Bioreactor Design and Scale‑Up
Expert-defined terms from the Certified Specialist Programme in Cell Culture Optimization course at LearnUNI. Free to read, free to share, paired with a professional course.
Accommodative Capacity – Concept #
the maximum volume a bioreactor can hold while maintaining optimal conditions. Related terms: scale‑up factor, volumetric productivity. Explanation: Determines the upper limit for batch size; example – moving from a 2 L lab reactor to a 200 L pilot unit. Challenge: maintaining uniform mixing and oxygen transfer at larger volumes.
Adsorption – Concept #
surface binding of molecules onto solids. Related terms: media beads, affinity chromatography. Explanation: Used in perfusion systems to capture growth factors; example – protein‑A resin retaining antibodies. Challenge: desorption efficiency and resin fouling over time.
Aeration Rate – Concept #
volume of air or oxygen supplied per unit time. Related terms: kLa, dissolved oxygen. Explanation: Controls oxygen availability; typical rates range from 0.5 to 2 vvm (volumes of air per volume of liquid per minute). Challenge: excessive aeration can cause shear damage to delicate cells.
Agitation Speed – Concept #
rotational speed of impellers measured in rpm. Related terms: shear stress, power input. Explanation: Higher speeds increase mixing but also elevate shear; example – 150 rpm for CHO cultures versus 300 rpm for robust microbial strains. Challenge: balancing mass transfer with cell viability.
Algal Photobioreactor – Concept #
a system designed for cultivating photosynthetic microorganisms. Related terms: light path, CO₂ supplementation. Explanation: Enables production of biofuels and high‑value pigments; example – flat‑panel reactors for Spirulina. Challenge: light attenuation and temperature control across the culture depth.
Alveolar Oxygen Transfer – Concept #
oxygen diffusion across a gas‑liquid interface resembling alveoli. Related terms: sparger design, bubble size. Explanation: Critical in high‑density mammalian cultures; fine bubbles increase interfacial area. Challenge: bubble coalescence reduces efficiency, requiring anti‑foam agents.
Ammonia Accumulation – Concept #
buildup of NH₃ from amino acid catabolism. Related terms: pH control, metabolic waste. Explanation: Toxic to many cell lines; monitored via off‑gas analysis. Example – limiting glutamine to reduce ammonia in CHO cultures. Challenge: balancing nutrient supply with waste production.
Amphiphilic Polymer – Concept #
polymers containing both hydrophilic and hydrophobic segments. Related terms: cell encapsulation, scaffold material. Explanation: Used to create protective micro‑environments for cells in suspension. Example – PEG‑PLA copolymers for stem‑cell aggregates. Challenge: ensuring polymer degradation does not release harmful by‑products.
Anti‑Foam Agent – Concept #
surfactant added to suppress foam formation. Related terms: foam control, gas sparging. Explanation: Prevents overflow and contamination; common agents include silicone‑based fluids. Challenge: excessive use can interfere with oxygen transfer and sensor readings.
Batch Culture – Concept #
closed‑system operation where all nutrients are supplied at the start. Related terms: fed‑batch, continuous culture. Explanation: Simple to implement; example – 5 L batch for recombinant protein production. Challenge: nutrient depletion limits final product titer.
Biomass Yield – Concept #
amount of cellular mass generated per unit substrate. Related terms: specific growth rate, substrate efficiency. Explanation: Expressed as g DCW/g glucose; higher yields indicate efficient metabolism. Example – 0.5 g DCW/g glucose for E. coli. Challenge: optimizing feed strategies to avoid overflow metabolism.
Biomass Monitoring – Concept #
real‑time measurement of cell concentration. Related terms: optical density, capacitance probe. Explanation: Enables on‑line control of feed rates; example – using near‑infrared spectroscopy for CHO cells. Challenge: calibration drift and signal interference from media components.
