Patent Publication Number: US-9423351-B2

Title: Sensor attachment arrangement for flexible bags

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a filing under 35 U.S.C. 371 of international application number PCT/SE2010/050668, filed Jun. 15, 2010, published on Jun. 23, 2011 as WO 2011/075036, which claims priority to application number 0950977-9 filed in Sweden on Dec. 17, 2009. 
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to an optical sensor holding device. 
     BACKGROUND OF THE INVENTION 
     Bioreactors are used in the bioprocess industry for growing cells, e.g. for the purpose of producing biopharmaceuticals. Disposable bioreactors have been used more and more and are an increasing trend in the industry. These disposable bioreactors are flexible bags made of plastic, for example welded polyethylene film. For the culturing of cells it is important to measure some features of the culture inside the bioreactor. The features could be for example temperature, pH, and dissolved oxygen (DO) etc. In flexible bags it is common to provide sensors from the upper side of the bag, like the Cellbag™ 50 L/pH from GE Healthcare. One disadvantage with this is the risk of the sensor not being inside the culture all the time. Optical sensors for measuring for example pH and DO are provided from for example PreSens. Such an optical sensor, sometimes called a sensor spot, is a spot of a dye material typically comprising two different fluorescent materials. When the sensor spot is illuminated, fluorescent substances of the spot will emit light. Using suitable fluorescent substances this emitted light can be indicative of a property of the culture, such as pH or DO. Thus the returned light can be analysed and for example pH or DO can be determined. For optimal performance, these sensors should be provided in the culture all the time. Providing the sensors in the bottom part of the bag is often not as convenient as providing the sensor from the upper side due to the support structure often provided under the bag. Furthermore these optical sensors typically can not be attached directly on the material of the bag due to chemical incompatibility. Another issue is that the sensor assembly should be as flat as possible to ensure that it always will remain under the liquid surface. 
     SUMMARY 
     It is an object of the present invention to provide an optical sensor holding device that solves the problems of prior art described above. 
     This is achieved in an optical sensor holding device according to claim  1 . 
     Suitable embodiments are described in the dependent claims and in the detailed description below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 a    is a schematic view of a bioreactor in a rocking support structure provided with an optical sensor according to the invention. 
         FIG. 1 b    is an exploded view of the system shown in  FIG. 1   a.    
         FIG. 2 a    shows a sensor holding part according to one embodiment of the invention from one side. 
         FIG. 2 b    shows the sensor holding part of  FIG. 2 a    from the other side. 
         FIG. 3 a    is a cross section of the sensor attaching arrangement according to one embodiment of the invention. 
         FIG. 3 b    is a cross section view of another embodiment of the sensor attaching arrangement before assembling. 
         FIG. 3 c    is a cross section view of the sensor attaching arrangement of  FIG. 3 b    when assembled. 
         FIG. 4 a    shows an adaptor part according to one embodiment of the invention in a non locked position. 
         FIG. 4 b    shows the adaptor part of  FIG. 4 a    in a locked position. 
         FIG. 5 a    is a closer view of the locking mechanism in one embodiment of the invention before locking. 
         FIG. 5 b    is the same view as  FIG. 5 a    but in locked position, i.e. the adaptor part has been turned to a locked position. 
         FIG. 6  is a cross section view showing the sensor holding part being locked in the adaptor part according to one embodiment of the invention. 
         FIG. 7 a    shows another embodiment of the sensor holding part where the sensor holding part is separated into an inner sensor holding part and an outer sensor holding part. 
         FIG. 7 b    is an exploded view of the inner and outer sensor holding parts of  FIG. 7   a.    
         FIGS. 8 a -8 d    shows three different embodiments of adaptor parts according to the invention. 
         FIGS. 9 a  and 9 b    show schematically a sensor holding part and an adaptor part according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1 a    is a schematic view of a bioreactor  1  in a rocking support structure  3 .  FIG. 1 b    shows the same bioreactor system but in an exploded view. In the bottom part of the bioreactor  1  a sensor holding part  11  is provided according to the invention. The sensor holding part holds an optical sensor on the inside of the bag. Details of this will be described further down in the description. An optical fibre  7  is provided to a position close to the position of the optical sensor but outside the bag with the help of an adaptor part  41  (described in detail below). A monitor  9  is also shown where the readings from the optical sensor can be monitored. 
