pH sensor integration to single use bioreactor/mixer

A pH sensing bioreaction system is provided. The system includes a bioreaction container having a plastic wall and a pH sensor attached to the plastic wall. The pH sensor includes a sensor body having a flange that is sealingly attached to the plastic wall. The sensor body has a reference electrolyte therein and a first sensing element disposed in the reference electrolyte. The first sensing element is configured to contact both the reference electrolyte and a sample solution inside the bioreaction container. A second sensing element is positionable into an interior of the bioreaction container. The pH sensor has a plurality of configurations that include a booted configuration in which at least one sensing element is isolated from the interior of the bioreaction container, and a service configuration in which the at least one sensing element is fluidically coupled to the interior of the bioreaction container.

BACKGROUND

The determination of pH is one of the most common process chemical measurements today. pH is a measure of a relative amount of hydrogen and hydroxide ions in an aqueous solution. In fermentation and cell culture, one of the most critical process challenges is to maintain the optimal pH level. Fermentation processes utilize a live organism, such as a yeast, bacteria, or fungus strain to produce an active ingredient. Fermentation processes normally have a relatively short duration (2-7 days). Cell culture is a process in which a mammalian cell is grown to produce an active ingredient. The cell culture process typically takes somewhat longer (2-8 weeks).

One significant challenge for pH measurement in the fermentation and cell culture fields is the cleaning processes involved with the fermenter or bioreactor. Specifically, the fermenter or bioreactor must be sterilized prior to the beginning of either process to ensure against cross batch contamination or any unwanted growths. In addition, pH sensors typically undergo a two point calibration using buffer solutions. The residual buffer chemicals must be removed prior to the beginning of a fermentation or culture batch. Such cleaning can include steaming the fermenter or bioreactor as well as the pH sensor. Exposure to high temperatures, steam and rapid thermal shock can significantly affect the sensor's life.

SUMMARY

A pH sensing bioreaction system is provided. The system includes a bioreaction container having a plastic wall and a pH sensor attached to the plastic wall. The pH sensor includes a sensor body having a flange that is sealingly attached to the plastic wall. The sensor body has a reference electrolyte therein and a first sensing element disposed in the reference electrolyte. The first sensing element is configured to contact both the reference electrolyte and a sample solution inside the bioreaction container. A second sensing element is positionable into an interior of the bioreaction container. The pH sensor has a plurality of configurations that include a booted configuration in which at least one sensing element is isolated from the interior of the bioreaction container, and a service configuration in which the at least one sensing element is fluidically coupled to the interior of the bioreaction container.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

It is believed that there exists an emerging need for a disposable pH sensor which is compatible with a plastic bag type, ready to use, disposable bioreactor. Many glass electrode-based pH sensors require that the active surface or membrane of the sensor be protected from physical and environmental damage. This function is typically served by the disposable “boot” or cup placed over the sensing end of the sensor.

Embodiments of the present invention generally include a pH sensor that is installed on the wall of a single use bioreactor/mixer with a mechanical design that allows the booting solution stored around the pH sensing and reference element during sterilization (gamma irradiation), storage, and shipping of the single use bioreactor/mixer. The mechanical design also allows the storage chamber that retains the booting solution to be opened to expose the sensing and reference element prior to the operation.

FIG. 1is a diagrammatic view of a pH sensing bioreactor system with which embodiments of the present invention are particularly useful. pH sensor40is electrically coupled to pH analyzer54which may be any suitable pH analyzer or other electrical instrument. pH sensor40is physically attached to the wall50of single-use bioreactor/fermenter51. A sample52is disposed within single use bioreactor50and is monitored, or otherwise measured, by pH sensor40.

Embodiments of the present invention generally include a number of configurations in which a pH sensor can be used effectively with a single-use bioreactor.

FIG. 2is a diagrammatic cross sectional view of a pH sensor60in accordance with an embodiment of the present invention. pH sensor60is illustrated in a “booted” position in that a sensing element, such as electrode62, is separated from and not in contact with sample52. As used herein, a sensing element is any electrode or portion of an electrode that may be exposed to a sample fluid and provide and electrical response thereto. Accordingly, a sensing element is intended to include glass bulb electrodes and reference junctions. pH sensor60includes plunger64that is coupled to electrode62such that axial movement of plunger64in the directions indicated at reference numeral66will generate corresponding movement of electrode62. Electrode62is disposed within access spear68. Access spear68is designated as such because it is physically shaped like a spear such that suitable actuation of plunger64will cause access spear68to pierce through rubber membrane70. When access spear68is pierced through rubber membrane70, ports72,74allow sample52to come into contact with electrode62. When access spear68pierces rubber membrane70, pH sensor60is said to be in a service position. Such configuration is illustrated inFIG. 3.

pH sensor60includes flange76that is fused, adhered, or otherwise bonded to wall50of the bioreactor51. In the embodiment illustrated inFIG. 2, flange76is bonded to the outside surface of wall50. However, embodiments of the present invention also include flange76being bonded to an inside surface of wall50. Flange76can be thermally welded, or otherwise permanently attached, to sidewall50of bioreactor51in any suitable manner.

FIG. 4is a diagrammatic perspective view of pH sensor60in accordance with one embodiment of the present invention shown in the service position.

