Scale Up

Definition and Overview

What is Scale Up?

Scale Up: process of increasing bioprocess volume from bench to commercial scale. Objective: maintain product quality, yield, and process reproducibility. Scope: fermentation, cell culture, downstream processing.

Stages Involved

Stages: laboratory scale (mL to L), pilot scale (10s to 100s L), industrial scale (1000s L+). Each stage validates process performance and identifies bottlenecks.

Scope and Impact

Impact: affects economics, timelines, and regulatory compliance. Poor scale up: leads to yield loss, contamination, or inconsistent product quality.

Importance of Scale Up in Bioprocessing

Economic Significance

Scale Up: critical for cost reduction. Bulk production lowers unit cost. Economies of scale achieved by efficient resource use.

Process Optimization

Enables optimization of parameters: mixing, aeration, nutrient supply, temperature control. Scaled processes must replicate lab results.

Product Consistency

Maintains product identity, purity, potency. Ensures batch-to-batch uniformity, critical for pharmaceuticals and biologics.

Scale Levels: Lab, Pilot, and Industrial

Laboratory Scale

Volume: 1 mL to 5 L. Focus: process development, strain improvement, media optimization. Equipment: shake flasks, benchtop bioreactors.

Pilot Scale

Volume: 10 to 1000 L. Focus: process validation, parameter adjustment, troubleshooting. Equipment: pilot fermenters, small-scale downstream units.

Industrial Scale

Volume: >1000 L. Focus: full-scale production, regulatory compliance, cost efficiency. Equipment: large fermenters, automated downstream systems.

Key Parameters in Scale Up

Mixing and Agitation

Mixing: ensures homogeneity of nutrients, cells, oxygen. Agitation speed affects shear stress, oxygen transfer rate (OTR).

Oxygen Transfer Rate (OTR)

OTR: critical for aerobic cultures. Depends on kLa (mass transfer coefficient), gas flow rate, agitation. Must be maintained during scale up.

Temperature and pH Control

Temperature: affects metabolic rates. pH: influences enzyme activity, product stability. Both must be tightly controlled at scale.

Foam Control

Foaming: problematic in large volumes. Antifoam agents or mechanical foam breakers used. Foam affects gas exchange and contamination risk.

Common Challenges in Scale Up

Maintaining Homogeneity

Scale up causes gradients in oxygen, nutrients, pH. Poor mixing leads to zones with suboptimal conditions.

Shear Sensitivity

Increased agitation can damage cells or proteins. Shear forces must be balanced against mixing needs.

Mass Transfer Limitations

Oxygen and substrate transfer rates decline with volume increase. Diffusional limitations affect cell growth.

Process Reproducibility

Process parameters vary with scale, causing batch variability. Scale up protocols must minimize these differences.

Scale Up Strategies and Approaches

Geometric Similarity

Maintain proportional vessel dimensions, impeller size, and shape. Simplifies scale up but insufficient alone.

Constant Power Input per Volume

Maintain power density (P/V) to replicate mixing and shear conditions. Requires measuring power consumption at lab scale.

Constant Tip Speed

Maintain impeller tip velocity to control shear and mixing. Useful for shear-sensitive cultures.

Constant kLa

Match volumetric oxygen transfer coefficient to ensure equivalent oxygen supply.

Bioreactor Scaling Principles

Diameter and Height Ratios

Maintain height-to-diameter ratio for similar hydrodynamics. Typical ratios: 2:1 to 3:1.

Impeller Design and Speed

Impeller type affects flow pattern, shear. Speed adjusted to maintain mixing and oxygen transfer.

Gas Sparging Systems

Scale gas spargers to maintain bubble size and distribution. Affects gas-liquid mass transfer.

Instrumentation and Control

Sensor placement critical for accurate pH, DO, temperature measurement. Automation increases reproducibility.

Kinetics and Mass Transfer Considerations

Growth Kinetics

Monod kinetics often used. Parameters: μmax (maximum growth rate), Ks (substrate affinity constant). Scaled processes must maintain substrate supply above Ks.

Substrate Consumption

Substrate depletion causes growth limitation. Feeding strategies used in fed-batch or continuous cultures.