Bioprocess Modeling – Concept #
mathematical representation of culture dynamics. Related terms: kinetic models, CFD simulation. Explanation: Predicts scale‑up outcomes; example – Monod model for substrate‑limited growth. Challenge: capturing complex interactions such as shear‑induced apoptosis.
Bioreactor Geometry – Concept #
shape and dimensions of the vessel. Related terms: aspect ratio, aspect height. Explanation: Influences mixing patterns; cylindrical tanks with a 1:1 height‑to‑diameter ratio are common. Challenge: scaling geometry without altering hydrodynamics.
Bioreactor Materials – Concept #
construction substances for vessel and internals. Related terms: stainless steel, single‑use plastic. Explanation: Materials affect sterility, leachables, and cleaning cycles. Example – polycarbonate for disposable reactors. Challenge: ensuring compatibility with aggressive cleaning agents.
Blending – Concept #
mixing of multiple feed streams before entry. Related terms: feed pre‑mixing, homogenization. Explanation: Prevents localized nutrient spikes; used in fed‑batch to combine glucose and amino acids. Challenge: maintaining homogeneity in high‑viscosity media.
Bubble Column Reactor – Concept #
vertical vessel where gas is sparged from the bottom. Related terms: mass transfer coefficient, gas holdup. Explanation: Simple design, no moving parts; suitable for aerobic microbes. Example – 10 m column for industrial ethanol production. Challenge: limited control of mixing intensity.
Capacitive Sensor – Concept #
device measuring cell dielectric properties. Related terms: biomass probe, on‑line monitoring. Explanation: Provides non‑invasive cell density data; useful for high‑cell‑density CHO cultures. Challenge: sensor fouling and temperature compensation.
Carbon Dioxide Stripping – Concept #
removal of excess CO₂ from the culture broth. Related terms: gas exchange, pH regulation. Explanation: Prevents acidification; achieved by increasing gas flow or using membrane contactors. Challenge: balancing CO₂ removal with oxygen supply.
Cell Aggregates – Concept #
clusters of cells forming spontaneously or by design. Related terms: spheroids, microcarriers. Explanation: Used in stem‑cell and tumor‑model research; aggregates improve cell‑cell signaling. Challenge: controlling aggregate size to avoid diffusion limitations.
Cell Density – Concept #
number of cells per unit volume. Related terms: viable cell concentration, growth curve. Explanation: Measured in cells/mL; high densities (>1 × 10⁷ cells/mL) are typical for perfusion processes. Challenge: oxygen and nutrient gradients at high density.
Cell Line Development – Concept #
engineering cells for desired traits. Related terms: gene amplification, stability testing. Explanation: Involves transfection, selection, and clone screening. Example – DHFR‑amplified CHO lines for monoclonal antibodies. Challenge: ensuring long‑term genetic stability under scale‑up conditions.
Cell Retention – Concept #
technique to keep cells inside the reactor while allowing product to exit. Related terms: tangential flow filtration, acoustic settlers. Explanation: Enables continuous high‑density culture; example – ATF system for recombinant protein. Challenge: membrane fouling and shear stress.
Cell Viability – Concept #
proportion of living cells in a culture. Related terms: trypan blue exclusion, flow cytometry. Explanation: Critical quality attribute; viability below 80 % often signals process upset. Challenge: rapid on‑line viability assessment without sampling.
Closed‑Loop Control – Concept #
automated feedback system adjusting parameters based on sensor data. Related terms: PIC, PID controller. Explanation: Maintains pH, DO, temperature within setpoints; reduces operator variability. Challenge: tuning controller gains for non‑linear cell behavior.
Computational Fluid Dynamics (CFD) – Concept #
simulation of fluid flow and mixing. Related terms: mesh generation, turbulence model. Explanation: Predicts shear zones and oxygen distribution; guides impeller selection. Example – CFD showed dead‑zone reduction after adding a Rushton turbine. Challenge: high computational cost for large‑scale geometries.
