■ FAQ - Bioprocess
■ Frequently Asked Questions ? Perfusion

"How many parameters can I control using a DASGIP or DASbox system? "
DASGIP Parallel Bioreactor Systems provide comprehensive concurrent monitoring and control of process parameters. During the process run, events are logged together with up to 70 online process variables per bioreactor. In addition to the various DASGIP modules for monitoring and control, with DASware analyze users can integrate analytical devices provided by third parties. Seamless integration into the DASGIP or DASbox system even allows for closed loop solutions such as automated feeding strategies based on the current glucose concentration. Each process value can be used as a trigger enabling users to automate their process.
"How many parameters can be displayed in a process overview in DASware control? "
DASware control users can freely select all relevant process variables of all or selected bioreactors to be displayed in one chart. There are no limitations in the number of process parameters. When using DASware analyze, the displayed process parameters even include integrated data from third party laboratory devices, such as nutrient analyzers, mass spectrometers or Raman. The software features tables and trend graphs of all measured values. It continuously logs and stores all data and events. These data are immediately accessible for evaluation using e.g. Microsoft Excel. Advanced charting functionalities ease further data analysis and comparison of runs.
"Do I need programming skills to automate my process in DASware control? "
Set-points, profiles, cascades, and scripts are online editable in DASware control. Offline values and events can be entered during or after the run and documented with a time stamp. These time stamps can be set individually, e.g to meet the time, when the sample was taken. This provides users with great flexibility to interact with the control system and reconsider parameter settings even in highly automated processes. All events, including online changes, are recorded in a SQL Server database.
"Can I change triggers, profiles, cascades and scripts online in DASware control? "
Set-points, profiles, cascades, and scripts are online editable in DASware control. Offline values and events can be entered during or after the run and documented with a time stamp. These time stamps can be set individually, e.g to meet the time, when the sample was taken. This provides users with great flexibility to interact with the control system and reconsider parameter settings even in highly automated processes. All events, including online changes, are recorded in a SQL Server database.
"How difficult is it to modify a DASGIP system subsequently? "
Due to the unique modular design of the DASGIP Parallel Bioreactor System upgrades and modifications can easily be done: Functions like OD monitoring, exhaust analysis or extra feed lines can be added as modules to the control system. It is just as easy to substitute the bioreactor type or to upgrade a 4-vessel system to eight vessels. Actually, system modifications are that simple, some customers even share specific modules. For instance, the DASGIP GA4 exhaust analyzer is renowned for being moved from one bioreactor system to another. Like this, it delivers reliable in-depth analysis of OTR, CTR, and RQ for many bioreactors on demand.
"How many speed-controlled pumps do the DASGIP bioreactors feature? "
Up to eight peristaltic speed-controlled pumps per vessel offer continuous flow rates from 0.3 mL/h - 5 L/h. Each pump can be operated independently. Two different pump head sizes for the multi pump modules DASGIP MP4 and MP8, fitting various tube sizes make the DASGIP multi pumps a flexible and accurate solution.
"How many speed-controlled pumps do the DASbox Mini Bioreactors feature? "
The DASbox Mini Bioreactor System provides two integrated peristaltic speed-controlled pumps per vessel as standard. Two extra feed lines per bioreactor can be added using a DASGIP MP8 multi pump module. Each peristaltic pump can be operated independently.
"How many mass flow sensors are available when gassing with DASGIP modules? "
DASGIP gas supply and gas mixing modules allow for several gassing strategies: While the MX4/4 provides mass flow-controlled gas blending for four bioreactors with up to four inlet gases (Air, CO2, O2, N2), the MX4/1 provides four mass flow-controlled gases to one output. The DASGIP MF4 gassing module features one mass flow controller per inlet but delivers the four gasses separately to four gas outlets without mixing. With this choice of DASGIP gassing devices Eppendorf offers high precision and customized gassing solutions for various applications. These cover a broad range of continuous gas flow rates from 0.1 - 1200 sL/h is served.