     According to the invention a sensor holding part (also called an optical sensor holding device) is provided inside the bag. The sensor holding part is integrated with the bag by means of for example welding. An adaptor part holding the optical fibre is provided outside the bag. The sensor holding part comprises an optical sensor and first locking parts protruding out from the bag. These first locking parts are adapted to mate with second locking parts of the adaptor part such that the optical fibre in the adaptor part will be safely positioned to and can communicate with the sensor inside the bag. Suitably the locking parts provide a locking mechanism that holds the optical fibre in a stable position in relation to the sensor in all directions. Suitably the optical fibre is provided lying flat along the bottom of the bag, i.e. the optical fibre is not pointing towards the sensor in the bag. Instead a mirror is provided in the adaptor part such that the light can be directed to the sensor when the adaptor part is positioned below the sensor. This is suitable because the support structure does not need to be adapted to the sensor attachment arrangement. Hereby this sensor attachment arrangement can be used on already existing systems without any adaptation. Furthermore, since no part of the sensor attachment arrangement is secured to the support structure, the bag can be freely moved together with the sensor and the sensor attachment arrangement. More description around the details of suitable embodiments of the invention is given below. 
       FIG. 2 a    is a view of a sensor holding part  11  (also called an optical sensor holding device  11 ) according to one embodiment of the invention. The sensor holding part  11  is in one embodiment positioned inside the bag and secured to the inner bag surface for example by means of welding. In another embodiment the sensor holding part is welded to the outside of the bag surface and a hole is provided in the bag surface around the sensor. In  FIG. 2 a    the side adapted to face the interior of the bag is shown. In this embodiment the sensor holding part  11  is circular. This is suitable because a circular shape will give rise to less tension in the joint between the bag and the sensor holding part than would a shape with sharp edges. Furthermore, tension stress can cause creeping deformation of the sensor holding part. The circular geometry also reduces the risk for dimension changes due to different shrinkage in the molding process. However other geometries of the sensor holding part would also be possible. In the centre of the sensor holding part  11  the optical sensor  13 , is provided. The optical sensor is a dye as described in the background chapter and can also be called a sensor spot. The sensor holding part should be provided in a material that can be welded to the bag material. The bag is often made from polyethylene and in this embodiment also the sensor holding part is made from polyethylene. However, the material of the sensor  13  can not be attached directly to polyethylene and therefore the sensor has been provided on a small piece of another material to which the sensor can be attached and which is transparent. In this embodiment polycarbonate has been used. This is described in more detail below in relation to  FIG. 3 . 
       FIG. 2 b    shows the sensor holding part  11  of  FIG. 2 a    from the other side, i.e. from the side pointing out from the bag. In this embodiment four first locking means in the form of hooks  17   a ,  17   b ,  17   c ,  17   d  are provided protruding out from the sensor holding part. The hooks are provided on the circumference of a circle. The number of the hooks can also be 2, 3, 5 or even more. The first locking means  17   a, b, c, d  are adapted to protrude out from the bag when the sensor holding part is positioned inside the bag. At least one hole needs to be provided in the bag surface to let the first locking means  17   a, b, c, d  through. In one embodiment a circular hole  23  as large as comprising all the first locking means  17   a, b, c, d  is provided in the bag. The sensor holding part is welded to the bag in order to prevent any leakage. In another embodiment the same circular hole is provided in the bag and furthermore a smaller circular piece of bag film is welded over the central part of the sensor holding part but inside the first locking means  17   a, b, c, d . This smaller circular piece of bag film will hereby cover the sensor in the middle of the sensor holding part. This could be suitable if there is any risk of leakage through the sensor attaching arrangement. This is described in more detail below in relation to  FIG. 3 . In another embodiment it would also be possible to provide one separate hole in the bag for each first locking means, i.e. in this embodiment four holes would be provided. The sensor holding part needs then to be welded to the bag around all these four holes in order to prevent any leakage. Alternatively, the bag surface could be welded to the sensor holding part in one circle on the inside of the locking means and one circle outside the locking means. 