Continuous Culture – Concept #
steady‑state operation where fresh medium enters and spent medium exits continuously. Related terms: chemostat, perfusion. Explanation: Allows constant product quality; example – 10 L continuous bioreactor for monoclonal antibody. Challenge: maintaining stable cell density over long runs.
Co‑culture Systems – Concept #
simultaneous cultivation of two or more cell types. Related terms: heterologous expression, symbiotic interaction. Explanation: Used for viral vaccine production where helper cells support target cells. Challenge: balancing growth rates and nutrient competition.
Coiled Tubular Reactor – Concept #
flexible tubing arranged in coils for continuous flow. Related terms: plug flow, residence time distribution. Explanation: Offers high surface‑to‑volume ratio; used for enzymatic biotransformations. Challenge: pressure drop and fouling in long runs.
Cold‑Shock Response – Concept #
cellular adaptation to rapid temperature decrease. Related terms: heat‑shock proteins, stress pathways. Explanation: Can improve recombinant protein folding when cultures are shifted from 37 °C to 30 °C. Challenge: timing the shift to avoid growth arrest.
Corrosion‑Resistant Alloy – Concept #
metal alloy designed to resist degradation in aggressive environments. Related terms: 316L stainless steel, titanium. Explanation: Used for bioreactors exposed to strong cleaning agents. Challenge: higher cost and potential impact on heat transfer.
Crystallization – Concept #
solid‑phase formation from supersaturated solution. Related terms: downstream processing, nucleation. Explanation: Final step for many biologics; requires precise temperature control. Example – protein crystallization in a 5 L stirred tank. Challenge: controlling crystal size distribution.
Culture Media Optimization – Concept #
tailoring nutrient composition for maximal productivity. Related terms: design of experiments, fed‑batch feed. Explanation: Uses statistical methods to evaluate carbon, nitrogen, vitamins. Example – glucose‑limited media improved monoclonal antibody yield. Challenge: media cost versus performance gain.
Cytokine Supplementation – Concept #
addition of signaling proteins to support cell growth. Related terms: IL‑2, growth factor. Explanation: Essential for lymphocyte expansion in vaccine manufacturing. Challenge: cytokine stability and batch‑to‑batch variability.
Dead‑Zone – Concept #
region of low mixing where nutrients and oxygen are depleted. Related terms: vortex, stagnation. Explanation: Identified by tracer studies; can cause localized cell death. Challenge: redesigning impeller layout to eliminate.
Design of Experiments (DoE) – Concept #
systematic approach to evaluate multiple variables simultaneously. Related terms: full factorial, response surface methodology. Explanation: Reduces number of runs needed for media or process optimization. Challenge: selecting appropriate factor ranges to capture non‑linear effects.
Diffusion Limitation – Concept #
restriction of mass transfer due to concentration gradients. Related terms: mass transfer coefficient, microcarrier. Explanation: Becomes critical in high‑density aggregates; oxygen may not reach core cells. Challenge: engineering porous carriers or perfusion to mitigate.
Dolomite Limestone – Concept #
calcium carbonate used for pH control. Related terms: buffering capacity, acid neutralization. Explanation: Provides gradual pH increase without sharp spikes. Challenge: insoluble particles can clog filters.
Downstream Processing – Concept #
series of steps after fermentation to recover and purify product. Related terms: chromatography, ultrafiltration. Explanation: Includes clarification, capture, polishing. Example – Protein A chromatography for antibodies. Challenge: scaling purification steps while maintaining product quality.
Dynamic Light Scattering (DLS) – Concept #
technique measuring particle size distribution via scattering of laser light. Related terms: nanoparticle analysis, aggregate detection. Explanation: Used to monitor protein aggregation in real time. Challenge: interference from high‑turbidity media.
Eddy Current – Concept #
circulating fluid motion generated by impeller rotation. Related terms: turbulent mixing, vortex formation. Explanation: Enhances mass transfer; measured by flow probes. Challenge: excessive eddies can cause cell shear.