“What is the benefit of exhaust analysis? ”
DASGIP GA exhaust analyzers measure oxygen and carbon dioxide concentrations in the exhaust, as well as the mass flow. The microorganisms' or cells' behavior strongly influences the gas concentrations in the bioreactor. Their growth usually correlates with oxygen consumption resulting in declining oxygen contents in the exhaust and carbon dioxide production. Measuring these enables calculation of oxygen and carbon dioxide transfer rates (OTR, CTR) as well as the respiratory quotient RQ. These parameters are influenced by the biological activity.
"How are DASGIP bioreactors protected against overheating? "
The DASGIP TC4SC4 controls the integrated temperature control unit, the DASGIP Bioblock, as well as standard heat blankets and also cooling valves of four bioreactors simultaneously. Each vessel of the DASGIP system can be individually switched to heating or cooling operation. A combined heating and cooling control is also possible. An extra temperature inlet for heating elements with an integrated overheating safety sensor is at hand. Both Bioblock (up to 1.8 L) and highly efficient cooling fingers (up to 3.8 L) allow high cell density fermentation at benchtop scale. Even highly different temperatures can be applied on the individual vessels.
"How are DASGIP vessels agitated?
DASGIP bioreactors feature powerful overhead drives with agitation speeds ranging 30 ? 1,600 rpm. The DASGIP TC4SC4 controls temperature and agitation in up to four bioreactors. Users can individually define each outlet set-point as well as choose from different operation modes (e.g. continuous or interval agitation).
"Can I integrate DASGIP with my existing historians & supervisory control? "
Yes, with the software DASware connect an optional server allows corporate-wide exchange of all process data via seamless integration with historians and supervisory control systems such as Delta V, OSI Pi, etc. This includes events, set-up information, and system status.
"How can I harness data generated by the DASGIP system? "
With DASware control all data and events are logged in one central SQL Server database. Further features such as export into Excel, PDF, and other file formats via one mouse click and strong charting capabilities ease plotting and data analysis. To harness data from numerous projects, on the long-run advanced archiving capabilities and data retrieval is required. DASware discover offers comprehensive and user-defined archiving functions and data retrieval for powerful data comparison and analysis. Users can, for example, link the utilized strain or cell line with its media composition, the controller setpoints and feeding profiles as well as with achieved product yields or viable cell densities to select for the best optimized combination and process.
"Can I get remote access to a running bioprocess outside my lab?"
With DASware access users can access all bioprocesses online - from an office, between business meetings or even from home on the weekend. A web browser application provides the web-based access via PC, Mac or Notebook. In addition, the DASGIP iApp allows the access via iPhone, iPad, and iPod touch. Users can not only monitor running processes online, but also remotely observe and access process data and change setpoints.
"Does DASware control give any alarms in case of critical deviation?"
Critical deviation of process parameters such as pH, DO, redox, and temperature are color-coded in the software and saved in the event log. DASware control professional additionally allows notification of supervisory control systems or mobile communication tools via SMS or e-mail.
"Can you help adjusting my controller loop parameters in DASware control?"
DASGIP controllers are PI controllers, which are configured with default controller parameters adapted to the type of vessel and default experimental requirements. Depending on special customer requirements it might be necessary to modify these parameters. Our service will be happy to help you finding the right settings.
"What can I do against the pH drift during longer experiments? "
It is a well known problem that the difference in ionic strength between media and the internal buffer of the pH probe leads to a pH drifting effect during an experiment. This means the measured pH value differs slightly from the pH value in the liquid. DASware control supports the online adaption of the pH calibration parameter to compensate this drift over the process runtime. During longer experiments we recommend to crosscheck the pH value in the bioreactor with an external pH meter and adapt the pH calibration parameter once a day. All user interactions and changes are documented in the event log.
"How to calibrate a pH sensor in DASware control? "
DASware control software allows for parallel calibration of all sensors used within one system with all data logged in the central database together with set-points, profiles, cascades, process values, user interactions and other events. Good maintenance will prolong the sensors' lifetime whereas high temperatures (i.e. during autoclavation), alkaline solutions (i.e. during alkaline deactivation), repeated etchings and improper maintenance will reduce the electrode's lifetime.
