Drug Delivery & Tissue Engineering Laboratory Bioreactors Hyuncheol Kim, PhD Drug Delivery & Tissue Engineering Laboratory Sogang University

What is a Bioreactor? An apparatus for growing organisms (yeast, bacteria, or animal cells) under controlled conditions. Used in industrial processes to produce pharmaceuticals, vaccines, or antibodies Also used to convert raw materials into useful byproducts such as in the bioconversion of corn into ethanol.

What is a Bioreactor? Bioreactors supply a homogeneous (same throughout) environment by constantly stirring the contents. Bioreactors give the cells a controlled environment by ensuring the same temperature, pH, and oxygen levels.

Types of Bioreactors Batch: Media and cells are added to the reactor and it is run until a predetermined set point (i.e. time, concentration). The bioreactor has a constant volume (the initial volume). Fed-Batch: The bioreactor is a batch process in the beginning and after a certain point a feed input is introduced and the volume of the vessel increases. Continuous: The bioreactor starts with an initial volume and media is constantly introduced and product is constantly taken out. The inputs and outputs are at the same rate, so the volume always remains the same.

Types of Bioreactors Bioreactors come in many different sizes and configurations.

Bioreactor Components Bioreactors consist of: Vessel Agitator Sparger Baffles Probes Temperature Dissolved Oxygen pH Pressure Gauge Cooling Jacket Ports for input and output of material Condenser Back Pressure Valve Inlet Filters and Exhaust Filters Valves Load Cell

Bioreactor - Vessel The bioreactor vessel is a container which holds the media and the cells Vessels can be made of glass, stainless steel, or a durable plastic. The durable plastic vessels are disposable (single-use). All the additional parts of a bioreactor connect to the vessel. The top of the vessel is called a head plate. On glass reactors, most additional parts are located on the head plate.

Bioreacotr - Vessel Head Plate Vessel

Bioreactor - Agitator An agitator is required to mix the contents in the vessel to ensure a homogeneous environment. Agitators consist of a shaft and impellers. Mixing of the bioreactor is crucial in order to supply nutrients and oxygen to the culture and to maintain a constant pH and temperature.

Bioreactor - Agitators Impellers come in many different shapes and sizes depending on what type of mixing is needed.

Bioreactor - Agitators Agitator Shaft Impellers

Bioreactor - Sparger The sparger is an apparatus used to introduce gasses into the vessel. Spargers are located at the bottom of the vessel and consist of a tube with tiny holes for the gas to escape through into the culture. The gas coming out of the sparger helps to aerate and mix the contents in the vessel, as well as supply oxygen to the cells.

Bioreactor - Sparger Ring Sparger Micro Sparger Openings on Ring Sparger Micro Sparger

Bioreactors - Baffles Baffles are obstructions on the side of the vessel that generate turbulence in the flow of the culture. Baffles are made out of stainless steel and are welded to the inside of the vessel. Baffles help to mix the culture by creating a more turbulent flow.

Bioreactor - Baffles Baffle Baffles obstruct the flow in the vessel to help mix the contents. Baffle

Bioreactor - Probes Bioreactors require probes to monitor the culture in the vessel. The probes are found at different locations on the vessel: head plate, top probe belt, bottom probe belt. Useful probes include temperature, pH, DO (dissolved oxygen), and CO2

Bioreactor - Probes Probe Belt Probes on head plate Probes

Bioreactor – Cooling Jacket Cells give off heat when growing and dividing. To maintain a constant temperature in the reactor, the vessel is covered by a cooling jacket. Coolant (cold water or glycol) flows through the cooling jacket to regulate the temperature. The temperature is controlled by the flow rate of the coolant.

Bioreactor – Cooling Jacket Stainless Steel Cooling Jacket surrounds the vessel.

Bioreactor - Ports Bioreactors require addition ports, where material is either introduced or removed from the vessel. Ports are needed to add the media (media port), cells (inoculation port), and nutrients (feed ports). Ports are also used for the addition of acid and base for pH control. A sample port is also located on each vessel to remove culture for off-line investigation.

Bioreactor - Ports Ports

Bioreactor - Condenser A condenser is an apparatus that captures saturated air leaving the vessel. The condenser is cooler than the saturated air allowing it to condense on the surface and return to the vessel as a liquid. Condensers help to minimize the loss of material out of the reactor due to evaporation.

Bioreactor - Condenser

Bioreactor - Filters Bioreactors need inlet filters to ensure the gasses entering the vessel are sterile. They require exhaust filters to keep the reactor sterile and allow gas to escape to regulate pressure. Filters require a filter housing – a stainless steel cabinet to hold and sterilize the filter.

Bioreactor - Filters Filter Housing Filter

Bioreactor – Back Pressure Valve A bioreactor must remain under constant pressure; we want the pressure in the reactor to be higher than the pressure surrounding it Constant pressure helps to ensure sterility of the reactor by keeping microbes out (they are less likely to overcome the pressure gradient) Pressure is added to the reactor by the introduction of air at the top of the reactor (head space). The pressure is regulated using a back pressure valve.

Bioreactor – Back Pressure Valve

Bioreactor - Valves Valves are used to control the flow of either gas or liquid Bioreactors use many different types of valves. Manual Valves – open and close the valves with your hand. Pneumatic Valves – automatic valve which opens and closes with the use of high pressured air (instrument air). Steam Lock Valves – (so called “block and bleed valves”) a two valve assembly so you can allow a fluid to flow through a portion of the valve and then close and use the other portion of the valve to sterilize the valve assembly after use to reduce contamination. These valves can be manual or pneumatic.

Bioreactor - Valves Valves are used at many different locations on the bioreactor Sample valve – where a sample from the bioreactor can be obtained. Harvest valve – location where the tank can be drained for harvest. Ports – contain an automatic steam lock valve, so liquid can be added to the vessel (the port can be sterilized after use to prevent contamination)

Bioreactor - Valves Pneumatic (Automatic) Valve Manual Valve Steam Lock Valves

Bioreactor – Load Cell A load cell is a scale that measures the weight of the bioreactor. The bioreactor sits on a series of load cells that compress when weight is added to the vessel. The weight of the bioreactor can be correlated to the volume of liquid in the vessel by using the density of the cell culture medium. Weight = Density x Volume

Bioreactor – Load Cell Compact Compression Load Cells Spacing of Load Cells

Bioreactor Utilities Bioreactors require utilities: Gasses Air Oxygen Carbon Dioxide Nitrogen Clean Steam - for sterilization of the reactor (condensed clean steam equals WFI (water for injection) that is clean enough to be injected) Coolant (cold water or glycol) – for cooling jacket Instrument Air - to operate pneumatic valves

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