Elasticity Modulus – Concept #
measure of material stiffness. Related terms: scaffold rigidity, cell mechanotransduction. Explanation: Influences stem‑cell differentiation on 3D carriers. Example – softer hydrogels promote neuronal lineage. Challenge: replicating tissue‑specific modulus at scale.
Enzyme Immobilization – Concept #
attachment of enzymes to solid supports for reuse. Related terms: covalent binding, carrier beads. Explanation: Facilitates continuous biocatalysis; example – glucose oxidase on silica beads. Challenge: loss of activity due to conformational changes.
Environmental Monitoring – Concept #
tracking parameters such as temperature, humidity, and particulate count. Related terms: GMP compliance, cleanroom. Explanation: Ensures sterile operation; includes ISO‑5 monitoring. Challenge: integrating sensors without compromising aseptic barrier.
Equilibrium Dissolved Oxygen (DO) – Concept #
steady‑state oxygen concentration achievable under given gas flow. Related terms: kLa, oxygen solubility. Explanation: Determines maximum cell density in aerobic cultures. Example – DO setpoint of 40 % saturation for CHO cells. Challenge: maintaining DO as viscosity rises.
Feed Strategy – Concept #
schedule and composition of nutrient addition. Related terms: exponential feed, bolus feed. Explanation: Controls growth rate; exponential feeding matches specific growth rate. Example – glucose feed at 0.05 g/L·h. Challenge: preventing substrate accumulation that leads to lactate overflow.
Fermenter – Concept #
large‑scale vessel for microbial or cell culture. Related terms: bioreactor, pilot plant. Explanation: Equipped with agitators, spargers, and sensors. Example – 10,000 L stainless‑steel fermenter for vaccine production. Challenge: ensuring consistent performance across multiple units.
Fluid Shear Stress – Concept #
force per unit area exerted by moving fluid on cells. Related terms: impeller tip speed, shear‑sensitive cells. Explanation: High shear can damage mammalian cells; measured in dyn/cm². Challenge: designing low‑shear impellers while preserving mixing.
Foam Fraction – Concept #
proportion of reactor volume occupied by foam. Related terms: foam index, anti‑foam dosage. Explanation: Excess foam can cause overflow and contamination. Example – foam fraction of 10 % observed in high‑protein cultures. Challenge: balancing foam suppression with oxygen transfer.
Gas Sparger Design – Concept #
configuration of gas inlet to create bubbles. Related terms: porous plate, venturi. Explanation: Determines bubble size distribution and gas holdup. Example – sintered stainless‑steel sparger for fine bubbles. Challenge: clogging by media particles.
Glucose Feeding – Concept #
addition of glucose to sustain growth. Related terms: substrate limitation, lactate production. Explanation: Controlled feeding avoids excess that leads to acetate formation. Example – constant glucose feed of 0.2 g/L·h. Challenge: real‑time monitoring to prevent spikes.
Growth Inhibition – Concept #
reduction of cell proliferation due to stressors. Related terms: toxicity, metabolic burden. Explanation: Can be caused by high product concentrations or waste accumulation. Example – product inhibition of recombinant protein at >2 g/L. Challenge: implementing removal or dilution strategies.
Heated Jacket – Concept #
external water‑filled layer for temperature control. Related terms: cooling coil, thermostatic bath. Explanation: Provides uniform temperature across reactor; commonly used for 37 °C cultures. Challenge: thermal lag during rapid temperature shifts.
Hydrodynamic Stress – Concept #
combination of shear and extensional forces in the fluid. Related terms: eddy current, impeller geometry. Explanation: Impacts cell morphology; high stress can induce apoptosis in CHO cells. Challenge: quantifying stress distribution for scale‑up.
Hydrostatic Pressure – Concept #
pressure exerted by liquid column height. Related terms: head pressure, vessel design. Explanation: Influences gas dissolution and sensor performance. Example – 2 bar hydrostatic pressure in a 10 m tall column. Challenge: ensuring pressure‑rated seals.