"How strong is the influence of temperature for my pH calibration? "
Temperature plays an important role as regards sample and buffer pH and an electrode's characteristics. The temperature dependency of buffers is fully known and is shown on the packing. The influence of temperature on the sensor sensitivity is compensated by the DASGIP PHPO amplifier modules - during calibration as well as during the process run. However, no compensation can be made for the pH shifts caused by altered reference potentials. If possible samples, buffers and sensors should all have the same temperature.
"What is 100 % DO and what is the difference to 100 V% oxygen? "
Dissolved oxygen (DO) is a relative unit for measuring the oxygen concentration in aquatic environments corresponding to the air pressure of the surrounding. In freshwater under an atmospheric pressure of 1013 mbar (1 atm, 760 Torr), 100 % DO equates the partial pressure of oxygen of 213 mbar. Temperature, pressure, and the presence of other substances in solution, such as salt or media components, have a great impact on the oxygen binding capacity. These influences make it necessary to calibrate the 100 % DO always in the air-saturated bioreactor filled with medium after autoclaving.
"What calibration parameters do you recommend for a DO probe? "
According to the working principle of a Clark electrode the measured signal is directly proportional to the concentration of oxygen. In an aquatic environment completely desaturated with oxygen the current (zero current) should be not more than 3 nA. In ambient air the calibration slope should be between 50 nA and 100 nA.
"Is it possible to receive a negative OTR in exhaust measurement? "
The DASGIP MP8 Module is capable to maintain continuous pump rates down to 0.3 mL/h depending on the tube diameter. With setpoints below this minimum, it automatically turns into duty cycling mode.
"How to clean Polytetrafluorethylen (PTFE) components? "
Single components of PTFE are resistant against corrosion. However they are not free of soiling and deposition. To elongate their life time, cleaning with ethanol can be carried out alternatively. Rinse all components several times with demineralized water (DI) after purification. Optionally use 70 - 80 % ethanol to disinfect. Cleaning of PTFE parts can also be carried out using a laboratory washer. For cleaning of PTFE feed lines customers benefit from the unique automated parallel Clean-in-Place (CIP) procedure: Up to 64 feed lines can be cleaned within one step via the DASware control software. We recommend to start the CIP procedure during vessel autoclavation. In the CIP procedure provided in the software, the feed lines are rinsed successively with Ethanol (70 %) and NaOH (2 N), and then flushed with demineralized water. Finally, tubings are filled with medium for the process run. This procedure is a recommendation and can be customized and applied as a user template then.
"How to clean metal spargers? "
Clean metal spargers immediately after each use with a soft brush. Then rinse with plenty of distilled water. We recommend a regular cleaning with 1 M sodium hydroxide (NaOH) solution followed by rinsing with demineralized water (DI). Wear protective clothing (laboratory coat, protective gloves, and goggles) during and after cleaning. Leave the sparger standing in 1 M NaOH for 30 ? 60 minutes or longer. Additionally, connect compressed air for cleaning of the pores. Alternatively use acetone. Then flush with 70?% ethanol to swamp out acetone. Afterwards flush with a lot of distilled water. Avoid cleaning agents containing tensides, because an easy removal by rinsing is not possible.
"How to clean stainless steel components? "
Fouling and calcination can contaminate stainless steel components. Before starting the cleaning procedure, remove non stainless steel components such as O-rings and use an ultrasonic bath for cleaning the stainless steel parts (10 minutes at 70 °C). Use detergents like P3-Ultrasil 53 or Tickopur RW77. Please contact us for more information. In order to remove calcination use a bath of weak organic acid like acidic or citric acid. Wear protective clothing (laboratory coat, protective gloves, and goggles) during and after cleaning. Rinse all components at least three times with demineralized water (DI) after ultrasonic purification. Optionally use 70 % ethanol to disinfect. Avoid solutions containing chloride like hydrochloric acid.