       FIG. 3 a    is a cross section of a central part of the sensor attachment arrangement according to one embodiment of the invention. According to the invention the sensor holding part  11  (also called the optical sensor holding device  11 ) comprises two parts. One bag attachment part  31  adapted to be welded to the bag and one sensor attachment part  33  where the sensor  13  is provided. The sensor attachment part  33  is made of a material to which the sensor  13  can be attached. This could be for example polycarbonate. The sensor attachment part  33  is pressed fit into an opening  34  in the bag attachment part  31 . The bag attachment part  31  is made from a material that can be welded to the bag. Many bags are made from polyethylene and in this example also the bag attachment part  31  is made from polyethylene. The reason why the sensor  13  is not attached directly to the bag attachment part  31  is that the sensor  13  used in this example can not be attached to a material that also can be welded to the bag. The bag is made from polyethylene and therefore a suitable material for the sensor holding part is polyethylene. However the material of the sensor  13  used in this example can not be attached to polyethylene. The press fit of the sensor attachment part  33  in the opening  34  in the bag attachment part  31  disclosed here in relation to  FIG. 3 a    is a way to solve this problem. The sensor attachment part  33  should be slightly bigger than the opening  34 . Furthermore the sensor attachment part  33  is provided with a chamfer  35 . This will give a radial pressure on the sensor attachment part  33  for the purpose of preventing leakage through the free press fit. This minimizes the risk of getting any liquid or dirt in the opening  37  below the sensor attachment part  33  where light will pass during the optical reading. 
     Furthermore, a locking shoulder  38  is provided in the opening  34  in the bag attachment part  31 . The locking shoulder  38  should keep the sensor attachment part  33  in place after having been forced to pass said locking shoulder  38  when pressed fitted into the opening  34 . 
     In this embodiment a circular piece of bag film  21  is also provided. This piece of bag film  21  is welded to the bag attachment part  31  around the central part of the bag attachment part  31  where the sensor  13  is provided. The purpose is to prevent any possible leakage outside the bag if such a leakage would occur through the press fit. However, if the press fit really is leakage free and reliable this circular piece of bag film  21  would not be necessary. 
     In  FIG. 3 a    an adaptor part  41  is also shown attached to the sensor holding part  11 . An optical fibre  7  is positioned into the adaptor part  41 . A combined mirror and lens  39  is provided in the adaptor part  41  connected to the optical fibre  7 . When the sensor holding part  11  and the adaptor part  41  are connected the combined mirror and lens  39  is provided right beneath the sensor in the sensor holding part  11 . The combined mirror and lens  39  directs and focuses the light from the optical fibre  7  onto the sensor spot  13 . The sensor  13  is hereby illuminated via the fibre  7  and the excited fluorescent sensor  13  emits light that is monitored via the fibre  7 . The light paths are shown by arrows. With this arrangement the optical fibre is provided along the surface of the bottom part of the bag and the support structure needs not to be adapted in any way. The first and second locking parts keeping the sensor holding part and the adaptor part together will be further described below. 
       FIG. 3 b    is a cross section view of a central part of the sensor attachment arrangement according to another embodiment of the invention before assembly.  FIG. 3 c    is a cross section of the embodiment shown in  FIG. 3 b    after assembly. According to the invention a sensor holding part  11 ′ (also called an optical sensor holding device  11 ′) comprises two parts. One bag attachment part  31 ′ adapted to be welded to the bag and one sensor attachment part  33 ′ where the sensor  13  is provided. The sensor attachment part  33 ′ is made of a material to which the sensor  13  can be attached. This could be for example polycarbonate. The sensor attachment part  33 ′ is pressed fit into an opening  34 ′ in the bag attachment part  31 ′. The bag attachment part  31 ′ is made from a material that can be welded to the bag. Many bags are made from polyethylene and in this example also the bag attachment part  31 ′ is made from polyethylene. The reason why the sensor  13  is not attached directly to the bag attachment part  31 ′ is that the sensor  13  used in this example can not be attached to a material that also can be welded to the bag. The bag is made from polyethylene and therefore a suitable material for the sensor holding part is polyethylene. However the material of the sensor  13  used in this example can not be attached to polyethylene. The press fit of the sensor attachment part  33 ′ in the opening  34 ′ in the bag attachment part  31 ′ disclosed here in relation to  FIGS. 3 b  and 3 c    is a way to solve this problem. The sensor attachment part  33 ′ should be slightly bigger than the opening  34 ′. In this embodiment described in  FIGS. 3 b  and 3 c    suitably a force is applied around the opening  34 ′ combined with a holding device  40  on the opposite side as shown by the force arrows in  FIG. 3 b    when the sensor attachment part  33 ′ should be pressed into the bag attachment part  31 ′. Hereby the entrance into the opening  34 ′ will get larger (see also deformation arrows) and it will be easier to insert the sensor attachment part  33 ′. When the sensor attachment part  33 ′ is in place the force will be released and the sensor attachment part  33 ′ will be positioned stably in the opening  34 ′. Furthermore the sensor attachment part  33 ′ is provided with a chamfer  35 ′. This will give a radial pressure on the sensor attachment part  33 ′ for the purpose of preventing leakage through the free press fit. 
