Influence of different packing methods on the hydrodynamic stability of chromatography columns.

It is well known that packing non-uniformity may cause peak asymmetry and limit the performance of packed-bed chromatographic columns. However, understanding of the reasons leading to packing non-uniformity is still limited. Therefore, the effect of different column packing methods, i.e. dynamic axial compression (DAC), flow packing, and combinations of both on the hydrodynamic packing heterogeneity and stability of packings composed of polymer-based compressible porous resins with a mean diameter of 90µm was investigated experimentally as well as in-silico. Deterministic Euler-Lagrange modeling of a small chromatographic column with a diameter of 9.6mm and a bed height of 30mm was applied by coupling Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). Interparticle micromechanics as well as the fluid-particle and particle-wall interactions were taken into account. Experiments and simulations revealed substantial non-uniformity of compression force transmission and axial packing density distribution during both dynamic axial compression and flow packing which was related to wall support and interparticle friction. By combining both packing methods sequentially (dynamic axial compression followed by flow packing or vice versa), the compression forces were more homogeneous resulting in improved packing procedures. Repeated alternating application of flow packing and DAC (the so-called hybrid packing method) resulted in the most homogeneous packing density distribution and the highest packing stability which was kept nearly constant during long-term operation with cyclic hydrodynamic load. The hydrodynamic stability of the chromatographic column was evaluated by calculating the integral porosity deviation and packing induced flow velocity dispersion. The hybrid packing method gave the best results for both parameters.

The differential effects of poly(2-hydroxyethyl methacrylate) and poly(2-hydroxyethyl methacrylate)/poly(caprolactone) polymers on cell proliferation and collagen synthesis by human lung fibroblasts.

Because of its chemical versatility and demonstrated biocompatibility, poly(2-hydroxyethyl methacrylate) (pHEMA) has been widely used as a polymer for biomedical applications. Since this hydrophilic material shows a poor interface with cells, blendings with other polymers were done to improve cytocompatibility. In our polymer, the presence of hydrophobic dominions on the material surface, due to the interpenetrating polymerization of pHEMA with poly(caprolactone) (PCL), seems to ameliorate the cytocompatibility in terms of cell adhesion and metabolism. For our experiments, we used IMR-90 human fibroblasts, as these cells strongly regulate DNA, RNA, and protein synthesis as anchorage-dependent variables. Cell attachment on a pHEMA/PCL interpenetrating polymer network was optimal, suggesting a strong adhesion between the cells and the polymer surface. Cell adhesion was weaker on pHEMA, as a significant fraction of the fibroblasts revealed a lack of spreading, with most cells remaining spherical. Moreover, only fibroblasts seeded on pHEMA significantly decreased mRNA synthesis; collagen production and cell shapes ranged from fully flat and proliferating, to minimally spread and nonproliferating. Finally, DNA synthesis, as a measure of cell proliferation, was markedly inhibited in cells cultured on pHEMA but not on pHEMA/PCL. In conclusion, our results suggest that control of cell growth and metabolism by biomedical polymers is based on physicochemical mechanism(s) in which the hydrophilicity/hydrophobicity ratio of the material surfaces may play an important role.