Abstract:
The invention relates to a device for pumping a fluid into a bioreactor. Polsatile pumping is made possible by valve arrangement so that growth of the cells in the bioreactor is increased. Pumping function can be achieved though several mechanisms. A piston can be displaced in a cylinder, especially by an electromagnet, wherein a permanent magnet or likewise an electromagnet can be arranged in the piston. The piston can also be displaced by compressed air. An elastic, hollow body can also be provided, wherein said hollow body can be deformed by mechanical electromagnetic forces so that pumping function is achieved by a change in volume. The pumping device can also be used as implant for assisting or replacing heart function.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a divisional application of application Ser. No. 10/482,072, filed Dec. 24, 2003; which was a §371 national stage of International application PCT/EP02/07025, filed Jun. 25, 2002; the application also claims the priority, under 35 U.S.C. §119, of German patent application No. 101 30 512.5, filed Jun. 25, 2001; the prior applications are herewith incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a device for cultivating and/or treating cells, especially a bioreactor. Furthermore, the invention relates to a device for pumping a fluid through a device for cultivating and/or treating cells, especially through a bioreactor. 
     A method and a device of the initially mentioned type is described in an older application of the inventor DE 199 35 643.2. 
     Meanwhile, it has been found that the formation of a cell layer and cell growth are clearly improved by putting cells under pressure. A known practical approach is to apply a mechanical force to a cell culture chamber, e.g. by a plunger, as described in U.S. Pat. No. 6,060,306. This implies not only high design requirements, but such load does not reflect in-vivo conditions due to the heterogeneous pressure distribution such obtained. The attempt made in U.S. Pat. No. 5,928,945 is to apply a mechanical force e.g. to cartilage cells chiefly via shear flow stress by means of a culture medium. But this is unphysiological, because no such perfusions are encountered e.g. in articulation areas. In U.S. Pat. No. 6,060,306, an apparatus is described in which a cartilage construct is moved within a culturing chamber like in a bellows by means of outer wall movements. A disadvantage to said movement processes is that the movement patterns impart high mechanical stress to the membrane structures. That causes the membranes to break after a few days and makes the products insterile and thus inappropriate for implantations. 
     Furthermore, due to the movement patterns permanently causing convex-concave deformations, the membranes can only generate punctual and thus inhomogeneously distributed pressure deformations. That causes oscillations to form in the culture medium zone and pressure heterogeneities to form in the biological tissues in the bioreactor. 
     A common characteristic of some of said devices is that the pressure loads are firmly integrated in the culture vessel as a type design. This includes e.g. the bioreactor according to Hoestrup et al. (Tissue Engineering Vol. 6, 1, 2000 pp 75-79) for vessels and heart valves. Such models are a sophisticated design and expensive to sell, because the pumping system, due to its integration in the bioreactor, must be shipped with the future bioimplant as a complete unit. There is no sterile separation from the pump head. 
     Alternating pressure sources are provided in several other systems such as in WO 97/49799, but not explained in more detail. U.S. Pat. No. 5,899,937 describes a system which can compress a liquid-filled bladder by means of an eccentric movement via a plunger and thus force the liquid out of the bag thereby creating a liquid flow. A bladder is also used in U.S. Pat. No. 5,792,603 (WO 97/49799). But the system comprises vessels leading with open ends into a culture chamber with thorough intermixing of intravascular and extravascular liquids. That is especially disadvantageous if different medium compositions are needed inside and outside the vessels, e.g. to be able to offer growth factors and chemotactic factors directionally. That prevents e.g. the induction of directed migration of myofibroblasts from the place of population towards the outsides and constitutes a significant disadvantage in the population process. Also, that prevents the locally specific repopulation with different cell populations. Another disadvantage is immediate pressure compensation, which makes it impossible to create different pressure profiles in the intravascular and extravascular spaces. In the bioreactor according to Laube et al., the valves are no longer movable already when high volume amplitudes are applied, because the outer walls of the valves need to be fixed to the housing by sewing. 
     However, the pulsatile or pulse-type flow is in most cases generated in a conventional way via a peristaltic pump such that the pressure amplitudes are rather low in terms of change in volume, show flat frequencies and also mean high stress loads for the hose during several weeks&#39; operation due to the permanent kneading effect. This is true e.g. for Niklason et al., Science 4, 1999 vol 284 pp 489-492, or EP 0320 441. 
     Further devices are described e.g. in DE 199 15610 A1, which are suitable especially for vessels and heart valves. 