FIG. 5is a diagrammatic cross sectional view of a pH sensor80in accordance with another embodiment of the present invention. pH sensor80bears some similarities to pH sensor60, and like components are number similarly. pH80includes a sensor body82through which plunger64may axially translate electrode62. Plunger64is coupled to spool84to which electrode62is affixed. Spool84includes a plurality of apertures86and end cap88. End cap88is fluidically sealed against an internal sidewall of body82by o-ring seal90. As shown inFIG. 5, in the booted position, a sensing element, such as distal sensing portion92, of electrode62is disposed within a chamber bound by surface94of spool84, cap88, and portions of housing82. The chamber within which distal sensing portion92of electrode62resides can be filled with a booting solution, if necessary. When the pH sensor is ready to be used, plunger64is advanced thereby pressing end cap88beyond flange76.

FIG. 6is a diagrammatic view of pH sensor80arranged in an in-service position. In this position, plunger64has been advanced to drive end cap88beyond flange76. As illustrated inFIG. 6, apertures86now allow fluidic communication between distal sensing portion92and sample52in the bioreactor.

FIG. 7is a diagrammatic cross sectional view of a pH sensor in accordance with another embodiment of the present invention. pH sensor100includes a sensor body102to which flange76is mounted. As with previous embodiments, flange76is generally permanently attached to a wall of a bioreactor via any suitable method, such as thermal welding. Plug104is rotatably disposed within sensor body102and maintains electrode62therein. Plug104generally defines a chamber near distal, sensing end92of electrode62. Plug104includes one or more fluid access ports106which are generally blocked, or otherwise occluded, from communicating with a sample when the sensor is in the booted position, as shown inFIG. 7. In order to change from the booted position to the service position, knob108is rotated in the direction indicated by arrow110, which rotation in turn, rotates plug104. Upon suitable rotation, sensor100enters the service position, as shown inFIG. 8. In this position, one or more of access apertures106at least partially aligns with an access port in sensor body102thereby allowing fluidic communication between sensing end92and sample52.

FIG. 9is diagrammatic view of a pH sensor120integrated with a single-use bioreactor/mixer in accordance with an embodiment of the present invention. Sensor120includes flange/support122that includes flange124coupled to wall50of a single-use bioreactor/mixer. Flange124is also coupled to support sleeve126that illustratively includes three o-ring groves128,130, and132on an internal surface thereof. An o-ring134is disposed within each of groves128,130,132.

Flange124is preferably thermally welded, or permanently attached via some other suitable method, to wall50of the single-use bioreactor. Additionally, wall50includes an aperture136that has an inside diameter that is larger than the outside diameter of endcap138. pH sensor120also includes sensor body140which contains a suitable reference electrolyte142and reference electrode144. Additionally, sensing element (glass electrode)146is disposed, at least partially, within sensor body140and extends such that distal sensing portion148is disposed within storage chamber150when the sensor is in the booted position as illustrated inFIG. 9. Additionally, a sensing element, such as reference junction152is physically isolated from storage chamber150.

The sensor design provides a number of positions that are useful in combination with a single-use bioreactor. In a first position (shown inFIG. 9) the sensor is in a booted position where the sensing portion148is protected from damage and may also be stored in a booting solution that is provided within storage chamber150. In a second position, (described in further detail with respect toFIG. 10) the reference junction is placed in the booting solution for sensor calibration purposes. In a third position (described with respect toFIG. 11), the storage chamber150is opened into sample52, to expose sensing element148, and reference junction152to sample52.

FIG. 10is diagrammatic view of pH sensor120arranged in the second (calibration) position. In the configuration shown inFIG. 10, sensor body140has been displaced in the direction of arrow154to such an extent that reference junction152has passed beyond o-ring grove130. As such, reference junction152is in fluidic communication with sensing portion148of sensing electrode146. Additionally, storage chamber150is still fluidically isolated from sample52by virtue of the o-ring disposed within o-ring grove134. Given that the booting solution within storage chamber150can be provided having a precisely known pH, sensor120can be calibrated to ensure that its output corresponds with the known pH of the booting solution.

FIG. 11is a diagrammatic view of pH sensor120in the service position. Sensor body140has moved axially in the direction of arrow154to such an extent that storage chamber150is now opened to sample52. Moreover, reference junction152is also disposed within sample52. In this configuration, sensing electrode146will provide an indication, in combination with reference electrode156that is indicative of the pH of sample52.

FIG. 12is a diagrammatic view of a pH sensor and boot integrated into a wall of a sing-use bioreactor in accordance with an embodiment of the present invention. pH sensor240includes flange242that is coupled to, preferably via thermal welding, sidewall244of single-use bioreactor246. Sensor240includes cabling248that is coupled to a suitable analyzer, such as analyzer54. Sidewall244is also coupled (preferably via thermal welding) to sensor boot250. Sidewall244includes a fold252that allows boot250to engage and protect the sensing end of sensor240. As illustrated inFIG. 13, a user can simply grasp boot250through the flexible sidewall144of bioreactor246and remove boot250from sensor240. Such removal thereby exposes the pH membrane and reference junction of pH sensor240to the interior of the single-use bioreactor/mixer246.

The cap or boot can actually be integrated with a second process analytic sensor, such as a dissolved oxygen sensor. In this manner, when pH sensor and dissolved oxygen sensor are decoupled for one another, both sensors are thereby prepared for use.FIG. 14Ais a diagrammatic view of a pH sensor200coupled to a dissolved oxygen sensor202where each sensor includes a flange that is welded, or otherwise bonded to bag film204to form a fluid-tight seal. Bag film204is folded such that pH sensor200can be coupled to a portion of dissolved oxygen sensor202, which can also act as a boot to pH sensor200. When operation of the sensors is required, the two sensors can simply be grasped and pulled apart from one another to yield the configuration shown inFIG. 14B.