Patent Application
20220373502
During the past two decades, single-use or disposable bioprocessing systems have gained significant momentum to replace stainless-steel systems in biopharma manufacturing. In contrast to the conventional systems that are constructed with stainless-steel equipment, single-use systems rely on highly-engineered polymers and come pre-sterilized via gamma irradiation. For end users, they offer several significant advantages including reduced initial investment, elimination of complex processes of pre-cleaning, sterilization, and validation, as well as improved process turnaround time. As a result, single-use bioprocessing systems have been adopted from initial R&D laboratories to large-scale commercial pharmaceutical manufacturing on an accelerated pace.
pH is a critical process parameter in many processes of biopharma manufacturing. In upstream bioreactor applications, medium culture pH is continuously monitored and controlled within a narrow physiological range and deviation from this ideal pH range can negatively affect viable cell concentration, protein productivity and quality. Traditional pH sensors used in biopharma manufacturing are based on electrochemical measurement methods with a pH sensitive glass electrode and a reference electrode. Due to its high reliability, accuracy, and stability, this is a well-established technology with proven success in biotechnology and pharmaceutical industries.
Conventional pH sensors, however, are designed to be compatible with conventional stainless-steel style bioreactor systems and therefore have several significant limitations when used in single-use systems. First, conventional sensors must be sterilized by the end user using autoclaving, steam-in-place, or clean-in-place procedures. They are generally not compatible with gamma irradiation sterilization process as gamma irradiation could damage their sensing components and lead to undesired performance degradation. To ensure satisfactory accuracy, conventional pH sensors usually require a two-point calibration conducted by end users prior to use, which is cumbersome and adds to complexity in the process. Furthermore, conventional pH sensors usually have a one-year shelf life because the pH sensing glass will age over time, leading to reduced sensor performance. Unfortunately for single-use systems, longer sensor shelf life is greatly preferred as the sensor could be attached to a plastic bioreactor bag as one single assembly or in a tube set for downstream applications with an expectation of a much longer shelf life.
A single-use electrochemical analytical sensor is provided. The sensor includes a sensing electrode configured to contact process fluid and a reference chamber containing an electrolyte. A reference electrode is disposed in the electrolyte. A reference junction is configured to contact the process fluid and is further configured to generate a flow of electrolyte into the process fluid. The reference chamber is configured to be stored in a depressurized state and then pressurized prior to operation. A method of operating a single-use electrochemical sensor is also provided.
Some electrochemical analytic sensors are considered amperometric in that they generate a current indicative of the process variable, such as pH. Other types of sensors, are considered potentiometric sensors, since they generate a potential that indicates the process variable. As used herein, electrochemical analytic sensors are intended to include any analytical sensor that has an electrical characteristic that varies with the process variable.
Sensor 100, as shown in
As shown in
The single-use pH sensor is compatible with gamma irradiation sterilization and can be attached to a single-use bioreactor bag to form one assembly. With the incorporation of a unique storage buffer solution, the sensor does not require a two-point calibration by end users and can be one-point standardized using this storage buffer solution. More importantly, the storage buffer solution is in contact with the pH and reference electrodes keeping them wet and fresh while the sensor is stored. This wet storage has led to a long shelf life of 2 years with outstanding sensor performance including high accuracy, sensitivity, and stability. Through rigorous real-time testing with prototypes that were not aged, 1-year aged and 2-year aged, it was demonstrated that the sensor performance remains at a high level without degradation after 2 years of storage.
After the cell culture process is complete in the bioreactor bag, the media is moved to the downstream part of the process. Here the media is pushed through filtration phases in small line size tubing at higher pressures of up to 90 psi. This higher process pressure may create problems with traditional pH sensors. A traditional glass electrode pH sensor has a reference junction that is a restricted path to connect the sensor's reference chamber, and the electrolyte buffer solution in it, to the process. An example of this junction is a porous ceramic cylinder placed between the reference chamber and the user's process. Another example is a polymeric junction. There must be positive ionic flow from the reference chamber of the sensor to the process fluid for the sensor to operate properly.
