Research
The main goal of our research is to analyze, control and exploit molecular interactions involving proteins and colloidal particles. The motivation is initially to obtain improved quantitative insights into existing processes, leading to more effective methods for designing and using them, but an auxiliary objective is to develop new products and operations. These themes bring together a diverse collection of research activities involving theoretical and experimental work dealing with both the fundamentals — transport, kinetic and thermodynamic phenomena — and their interaction in the process environment.
The path from molecular structure through continuum properties to process design represents the central paradigm in modern chemical engineering, but it has been applied much less extensively to species such as proteins than to small molecules; such processes as protein separations still depend very heavily on empirical methods for design and optimization. Most of our group’s efforts are devoted to understanding the fundamentals of bioseparations, especially in chromatography and in separations driven by protein phase behavior, and of protein formulations, involving primarily structural and thermodynamic properties of proteins in liquid and solid phases. An ongoing area of interest that spans full bioprocesses is that of proteomics, specifically the identification and characterization of host-cell protein impurities and their removal from process streams. We have also worked on numerous other applications, ranging from fundamental fluid mechanics and mass transfer to colloidal adsorption to development of novel materials.
Principal Research Areas
Bioseparations: Protein Chromatography and More
Protein separation processes are crucial to protein production, with chromatography being the workhorse of most separation and purification processes. Understanding, modeling and designing this and other unit operations is intrinsically a multiscale activity, ranging from the molecular level, through continuum-level accounting for transport effects (convection, diffusion) as well as kinetics and thermodynamics, to macroscopic behavior. Each of the constituent phenomena should be understood and described quantitatively; this is the focus of our efforts. We are seeking in particular to relate key properties of proteins, e.g., adsorption equilibria, to their molecular structures. Coupled to this is the role of separations media, where we are, for instance, examining the effect of the chemical structure and the pore structure of chromatographic packings or depth filters on separations performance. The experimental tools that we use also provide insights at levels ranging from macroscopic to molecular; we use column liquid chromatography, batch uptake measurements, scanning confocal microscopy, electron microscopy and colloid science tools such as scanning probe microscopy (SPM). Similarly, our theoretical work is performed at different levels: we seek predictions of adsorption equilibria from molecular-level computations, and of column performance from traditional and novel transport and adsorption models.
Protein Thermodynamics and Phase Behavior
Protein separations processes such as crystallization and precipitation, as well as drug formulation, food processing and other areas of bioengineering depend on the properties of proteins in solution as well as their phase behavior. We are seeking to understand these phenomena mechanistically in terms of the molecular structures of the proteins involved. Again we do so via experimental and theoretical work at various levels. Our experimental work includes measurements of protein interactions, generally in terms of osmotic virial coefficients, using scattering methods and self-interaction chromatography, as well as measurements of phase behavior. The dense phases may include crystals, gels, precipitates, concentrated solutions or dired protein phases, and we explore both their formation and its relation to the interaction measurements as well as relevant applications such as to controlled release and drug delivery. We also work with the group of Prof. Norman Wagner in using scattering methods to determine the internal structure of amorphous dense phases. Associated theoretical and computational work is aimed at explaining trends in the protein interaction results and simulating actual phase behavior. For this purpose we use molecular biophysical methods, accounting in particular for specific biological interactions and interactions in which the modulating role of water is critical.
Proteomics of Bioprocessing
Products such as therapeutic proteins that are produced by cell culture must be purified from a variety of impurities, among which are the proteins naturally produced by the host cells (host-cell proteins, or HCPs). Although overall HCP levels are monitored closely in bioprocessing, it is possible for individual HCPs that may impair the stability of the product to persist into the final formulation. In collaboration with Prof. Kelvin Lee‘s group, we use proteomic methods to determine the identities and levels of individual HCPs in bioprocess steps, the mechanisms by which they are removed or retained, and possible methods for improving their removal. Our interests include overall HCP removal in a downstream process as well as the performance of individual unit operations in clearing different HCPs or classes of HCPs.