Oxygen Mass Transfer

Described by: OTR = kLa (C* - CL), where C* is saturation conc., CL is liquid conc.

Shear Stress Effects

Excess shear reduces cell viability, productivity. Shear thresholds must be identified and respected.

Methods and Models for Scale Up

Dimensionless Numbers

Reynolds number (Re): flow regime. Froude number (Fr): mixing. Power number (Np): impeller power consumption.

Computational Fluid Dynamics (CFD)

Simulates flow patterns, mixing, oxygen transfer. Helps predict scale up issues and optimize design.

Empirical Correlations

Relate process variables to scale using experimental data. Examples: kLa vs. agitation speed, power input.

Mathematical Modeling

Includes kinetic models, mass transfer equations, and process simulations to predict scale up outcomes.

Case Studies in Scale Up

Antibiotic Production

Scale up from 5 L lab fermenter to 10,000 L industrial vessel. Challenges: oxygen supply, shear sensitivity. Solutions: increased aeration, impeller redesign.

Recombinant Protein Expression

Fed-batch E. coli culture scaled from 1 L to 1000 L. Key factors: substrate feeding strategy, foaming control.

Cell Culture for Monoclonal Antibodies

Scale up mammalian cell culture from 3 L to 2000 L bioreactor. Focus on maintaining shear stress below 0.1 Pa, dissolved oxygen > 30%.

Equipment and Instrumentation

Bioreactors and Fermenters

Types: stirred tank, airlift, wave bioreactors. Selection based on organism, process type, scale.

Sensors and Probes

pH, dissolved oxygen (DO), temperature, foam sensors. Real-time monitoring critical for control.

Control Systems

Automated feedback loops for pH, temperature, agitation, gas flow. SCADA systems often used in industrial scale.

Downstream Equipment

Clarifiers, centrifuges, filtration units scaled accordingly. Must handle increased volumes without product loss.

Regulatory and Quality Aspects

Good Manufacturing Practices (GMP)

Scaled processes must comply with GMP standards. Documentation, validation, and quality control mandatory.

Process Validation

Verification that scaled process meets predefined criteria. Includes installation qualification (IQ), operational qualification (OQ), performance qualification (PQ).

Quality by Design (QbD)

Systematic approach integrating scale up with product quality goals. Defines critical process parameters (CPPs) and quality attributes (CQAs).

Regulatory Submissions

Scale up data included in regulatory filings (e.g., IND, NDA). Demonstrates process control and product consistency.

Tables and Data Examples

Table 1: Typical Scale Up Parameters Across Scales

Table 2: Dimensionless Numbers Relevant to Scale Up

Key Formulas and Algorithms

Oxygen Transfer Rate (OTR) Calculation

OTR = kLa × (C* - CL)Where:kLa = volumetric mass transfer coefficient (1/hr)C* = oxygen saturation concentration (mg/L)CL = dissolved oxygen concentration (mg/L)

Reynolds Number (Re)

Re = (ρ × N × D²) / μWhere:ρ = fluid density (kg/m³)N = impeller speed (1/s)D = impeller diameter (m)μ = dynamic viscosity (Pa·s)

Power Number (Np)

Np = P / (ρ × N³ × D⁵)Where:P = power input (W)ρ = fluid density (kg/m³)N = impeller speed (1/s)D = impeller diameter (m)

References

• Shuler, M.L., Kargi, F. Bioprocess Engineering: Basic Concepts. 2nd ed., Prentice Hall, 2002, pp. 345-390.
• Doran, P.M. Bioprocess Engineering Principles. 2nd ed., Academic Press, 2013, pp. 415-460.
• Garcia-Ochoa, F., Gomez, E. "Bioreactor scale-up and oxygen transfer rate in microbial processes: an overview." Biotechnol. Adv., vol. 27, 2009, pp. 153-176.
• Hewitt, C.J., Nienow, A.W. "The scale-up of mammalian cell culture processes." Chem. Eng. Res. Des., vol. 84, 2006, pp. 885-892.
• Junker, B. "Scale-up methodologies for microbial processes: an overview." J. Ind. Microbiol. Biotechnol., vol. 33, 2006, pp. 647-654.