Immobilized Cell Reactor – Concept #
system where cells are fixed on a support matrix. Related terms: biofilm, carrier beads. Explanation: Facilitates continuous operation and product recovery. Example – alginate‑encapsulated yeast in a packed‑bed reactor. Challenge: mass transfer limitations inside the matrix.
In‑Line Filtration – Concept #
removal of particulates from the stream without stopping the process. Related terms: depth filter, sterile filter. Explanation: Protects downstream equipment; typical pore size 0.2 µm. Challenge: filter clogging and pressure drop.
Inoculum Development – Concept #
preparation of seed culture to start production run. Related terms: seed train, starter culture. Explanation: Determines initial cell health and density. Example – 10‑L seed culture grown to 5 × 10⁶ cells/mL before transfer. Challenge: scaling inoculum while preserving phenotype.
Insulating Jacket – Concept #
layer to minimize heat loss or gain. Related terms: thermal insulation, temperature control. Explanation: Used in large reactors to stabilize temperature. Challenge: material selection to avoid contamination.
Ion Exchange Chromatography – Concept #
purification based on charge interactions. Related terms: anion exchange, cation exchange. Explanation: Captures impurities or target protein; example – Q‑Sepharose for virus removal. Challenge: buffer compatibility and resin fouling.
Isothermal Operation – Concept #
maintaining constant temperature throughout the process. Related terms: temperature control, heat balance. Explanation: Critical for temperature‑sensitive enzymes. Example – 30 °C isothermal fermentation for thermostable lipase. Challenge: compensating for metabolic heat in large volumes.
Laminar Flow – Concept #
smooth fluid motion where layers slide past each other. Related terms: Reynolds number, low shear. Explanation: Desired for shear‑sensitive cell cultures; occurs at Re < 2000. Challenge: achieving adequate mixing without turbulence.
Liquid‑Liquid Extraction – Concept #
separation of compounds between two immiscible liquids. Related terms: solvent extraction, partition coefficient. Explanation: Used to recover hydrophobic products from broth. Example – using ethyl acetate to extract organic acids. Challenge: solvent toxicity and downstream removal.
Load‑Bearing Capacity – Concept #
maximum mechanical stress a scaffold can sustain. Related terms: compressive strength, tissue engineering. Explanation: Determines suitability for bone‑like constructs. Challenge: scaling scaffold production while preserving mechanical properties.
Mass Transfer Coefficient (kLa) – Concept #
combined rate of gas transfer per unit volume. Related terms: oxygen transfer, agitation speed. Explanation: Higher kLa improves DO but may increase shear. Example – kLa of 0.2 h⁻¹ in a 5 L stirred tank. Challenge: measuring accurately at scale.
Microcarrier – Concept #
small bead providing surface for adherent cells in suspension. Related terms: solid support, bead coating. Explanation: Enables high‑density expansion of anchorage‑dependent cells. Example – Cytodex‑3 for MSC culture. Challenge: bead aggregation and uniform cell seeding.
Microscale Bioreactor – Concept #
miniaturized reactor (≤10 mL) for rapid screening. Related terms: high‑throughput, parallel bioreactors. Explanation: Allows parallel testing of media formulations. Example – 48‑well micro‑fermenter for early‑stage optimization. Challenge: scaling data to larger vessels.
Mixing Time – Concept #
duration required for homogenous distribution of a tracer. Related terms: impeller speed, dead‑zone. Explanation: Short mixing times (<30 s) are preferred for fast‑growing cultures. Challenge: measuring in viscous, high‑cell‑density media.
Monod Kinetics – Concept #
mathematical model describing microbial growth as a function of substrate concentration. Related terms: μmax, Ks. Explanation: μ = μmax · S/(Ks + S). Example – fitting E. coli data to estimate μmax. Challenge: deviations at high substrate levels due to inhibition.