     BRIEF SUMMARY OF THE INVENTION 
     The task of the present invention is to provide a device without the above-described disadvantages. An object of the invention is to provide a possibility for generating physiological, homogeneously acting pressure and volume amplitudes equally in a volumetric flow of liquid. Specifically, an object of the invention is to make it possible to generate entirely homogeneous pressure relations in all areas also in the bioartificial tissue within the bioreactor. The device is to be variably adaptable to the pressure-volume compliance of the system to be perfused. The device is to be modular, small, weight-saving, reliable, of low energy consumption and able to be coupled or combined with any systems to be perfused and is to apply minimal mechanical stress or no mechanical stress at all to the volumetric flow so that it can be connected with blood or other stress-sensitive fluids with or without biological components such as cells or proteins. Another object of the invention is to achieve a high degree of parallelization in the smallest space to be obtained by miniaturizing the module and by the direct ability to be coupled to and integrated in any possible perfusion systems. 
     In the present description, the term fluid is meant to designate not only liquids, especially blood, nutrient solutions, oils, or technical solutions, but also gases. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in “device for pressurized perfusion especially for culturing and/or treating cells”, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  shows a first embodiment of a device for pressurized perfusion according to the present invention, 
         FIG. 2  shows a second embodiment of a device for pressurized perfusion according to the present invention, 
         FIG. 3  shows a third embodiment of a device for pressurized perfusion according to the present invention, 
         FIG. 4  shows a fourth embodiment of a device for pressurized perfusion according to the present invention, 
         FIG. 5  shows a fifth embodiment of a device for pressurized perfusion according to the present invention, 
         FIG. 6  shows a sixth embodiment of a device for pressurized perfusion according to the present invention, 
         FIG. 7  shows an embodiment of a device for pumping fluids according to the present invention, 
         FIG. 8  shows another embodiment of a device for pumping fluids according to the present invention, 
         FIG. 9  shows another embodiment of a device for pumping fluids according to the present invention, 
         FIG. 10  shows another embodiment of a device for pumping fluids according to the present invention, 
         FIG. 11  shows another embodiment of a device for pumping fluids according to the present invention, 
         FIG. 12  shows another embodiment of a device for pumping fluids according to the present invention, 
         FIG. 13   a  through  13   c  show another embodiment of a device for pumping fluids according to the present invention, 
         FIG. 14  shows another embodiment of a device for pumping fluids according to the present invention, 
         FIG. 15  shows another embodiment of a device for pumping fluids according to the present invention, 
         FIG. 16  shows an embodiment of a device for pressurized perfusion according to the present invention, 
         FIG. 17  shows an embodiment of a device for pressurized perfusion according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a modular component, which is coupled to a bioreactor  3 . The module is composed of two valves  1 A and  1 B as well as of a piston 2  and is adaptable to the bioreactor via a sterile coupling and directly, as shown in  FIG. 1 , integratable in the influence area. Both valves  1 A and  1 B open in the same direction, in  FIG. 1  to the left, towards the bioreactor. This generates a volumetric flow which is introduced into the reactor area at a high amplitude and pressure curve. So it is possible to achieve the opening and closing of an implant placed in the bioreactor, e.g. an allogenic heart valve. Two-leaflet valves opening or closing passively from flow changes are especially suited for the valves  1 A and  1 B. Other non-return valves, such as balls in a conically tapered tube section, are also possible. 
       FIG. 1  shows the perfusion module in a sagitally directed form. The advantage is that the backward movement of the piston 2  across the opening of valve  1 A enhancedly causes the heart valve leaflet to close and thus also allows the bioreactor to be emptied. The forward movement of the piston 2  causes the valve  1 B to close and the valve  1 A to open with subsequent opening of the biovalve in the bioreactor. During the backward movement of the piston 2 , fluid or medium is taken in from the reservoir  4  thereby filling the chamber in the perfusion module. The latter is refilled in circuit. Pressure compensation is via a sterile filter  5 . 
       FIG. 5  shows that the changes in volume in the perfusion module can also be achieved by displacing a plate  6 , which can be moved alternately by means of compressed air or vacuum via two valves  7 A and  7 B. The advantage is that the classical and sophisticated piston technology is done away with. The latter also requires an additional outer motor as shown in  FIG. 1 . 
     The device according to  FIG. 2  is even compacter in construction, in which the movable plate  6  is a permanent magnet with a biocompatible or liquid-proof or non-erosive encapsulation with e.g. a plastic layer of silicone or Teflon  6 ′ able to simultaneously provide a sealing function. Also, a jacket with a further metal (e.g. titanium, highgrade steel) can be provided. A sealing ring of e.g. Teflon or silicone is combinable for this purpose. But what is essential is that an alternately attracting or repelling force field can be created on the permanent magnet by integration of a current coil used to alternately generate negative poles  7 ′ or positive poles  7 ″. As an alternative to using permanent magnets, it is possible to integrate paramagnetic particles in the plate  6  so that a yet better directionalization can be achieved with regard to the force field of coil  7 . But the advantage of the mechanical principle is that costly external motors or compressed air or vacuum systems like those as still described herein in combination with perfusion technology can be done away with. Only then, the entire module will become very small, because the force-generating module or module responding to external forces is integrated in the movement module. Just a current source and a conventional electronic control are needed. 