     Furthermore, a hook  36  is provided on the sensor attachment part  33 ′ which hook  36  will be pressed into the walls of the opening  34 ′ of the bag attachment part  31 ′ after insertion and assure a stable position of the sensor attachment part  33 ′ in the bag attachment part  31 ′. 
       FIG. 3 c    is a cross section view of the sensor attaching arrangement of  FIG. 3 b    when assembled. In  FIG. 3 c    an adaptor part  41  is also shown attached to the sensor holding part  11 ′. An optical fibre  7  is positioned into the adaptor part  41 . A combined mirror and lens  39  is provided in the adaptor part  41  connected to the optical fibre  7 . When the sensor holding part  11 ′ and the adaptor part  41  are connected the combined mirror and lens  39  is provided right beneath the sensor in the sensor holding part  11 ′. The combined mirror and lens  39  directs and focuses the light from the optical fibre  7  onto the sensor spot  13 . The sensor  13  is hereby illuminated via the fibre  7  and the excited fluorescent sensor  13  emits light that is monitored via the fibre  7 . The light paths are shown by arrows. With this arrangement the optical fibre is provided along the surface of the bottom part of the bag and the support structure needs not to be adapted in any way. The first and second locking parts keeping the sensor holding part and the adaptor part together will be further described below. In this embodiment a circular piece of bag film  21  is also provided. This piece of bag film  21  is welded to the bag attachment part  31 ′ around the central part of the bag attachment part  31 ′ where the sensor  13  is provided. The purpose is to prevent any possible leakage outside the bag if such a leakage would occur through the press fit. However, if the press fit really is leakage free and reliable this circular piece of bag film  21  would not be necessary. 
       FIG. 4 a    shows an adaptor part  41  according to one embodiment of the invention. Suitably the adaptor part is provided in a material that is stiffer than the material of the sensor holding part  11 . One example of a suitable material for the adaptor part is POM (Polyacetal plastic or Delrin plastic) or Peek (polyetereterketone plastic). In  FIG. 4 a    it is shown how the first locking means  17   a, b, c, d  of the sensor holding part  11  are fitted into second locking means  43   a, b, c, d , in the adaptor part  41  in a non locked position. However, the rest of the sensor holding part  11  is not shown in order to make it clearer. The second locking means  43   a, b, c, d  are in this embodiment provided as four tracks on the circumference of a circle. The dimensions are adapted for receiving the first locking means  17   a, b, c, d  of the sensor holding part  11 . In this embodiment each track  43   a, b, c, d  comprises guiding surfaces leading the hooks into a locking position, i.e. after having rotated the adaptor part  41  in relation to the sensor holding part  11  (as shown in  FIG. 4 b   ) the first locking means  17   a, b, c, d  have been guided into a second position within the tracks which is a locked position. These details are described in relation to  FIGS. 5 a    and  5   b.    
       FIG. 4 b    shows the adaptor part of  FIG. 4 a    in a locked position. 
       FIG. 5 a    is a closer view of the locking mechanism in one embodiment of the invention before locking. One first locking means  17   a  in the form of a hook is shown inserted into one second locking means  43   a  in the form of a track. A radial guiding surface  44  on the inner surface of the track  43   a  is provided for guiding a corresponding hook guiding surface  46  on the hook  17   a  into a radial locked position. Possibly the hook  17   a  is also pressed somewhat outwardly by the guiding surface  44 . Furthermore a locking bump  45  is shown in the track  43   a . A gripping part  48  of the hook  17   a  will be caught by an inclined surface  42  of the track leading up to the locking bump  45  and the hook  17   a  will pass over the locking bump  45  when the adaptor part  41  is rotated in relation to the sensor holding part  11 . The purpose of the locking bump  45  is to prevent the hook  17   a  from rotating back. 
       FIG. 5 b    is the same view as  FIG. 5 a    but in locked position, i.e. the adaptor part has been rotated to a locked position. Because all four locking parts provided in a circle are locked and because the locking mechanism is securing the adaptor part  41  in relation to the sensor holding part  11  in all directions the combined mirror and lens  39  of the adaptor part  41  can be kept steadily in relation to the sensor  13 . Furthermore, this locking mechanism provides a very low tension stress on the sensor holding part. This is important because the sensor holding part is made from polyethylene and this material tends to be subjected to creepings/relaxation. Hereby the risk for creeping/relaxation in the sensor holding part is reduced to a minimum by the locking mechanism described here. 