Morphology Control – Concept #
regulation of cell shape and structure. Related terms: filamentous growth, shear stress. Explanation: Influences product quality; e.g., filamentous fungi require low shear to avoid hyphal breakage. Challenge: monitoring morphology in real time.
Multivariate Monitoring – Concept #
simultaneous tracking of several process variables. Related terms: PCA, soft sensors. Explanation: Enables predictive control; example – combining DO, pH, and off‑gas CO₂ to predict metabolic shifts. Challenge: data integration and model robustness.
Nanoparticle Production – Concept #
synthesis of nanoscale particles within a bioreactor. Related terms: bottom‑up synthesis, surfactant. Explanation: Used for drug delivery carriers; example – PLGA nanoparticles formed by emulsion. Challenge: controlling size distribution at scale.
Negative Pressure – Concept #
pressure below atmospheric within a closed system. Related terms: vacuum, containment. Explanation: Used for aseptic sampling ports to prevent ingress of contaminants. Challenge: ensuring seals maintain integrity under pressure fluctuations.
Osmolality Control – Concept #
regulation of solute concentration in the medium. Related terms: tonicity, cell swelling. Explanation: Critical for mammalian cells; typical range 280–320 mOsm/kg. Challenge: accumulation of metabolites altering osmolality over time.
Oxygen Transfer Rate (OTR) – Concept #
amount of oxygen transferred into the liquid per unit time. Related terms: kLa, DO setpoint. Explanation: Determines maximum cell density; measured in mmol O₂/L·h. Example – OTR of 0.5 mmol L⁻¹ h⁻¹ for high‑density CHO culture. Challenge: balancing OTR with shear.
pH Control Strategy – Concept #
method for maintaining desired pH. Related terms: acid/base addition, CO₂ sparging. Explanation: Automated control via PID loops; example – adding 0.5 M NaOH to counteract acidification. Challenge: avoiding localized pH spikes that affect cell metabolism.
Perfusion Culture – Concept #
continuous removal of spent medium while retaining cells. Related terms: cell retention, high‑density culture. Explanation: Achieves cell densities >1 × 10⁸ cells/mL; example – ATF system for monoclonal antibodies. Challenge: membrane fouling and shear.
Pharmacokinetic Modeling – Concept #
simulation of drug behavior within biological systems. Related terms: PK/PD, clearance. Explanation: Applied to bioprocesses to predict product concentration in final formulation. Challenge: integrating process variability into models.
Photon Flux – Concept #
number of photons striking a unit area per unit time. Related terms: light intensity, photosynthetic rate. Explanation: Governs algal growth; measured in µmol m⁻² s⁻¹. Example – 150 µmol m⁻² s⁻¹ for Chlorella cultures. Challenge: uniform distribution in deep reactors.
Plasma‑treated Surface – Concept #
surface modification using ionized gas to enhance cell attachment. Related terms: surface energy, hydrophilicity. Explanation: Improves adhesion of anchorage‑dependent cells on polymeric carriers. Challenge: ensuring consistency across large batches.
Plug Flow Reactor (PFR) – Concept #
reactor where fluid moves as a piston with minimal back‑mixing. Related terms: residence time, axial dispersion. Explanation: Ideal for fast reactions; example – enzymatic conversion of substrate in a tubular reactor. Challenge: maintaining laminar flow at high flow rates.
Polysaccharide Hydrogel – Concept #
network of carbohydrate polymers used as 3D scaffold. Related terms: alginate, viscoelasticity. Explanation: Supports cell encapsulation for protected perfusion. Challenge: diffusion of nutrients through dense gel.
Process Analytical Technology (PAT) – Concept #
framework for real‑time quality monitoring. Related terms: soft sensors, on‑line analytics. Explanation: Implements sensors for DO, pH, and metabolite levels to enable immediate adjustments. Challenge: regulatory acceptance and sensor robustness.
