Crystallization is
a potential cost-effective alternative to chromatography
for the purification of biotherapeutic proteins. Crystallization kinetics
are required for the design and control of such processes, but only
a limited quantity of proteins is available during the initial stage
of process development. This article describes the design of a droplet-based
evaporative system for the evaluation of candidate crystallization
conditions and the estimation of kinetics using only a droplet (on
the order of μL) of protein solution. The temperature and humidity
of air fed to a flow cell containing the droplet are controlled for
evaporation and rehydration of the droplet, which are used for manipulating
supersaturation. Dual-angle images of the droplet are taken and analyzed
on-line to obtain the droplet volume and crystal sizes. Crystallization
kinetics are estimated based on a first-principles process model and
experimental data. Tight control of temperature and humidity of the
air, fast and accurate image analysis, and accurate estimation of
crystallization kinetics are experimentally demonstrated for a model
protein lysozyme. The estimated kinetics are suitable for the model-based
design and control of protein crystallization processes.
Batch low-pH hold is a common processing step to inactivate enveloped viruses for biologics derived from mammalian sources. Increased interest in the transition of biopharmaceutical manufacturing from batch to continuous operation resulted in numerous attempts to adapt batch low-pH hold to continuous processing. However, control challenges with operating this system have not been directly addressed. This article describes a low-cost, column-based continuous viral inactivation system constructed with off-the-shelf components. Model-based, reaction-invariant pH controller is implemented to account for the nonlinearities with Bayesian estimation addressing variations in the operation. The residence time distribution is modeled as a plug flow reactor with axial dispersion in series with a continuously stirred tank reactor, and is periodically estimated during operation through inverse tracer experiments. The estimated residence time distribution quantifies the minimum residence time, which is used to adjust feed flow rates. Controller validation experiments demonstrate that pH and minimum residence time setpoint tracking and disturbance rejection are achieved with fast and accurate response and no instability. Viral inactivation testing demonstrates tight control of logarithmic reduction values over extended operation. This study provides tools for the design and operation of continuous viral inactivation systems in service of increasing productivity, improving product quality, and enhancing patient safety.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.