non-flexible part  61  ensures an optimal distribution of the pressure exerted by the piston  11  upon the flexible wall  22  and further facilitates the emptying of the reservoir  10 . In addition, the preformed flexible wall  22  makes it easier to fill the reservoir to the right dose without the piston  11  already placed against the flexible wall  22 . If a fully flexible drug reservoir  10  would be filled to the rim, the viscosity of the drug may result in too much resistance for the piston to start moving. 
         [0026]      FIG. 7  shows a partly compressed drug reservoir  10  with multiple rigid parts  71  in the flexible wall. The rigid parts  71  are alternated with flexible parts  72  for providing the required flexibility to the flexible wall  22 . 
         [0027]    It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.