       FIG. 6  is a cross section view showing the sensor holding part  11  being locked in the adaptor part  41  according to one embodiment of the invention. In this view a contact surface  49  between the sensor holding part (possibly through the piece of bag film  21 ) and the adaptor part  41  can be seen. When the gripping part  48  of the hook  17  is pressed by the track  43  into the locked position the sensor holding part and the adaptor part will come into contact at contact surface  49  (possibly through the piece of bag film  21 ). This contact is important because the distance between the sensor and the combined mirror and lens need to be kept constant and contact surfaces pressed towards each other. This will work well if the tension stress is kept at a minimum level and therefore reduces the risk for creeping of the sensor part. 
       FIG. 7 a    shows another embodiment of a sensor holding part  51  where the sensor holding part is separated into an inner sensor holding part  53  and an outer locking part  55 .  FIG. 7 b    is an exploded view of the sensor holding part of  FIG. 7 a   . In this embodiment the bag  65  needs not to be penetrated by the first locking means. The bioreactor bag surface can be kept intact. This could be good for preventing any contamination risk for the cell growth process. First locking means  57  are provided on the outer locking part  55 . The inner sensor holding part  53  is welded to the bag surface and it comprises the sensor  59  in the middle facing the interior of the bag. The sensor attachment arrangement is suitably the same as described in relation to  FIG. 3 . The outer sensor holding part  55  is welded to the outside of the bag. The inner sensor holding part  53  and the outer locking part  55  will be welded together by bending the bag  65  according to  FIG. 7 a    and then an inner bag support ring  61  and an outer bag support ring  63  will be welded on top and on the bottom and secure the assembly. The adaptor part is suitably the same as described in relation to  FIGS. 4 a    and  4   b.    
       FIGS. 8 a -8 d    shows four different embodiments of adaptor parts according to the invention. Of course both the first and second locking means of the invention can be designed in different forms. The result that should be achieved is a locking position where the two parts are kept together and are locked together in all directions. Furthermore the geometry of the locking is important such that any creeping in the sensor holding part can be prevented. Four alternative embodiments of the adaptor part are shown in  FIGS. 8 a -8 d    where  FIG. 8 a    shows the adaptor part already described in relation to  FIGS. 4 and 5 . In this embodiment the locking is made in axial direction. The embodiments shown in  FIGS. 8 b , 8 c  and 8 d    provide a locking in radial direction. 
     The sensors described above are optical sensors. These could be for example sensors for pH, DO, carbondioxide (CO 2 ), biomass, UV detection and IR detection. 
       FIGS. 9 a  and 9 b    show schematically another embodiment of the invention where the first and second locking parts are designed differently. A sensor holding part  91  is shown having four first locking means  93   a, b, c, d  in the form of plugs with larger heads  95   a, b, c, d . An adaptor part  97  is also shown having four second locking means  99   a, b, c, d  in the form of receiving holes. In  FIG. 9 b    one of the second locking means  99   a  is shown in cross section. The second locking means  99   a  comprises a retaining means  101   a  in the form of a section in the receiving hole having a smaller diameter than the rest of the hole and edges adapted for letting the larger head  95   a  of the first locking means  93   a  pass through the retaining means  101   a  when a force is applied from above. The edges of the retaining means  101  are further adapted for retaining the head  95   a  below the retaining means  101  when it has been pressed down there. A sensor is provided in the middle of the sensor holding part in the same way as described in for example relation to  FIGS. 2 a  and  b    and an optical fibre is provided in the adaptor part in the same way as described in relation to  FIG. 3 . There are of course many other possible ways of designing the first and second locking means. 
     One important benefit with the invention is that a support structure provided under the flexible bag need not be adapted in any way to the sensor attachment arrangement. The bag can be freely moved together with the sensor attachment arrangement and be used in any system. Another feature of the sensor attachment arrangement is that it is very flat and of low height. This is advantageous since it is important that its effect on the mixing of the culture in the bioreactor bag by protruding into the bag is limited. At the same time also small volumes of culture in the bag will cover the sensor. The different locking mechanisms described above and the mirror provided in the adaptor part are both important components in making the sensor attachment arrangement as flat as possible.