Process Scale‑Up – Concept #
transition from laboratory to pilot or commercial scale while preserving performance. Related terms: geometric similarity, kinetic similarity. Explanation: Uses dimensionless numbers to guide equipment sizing. Example – scaling a 2 L shake flask to a 200 L stirred tank. Challenge: replicating mixing and oxygen transfer characteristics.
Process Validation – Concept #
documented evidence that a process consistently produces a product meeting specifications. Related terms: IQ/OQ/PQ, GMP. Explanation: Involves installation qualification, operational qualification, and performance qualification. Challenge: designing robust validation protocols for complex bioreactors.
Protein Folding – Concept #
acquisition of functional three‑dimensional structure by a polypeptide. Related terms: chaperones, temperature shift. Explanation: Misfolded proteins aggregate, reducing yield. Example – lowering temperature to 30 °C improves antibody folding. Challenge: balancing folding efficiency with growth rate.
Pyrophosphate Accumulation – Concept #
buildup of inorganic pyrophosphate from nucleotide synthesis. Related terms: metabolic bottleneck, ATP regeneration. Explanation: Can inhibit DNA polymerases and affect cell growth. Challenge: engineering pathways to recycle pyrophosphate.
Quality by Design (QbD) – Concept #
systematic approach to building quality into product and process from the start. Related terms: critical quality attributes, design space. Explanation: Uses risk assessment and DoE to define acceptable operating ranges. Challenge: integrating QbD into existing manufacturing pipelines.
Quorum Sensing – Concept #
cell‑to‑cell communication using signaling molecules. Related terms: autoinducer, biofilm formation. Explanation: Influences gene expression in bacterial cultures; example – AHL‑mediated regulation in Pseudomonas. Challenge: controlling quorum signals to prevent unwanted phenotypes.
Rheology – Concept #
study of flow and deformation of fluids. Related terms: viscosity, shear thinning. Explanation: Culture media become non‑Newtonian at high cell densities. Example – viscosity rises from 1 cP to 5 cP at 1 × 10⁸ cells/mL. Challenge: predicting pump and impeller performance.
Residence Time Distribution (RTD) – Concept #
probability distribution of time fluid elements spend inside a reactor. Related terms: plug flow, mixing. Explanation: Assessed by tracer experiments; narrow RTD indicates good plug flow. Challenge: minimizing dead zones that broaden RTD.
Reverse Osmosis (RO) – Concept #
membrane filtration driven by pressure to separate solutes. Related terms: concentration step, water recovery. Explanation: Used for product concentration and buffer recycling. Challenge: membrane fouling and high energy consumption.
Rising Bubble Column – Concept #
column where gas bubbles rise, creating upward flow. Related terms: gas holdup, liquid circulation. Explanation: Enhances mixing without mechanical agitation; suitable for shear‑sensitive cultures. Challenge: controlling bubble size distribution.
Robustness Testing – Concept #
evaluation of process resilience to variations. Related terms: stress testing, design of experiments. Explanation: Identifies critical parameters; example – varying temperature by ±2 °C to assess impact on yield. Challenge: extensive testing required for complex systems.
Scale‑Down Model – Concept #
laboratory‑scale system that mimics large‑scale behavior. Related terms: pilot plant, mimicry. Explanation: Used to study scale‑up effects; example – 10 L reactor replicating 2000 L mixing patterns. Challenge: accurately reproducing hydrodynamics.
Shear‑Sensitive Cell Line – Concept #
cells that experience reduced viability under high shear. Related terms: CHO, stem cells. Explanation: Requires low‑tip‑speed impellers; example – human embryonic stem cells thrive at < 50 rpm. Challenge: achieving sufficient oxygen transfer without damaging cells.
Shear Rate – Concept #
velocity gradient within the fluid, expressed in s⁻¹. Related terms: impeller tip speed, viscosity. Explanation: Directly linked to cell damage; threshold for CHO cells often < 500 s⁻¹. Challenge: measuring shear in opaque media.
