The introduction of single-use components into biological production processes started in the early 1970s with liquid filters
and tubings, but by the end of the 1980s, bags also became available for storing small volumes. The beginning of the 2000s
saw the development of fully-disposable upstream harvest lines and further development of bufferpreparation systems. Today,
single-use cell culture reactors up to 2000 L and bioreactors up to 500 L are available on the market. Research also is ongoing
to find high-quality, economical solutions for TFF and chromatography single-use systems.
There are many advantages associated with single-use systems, including reduced changeover times (i.e., cleaning, setup, and
storage), reduced cross-contamination risks, availability of fully contained systems, reduction of initial capital expenditure
(in most instances), reduced set-up time, and reduced cleaning validation. These benefits, however, also must be balanced
with other factors, including risk of leachables, compatibility problems, integrity failures, supply-chain interruptions,
scalability limitations, waste management, and operational cost evaluations. A detailed case-by-case evaluation should always
be conducted, particularly for routine production. Figure 3 shows an image of single-use TFF cassettes used for concentration,
diafiltration, and the formulation of biologics.
Figure 3: Tangential flow filltration cassettes. (ALL FIGURES COURTESY OF THE AUTHOR)
Specific ligands and chromatographic media
Being able to obtain a high-quality product after only two or three purification steps is a real achievement in the process
development of biologics. However, the process also needs to be scaleable with high productivity. Specific ligands coupled
to rigid chromatographic media for the targeted product can be beneficial in this process. One prominent example is a typical
antibody capture step with Protein A ligands, which can reach up to 90% purity. Ligands can also be developed to polish impurities,
such as residual host cell proteins and transmissible spongiform encephalopathies particles. In the case of polishing, the
capacity is less important, so ligands could be coupled onto membranes to create membrane adsorbers.
With regard to the specificity and stability of the ligand, the structure (i.e., particle size, size distribution, pore size,
pore distribution, mechanical and chemical stability) of the chromatographic beads and the coupling chemistry are also important.
Optimized chromatographic media can increase process performance. In terms of mechanical and chemical stability, pore size,
pore size homogeneity and the coupling chemistry are important for membrane adsorber development.
Productive process dimensioning
Traditional production processes for biologics are batch based, which means that almost every process flow is collected after
each step in one or several tanks, and often checked for product quality before processing in the next step. Based on development
data, processes could often be more intensive.
In addition to the biopharmaceutical industry, the process intensification phase is mandatory for other industrial biotechnology
sectors such as the processing of antibiotics, amino acids, organic acids and food ingredients. One recent example where a
process migrated from an industrial biotechnology platform to biopharmaceutical production is sequential multicolumn chromatography
(SMCC). This process allows the use of processing time as another dimension; therefore, velocity, resin volume, and the number
of columns can be calculated to fit in a predefined processing time. A significant increase in productivity can be reached
(Examples on Protein A antibody capture showed up to a threefold increase). Buffer and stationary phase consumption was also
cut by at least half (3). This process also can enable continuous downstream processing, where the process steps are connected
to each other to obtain a continuous process flow up to the bulk stage.
Figure 4: Principles of a sequential multicolumn chromatographic (SMCC) process and comparison with a batch one. (ALL FIGURES
COURTESY OF THE AUTHOR)
Cost studies on monoclonal antibody downstream processing performed by BioPharm Services showed up to a 79% reduction in operational
cost when processes were transformed from batch to continuous ones (4). Additionally, process simulation tools are important
to optimize process dimensioning, production and investment costs, which also can be a support for process characterization
and validation. Figure 4 shows the principles of the SMCC process and compares it with a batch one. Figure 5 shows an industrial
system that enables the operation of SMCC processes.
Figure 5: Example of an industrial system that allows sequential multicolumn chromatography. (ALL FIGURES COURTESY OF THE