"Do stainless steel components bear any risk of corrosion? "
As it is highly resistant to most laboratory chemicals, stainless steel, e.g. 1.4571 (AISI-316Ti), 1.4404 (AISI-316L), is used for wetted parts in DASGIP Bioreactor Systems. A passive coating made of chrome oxide protects the steel from oxidizing agents. Despite these protective properties, corrosion can still occur in extreme situations such as mechanical surface damage or when the parts come in contact with concentrated acids or alkaline solutions. An indication of corrosion can be discoloration that is visible even after a thorough cleaning (ultrasonic bath with an approved stainless steel cleaning solution).
"Is it possible to automatically control the foam in DASGIP vessels? "
All DASGIP vessels can be equipped with foam control components. All you need is a level/foam sensor connected to the DASGIP sensor module (e.g. PH4PO4L) and a feed line for dosing of the antifoam agent. Now foam formation can be detected by the level sensor and antifoam agent is automatically pumped into the vessel until all foam is collapsed. The DASware control software allows any feed line to be used for antifoam or level control. Since medium composition has a strong impact on the electrical conductivity of medium and foam, every conductivity-based level sensor needs to be adjusted to foam and medium conductivity. DASware control supports monitoring conductivity and free adjustment of the conductivity threshold.
"What maintenance is required for Eppendorf bioprocess systems? "
As all complex technical systems Eppendorf bioprocess equipment should be maintained regularly to keep all parts in good condition. This maintenance avoids cost-intensive down times and contributes to preservation of value. A complete preventive maintenance is recommended once a year. Additional maintenance actions are recommended to be executed by the user prior to every run or in regular cycles (e.g. every month). Our service will be happy to advice.
"What does your warranty cover? "
Eppendorf issues a warranty of one year from the day of delivery on its products in accordance with our terms and conditions. Excluded are consumables such as cables, tubing, glassware, and sensors as well as used material.
"Does Eppendorf offer bioreactor training? "
We highly recommend a training at the customer’s site for all new customers. Besides this initial training, Eppendorf also offers individual trainings adapted to the user’s requirements like training of new employees or advanced training/recapitulation for employees already having experience with DASGIP or DASbox systems. All trainings are performed at the customer’s site using the customer’s equipment to have the training focused on the customer’s demands. The structure and methods of the training can be chosen to the customer’s requirements from general overview to detailed sessions on specific products or issues. Training in small groups is as possible as personal guidance.
"What is the definition of OTR, CTR and RQ? "
OTR and CTR stand for oxygen and carbon dioxide transfer rate. The OTR denotes the amount of oxygen that is transferred from the gaseous phase to the liquid phase per time interval and volume. The CTR consequently describes the amount of carbon dioxide that is stripped from the liquid phase during a certain period of time in a given volume. The respiratory quotient RQ is the quotient of these two transfer rates (CTR/OTR).
"What is the definition of a PID controller? "
The PID controller calculates required control action in processes based on deviations between setpoint and process values in the control loop. Calculations include three different parameters: the proportional response (P), the integral response (I), and the derivative response (D). The Proportional Response depends only on the difference between the setpoint and the process value. This difference is referred as ‘error’ (ε). The proportional factor or gain (P) determines the output response to the error signal. Increasing the proportional factor will increase the response of the controller. However if the proportional factor is too high the system will become unstable and oscillate around the setpoint. If the proportional factor is too small the system is not able to reach the setpoint in a given time. The Integral Response sums the error value over time. The result is that even a small error term will cause the integral component to increase slowly. This means there is a continually increase over time until the error term reaches zero. The Derivative Response causes the output to decrease if the process variable is increasing rapidly. The response itself is proportional to the rate of change of the process variable. Increasing the derivative time (Td) will cause the controller system to react more strongly to changes in the error term and will increase the speed of the overall control system response. The derivative response is very sensitive to noise in the process variable signal. If the sensor feedback signal is noisy or the control loop is too slow, the derivative response can make the control system unstable. These reasons and the absence of fast increasing process variables make it unnecessary for a biological control system to have a derivative component. DASGIP and New Brunswick controllers are PI controllers, since derivative action is very sensitive to measurement noise, and the absence of an integral value may prevent the system from reaching its target value due to the control action.
"What is the definition of a standard liter? "
All DASGIP and DASbox systems use the US standard liter which is defined at 0°C (273.15 K) and 1013.25 hPa.