Biomedical Engineering Reference
In-Depth Information
12.2 CELL CULTURE AND FERMENTATION PAT TOOLS
The richest and most rewarding environments for PAT exploration are in the “upstream
process” disciplines of mammalian cell culture and fermentation. The practices of cell
culture and fermentation have long been described colloquially as “black box” because
of the less well-understood internal functions that take place when combining living
organisms with plastic biobags, glass, and stainless steel. Several areas are being
explored by process development scientists and engineers with current process analytical
tools.
12.2.1 Miniaturization as Process Understanding
Tool in Development
Microbial and mammalian expression process design space is being explored with the
use of microbioreactor arrays in various formats and forms of automation. Arrays can
range from fully automated robotic reactor arrays with full control logic to simple 96
well-based systems in which multivariate experiments may be performed rapidly. These
systems may contain probes or sensors fabricated into the design to monitor various
attributes such as pH, optical density (OD), and dissolved oxygen. Some of the more
complex systems may rely on robotic workstations with adaptations to the robotic arm
movements that include plate lifters that tilt cell culture plates to allow complete removal
of media. Plates are transferred to 37
CCO
2
incubators and monitored and fed
automatically with feedback loops that adjust for pH and feed additions by liquid
dispensing systems. The entire station is enclosed within laminar airflow housing with
automated UV decontamination. Other array-based technologies include SimCell
miniaturized bioreactors that mimic the conventional controlled andmonitored bench-top
systems in a 150-1000
L volume. The system uses microfluidics, permeable films,
membranes, and advanced optical measurement systems to generate scalable processes.
Core applications are for media development, process optimization, platform process
creation, and clone selection [1, 57].
m
12.2.2 In-Line Analytics
In addition to conventional in-line probes for pH, dissolved oxygen, temperature, and
carbon dioxide, other in-line probes are also used in fermentation and cell culture
including optical density, capacitance, Raman, near-infrared, Fourier transformed
infrared, fluorescence, pulsed terahertz spectroscopy (PTS), optical biosensors, in situ
microscopy, SPR, and reflectometric interference spectroscopy (RIF). Early attempts at
acousticmonitoring of bioprocesses have had little success. Many of these techniques are
capable of measuring similar critical process parameters such as carbon source, pyruvate,
lactate, and other metabolic by-products such as ammonia. Interfering spectral para-
meters, such as light scattering, path length variations, and random noise from variable
sample matrix properties or instrumental effects, call for mathematical corrections. To
reduce, eliminate, or standardize their impact on the spectra, data pretreatments prior to
multivariate modeling are often necessary. Data generated by various in-line probes are
