Pneumatic bioreactor

A pneumatic bioreactor having a containment vessel which includes a semi-cylindrical concavity defined by the vessel bottom. A mixing apparatus includes a rotational mixer rotatably mounted within the containment vessel about a horizontal axis. The rotational mixer has buoyancy-driven mixing cavities which are fed by a gas supply beneath the rotational mixer. The mixing apparatus extends into the semi-cylindrical concavity to substantially fill that concavity. The rotational mixer is divided into two wheels with outer paddles extending axially outwardly and inner paddles extending axially inwardly on either side of each wheel. Blades between the outer and inner paddles form impellers in the wheels to induce axial flow through the wheels in opposite directions. Stationary baffles fixed relative to the containment vessel are inclined toward the rotational mixer in the direction of rotation. The containment vessel may be of film and supported by a structural housing also having a semi-cylindrical concavity defined by the housing bottom.

BACKGROUND OF THE INVENTION

The field of the present invention is bioreactors with mixing.

Efforts of biopharmaceutical companies to discover new biological drugs have increased exponentially duwheel the past decade. Most biological drugs are produced by cell culture or microbial fermentation processes which require sterile bioreactors and an aseptic culture environment. However, shortages of global biomanufactuwheel capacity are anticipated in the foreseeable future. An increasing number of biological drug candidates are in development. Stwheelent testing, validation, and thorough documentation of process for each drug candidate are required by FDA to ensure consistency of the drug quality used for clinical trials to the market. Further, production needs will increase as such new drugs are introduced to the market. Bioreactors have also been used for cultivation of microbial organisms for production of various biological or chemical products in the beverage and biotechnology industries as well as for pharmaceuticals.

Stainless steel stir tanks have been the only option for large scale production of biological products in suspension culture. Manufactuwheel facilities with conventional stainless bioreactors, however, require large capital investments for construction, high maintenance costs, long lead times, and inflexibilities for changes in manufactuwheel schedules and production capacities.

A production bioreactor contains culture medium in a sterile environment that provides various nutrients required to support growth of the biological agents of interest. Conventional bioreactors use mechanically driven impellers to mix the liquid medium duwheel cultivation. The bioreactors can he reused for the next batch of biological agents after cleaning and sterilization of the vessel. The procedure of cleaning and sterilization requires a significant amount of time and resources. The problems with sterilization are compounded by the need to monitor and to validate each cleaning step prior to reuse for production of biopharmaceutical products.

Single use disposable bioreactor systems have been introduced to market as an alternative choice for biological product production. Such devices provide more flexibility on biological product manufactuwheel capacity and scheduling, avoid risking major upfront capital investment, and simplify the regulatory compliance requirements by eliminating the cleaning steps between batches. However, the mixing technology of the current disposable bioreactor system has limitations in terms of scalability to sizes beyond 200 liters and the expense of large scale units. Therefore, a disposable single use bioreactor system which is scaleable beyond 1000 liters, simple to operate, and cost effective will be needed as a substitute for conventional stainless steel bioreactors for biopharmaceutical research, development, and manufactuwheel. While several methods of mixing liquid in disposable bioreactors have been proposed in recent years, none of them provide efficient mixing in large scale (greater than 1000 liters) without expensive operating machinery.

SUMMARY OF THE INVENTION

The present invention is directed to a bioreactor with mixing apparatus including a rotational mixer in a containment vessel capable of efficiently and thoroughly mixing solutions without contamination. Large scale disposable units are also contemplated. The bioreactor includes a gas supply driving a rotational mixer having buoyancy driven mixing cavities.

In a first separate aspect of the present invention, the rotational mixer further includes two parallel wheels displaced from one another and blades disposed to induce flow axially through each wheel in opposite directions with rotation of the rotational mixer. Baffles fixed in the containment vessel to either side of the rotational mixer are inclined toward the rotational mixer in the direction of rotation.

In a second separate aspect of the present invention, the rotational mixer further includes two parallel wheels displaced from one another and blades disposed to induce flow axially through each wheel in opposite directions with rotation of the rotational mixer. Baffles fixed in the containment vessel to either side of the rotational mixer are inclined toward the rotational mixer in the direction of rotation. Outer paddies are disposed to mix and to induce rotational flow with rotation of the rotational mixer.