       FIG. 3  shows that the plate  6  can have its own integrated electric coil  8 , which is connected via an elastic cable connector to a current source  10 ′ and  10 ″ alternately polarized to  7 ′ and  7 ″. 
       FIG. 4  shows how a cartilage-cell/bone-cell bioreactor  12  is integrated in the circuit. Stem cell integration is also possible here. Due to the use of a stop valve  11 , a pressure increase coupled with a volumetric flow is realizable. This is particularly important for the differentiation of cartilage but also bone structures, as well as of combinations, e.g. by using pure-phase beta-tricalcium phosphates as a seeding basis. 
       FIG. 6  shows an integrative system in which the magnetic perfusion principle is integrated in a bioreactor for the production of cartilage structures. The advantage is that the construction of the system is simpler in terms of apparatus while maintaining controlled physiological pressure amplitudes and volumetric flows. In this case, the cell culture can be located in a removable insert  13 . The piston can be lowered down to the insert  13  so as to be able to apply also immediate mechanical pressure to the cartilage structures. In addition to that, the system thus is emptied entirely so that mixing processes in the culture system can be directly controlled in terms of volume in order to be able to define the growth factor concentrations in situ. For the removal of the insert, the bioreactor can be opened or closed at  14  by means of e.g. a rotary or a clamp-type lock. 
       FIG. 7  shows the use of a magnetic pumping mechanism for imparting movement to a membrane thereby creating a volumetric flow. 
       FIG. 8  shows the use of a magnetic pumping system for pumping liquids such as blood, aqueous solutions or gases without supplying a treatment module such as a cell culture system (e.g. a bioreactor). An application is e.g. extracorporal perfusion for heart-lung machines or for assisting liver transplantation operations after hepatectomy. Previous rotary pumps produce even volumetric flows, but their manufacture is very costly and sophisticated. Using the pumping principle according to the invention in extracorporal perfusion has the advantage of restituting physiological pressure amplitudes. They are important for preserving organ functions and cellular differentiation especially in longer-term use. 
       FIG. 9  shows a double-sided pumping chamber. The plate  16  moves in the chamber in an oscillating manner and each of the outlet openings  17 ′ and  17 ″, which are coupled to valves, is controlled in a direction opposite to the inlet openings  18 ′ and  18 ″. In the centre, there is again a movable plate with a permanent magnet, paramagnet, or a magnetismsensitive material, or an electric coil. 
       FIG. 10  shows the construction for a piston motor. In this case, the plate is supported the rollers  19 ′ through  19 ″″ and moves in a chamber. The inner surfaces of the chambers  20 ′ and  20 ″ are equipped with electric conductors, which via the rollers  20 ′ through  20 ″″ come in contact with the plate  6 , within which an electric coil is again located. The plate  6  is equipped with a rod, which transfers the force of movement like a piston towards the outside. This can be used in vehicles or as a substitute for classical combustion engines. 
       FIG. 11  represents the same principle as  FIG. 10 , but this time both an extension direction and a compression direction are possible simultaneously for the pistons  21  and  21 ′. In this case, the electric magnetic fields in  22  and  23  can always be oriented in directions opposite to one another and the magnetic field in the plate (plunger)  6  remains unchanged. As an alternative, the field in  6  can constantly alternate with the fields in  22  and  23  remaining unchanged. The coil in the plate  6  is supplied with current, like in  FIG. 10 , through the roller mechanism  19 ′- 19 ″″.  FIG. 12  relates to how a permanent magnet is used in plate  6 . 
       FIG. 13  shows an embodiment in which the magnetic pumping mechanism located in an elastic tube, such as in a hose, is directly installed in the wall structures either as half-shells or as attachments to be fixed or to be integrated. The advantage is to provide a universal pumping module that is directly integratable in circuits or in hose or tube systems. In  FIG. 13   a , half-shells  24  and  25  are shown, which are connected with the wall of the hose system through elastic plastic materials. Said materials can be composed of conventional elastic tapes or can also have a direct integration in the wall structure of the hose. Additional coils  26  and  27  can be installed on the outside in order to increase the pumping force. So the internally movable pump in combination with the passively movable valves  1 A and  1 B is a universally applicable pumping element. 