The higher process pressure of the downstream application can disrupt this ionic flow and causes the pH readings to fluctuate or drift. This disruption can be improved by pressurizing the reference chamber. However, previous methods for pressurizing a reference require pressurization with special methods at the factory. Because the reference junction is porous and the reference chamber is pressurized, the pressure decays over time and limits the shelf life and useful life of the sensor.
Sidewall 236 is mounted or otherwise affixed to end 242 which includes a flange 244 that is sized to extend beyond and around end 246 of sidewall 248. End 242 may be constructed from the same polymer as sidewall 236 and/or sidewall 248 and may be affixed thereto by any suitable method including solvent welding, adhesive, ultrasonic welding, et cetera.
Sensor 200 also includes an insert 250 that contacts an internal diameter 252 of sidewall 248 and includes a center bore 254 that is sized to mount pH electrode 224 along a longitudinal axis of the sensor 200. Insert 250 also includes a sleeve 256 that runs along a length of pH electrode 224 and passes through an aperture in reference junction disc 258. Disc 258 can be a porous ceramic disc that is configured to release a controlled amount of electrolyte into the process over time. However, embodiments can be practiced where the reference junction has other types of physical configurations, such as a small conduit, or a plurality of such conduits.
Sidewall 248 defines a pair of references chambers 260, 202 as well as a conduit 262 fluidically coupling primary reference chamber 260 to secondary reference chamber 202. An at least partially fluidic electrolyte is disposed within reference chambers 260, 202. The electrolyte may be a liquid or a gel, but must have the ability to flow through reference junction 258 to some extent. As can be seen, by pressurizing secondary reference chamber 202, primary reference chamber 260 will also be pressurized. This pressurization help maintain flow of electrolyte out of the reference junction even when the process fluid pressure is elevated. In the configuration shown in
It can thus be seen, that a sensor and method are provided that facilitate long-term shelf life, since the sensor is not pressurized during storage. Then, just prior to operation, the sensor is pressurized, in order to allow accurate and precise operation in pressurized process fluid environments, such as downstream processing. Additionally, it is believed that the shelf life and product lifetime of a pH sensor can be extended by increasing viscosity of the reference electrolyte within the device. For example, a thick reference gel can be used for this purpose. Using a higher viscosity reference gel will lead to a longer service life. In addition, the introduction of the reference gel will reduce the internal pressure required for the sensor to perform well under high external process pressure.
Actuation of the piston can be done in several ways. In one embodiment, the spring is compressed during sensor assembly and the piston is locked in place by features in the cylinder body keeping it from pressurizing the system. When the piston cap is rotated 90 degrees the piston moves off the retaining features and provides the force to generate pressure in the system. Further, the actuated piston may also be locked in the actuated position by a locking mechanism.
In another embodiment the installer pushes or pulls the piston cap while features on the cylinder body retain the cap as the user turns it 90 degrees. Alternatively, the cap could be retained by snap features without rotation.
Note that the pressurization methods described herein not limited to only pH sensors, but can be applied to other potentiometric ion sensors in general. These ion sensors include but are not limited to potassium, sodium, chloride, and fluoride sensors, just to name a few. As long as the sensor reference electrode relies on the diffusion of the internal reference electrolyte through a porous junction material, it could be pressurized via the methods described above.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, while the description provided above illustrates the pressurization of the reference chamber in one particular manner, such pressurization can take a variety of forms. The sensor could include a spring member that is preloaded at the factory and that is released on-site to apply pressure to reference chamber. In another example, an unloaded spring member could be compressed via pushing on-site. In yet another example, an unloaded spring member could be compressed via pulling on-site. In still another example, an unloaded spring member could be compressed via a screw member on-site.
In another example, an unloaded spring member could be compressed via pushing and twisting on-site. In another example, an unloaded spring member could be compressed via pulling and twisting on-site.
The present application is based on and claims the benefit of U.S. Provisional Patent Application Ser. No. 63/191,608 filed May 21, 2021; the content of which application is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63191608 | May 2021 | US |