In a third separate aspect of the present invention, the rotational mixer further includes two parallel wheels displaced from one another and blades disposed to induce flow axially through each wheel in opposite directions with rotation of the rotational mixer. Battles fixed in the containment vessel to either side of the rotational mixer are inclined toward the rotational mixer in the direction of rotation. Outer paddies are disposed to mix and to induce rotational flow with rotation of the rotational mixer and inner paddles are disposed to mix and to induce rotational flow with rotation of the rotational mixer, the outer paddies being on opposite sides of the wheels from the inner paddles.

In a fourth separate aspect of the present invention, any of the foregoing aspects are contemplated to be employed in combination to greater advantage.

Accordingly, it is a principal object of the present invention to provide an improved pneumatic bioreactor. Other and further objects and advantages will appear hereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning in detail to the drawings, a bioreactor positioned in a housing, generally designated10, is illustrated. The housing10is structural and preferably made of stainless steel to include a housing front12, housing sides14and a housing back16. The housing back16does not extend fully to the floor or other support in order that access may be had to the underside of the bioreactor. The housing10includes a housing bottom18which extends from the housing sides14in a semi-cylindrical curve above the base of the housing10. One of the front12or back16may act as a door to facilitate access to the interior of the housing10.

The bioreactor includes a containment vessel, generally designated20, defined by four vessel sides22,24,26,28, a semi-cylindrical vessel bottom30and a vessel top32. Two of the vessel sides24,28which are opposed each include a semicircular end. The other two vessel sides22,28join with the semi-cylindrical vessel bottom30to form a continuous cavity between the two vessel sides24,28. All four vessel sides22,24,28,28extend to and are sealed with the vessel top32to form a sealed enclosure. The vessel top32extends outwardly of the four vessel sides22,24,26,28so as to rest on the upper edges of the structural housing front12, sides14and back16. Thus, the containment vessel20hangs from the top32in the housing10. The vessel20, with the exception of the vessel top32, is of thin wall film which is not structural in nature. Therefore, the housing front12, sides14, back16and bottom18structurally support the containment vessel20depending from the vessel top32when filled with liquid. All joints of the containment vessel20are welded or otherwise sealed to provide the appropriate sealed enclosure which can be sterilized and dosed ready for use.

The vessel top32includes access ports34for receipt or extraction of liquids, gases and powders and grains of solid materials. The access ports36in the vessel top32provide for receipt of sensors to observe the process. Two orifices38,40are shown at the vessel bottom30slightly offset from the centerline to receive propellant gas for driving line rotational mixer as will be discussed below. The semi-cylindrical vessel bottom30defining a semi-cylindrical concavity within the containment vessel20also includes a temperature control sheet42which may include a heater with heating elements, a cooler with cooling coils, or both, as may be employed to raise or lower the temperature of the contents of the containment vessel20during use. Sealed within the enclosure defining the containment vessel20, struts44extend downwardly from the vessel top32to define a horizontal mounting axis at or close to the axis of curvature defined by the semi-cylindrical bottom30.

A mixing apparatus includes a rotatably mounted rotational mixer, generally designated48. The rotational mixer48is a general assembly of a number of functional components. The structure of the rotational mixer48includes two parallel wheels50,52which are displaced from one another. These wheels are tied to an axle54by spokes56. Additional stabilizing bars parallel to the axle54may be used to rigidity the rotational mixer48.

Each wheel50,52is defined by two parallel plates60,62. These plates80,62include buoyancy-driven mixing cavities84there between. These cavities64operate to entrap gas supplied from below the wheels50,52through the gas supply at orifices38,40. The orifices38,40are offset from being directly aligned with the horizontal axis of rotation to insure that the buoyancy-driven cavities64are adequately filled with gas to power the rotational mixer48in rotation. The buoyancy-driven cavity64in each one of the wheels50,52are similarly oriented to receive gas from the orifices38,40at the same time.