Shelf‑Life Stability – Concept #
durability of product over storage time. Related terms: degradation, temperature excursion. Explanation: Influenced by residual impurities from upstream; example – antibody aggregation after 12 months at 4 °C. Challenge: linking upstream parameters to downstream stability.
Silicone Elastomer – Concept #
flexible polymer used for seals and gaskets. Related terms: O‑ring, chemical resistance. Explanation: Provides airtight sealing in high‑pressure vessels. Challenge: leaching of silicone compounds into the culture.
Single‑Use Bioreactor (SUB) – Concept #
disposable vessel made of polymer film. Related terms: bag reactor, closed system. Explanation: Eliminates cleaning validation; example – 200 L SUB for viral vaccine production. Challenge: limited temperature control and potential extractables.
Sparger Geometry – Concept #
shape and arrangement of gas‑inlet devices. Related terms: porous plate, venturi. Explanation: Influences bubble formation and gas holdup. Example – sintered titanium sparger yields 0.2 mm bubbles. Challenge: preventing blockage by media particles.
Specific Growth Rate (μ) – Concept #
rate of increase in cell concentration per unit time. Related terms: Monod model, exponential phase. Explanation: Calculated as μ = (ln X₂ − ln X₁)/(t₂ − t₁). Example – μ = 0.03 h⁻¹ for a typical CHO batch. Challenge: maintaining constant μ during fed‑batch.
Specific Productivity (qP) – Concept #
amount of product formed per cell per unit time. Related terms: qS, yield coefficient. Explanation: Measured as mg product/million cells·h. Example – qP = 0.5 pg cell⁻¹ h⁻¹ for antibody. Challenge: optimizing feed to increase qP without compromising viability.
Specific Substrate Consumption (qS) – Concept #
rate at which a substrate is consumed per cell. Related terms: qO₂, metabolic flux. Explanation: Used to design feeding strategies; example – qS = 0.03 pmol cell⁻¹ h⁻¹ for glucose. Challenge: accurate measurement in high‑density cultures.
Stirred‑Tank Reactor (STR) – Concept #
vessel equipped with an impeller for mixing. Related terms: Rushton turbine, anchor impeller. Explanation: Most common bioreactor type; scalable from 1 L to >10 000 L. Challenge: selecting impeller geometry for target shear and mixing.
Substrate Inhibition – Concept #
reduction of growth rate at high substrate concentrations. Related terms: Haldane model, overflow metabolism. Explanation: Excess glucose can trigger acetate formation in E. coli. Challenge: implementing feed control to avoid inhibitory levels.
Supercritical Fluid Extraction – Concept #
use of fluids above critical temperature and pressure for separation. Related terms: SCCO₂, extraction efficiency. Explanation: Allows solvent‑free recovery of hydrophobic products. Challenge: equipment cost and safety considerations.
Syringe Pump Feeding – Concept #
precise delivery of liquid feeds via syringe. Related terms: peristaltic pump, flow rate control. Explanation: Enables low‑volume, high‑precision feeds; example – feeding trace nutrients in a 500 mL culture. Challenge: pump wear and bubble formation.
Temperature Ramp – Concept #
gradual change of temperature over time. Related terms: heat shock, cold shock. Explanation: Used to induce protein expression in recombinant systems; example – raising temperature from 30 °C to 37 °C over 2 h. Challenge: avoiding metabolic shock that reduces viability.
Thermal Conductivity – Concept #
ability of a material to conduct heat. Related terms: heat transfer coefficient, jacket material. Explanation: Impacts cooling rates; stainless steel has higher conductivity than polymeric SUBs. Challenge: managing heat removal in high‑exotherm fermentations.
Titer – Concept #
concentration of product in the culture broth. Related terms: product concentration, yield. Explanation: Expressed as mg/L or g/L; higher titer reduces downstream processing volume. Example – 5 g/L IgG in a perfusion run. Challenge: achieving high titer without compromising cell health.
Tip Speed – Concept #
linear velocity at the