     The very gentle treatment of the internal perfusate also allows it to be installed in the body as a heart-assisting system in combination with a battery (internal) or a magnetic field, which is installed outside on the body (e.g. thorax). Force transmission inwards to the implant is not invasive and without mechanical stress for the body. For implants, it is wise to integrate permanent magnets or so-called paramagnets in (nano-)particle form in the wall structures of the hose implant in a way to be able to achieve a contraction of the hose volume by changing the external magnetic field direction. For this purpose, the external poles can be arranged controlaterally, i.e. in front of and behind the thorax. The  FIGS. 13   b  and  c  show how an external battery unit  28 ,  29  is installed around a hose  27  with 2 movable plates  6  and  6 ′, which lead to passive changes of volume of the hose  6  (sic!, the translator). 
     In  FIG. 14 , it is shown how magnetic or magnetizable rods  30  are integrated in the wall structure  31  of a hose  32 . A circumferentially installed electric coil generates an inner magnetic field causing passive changes in volume in hose  32 . The hose is surrounded by an electric coil  34 . 
       FIG. 15  shows an electric coil  34  integrated in the hose itself. There is an electric coil  33  installed on the outside. 
     Another simplification is the introduction or the elastic jacketing of a hose with an elastic coil  35 . Changing the electric flow directions will cause field changes and thus cause the elastic coil rings to attract or repel one another. The connection with the elastic hose leads to pumping processes, which can again be directionalized by passive valves. 
       FIG. 16  shows an example for parallelization. For this purpose, e.g. miniaturized pump modules  36  are placed on chambers  44 , which can contain cell cultures  45 . The volume in the chambers is equivalent to e.g. 200-500 .mu.l and contains primary cells in reconstructed tissue section cultures. The plate  37 , which can be attracted and repelled magnetically, can move up and down directionally in the pump module. A movement away from the cell culture chamber or from the reaction chamber  44  provided for reaction without cellular systems causes the valve  40  to open and fresh medium is introduced by way of volume increase into the reaction chamber  44 . The reversing movement increases the internal pressure in the reaction chamber and causes the valve  38  to open so that a volumetrically definable portion of the reaction chamber contents can be forced out. The advantage of this mixing process, e.g. in cell culture, is that portions of the cytokines and growth factors produced in situ by the cells and enriched therewith can remain in the chamber despite the feeding of fresh medium. This culturing approach is gentler than the complete replacement of nutrient liquid. So this technology allows locally defined mixing to be achieved even for batchwise nutrient processes, i.e. for the first time also in non-recirculating systems. This makes it possible to combine the advantages of non-recirculating systems, such as meterability as well as definability and programmability, especially for pharmacological studies in minisystems, with the cell-biological advantages of largest possible biological milieu constancy. The vertical movements of the intermediate plates  37  can be caused by appropriate positioning and vertical movement of a cover plate structure  35 , which houses accordingly positioned magnets or coils. Operation is possible also with a fixed cover plate structure  35 , if in such case changing orientations of magnetic fields in said structure are induced by changing current flows in electric coils. 
       FIG. 17  represents a further embodiment of the invention, which comprises a culture bottle or bioreactor  60  with a cylindrical shape. The culture bottle is surrounded by a jacket  61 , which is made up of an elastic material, especially a plastic or rubber material, and has a cylindrical shape too. The culture bottle  60  with its jacket rests on the rollers  62 ,  63 , which are rotated by a drive not shown. 
     The jacket  61  is provided with a hollow space  64 , which is limited by valves in the area of the end faces of the cylindrical jacket to interact with them and thus act as a pump through a change in volume. Advantageously, the change in volume can be achieved by permanent magnets with one permanent magnet  66  located in the jacket between the hollow space  64  and the culture bottle  60  and a second permanent magnet  65  beneath the jacket  61 . So the hollow space  64  is compressed when the permanent magnet  64  enters its lower position, because the magnets are arranged such that they attract one another in said position with the compression being assisted by the dead weight of the permanent magnet  66 . The hollow space is on the contrary compressed when the permanent magnet is in its upper position. So the pumping effect is eventually achieved in a simplest way by the drive for the running rollers  62 ,  63 . They are connected with the hollow space  64  through hoses at the end faces of the culture bottle so that the fluid can circulate between the culture bottle and the hollow space in a batchwise flow initiated by the rotating movement of the apparatus. 
     As an alternative to the embodiment according to  FIG. 17 , it is also possible to do without the permanent magnet  65  and replace the permanent magnet  64  by a weight. But another possibility is to replace the permanent magnet  66  by an electromagnet.