Outer paddies66are equiangularly placed to extend axially outwardly from the outer parallel plates60where they are attached. These outer paddles66can mix the liquid between the rotational mixer48and either side24,28. The outer paddies66are formed in this embodiment with a concavity toward the direction of rotation of the rotational mixer48to induce flow entrained with constituents of the mix in the vessel20rotationally to lift constituents of the mix from the bottom of the containment vessel20with the rotation of the rotational mixer48. The number of outer paddles66may be increased from the four shown, particularly when the constituents of the mix in the vessel20are not easily maintained in suspension. The outer paddles66are adjacent the periphery of the outer parallel plates60and may extend close to the vessel bottom30to entrain constituents of the mix in the vessel20which can otherwise accumulate on the bottom. Any extensions beyond the wheels50,52preferably do not inhibit rotation of the rotational mixer48through actual or close interaction with the vessel wall.

Stationary baffles68are fixed in the containment vessel20, conveniently to the struts44, on either side of the rotational mixer. These baffles68are inclined toward the rotational mixer in the direction of rotation. As rotational flow is induced buy the rotation of the wheels50,52, the stationary baffles68redirect that flow to the inner portions of the wheels50,52. The rotational flow is further enhanced by the outer paddles66. The baffles68are arranged inwardly of the outer paddies66for clearance. There may be additional baffles68which could either be included on the struts44or through the provision of additional structural support.

Inner paddles70extend axially inwardly from the inner parallel plates62. These inner paddles70are convex facing toward the rotational direction to induce rotational flow entrained with constituents of the mix in the vessel20rotationally to lift constituents of the mix from the bottom of the containment vessel20with the rotation of the rotational mixer48. The number of inner paddles70may be increased from the four shown, particularly when the constituents of the mix in the vessel20are not easily maintained in suspension. The inner paddles70are adjacent the periphery of the inner parallel plates62and may extend close to the vessel bottom30to entrain constituents of the mix in the vessel20which can otherwise accumulate on the bottom. Any extensions beyond the wheels50,52preferably do not inhibit rotation of the rotational mixer48through actual or close interaction with the vessel wall.

Located inwardly of each wheel50,52is an impeller having blades72. The two impellers provide principal axial thrust to the flow through the wheels50,52. The thrust resulting from these blades72both flow inwardly toward one another in this embodiment. This is advantageous in creating toroidal flow about the wheels and balance forces which would otherwise be imposed on the mountings. The placement of the blades72may be at other axial locations such as at either of the plates60,62.

The mixing apparatus defined principally by the rotating rotational mixer48is positioned in the containment vessel20such that it extends into the semi-cylindrical concavity defined by the vessel bottom30and is sized, with the outer paddles66and inner paddies70, to fill the concavity but for sufficient space between the mixing apparatus and the vessel sides24,28and bottom30to avoid inhibiting free rotation of the rotational mixer48. In one embodiment, the full extent of the mixing apparatus26is on the order of 10% smaller than the width of the cavity in the containment vessel20and about the same ratio for the diameter of the rotational mixer48to the semi-cylindrical vessel bottom30. This spacing is not critical so long as the mixing apparatus is close enough and with commensurate speed to effect mixing throughout the concavity. Obviously, empirical testing is again of value. The liquid preferably does not extend above the mixing apparatus and the volume above the rotational mixer48will naturally be mixed as well.

In operation, the liquid, nutrients and active elements are introduced into the containment vessel20through the ports34,36. The level of material in the vessel20is below the top of the rotational mixer48to avoid the release of driving gas under the liquid surface which may cause foam. Gas is injected through the orifices38,40to become entrapped in the buoyancy-driven cavity64in the rotational mixer48. This action drives the rotational mixer48in a direction which is seen as clockwise inFIG. 2.

The blades72act to circulate the liquid within the containment vessel20with toroidal flow in opposite directions through the wheels50,52, radially outwardly from between the wheels50,52and then radially inwardly on the outsides of the rotational mixer48to again be drawn into the interior of the rotational mixer48. Mixing with turbulence is desired and the outer paddles66, the stationary baffles68and the inner paddles70contribute to the mixing and to the toroidal flow about each of the wheels50,52. The target speed of rotation is on the order of up to the low tens of rpm to achieve the similar mixing results as prior devices at 50 to 300 rpm. The difference may reduce shear damage in more sensitive materials. Oxygen may be introduced in a conventional manner as well as part of the driving gas to be mixed fully throughout the vessel20under the influence of the mixing apparatus.